European Journal of Inorganic Chemistry

Current research reports and chronological list of recent articles.

The scientific European Journal of Inorganic Chemistry - EurJIC - is the fastest growing journal in inorganic chemistry. It publishes Full Papers, Short Communications, and Microreviews from the entire spectrum of inorganic, organometallic, bioinorganic, and solid-state chemistry.

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Additional research articles in the field of inorganic chemistry, see Current Chemistry Research Articles. Magazines with similar content:

 - Dalton Transactions,

 - Inorganica Chimica Acta,

 - Inorganic Chemistry,

 - Inorganic Chemistry Communications,

 - European Journal of Inorganic Chemistry,

 - Russian Journal of Inorganic Chemistry.

European Journal of Inorganic Chemistry - Abstracts

Lanthanide Complexes of a Calix[4]arene Ligand with Dangling Phosphonate and Picolinamide Arms: Synthesis, Crystal Structures, and Extraction Properties

The coordination behavior of the neutral calix[4]arene-based ligand L exhibiting dangling phosphonate ester and picolinamide groups in 1,3- and 2,4-distal positions towards a series of lanthanide ions was examined. Reaction of L with Ln(NO3)3 in MeOH afforded mononuclear [LnL(µ1,3-NO3)2]NO3 complexes [Ln = La (6), Pr (7), Eu (8), Gd (9)]. X-ray crystallography for 6 and 7 revealed tenfold coordination by phosphoryl O, amide O, and pyridine N atoms from L and four O atoms from two chelating nitrato coligands. Treatment of the [LnL(µ1,3-NO3)2]NO3 salts with NaBPh4 leads to metathesis of the counterion and, in the case of Pr, Eu, and Gd, to substitution of one nitrato coligand by a methanol molecule yielding [LnL(µ1,3-NO3)2–n(MeOH)n](BPh4)n+1 for n = 0, Ln = La (10) and n = 1, Ln = Pr (11), Eu (12), Gd (13). X-ray crystallography of complexes 11–13 revealed an isostructural series of ninefold-coordinated lanthanide complexes in which one nitrato coligand is exchanged by a methanol molecule. UV/Vis batch titration experiments showed the formation of 1:1 complexes of L with trivalent lanthanides (La3+, Pr3+, Eu3+, Gd3+, Yb3+). The stability constants of the complexes determined by UV/Vis spectroscopic titrations are log K11 = 6.44 ± 0.02 (La), 5.96 ± 0.01 (Pr), 6.37 ± 0.01 (Eu), 7.38 ± 0.3 (Gd), and 9.6 ± 0.2 (Yb). Solvent-extraction experiments with lanthanide picrates revealed that L is able to extract both La3+ and Eu3+ in 1:1 stoichiometry from aqueous media into chloroform.A preorganized calix[4]arene ligand with dangling phosphonate ester and picolinamide side arms forms stable 1:1 complexes with LaIII, PrIII, EuIII, GdIII, and YbIII. The lipophilic calixarene scaffold also enables extraction of lanthanum and europium picrates from aqueous solutions.
Datum: 20.05.2016

Preparation of Secondary Phosphine Oxide Ligands through Nucleophilic Attack on Imines and Their Applications in Palladium-Catalyzed Catellani Reactions

Several new amino-type secondary phosphine oxide (SPO) pre-ligands (3a–3h) that contain P–N bonds were synthesized and characterized. SPOs 3a–3h can tautomerize to phosphinous acids (PA, 3a–3h) as genuine ligands. The formation of SPOs 3a–3h occurred first through nucleophilic attack on the imine carbon atom, then by the addition of RPCl2 (R = Ph, Cy, tBu, or iPr), and work-up under acidic conditions. The P–N bond in the newly prepared SPOs is evident from the crystal structures of SPOs 3d and 3h. Reactions of SPOs 3f, 3g, or 3h with Pd(COD)Cl2 (COD = cyclooctadiene) yielded palladium complexes 6f, 6g, or 6h. In these crystal structures, PAs 3f, 3g, and 3h act as didentate ligands through P and N donors. Intriguingly, the reaction of SPO 3f with Pd(COD)Cl2 also gave rise to palladium complexes 7fa, 7fb, and 8f. The crystal structures of 7fa and 7fb show that the palladium atom is chelated by PA 3f and coordinated by a phosphine-like ligand fragmented from SPO 3f through C–N bond dissociation. Finally, the syntheses of carbazole derivatives were pursued in Catellani reactions with SPOs 3g and 3h as pre-ligands. A mechanism is proposed to account for the catalytic reaction (see the Supporting Information). The optimized conditions for Suzuki reactions using selected SPO ligands are also reported. Several new secondary phosphine oxide (SPO) type ligands, 3a–3n, were prepared. In addition, some SPOs as well as coordinated palladium complexes of ligand 3f, that is, 7fa, 7fb, and 8f, with fascinating bonding modes were characterized by X-ray diffraction methods. Some of these ligands were chosen to assist in palladium-catalyzed Catellani reactions.
Datum: 19.05.2016

Preparation of a Single-Walled Carbon Nanotube/Cd0.8Zn0.2S Nanocomposite and Its Enhanced Photocatalytic Hydrogen Production Activity

Single-walled carbon nanotube (SWCNT) and Cd0.8Zn0.2S nanocomposites were fabricated by a coprecipitation process with prefunctionalized SWCNTs as the starting material. The resultant SWCNT/Cd0.8Zn0.2S composites were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform IR (FTIR) spectroscopy, Raman spectroscopy, UV/Vis diffuse reflectance absorption spectroscopy (DRS) and photoluminescence (PL) spectroscopy. The addition of SWCNTs improve both the visible-light-induced activity and stability for H2 production of Cd0.8Zn0.2S, and 10 wt.-% SWCNT/Cd0.8Zn0.2S exhibits a maximum activity (632 mmol h–1) for H2 production that is ca. 1.40 times higher than that (451 mmol h–1) of Cd0.8Zn0.2S alone. This enhanced photoactivity of Cd0.8Zn0.2S through the incorporation of SWCNTs can be attributed to the synergetic effects of the intrinsic properties of its components; the functionalized SWCNTs act as the supporting matrix and electron acceptor of Cd0.8Zn0.2S and cause an effective charge separation at the SWCNT/Cd0.8Zn0.2S interfaces and an improvement in the photoactivity and stability for H2 production. Single-walled carbon nanotube (SWCNT) and Cd0.8Zn0.2S nanocomposites are fabricated by a coprecipitation process with prefunctionalized SWCNTs as the starting material. The SWCNTs improve both the visible-light-induced activity and stability for H2 production of Cd0.8Zn0.2S, and the activity (632 µmol h–1) is ca. 1.40 times higher than that (451 µmol h–1) of Cd0.8Zn0.2S alone.
Datum: 19.05.2016

Correlating the Structural, Electronic, and Explosive Sensitivity Properties of CuII Tetrazine Complexes

The synthesis and characterization of explosive coordination complexes of CuII with nitrogen-rich tetrazine ligands and nitrate counter-anions have been achieved. The complexes adopt a variety of coordination geometries including monomeric and dimeric architectures with five and six coordinate CuII centers. The thermal stabilities of the complexes correlate to the strength of the Cu–nitrate interaction such that more strongly bound nitrates exhibit higher thermal stability. Exchanging amine groups on the coordinating ligands with 3,3′-dinitroazetidine groups led to changes in the solid-state structures and increases to the impact sensitivity of the resulting complexes relative to the corresponding amine derivatives.The coordination geometries and solid state packing properties influence the thermal stabilities, and mechanical sensitivities of new CuII tetrazine-based explosive complexes.
Datum: 19.05.2016

Rational Synthesis of the Carbonylí(perthiolato)diiron [Fe2(S3CPh2)(CO)6] and Related Complexes

The photochemical reaction of Fe2(S2)(CO)6 and Ph2CS affords the perthiolate Fe2(S3CPh2)(CO)6 (1) in good yield. As confirmed crystallographically, 1 contains a previously elusive perthiolate ligand. The related reaction of Fe2(S2)(CO)5(PPh3) and Ph2CS gave Fe2(S3CPh2)(CO)5(PPh3). Although Fe3S2(CO)9 and Ph2CS failed to efficiently give Fe2(S2CPh2)(CO)6, this compound could be prepared by desulfurization of 1 using PPh3.The photoaddition of Ph2CS to Fe2(S2)(CO)6 gives the rare diiron perthiolate Fe2(S3CPh2)(CO)6. Desulfurization of the perthiolate gives Fe2(S2CPh2)(CO)6. These simple reactions provide access to Fe-S-CO compounds that previously were difficult to prepare.
Datum: 19.05.2016

Photodecompostion of the Oligogermanes nBu3GeGePh2GenBu3 and nBu3GeGePh3: Identification of the Photoproducts by Spectroscopic and Spectrometric Methods

The oligogermane nBu3GeGePh2GenBu3 was photolyzed using UV-C light in the presence of acetic acid as a trapping agent and the photoproducts were identified using 1H NMR spectroscopy, gas chromatography/electron-impact mass spectrometry, and high resolution accurate mass mass spectrometry. The products identified were the germanes nBu3GeH, nBu3GeOAc, and Ph2Ge(H)OAc (OAc = C2H3O2) and the digermane nBu6Ge2. This indicates that both germanium–germanium single bonds are cleaved homolytically upon irradiation to generate two nBu3Ge· radicals and the germylene Ph2Ge:. The digermane nBu3GeGePh3 was also photolyzed under identical conditions, and in this case the photoproducts were identified as nBu3GeH, nBu3GeOAc, Ph3GeH, Ph3GeOAc and the digermanes nBu6Ge2 and Ph6Ge2.Photolysis of a trigermane and digermane results in homolytic scission of the germanium–germanium bonds in these molecules to yield germanium radicals and germylenes.
Datum: 19.05.2016

Scandium Complexes Bearing Bis(oxazolinylphenyl)amide Ligands: An Analysis of Their Reactivity, Solution-State Structures and Photophysical Properties

The coordination chemistry of scandium supported by bis(oxazolinylphenyl)amide (R-BOPA) ligands is reported. The R-BOPA ligand is too sterically demanding to afford bis(amide) complexes [Sc(R-BOPA){N(SiMe3)2}2], but reaction of the protio-ligand with [Sc{N(SiMe3)2}2Cl(THF)] (1) afforded the mixed amido-chloride complexes [Sc(R-BOPA){N(SiMe3)2}Cl] (2). The selective reaction of the amido and chloride co-ligands in 2 has been investigated; whilst the chloride ligand can be removed cleanly by metathesis, protonation of the N(SiMe3)2 ligand results in competitive protonation of the R-BOPA ligand. The complexes [Sc(R-BOPA)(CH2SiMe2Ph)2] (5) have been synthesised. Each R-BOPA-containing complex exists in two isomeric forms. The equilibrium has been investigated both experimentally and computationally, and the data suggest that a concerted rotation of the phenyl rings interconverts the two diastereomeric isomers. All of the R-BOPA complexes were found to be luminescent; an analysis of the photophysics, aided by TD-DFT calculations, suggests ligand-centred luminescence with distinct emission lifetimes for each isomer.We report on the coordination chemistry of scandium bearing bis(oxazolinylphenyl)amide (BOPA) ligands. These complexes exist in two isomeric forms and have been characterised using luminescence spectroscopy. Stoichiometric reactions have been probed, showing the scope and limitations of the chemistry of oxazoline-bearing organometallic-type complexes.
Datum: 19.05.2016

Unexpected Reaction Promoted by NH+···O=Mo Hydrogen Bonds in Nonpolar Solvents

A new synthetic method using [MoIV(S-tBu)4], 1,2-benzenedithiol containing bulky hydrophobic acylamino substituents, 3,6-[(4-tBuC6H4)3CCONH]2C6H2-1,2-(SH)2 (LH2), a tertiary amine [R3N = Et3N or 2,6-lutidine (Lu)], and an equimolar amount of water afforded (R3NH)2[MoIVO(L)2] [(R3NH)2[1]]. Each compound formed a strong NH+···O=Mo hydrogen bond between the tertiary ammonium cation and the terminal oxo ligand in toluene, which unexpectedly promoted the one-electron oxidation of MoIV by lutidinium ion or 0.5 equiv. Me3NO to produce [MoVO(L)2]–. In contrast, in polar solvents, typical oxygen atom transfer (OAT) from Me3NO to [1]2– was observed. A possible mechanism is presented and the role of the hydrogen bond in molybdenum enzymes is discussed. Tertiary ammonium salts of monooxomolybdenum(IV) benzenedithiolates containing bulky hydrophobic acylamino substituents were synthesised. In toluene, the NH+···O=Mo hydrogen bond unexpectedly promoted one-electron oxidation to MoV species by 2,6-lutidinium ion or 0.5 equiv. Me3NO, although normal oxygen atom transfer (OAT) was observed in polar solvents.
Datum: 19.05.2016

Cooperative High-Temperature Spin Crossover Accompanied by a Highly Anisotropic Structural Distortion

Spin transitions are a spectacular example of molecular switching that can provoke extreme electronic and structural reorganizations in coordination compounds. A new 3D cyanoheterometallic framework, [Fe(pz){Au(CN)2}2], has been synthesized in which a highly cooperative spin crossover has been observed at 367 and 349 K in heating and cooling modes, respectively. Mössbauer spectroscopy revealed a complete transition between the diamagnetic and paramagnetic states of the iron centres. The low-spin-to-high-spin transition induced a drastic structural distortion involving a large one-directional expansion (ca. 10.6 %) and contraction (ca. 9.6 %) of the lattice. Negative thermal expansion along the c axis was detected below and above the transition temperature.A new 3D cyanoheterometallic framework, [Fe(pz){Au(CN)2}2], displays a highly cooperative spin crossover at elevated temperatures. The low-spin-to-high-spin transition induces a drastic structural distortion that involves a large one-directional expansion (10.6 %) and contraction (9.6 %) of the lattice.
Datum: 19.05.2016

Wide-Range Tuning of the Mo Oxidation State in La1–xSrxFe2/3Mo1/3O3 Perovskites

La1–xSrxFe2/3Mo1/3O3 (0 ≤ x ≤ 1) perovskites allow exceptionally wide tuning of the Mo oxidation state from +3 (x = 0) to +6 (x = 1) with the FeIII oxidation state virtually unchanged. The end members of this series show antiferromagnetic ordering in LaFe2/3Mo1/3O3 at TN = 520 K and ferrimagnetic ordering in SrFe2/3Mo1/3O3 at TC = 420 K. The crucial role of electron correlations in the Mo 4d shell suggests that LaFe2/3Mo1/3O3 with a half-filled band is a Mott insulator, whereas SrFe2/3Mo1/3O3 is a band insulator. In both cases, the magnetic structure is dictated by antiferromagnetic superexchange between localized magnetic moments. At intermediate compositions, an interplay of antiferromagnetic-superexchange and double-exchange interactions results in nonmonotonous variations of both the magnetic-ordering temperature and saturation magnetization. La1–xSrxFe2/3Mo1/3O3 perovskites allow wide tuning of the Mo oxidation state from +3 (x = 0) to +6 (x = 1) with the FeIII oxidation state virtually unchanged. The magnetic properties vary between antiferromagnetic (AFM) for x = 0 to ferromagnetic (FIM) for x = 1.0.
Datum: 18.05.2016

The Valence States of Copernicium and Flerovium

Compared with its lighter congener HgF4, copernicium tetrafluoride, CnF4, is predicted to be significantly more stable with respect to decomposition to the elements. Tetravalent flerovium on the other hand is unlikely to be experimentally accessible, except possibly as FlF4. Because of the large 7p1/2–3/2 energy splitting, many divalent flerovium compounds are also expected to be thermodynamically unstable. The two dihalides FlF2 and FlCl2, however, are predicted to be thermodynamically stable; flerovium thus is not quite as noble as xenon, which is not known to form a chloride.Relativistic DFT calculations indicate that copernicium tetrafluoride should be substantially more stable than HgF4. Tetravalent flerovium on the other hand is unlikely to be experimentally accessible. Less noble than xenon, flerovium is predicted to yield both FlF2 and FlCl2 as stable molecules.
Datum: 18.05.2016

A Three-Dimensional Tetraphenylíethene-Based Metal–Organic Framework for Selective Gas Separation and Luminescence Sensing of Metal Ions

A three-dimensional porous metal–organic framework (MOF), UTSA-86, made up of cadmium ions and a chromophoric tetraphenylethene-based tetracarboxylate ligand, 4′,4′′′,4′′′′′,4′′′′′′′-(ethene-1,1,2,2-tetrayl)tetrakis(1,1′-biphenyl-4-carboxylic acid (H4ettc), has been synthesized and characterized by single-crystal X-ray diffraction analysis. This multifunctional MOF exhibits permanent porosity, selective gas uptake, and luminescence sensing of metal ions.A three-dimensional multifunctional metal–organic framework (MOF), UTSA-86, made up of cadmium ions and a tetraphenylethene-based tetracarboxylate ligand has been synthesized and characterized by single-crystal X-ray diffraction analysis. This MOF exhibits permanent porosity, selective gas uptake, and luminescence sensing of metal ions.
Datum: 18.05.2016

(β-Diketiminato)cadmium Bis(trimethylsilyl)amide: Facile Access to Low-Coordinate Cadmium Complexes

A new route to access low-coordinate (β-diketiminato)cadmium complexes has been developed. Treatment of [Cd(HMDS)2] with BDI-H (HMDS = [N(SiMe3)2]; BDI = [{N(2,6-iPr2C6H3)C(Me)}2CH]) forms [(BDI)Cd(HMDS)], which is a useful synthon for the generation of other low-coordinate cadmium complexes such as anilido complex [(BDI)Cd(NH{N(2,6-iPr2C6H3})(THF)], aryloxo complex [(BDI)Cd(O-2,6-tBu2C6H3)], as well as chloro complex [{(BDI)CdCl}2]. [(BDI)Cd(HMDS)] is extremely sensitive to hydrolysis, generating [{(BDI)Cd(OH)}2] upon exposure to “dry” tert-butyl alcohol. [(BDI)Cd(HMDS)] is shown to be a useful synthon in the synthesis of low-coordinate (β-diketiminato)cadmium complexes, including terminal (aryloxo)- and (anilido)cadmium complexes. An elusive homometallic (β-diketiminato)cadmium halide complex was also generated (halide = chloride).
Datum: 18.05.2016

On the Extended Series of Quaternary Zintl Phases Ca13REMnSb11 (RE = La–Nd, Sm, Gd–Dy)

Eight new compounds with a general formula Ca14–xRExMnSb11 (RE = La–Nd, Sm, Gd–Dy; x ≈ 1) were synthesized by the molten flux method and their structures were established via single-crystal X-ray diffraction. The overarching goal of this study was to investigate the effect of electron doping, via substitution of RE3+ at Ca2+ sites, on the crystal structure and physical properties of Ca14MnSb11, which is a candidate for thermoelectric applications. All studied phases are isostructural, and crystallize in the tetragonal body-centered space group I41/acd (Ca14AlSb11 structure type, Pearson index tI208). The structure is made up of MnSb410– tetrahedra, randomly mixed Ca2+ and RE3+ cations, Sb3– anions, and linear Sb37– polyanions. Comprehensive structural work confirms high rare-earth metal content with Ca2+/RE3+ randomly mixed on all four cation sites, with the caveat that the larger RE atoms (La–Nd) prefer to occupy the Ca2 site, while the smaller RE atoms (Sm, Gd, Tb, and Dy) preferably occupy the Ca1 site. Nearly phase-pure polycrystalline samples have been synthesized using solid-state reactions, and have been used for physical property measurements. The resistivities of the bulk Ca14–xRExMnSb11 (RE = La–Nd, Sm, Gd; x ≈ 1) samples reveal semiconducting behavior, consistent with the notion of electron doping in the parent p-type Ca14MnSb11 material. Magnetic susceptibilities suggest complex magnetic ordering at temperatures below ca. 50 K, likely originating from coupling between two or more magnetic sub-lattices.A new series of quaternary compounds with a general formula of Ca14–xRExMnSb11 (RE = La–Nd, Sm, Gd–Dy; x ≈ 1) were synthesized, and their crystal structures, electrical, and magnetic properties were investigated
Datum: 18.05.2016

Ratiometric Thermometer Based on a Lanthanoid Coordination Polymer

The new luminescent lanthanum-based coordination polymer LaHL, ({[La(HL)(H2O)2]·H2O}n, H4L = 5-hydroxy-1,2,4-benzenetricarboxylic acid) has been synthesized by hydrothermal methods. By the addition of 5 % of a Tb or Eu salt to the reaction mixture, the doped compounds La0.95Tb0.05HL and La0.95Eu0.05HL were obtained, with the same structure as LaHL. The compound La0.95Tb0.05HL can be used as a ratiometric thermometer over the temperature range 90–280 K with a sensitivity of up to 0.53 % K–1 at 280 K. The mixed lanthanoid coordination polymer {[La0.95Tb0.05HL(H2O)2]·H2O}n (H4L = 5-hydroxy-1,2,4-benzenetricarboxylic acid) was prepared and fully characterized. This compound can be used as a ratiometric thermometer based on the emission intensity ratio of ligand phosphorescence and TbIII luminescence over the temperature range 90–280 K with a relative sensitivity of up to 0.53 % K–1.
Datum: 18.05.2016

Proline and α-Methylproline as Chiral Auxiliaries for the Synthesis of Enantiopure Bis-Cyclometalated Iridium(III) Complexes

A convenient proline- and α-methylproline-mediated method for the synthesis of enantiomerically pure bis-cyclometalated iridium(III) complexes is reported. The reactions of l-proline or l-α-methylproline with [Ir(µ-Cl)(C^N)2]2 (C^N = cyclometalating 2-phenylpyridine, 2-phenylbenzoxazole, or 2-phenylbenzothiazole ligand) afforded diastereomeric mixtures of intermediate prolinatoiridium(III) complexes from which the Λ-(S) diastereomers were isolated with excellent diastereomeric purity by washing, precipitation, or crystallization. A subsequent trifluoroacetic acid (TFA) induced substitution of the prolinate ligands with 2,2′-bipyridine with the retention of configuration provided the chiral-only-at-metal complexes with >99 % ee.Proline and α-methylproline are very suitable chiral auxiliaries for the synthesis of enantiopure bis-cyclometalated iridium(III) complexes in a straightforward and convenient fashion without the tedious chromatographic separation of the intermediate diastereomers.
Datum: 18.05.2016

Robust Metal-Organic Frameworks Based on Tritopic Phosphonoaromatic Ligands

Microporous metal-organic frameworks (MOFs) based on phosphonic ligands are still a very small family of materials if compared to carboxylate-based MOFs, due to some inherent features that make them challenging to synthesize and to characterize. Nonetheless, metal phosphonates display remarkable chemical and thermal robustness that could represent an asset in terms of their employment for practical applications. This feature makes them attractive as alternative materials to classical carboxylate-based MOFs, which often suffer from limited stability. In recent years a number of tritopic phosphonoaromatic ligands have been used as building blocks with the aim of generating open-framework structures. The approach has often proved to be successful and several microporous compounds have been discovered. Tritopic phosphonoaromatic ligands have recently been used with the aim of synthesizing microporous compounds. The most relevant results are reviewed.
Datum: 17.05.2016

Vibrational–Structural Combined Study into Luminescent Mixed Copper(I)/Copper(II) Cyanide Coordination Polymers

Herein, we report the characterization of a series of CuCN-based coordination polymers that display different crystal packing and electronic properties, namely, [Na2Cu(CN)3·3H2O]n (1), [Cu4(CN)5(NH3)2(H2O)]n (2), [Cu3(CN)4(NH3)3]n (3), [Cu3(CN)3(O)0.25(NH3)]n (4), [Cu5(CN)6(NH3)4]n (5), and [Cu5(CN)6(NH3)2]n (6). Spectroscopic evidence of the presence of ammonia molecules coordinated to the metal centers is provided, in particular for 4, which is a new structure. The characterization has been performed by single-crystal XRD (SCXRD), micro- IR spectroscopy, micro-Raman spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The photophysical properties have been studied through solid-state luminescence spectroscopy by acquiring the emission and excitation spectra and evaluating the emission quantum yields, which is an approach that has recently grown in importance in the solid-state field. The goals of this work are (1) to elucidate the correlation between the luminescence properties and the presence of either CuI or mixed CuI/CuII oxidation states, (2) to evaluate the presence of NH3, H2O, or both in the polymers through a combined crystallographic–spectroscopic study, and (3) to rationalize the supramolecular architecture and its influence on the resulting luminescence. A series of CuCN-based coordination polymers are characterized by single-crystal XRD, IR spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Luminescence measurements indicate that these substances are promising photoactive materials. We aims to establish a relationship between the crystal structure and emission pathways of this class of compounds.
Datum: 17.05.2016

Synthesis, Structure, and Characterization of Emissive Neutral Dinuclear CuI Complexes with a Tetraphosphane Bridging Ligand

A series of new dinuclear copper complexes with a tetraphosphane bridging ligand, [{(pz4B)Cu}2(µ-tpbz)] (1), [{(pz2BH2)Cu}2(µ-tpbz)] (2), and [{(tz2BH2)Cu}2(µ-tpbz)] (3) [tpbz = 1,2,4,5-tetrakis(diphenylphosphanyl)benzene, pz4B = tetrakis(pyrazol-1-yl)borate, pz2BH2 = bis(pyrazol-1-yl)borohydrate, and tz2BH2 = bis(1,2,4-triazol-1-yl)borohydrate], have been synthesized and structurally characterized. The CuI atoms in these complexes are four-coordinate and adopt a tetrahedral coordination geometry. In each complex, the copper centers are bridged by a tpbz ligand and each CuI is further terminally chelated by a borate diimine anion. The central phenylene ring and the phosphine atoms of the tpbz ligand are essentially planar. The two CuI atoms in each molecule are located above and below the (P2C6H2P2) mean plane, respectively, leading to a chair-like conformation for the [Cu](P2C6H2P2)[Cu] fragment. The distances between the CuI atoms in each complex are about 8.7 Å. In the solid state, these complexes are emissive and exhibit yellow–orange photoluminescence [emission peaks, λmax = 580 nm (1), 569 nm (2), 540 nm (3)] with lifetimes of 7.4–20.5 µs and quantum yields Φ = 0.07–0.45 at room temperature. Theoretical and experimental results indicate that these complexes have the lowest singlet (S1) state and the lowest triplet (T1) state with very close energy levels, and display thermally activated delayed fluorescence (TADF) at ambient temperature.Three neutral dinuclear CuI complexes with a tetraphosphane bridging ligand have been synthesized. The emissive properties at 298 and 77 K as well as theoretical studies point to thermally activated delayed fluorescence (TADF).
Datum: 13.05.2016

Secondary Interactions versus Intramolecular π–π Interactions in CuII–Diradical Complexes

Two new non-innocent ligands, H2LOPh and H2LSPh, were synthesized. Both ligands reacted with 0.5 equiv. of CuCl2·2H2O to provide the corresponding mononuclear diradical-containing CuII complexes [Cu(LOPh(SQ))2] (1) and [Cu(LSPh(SQ))2] (2). Both complexes were characterized by single-crystal X-ray diffraction measurements. Molecular structure analyses indicated that, in complex 1, the two –OPh groups of two [LOPh(SQ)]– ligands are situated trans to each other, while in complex 2, the two –SPh groups of two [LSPh(SQ)]– ligands were found to maintain a cis relationship. In complex 1, Cu–CPh interactions as well as two π–π interactions were observed between –OPh-group-containing C6 phenyl rings and the radical-containing coordinated chelate rings. In complex 2, Cu–CPh interactions were absent, although intramolecular π–π interactions within one of the two coordinating ligands were present. The π–π interactions were between the C6 phenyl ring of an –SPh group and the 3,5-di-tert-butyl-amidophenolate unit. Variable-temperature magnetic susceptibility measurements indicated that both complexes acquire an S = 1/2 ground state. X-band EPR measurements confirmed that the unpaired electron is on the CuII center in both complexes. This implies that the expected CuII–S secondary interactions in complex 2 are suppressed by the dominating π–π stacking interactions, and the ground-state electronic configuration was found to be () instead of the expected ().Secondary interactions between the CuII atom and the secondary coordination atoms of tethered groups in mononuclear diradical-containing CuII complexes determine the ground-state electronic configuration of the complex. These secondary interactions can be overcome by weak intramolecular π–π interactions.
Datum: 13.05.2016

Receptor-Targeted Luminescent Silver Bionanoparticles

Luminescent Ag nanoclusters (Ag-NC) provide the next generation in bionanoparticles, wherein the luminescence (650 nm) and large Stokes shift of these inorganic nanoclusters are favorable for biological imaging. By combining these characteristics with those of human serum albumin (HSA; a protein capable of binding multiple endo- and exogenous compounds), the Ag nanoclusters can be shielded from the environment and functionalized with (receptor) targeting moieties. Encapsulation of the 1.5 nm Ag nanoclusters by HSA resulted in a threefold increase in luminescence intensity and a twofold increase of the luminescence lifetime (1.7 vs. 3.6 µs). To exemplify the potential of this targeted concept, we functionalized HSA-Ag nanoparticles with chemokine receptor 4 (CXCR4) targeting peptides [Ac-TZ14011(CO2H)]. The resulting Ac-TZ14011-HSA-Ag nanoparticles demonstrated specific binding to CXCR4-overexpressing tumor cells. Upon exposure to (ambient) light, particle-functionalized tumor cells were killed. Combined, these experiments illustrate that HSA-Ag nanoparticles may have a potential in biological imaging and possibly even in targeted theranostic applications.Luminescent silver nanoclusters can be encapsulated by human serum albumin, resulting in improved optical properties. This protein scaffold can be further functionalized with targeting moieties, resulting in HSA-Ag nanoparticles that can be applied as targeted imaging agents and possibly even as theranostic agents.
Datum: 13.05.2016

Structure-Property Relationships in Tricyanoferrate(III) Building Blocks and Trinuclear Cyanide-Bridged Complexes

The preparation, structures, and magnetic properties of two tricyanoferrates, [NEt4]2[(Tp*Me)FeII(CN)3]·MeCN (1) and [NEt4][(Tp*Me)FeIII(CN)3]·H2O (2), and three trinuclear derivatives, {[(Tp*Me)FeIII(CN)3]2[NiII(L)2]}·n(solvent) (L = bpy, 3; tren, 4; DETA, 5) are described. Magnetic measurements show that 2 is an S = 1/2 complex [g = 2.65(1)], while 3–5 display ST = 2 spin ground states, owing to cyanide-mediated ferromagnetic exchange between FeIIILS (S = 1/2) and NiII (S = 1) ions. The χT vs. T data for 3–5 were modelled using an isotropic Heisenberg model and give J/kB and gavg values of +11.1(1) K and 2.48(1) for 3, 9.1(1) K and 2.6(1) for 4, and +11.2(1) K and 2.41(5) for 5 (with zJ′ = –0.28 K). High-field/frequency EPR data indicates significant g-anisotropy in 2 (gz = 3.6, gy = 2.2, gx = 2.0) and [NEt4][(Tp*)FeIII(CN)3]·H2O (6) (gz = 3.5, gy = 2.0, gx = 1.3), while 5 shows D = –2.09 cm–1, E = 0.08 cm–1, and B40 = –2.3 × 10–3 cm–1 with gz = 2.4 and gx = gy = 1.95. Despite significant magnetic anisotropy in 3–5, frequency-dependent behavior is only seen for 5 above 1.8 K, suggesting that rapid quantum tunnelling of the magnetization is operative.The preparation, structures, and magnetic properties of a tricyanoferrate, [NEt4][(Tp*Me)Fe(CN)3] (2), and three trinuclear {FeIII2NiII} derivatives are described. High-field/frequency EPR data indicates significant g-anisotropy in 2 and considerable magnetic anisotropy in one {FeIII2NiII} complex (5).
Datum: 13.05.2016

Boron-Centered Scorpionate-Type NHC-Based Ligands and Their Metal Complexes

The success enjoyed in the last 50 years by use of poly(pyrazolyl)borates as ligands has inspired the development of a great number of scorpionates containing other donor elements. These include polytopic bis- and tris(NHC)borate ligands, featuring N-heterocyclic carbene (NHC) moieties that generally coordinate as bidentate κ2C or tridentate κ3C, respectively. In spite of structural similarities between poly(pyrazolyl)borates and poly(NHC)borates, their methods of synthesis and their reactivity are different and reflect the variations in topology, flexibility, and donor properties. The structural and electronic properties of poly(NHC)borate ligands are compared and correlated with their coordination chemistry, particularly towards transition metals. The advances in the chemistry of scorpionate-type bis- and tris(NHC)borate ligands are reviewed by highlighting and comparing their structural properties and their ability to stabilize low to high metal oxidation states in transition-metal complexes. The advances in the design and coordination chemistry of scorpionate-type poly(NHC)borate ligands are described, highlighting their topology, flexibility, donor properties, synthesis, and reactivity pathways. The structural and electronic properties of these ligands are compared and correlated with their chemistry, particularly that of the transition metals.
Datum: 12.05.2016

Cover Picture: Advanced Complex Inorganic Nanomaterials (Eur. J. Inorg. Chem. 13-14/2016)

The front cover picture shows an active enzyme with a single catalytic center under ambient conditions. Above physiological temperature it denatures, whereas a synthetic nanoparticle containing many catalytic sites is still active. Details are presented in the Microreview by W. Tremel et al. on p. 1906 ff. For more on the story behind the cover research, see the Cover Profile.
Datum: 06.05.2016

Advanced Complex Inorganic Nanomaterials –A New Era of Nanotechnology

Guest editors Yann Garcia and Bao-Lian Su highlight the great current interest in the field of inorganic nanomaterials and offer a glimpse into the diversity of the topics discussed in this cluster issue. Guest editors Yann Garcia and Bao-Lian Su highlight the great current interest in the field of inorganic nanomaterials and offer a glimpse into the diversity of the topics discussed in this cluster issue.
Datum: 06.05.2016

Inside Cover: Advanced Complex Inorganic Nanomaterials (Eur. J. Inorg. Chem. 13-14/2016)

The inside cover picture shows the reduction of the size of coherent domains in a spin-crossover metal coordination polymer upon thermal cycling. The length of the domains displays a continuous decrease when the number of successive high-spin/low-spin/high-spin sequences increases. This observation reveals an irreversible structural fatigability, indicating a potential break in the 1D-chain morphology, and therefore sheds new light on a deeply investigated family of switchable materials. Details are discussed in the article by P. Guionneau et al. on p. 1961 ff.
Datum: 06.05.2016

Back Cover: Advanced Complex Inorganic Nanomaterials (Eur. J. Inorg. Chem. 13-14/2016)

The back cover picture shows in the background, a schematic representation of the structure of metal–organic framework (MOF) MIL-103 built from edge-sharing [LnO9] (Ln = Eu3+, Tb3+) polyhedral chains connected by the tritopic linker 1,3,5-tris(4-carboxyphenyl)benzene. Upon UV excitation, the latter transfers energy to the metal cations, pumping up their light emission. Because the intensity ratio of the Eu3+ 5D07F2 (most intense peak) and Tb3+ 5D47F5 (next most intense peak) transitions is very sensitive to temperature, below 100 K, MIL-103 nanoparticles are among the best luminescent MOF cryogenic thermometers, with a relative thermal sensitivity of 2.85 % K–1 at 14 K. Details are discussed in the article by D. Ananias, J. Rocha et al. on p. 1967 ff.
Datum: 06.05.2016

Solids Go Bio: Inorganic Nanoparticles as Enzyme Mimics

Invited for the cover of this issue is the group of Wolfgang Tremel from Johannes Gutenberg University, Mainz, Germany. The cover image shows inorganic nanoparticles that mimic the catalytic activity of naturally occurring enzymes. The nanoparticles are more stable and cost-efficient, and their high surface area endows them with a large number of active sites. It is intriguing to see that inorganic nanoparticles can mimic the catalytic activity of enzymes that evolved to perfection over millions of years...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 1906 ff.
Datum: 06.05.2016

Spotlights on our sister journals: Eur. J. Inorg. Chem. 13-14/2016

Datum: 06.05.2016

New Avenues in Inorganic Chemistry

Editor Karen Hindson stresses the importance of nanochemistry for inorganic chemists and presents the cluster issue on inorganic nanomaterials. Editor Karen Hindson stresses the importance of nanochemistry for inorganic chemists and presents the cluster issue on inorganic nanomaterials.
Datum: 06.05.2016

Side-Chain Metallopolymers Containing Second-Order NLO-Active Bimetallic NiII and PdII Schiff-Base Complexes: Syntheses, Structures, Electrochemical and Computational Studies

Unsymmetric Schiff-base metalloligand precursor 2 is synthesized by condensation of phenol-functionalized ferrocenylenaminone 1 with 2-hydroxy-5-nitrobenzaldehyde. Heterobimetallic complexes 3 and 4 result from the N2O2-tetradentate coordination of NiII and PdII metal ions with the doubly deprotonated form of 2, respectively. Linking 3 and 4 to polyacrylic acid through an esterification reaction leads to the formation of the corresponding side-chain metallopolymers 5 and 6. The new compounds were fully characterized (IR, UV/Vis, NMR, MS, CV, SEC) and structures of 2–4 unequivocally determined by single-crystal X-ray diffraction techniques. Decomposition temperatures higher than 250 °C were found by DSC and TGA techniques for 3–6. Harmonic light scattering measurements showed that compounds 2–5 exhibit rather high second-order nonlinear responses, between 200 × 10–30 and 970 × 10–30 esu, with the hyperpolarizability β1.91 value increasing significantly on passing from NiII complex 3 to its respective metallopolymer 5. The structural and electronic properties of 2–4 are analyzed by DFT and TD-DFT calculations. The redox active heterobimetallic subunits and their derived side-chain metallopolymer Schiff-base compounds exhibit good thermal stability and high second-order NLO responses. The electronic structure of the bimetallic species is analyzed by DFT and TD-DFT calculations.
Datum: 28.04.2016

Synthesis and Oxidation Catalysis of [Tris(oxazolinyl)borato]cobalt(II) Scorpionates

The reaction of CoCl2·THF and thallium tris(4,4-dimethyl-2-oxazolinyl)phenylborate (TlToM) in tetrahydrofuran (THF) provides ToMCoCl (1) in 95 % yield; however, appropriate solvents and starting materials are required to favor 1 over two other readily formed side-products, (ToM)2Co (2) and {HToM}CoCl2 (3). ESR, NMR, FTIR, and UV/Vis spectroscopies were used to distinguish these cobalt(II) products and probe their electronic and structural properties. Even after the structures indicated by these methods were confirmed by X-ray crystallography, the spectroscopic identification of trace contaminants in the material was challenging. The recognition of possible contaminants in the synthesis of ToMCoCl in combination with the paramagnetic nature of these complexes provided impetus for the utilization of X-ray powder diffraction to measure the purity of the ToMCoCl bulk sample. The X-ray powder diffraction results provide support for the bulk-phase purity of ToMCoCl in preparations that avoid 2 and 3. Thus, 1 is a precursor for new [tris(oxazolinyl)borato]cobalt chemistry, as exemplified by its reactions with KOtBu and NaOAc to give ToMCoOtBu (4) and ToMCoOAc (5), respectively. Compound 5 is a catalyst for the oxidation of cyclohexane with meta-chloroperoxybenzoic acid (mCPBA), and the rate constants and selectivity for cyclohexanol versus cyclohexanone and ϵ-caprolactone were assessed. A series of high-spin [tris(oxazolinyl)borato]cobalt(II) scorpionate complexes are synthesized and characterized by X-ray diffraction and spectroscopic investigations. The bulk-phase purity of these complexes is verified by X-ray powder diffraction.
Datum: 28.04.2016

Anionic Metal–Organic Framework for Selective Dye Removal and CO2 Fixation

A microporous Zn-based anionic metal–organic framework (MOF) was synthesized with triangular 4,4′,4″-(pyridine-2,4,6-triyl)tribenzoic acid. The anionic MOF material featuring open channels proved to be a good capturing agent for the cationic dye methylene blue. In addition, the Zn-MOF demonstrated excellent catalytic activity for CO2 fixation by cycloaddition reaction with epoxides for the generation of cyclic carbonates. A microporous Zn-based anionic metal–organic framework (MOF) is synthesized with triangular 4,4′,4″-(pyridine-2,4,6-triyl)tribenzoic acid; it features open channels and proves to be a good capturing agent for cationic dyes. In addition, the Zn-MOF demonstrates excellent catalytic activity for CO2 fixation by cycloaddition reaction with epoxides.
Datum: 27.04.2016

Expansion of a Discrete [3 × 3] Mn9 Metallogrid to a µ-Carboxylato-­Bridged Polymeric {Mn11}n Assembly

Compounds based on the [3 × 3] nonamanganese(II) square grid motif and featuring additional manganese(II) ions linked to the grid core were isolated through a strict self-assembly approach. Extended tritopic picolinic dihydrazide ligands were used, which contain terminal ester groups and differ in the R substituent on the para position of the central pyridine ring (H2L1, R = OCH3; H2L2, R = H). Upon reaction with Mn(OAc)2·4H2O, the ligand H2L1 undergoes hydrolysis and spontaneous self-assembly to afford [Mn10(L1′)6(H2O)5][Mn(H2O)6]2·11H2O, where a pentaaquomanganese(II) unit is connected to one of the terminal carboxylate functions of the grid through a Mn–O bond. The same reaction carried out with H2L2 affords an unprecedented 2D polymeric structure [Mn11(L2′)6(H2O)8][Mn(H2O)6] 24H2O, in which each nonamanganese grid is connected to its four neighbors through tetraaquomanganese(II) centers, again linked to the carboxylate functions. The two compounds also contain [Mn(H2O)6]2+ complexes in the lattice. These metallogrid-based compounds, for which DC magnetic data were collected and analysed in detail, emphasize the rich binding affinity and bridging versatility of the used ligands, which provide access to both discrete complex and extended polymeric assembly. Discrete and polymeric metallogrid compounds based on the [3 × 3] nonamanganese(II) square grid motif and featuring additional manganese(II) ions linked to the grid core were isolated. DC magnetic data show the successful expansion of the grid-type architectures based on tritopic bis(hydrazone) ligands appended with terminal pyruvate groups.
Datum: 27.04.2016

Polar Liquid Crystals Derived from Sulfonium Zwitterions of the [closo-1-CB11H12]– Anion

A series of substituted 12-sulfonium zwitterions 1[n] and one example of a 1-sulfonium analogue 2[5]a were prepared in four steps. Derivatives 1[n] exhibit rich crystalline polymorphism and a high-temperature SmBcry phase stabilized by dipolar interactions. Solution studies in a nematic host demonstrated positive dielectric anisotropy of compounds 1[5]a–1[5]c (Δϵ ≈ +18 extrapolated from 8 mol-% solutions) resulting from a longitudinal electric dipole moment of ca. 9.5 D. The effectiveness of additives 1[5] was analyzed by using the Maier–Meier formalism and DFT methods and compared to those of more polar derivatives 3[6]a and Pyr[10]. Zwitterionic derivatives of the [closo-1-CB11H12]– anion form liquid-crystalline phases and improve the dielectric properties of nematic liquid-crystal materials.
Datum: 27.04.2016

Highly DNA-Photoreactive Ruthen­ium 1,4,5,8-Tetraazaphenanthrene Complex Conjugated to the TAT Peptide: Efficient Vectorization inside HeLa Cells without Phototoxicity – The Importance of Cellular Distribution

The photoreactive [Ru(TAP)2(phen)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene; phen = 1,10-phenanthroline) complex tethered to the cell-penetrating peptide (CPP) TAT was studied in vitro and in cellulo. The tethering of the complex does not affect its behavior under blue-light irradiation in the presence of guanine-containing oligodeoxyribonucleotides (ODNG). Thus, the luminescence is quenched in the presence of ODNG, and gel electrophoresis experiments showed the appearance of products corresponding to the irreversible attachment of the conjugate to ODNG upon illumination. The cellular uptake of the conjugate was examined by flow cytometry, inductively coupled plasma mass spectrometry (ICP-MS), and confocal imaging microscopy. These experiments showed that the [Ru(TAP)2(phen-TAT)] conjugate is readily taken up by HeLa cells and, despite these favorable factors, the cellular survival was 100 %, as measured by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. A possible origin of the inactivity of [Ru(TAP)2(phen-TAT)] under irradiation is proposed on the basis of the fluorescence-activated cell sorting (FACS), ICP-MS, and confocal microscopy results. Photoreactive [Ru(TAP)2(phen)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene; phen = 1,10-phenanthroline) is tethered to the cell-penetrating peptide TAT. Despite its ability to form stable photoadducts with DNA and efficient transportation into the cells, no photocytotoxicity was observed. A possible origin of the inactivity of the TAT-conjugated [Ru(TAP)2(phen)]2+ under illumination is proposed.
Datum: 27.04.2016

Organosilatranes with Acylthiourea Derivatives – Metal-Ion Binding, Substituent-Dependent Sensitivity, and Prospects for the Fabrication of Magnetic Hybrids

A variety of topologically interesting acylthiourea-tethered organosilatranes (AcTu-OS) were prepared, and their function as metal-ion binding sites was investigated. The prepared compounds have been characterized by elemental analysis; FTIR, UV/Vis and NMR (1H and 13C) spectroscopy; and mass spectrometry. The organosilicon complexes 4a–4e possess diverse coordination abilities for the surveyed metal ions (Cu2+, Cd2+, Hg2+ and Pb2+), as was appraised by the corresponding absorption shifts in the UV/Vis spectra. In addition, a facile preparatory route for the covalent grafting of the most efficient receptor 4e onto a silica-encrusted magnetic nanosupport was implemented. The resultant organic–inorganic hybrid nanoparticles (H-NPs) were characterized by physicochemical techniques such as FTIR spectroscopy, XRD, thermogravimetric analysis (TGA), TEM, field-emission SEM (FE-SEM) and energy-dispersive X-ray spectroscopy (EDX). The grafting of the sensory module afforded active sites for the adsorption of metal ions from the aqueous solution which is outlined using the Langmuir adsorption isotherm. The potential in sensing, sorbent properties and facile magnetic recovery of the hybrid evinces the separation process practical to undertake environmental issues. Acylthiourea-tethered organosilatranes are synthesized by the coupling of carboxylic acids with (aminopropyl)silatrane through acyl isothiocyanates. These derivatives are probed for metal-ion sensing. One of the silatranes is further immobilized onto the surface of magnetic silica nanospheres, and the hybrid is characterized and tested for the adsorption of copper and lead ions.
Datum: 26.04.2016

Adenine-Based Coordination Polymers: Synthesis, Structure, and Properties

A solvothermal reaction of metal nitrate (M = Zn, Cd), cyclohexanedicarboxylic acid, and adenine resulted in the isolation of three new coordination polymers, [Zn4(1,4-CHDA)2.5(ad)3·2H2O] 7H2O 2DMA (CHDA = cyclohexane dicarboxylic acid, ad = adenine, DMA = dimethylacetamide), I, [Cd3(1,4-CHDA)2(ad)2·H2O], II, [Cd(1,2-CHDA)(9-HEA)·H2O] 4H2O [9-HEA = 9-(2-hydroxyethyl)adenine], III. Single-crystal structural studies show that compounds I and II have three-dimensional structures whereas III has a two-dimensional one. The formation of a Cd8 macrocycle in II, based on a polyhedral arrangement, appears to be new. In all the compounds, the amino group of the adenine appears to be free and can be utilized for the detection of explosives such as nitrophenol, dinitrophenol, and trinitrophenols. The hydroxyl nitro aromatics appears to have a much stronger influence on the luminescence behavior of the compounds with very low detection limits. This, in fact, provides a new opportunity for exploring these compounds for the detection of harmful nitro aromatics in solution. The present compounds also exhibit considerable sensitivity towards metal ion detection, especially Fe2+/Fe3+, Cr3+, Ag+, and Hg2+ ions in solution. Base-catalyzed Knoevenagel condensation studies exhibit good conversion and selectivity. The synthesis and characterization of adenine-based coordination polymers are presented. The compounds exhibit significant quenching towards nitrophenolic analytes and Fe3+ ions in solution.
Datum: 26.04.2016

Rapid Synthesis of a Functional Resin-Supported Scorpionate and Its Copper(I, II), Rhodium(I), and Chromium(III) Complexes

Boron-scorpionates are readily prepared by microwave (MW) assisted methods. Such a method is described here, leading to the rapid preparation of a heterogeneous resin-supported scorpionate as its sodium salt, BdPhTpNa [BdPhTp = phenyltris(1-pyrazolyl)borate covalently bound through the phenyl ring to commercial cross-linked polystyrene resin beads]. Formation of a functional heterogeneous scorpionate was confirmed from the subsequent reactions of several metal complexes. This supported ligand system coordinates a variety of transition metal ions including copper(I and II), chromium(III) and rhodium(I). Chromium(III) provided definitive electronic spectral evidence for supported–TpCrIII coordination spheres, including reversible ligand-substitution reactions. The copper(I) case exhibited typical scorpionate CuI reactivity including spectroscopically characterized (IR and 31P NMR) complexes with CO, PPh3, and HCCH. Copper(II) provided EPR evidence for heterogeneous scorpionates. The supported rhodium(I) complex was demonstrated to be a recyclable heterogeneous rhodium–scorpionate catalyst. These results all support the conclusion that the immobilized chelate forms coordinatively unsaturated half-sandwich metal complexes (LMn+) capable of efficient ligand-substitution reactions or catalytic activity. A microwave-assisted method is described for the rapid preparation of a heterogeneous resin-supported scorpionate as its sodium salt. Formation of functional heterogeneous metal scorpionates was confirmed from subsequent reactions of its varied metal (Cr, Cu, Rh) complexes.
Datum: 26.04.2016

Reactivity of an N-Heterocyclic Carbene Stabilized Hydrosilylene ­towards a Ketone and CO2: Experimental and Theoretical Study

The reaction of N-heterocyclic carbene (NHC)-stabilized hydrosilylene 1, tBu3SiSi(H)NHC, with one and two equivalents of benzophenone gave rise to bicyclic compounds 2 and 3, tBu3Si(R)[Si-CH2-N(CMeCMeNMe)-CPh2-O] (R = H, OCHPh2). The NHC plays a crucial role in this reactivity, as it is directly involved in C–C bond formation and supplies the C–H-activated methyl group. In the formation of 3, the terminal Si–H bond of the hydrosilylene is involved in transition-metal-free hydrosilylation. All steps in these mechanisms are based on NHC-stabilized zwitterionic transition states and intermediates and were investigated by utilizing DFT calculations. In addition, the CO2 activation of 1 to yield cis/trans-cyclotrisiloxane 4, [(tBu3Si)(H)Si-O]3, stereoselectively and its mechanistic study are reported. Reaction of an N-heterocyclic carbene stabilized hydrosilylene with benzophenone yields a bicyclic compound through C–C bond formation and transition-metal-free hydrosilylation. In contrast, the reaction of the same silylene with carbon dioxide affords a cis/trans-cyclotrisiloxane by oxygen transfer. Both reaction mechanisms are studied in detail by DFT calculations.
Datum: 26.04.2016

Recent Progress in Asymmetric Synthesis and Application of Difunctionalized Silicon-Stereogenic Silanes

During the past decades, silicon-stereogenic compounds have continuously been attracting attention in synthetic chemistry. The preparation of representatives containing reactive silicon–element bonds is thus an interesting task to allow further transformations. Provided that the chiral information can efficiently be transferred in these conversions, reactive silicon-chiral silanes may lead to interesting new applications. In this microreview we give an overview of difunctionalized silanes containing asymmetrically substituted silicon centers. Several intriguing approaches have been discovered over the years and are presented in terms of their synthetic potential and stereochemical behavior. With a special focus on our recent achievements in the field of silicon-stereogenic N,O-silanes, new mechanistic aspects of stereocontrolled nucleophilic substitutions are also discussed, along with innovative coordination capabilities that arise from the unique silicon-centered asymmetry. Difunctionalized silicon-chiral silanes are an attractive class of building blocks. They open new possibilities in design and application of chirally modified compounds and shed light on substitution mechanisms at silicon. Here we review important developments during the last decades, focusing on our recent contributions in this field of research.
Datum: 26.04.2016

Selective Formation of cis-N-Heterocyclic Carbene-PtII-Pnictogen Complexes and in vitro Evaluation of Their Cytotoxic Activities toward Cancer Cells

A series of heterotopic platinum complexes combining N-heterocyclic carbene (NHC) and pnictogen-based ligands [Pn = P(nBu)3, PPh3, AsPh3 and SbPh3] has been synthesized and fully characterized. Use of an excess of Pn ligand led to the formation of cationic bis-Pn platinum-NHC complexes in high yield, with both Pn ligands being arranged trans to each other. Several representative complexes could be characterized by X-ray crystallographic studies thus confirming the ligand arrangement around the metal. This simple approach allows the generation of diversity in metallodrug candidates. Biological activities on various human cancer cells have been studied and compared with those of cisplatin. The results confirmed the high cytotoxicity of these NHC-platinum complexes bearing pnictogen ligands. We report on the synthesis of neutral and cationic heterotopic platinum complexes combining N-heterocyclic carbene (NHC) and pnictogen-based ligands.
Datum: 26.04.2016

Coordination Chemistry of an Unsymmetrical Naphthyridine-Based Tetradentate Ligand toward Various Transition-Metal Ions

An unsymmetrical ligand, 2-(2-pyridinyl)-7-(pyrazol-1-yl)-1,8-naphthyridine (L5) was prepared for the construction of a series of dinuclear complexes. Treatment of L5 with [Ru2(µ-OAc)4Cl] followed by anion metathesis afforded [(L5)(µ-OAc)3Ru2](PF6) (3). Reaction of L5 with 2 equiv. of Ni(OAc)2 provided [Ni4(L5)2(µ-OH)4(CF3COO)2](CF3COO)2 (5). Reaction of [Re2(CO)8(CH3CN)2] with L5 in a refluxing chlorobenzene solution gave a mixture of dirhenium (6) and monorhenium (7) complexes. The monocobalt complex 8 was obtained from complexation of L5 with CoCl2. These new complexes were characterized by elemental analysis and spectroscopic techniques. The structures of complexes 3, 5 and 8 were further confirmed by X-ray crystallography. Nickel complex 5 was evaluated as a catalyst for reduction reactions involving the conversion of ester functionalities into their corresponding alcohols. Diruthenium, dinickel and dirhenium complexes containing an unsymmetrical ligand, 2-(2-pyridinyl)-7-(pyrazol-1-yl)-1,8-naphthyridine, were prepared and characterized. The nickel complex is an effective catalyst for the reduction of esters to the corresponding alcohols.
Datum: 26.04.2016

Tuning the Magnetoluminescence Behavior of Lanthanide Complexes Having Sphenocorona and Cubic Coordination Geometries

The reaction of the tripodal fluorophoric ligand tris(benzimidazol-2-ylmethyl)amine (ntbi) with two different lanthanide salts [Ln(NO3)3 and LnCl3 (Ln = Dy, Ho, Tb)] afforded two new classes of mononuclear complexes. The class 1 complexes [{Ln(ntbi)(NO3)3}2·3CH3OH; Ln = Dy (1) and Ho (3)] exhibit very rare “sphenocorona” coordination geometries around the Ln centers, whereas the class 2 complexes [{Ln(ntbi)2}5·15Cl·xH2O; Ln = Dy, x = 18 (2) and Ln = Tb, x = 27 (4)] show “cubic” coordination geometries, as revealed by single-crystal X-ray diffraction studies. The class 2 complexes also exhibit a unique “double-propeller”-type structural feature. Owing to the significant difference in the coordination geometries around the Ln centers, prominent variations in the slow magnetic relaxation behaviors as well as the luminescence intensities are observed by alternating current magnetic susceptibility and solid-state luminescence studies, respectively. LnIII complexes (Ln = Dy, Ho, Tb) with distinctly different coordination geometries, namely, sphenocorona and cubic, are synthesized. The different coordination geometries around the LnIII centers significantly modulate the slow magnetic relaxation and photoluminescence behaviors of the complexes, as revealed from AC magnetic susceptibility and solid-state luminescence studies, respectively.
Datum: 26.04.2016

Hole-Size Relationships in the Assembly of a Furandicarboxylate-Based Metallolinker in Praseodymium Coordination Polymers Synthesized under Basic Conditions

Datum: 26.04.2016

Synthesis of Gold(I) Derivatives Bearing Alkylated 1,3,5-Triaza-7-phosphaadamantane as Selective Anticancer Metallodrugs

The alkylation of one of the nitrogen atoms of the molecule 1,3,5,triaza-7-phosphaadamantane (PTA) with para-substituted benzylic units and the L-phenylalanine methyl ester moiety are reported. The crystalline structures of the two alkylated PTA species [PTA-CH2-p-COOH-C6H4]Br (1a) and [PTA-CH2-p-CH2COOH-C6H4]Br (2) reveal the presence of interactions between the bromide anion and the OH group of the acid moiety. Bis-phosphane derivatives were prepared by the alkylation of two PTA molecules with a dibromide salt to afford more water-soluble species. The corresponding mono- and dinuclear chloro-, thiocyanato- and pentafluorophenyl gold(I) derivatives are described. Most of the new complexes have been tested as anticancer agents, exhibiting higher cytotoxicity than cisplatin against human colon cancer cell lines. Some of them display low cytotoxicity towards differentiated cells (non-carcinogenic), as determined from viability studies, thereby demonstrating a significant specificity in this type of cancer. The preparation of new water-soluble mono- and bis-phosphanes derived from 1,3,5-triaza-7-phosphaadamantane (PTA) is described. Antiproliferative effects against colon cancer cell lines and low cytotoxicity towards differentiated cells (non-carcinogenic) have been observed for some of the gold complexes formed with these phosphanes.
Datum: 25.04.2016

Paddlewheel-Type Dirhodium Tetrapivalate Based Coordination Polymer: Synthesis, Characterization, and Self-Assembly and Disassembly Transformation Properties

An extended one-dimensional chain-type coordination polymer, [Rh2(piv)4(tpy)]n (1; piv = pivalate, tpy = 2,2′:6′,2″-terpyridine), has been synthesized and characterized by single-crystal and powder X-ray diffraction analyses, elemental analysis, IR spectrosopy, thermogravimetric analysis, UV/Vis diffuse reflectance spectroscopy, and magnetic measurements at 300 K. This complex shows unique repeatable self-assembly and disassembly transformation properties. Polymer 1 readily decomposed to its constituent building blocks, that is, [Rh2(piv)4] and tpy, in organic solvents at 300 K, but the disassembly product of 1 readily re-self-assembled to give 1 as a crystalline product in aqueous ethanol solution at 373 K. In addition, 1 was obtained as a crystalline powder by a water-assisted mechanochemical synthesis route. An extended one-dimensional chain-type coordination polymer, [Rh2(piv)4(tpy)]n, has been obtained by solvothermal reaction of [Rh2(piv)4] and tpy in aqueous EtOH solution. This complex shows unique repeatable self-assembly and disassembly transformation properties in (aqueous) organic solvents.
Datum: 25.04.2016

Synthesis, Characterization and ­Aerobic Alcohol Oxidation Catalysis of Palladium(II) Complexes with a Bis(imidazolyl)borate Ligand

Chloro- and hydroxo-palladium(II) complexes with an imidazole-based scorpionate ligand bis(1-methylimidazolyl)methylphenylborate, [B(ImN–Me)2MePh]– (= LPh), have been synthesized. Reaction of a lithium salt of LPh with [PdCl2(NCPh)2] yields a miscellaneous mixture involving a homoleptic complex [Pd(LPh)2]. Replacement of the neutral ligand (benzonitrile) in the starting material with pyridine leads to the desired chloride complex 1. X-ray crystallographic analysis reveals the formula of 1 to be [PdCl(LPh)(py)] with a square-planar palladium(II) center supported by the bidentate LPh ligand. Treatment of 1 with NaOH yields non-pyridine-containing hydroxo species with LPh such as [Pd(OH)(LPh)(H2O)] and [(PdLPh)2(µ-OH)2]. The hydroxo species 2 can convert into active species for catalytic secondary alcohol oxidation with O2 in the absence of extra base. The utility of 2 as a catalyst precursor and the inertness of chloride complex 1 suggest that the basic nature of the co-ligand (i.e. OH–) on the palladium center supported by LPh is essential to the formation of a putative palladium–alkoxide intermediate. Chloro- and hydroxo-palladium(II) complexes containing the imidazole-based scorpionate ligand bis(1-methylimidazolyl)methylphenylborate, [B(ImN–Me)2MePh]– (= LPh), have been synthesized. The hydroxo species can be converted into an active species that catalyzes secondary alcohol oxidation with O2 in the absence of base; the chlorido complex is inactive.
Datum: 25.04.2016

Double-Decker Coordination Cages

Bis(pyridin-3-ylmethyl) pyridine-3,5-dicarboxylate (L) possessing one internal and two terminal pyridine moieties displayed differential coordination ability when combined with suitable PdII components. The compound L acted as a bidentate chelating ligand to form mononuclear complexes when combined with cis-[Pd(tmeda)(NO3)2] or Pd(NO3)2 in calculated ratios. The combination of Pd(NO3)2 with L in a ratio of 3:4, however, afforded the trinuclear “double-decker” cage [(NO3)2⊂Pd3(L)4](NO3)4, in which L acts as a nonchelating tridentate ligand and the counter anion (i.e., NO3–) acts as template. The encapsulated NO3– can be replaced by F–, Cl–, or Br– but not by I–. The F–-encapsulated cage could not be isolated due to its reactivity, whereas the Cl– or Br– encapsulated cages could be isolated. Although anionic guests such as NO3–, Cl–, or Br– stabilized the cages, the presence of excess Cl– or Br– (not NO3–) facilitated decomplexation reactions releasing the ligand. The complexation of Pd(Y)2 (Y = BF4–, PF6–, CF3SO3–, or ClO4–) with L afforded the corresponding mononuclear complexes under appropriate conditions. However, these counter anions could not act as templates for the construction of double-decker cages. A trinuclear “double-decker” cage has been constructed from Pd(NO3)2 and a tridentate ligand. The NO3– counter anion acted as a template and was encapsulated into the cage structure. The encapsulated NO3– could be replaced by F–, Cl–, or Br– but not by I–. Excess NO3– did not harm the cages but excess Cl– or Br– destroyed the cages releasing the ligand.
Datum: 25.04.2016

Systematic Synthesis of Di-, Tri-, and Tetranuclear Homo- and Heterometal Complexes Using a Mononuclear Copper Synthon with a Tetra­dentate Amino Alcohol Ligand

The reaction of Cu(NO3)2·3H2O with an N2O2 tetradentate amino alcohol, N,N-dibenzyl-N′,N′-bis(2-hydroxyethyl)ethylenediamine (H2L), afforded the mononuclear copper complex [Cu(H2L)(NO3)](NO3) (1), which has been used to construct a series of di-, tri-, and tetranuclear homo- and heterometallic complexes. Complex 1 dimerized in the presence of NEt3 to form the Cu2 complex [Cu2(HL)2](NO3)2 (2) by the deprotonation of one of the two hydroxy groups in the H2L ligand. The reaction of 1 with Cu(OCOH)2 in the presence of NEt3 afforded the Cu3 complex [Cu3(HL)2(OCOH)2](NO3)2 (5). The metalloligand {Cu(HL)}+ derived from 1 reacted with M(OAc)2 (M = Cu, Co, Zn, Ni) in the absence of NEt3 to form the asymmetric CuM dinuclear complexes [CuM(HL)(OAc)(NO3)2] [M = Cu (3a), Co (3b), Zn (3c), Ni (3d)], whereas in the presence of NEt3 a unit of M(OAc) was captured by two metalloligands to give the bent CuMCu trinuclear complexes [Cu2M(HL)2(OAc)2(NO3)](NO3) [M = Cu (4a), Co (4b), Mn (4c)], which were further transformed into the linear CuMCu trinuclear complexes [Cu3(HL)2{(PhO)2PO2}2](NO3)2 (7a) and [Cu2M(HL)2{(PhO)2PO2}2(MeOH)2](NO3)2 [M = Co (7b), Mn (7c)] with the aid of diphenyl phosphate bridging ligands. When (PhO)PO2(OH) was used as an auxiliary bridging ligand in the reaction of 1 with M(OAc)2 and NEt3, the Cu2M2 tetranuclear complexes [Cu2M2(HL)2{(PhO)PO3}2(NO3)2] [M = Co (8a), Zn (8b)] were synthesized. These results demonstrate that the mononuclear copper synthon with the N2O2 tetradentate amino alcohol ligand {Cu(H2L)}2+ generates the quite useful metalloligand {Cu(HL)}+ by the deprotonation of a hydroxy group, and subsequent reactions lead to the construction of a series of homo- and heterometal complexes containing Cu2, CuM (M = Cu, Co, Zn, Ni), bent-CuMCu (M = Cu, Co, Mn), linear-CuMCu (M = Cu, Co, Mn), and Cu2M2 (M = Co, Mn) cores in a systematic and selective manner. A mononuclear copper complex bearing by an N2O2 tetradentate ligand is a suitable metalloligand for the systematic synthesis of di-, tri-, and tetranuclear homo- and heterometal complexes.
Datum: 25.04.2016

Electronic Control of RuII Complexes with Proximal Oxophilic Phenylselenium Tethers: Synthesis, Characterization, and Activation of Molecular Oxygen

Various ruthenium(II) complexes with proximal oxophilic phenylselenium groups of the general formula [RuIILALB]X2 {LA = LB = 6,6′-bis[(4-methoxyphenyl)selanyl]-2,2′-bipyridine; 6,6′-bis[(nitrophenyl)selanyl]-2,2′-bipyridine; 3,6-bis(phenylselanyl)dipyrido[3,2-a:2′,3′-c]phenazine; LA = 6,6′-bis(phenylselanyl)-2,2′-bipyridine, LB = terpyridine} were prepared. The substitution patterns of these compounds were designed to have different electron-withdrawing/-donating properties or different binding motifs in comparison to the previously reported compound with LA = LB = 6,6′-bis(phenylselanyl)-2,2′-bipyridine. The research objective was to evaluate the potential of these compounds to activate ground-state molecular oxygen to form higher-valent Ru–O–Se bonds by cleavage of the O–O bond of O2. All of the compounds prepared indeed activated O2 to form Ru–O–Se moieties, as observable by UV/Vis spectroscopy, mass spectrometry, or X-ray crystallography. Various ruthenium complexes with bipyridine or phenanthroline ligands with phenylselenium appendages react with molecular oxygen by oxygen–oxygen bond cleavage to form products with Ru–O–Se bonding motifs.
Datum: 25.04.2016

The Importance of Heterolepticity in Improving the Antibacterial Activity of Bismuth(III) Thiolates

Five mixed thiolatobismuth(III) complexes [BiPh(5-MMTD)2{4-MMT(H)}] (1), [Bi(1-MMTZ)2{(PYM)(PYM(H))2}] (2), [Bi(MBT)2(5-MMTD)] (3), [Bi(4-BrMTD)3{2-MMI(H)}] (4) and [Bi(1-MMTZ)2{1-MMTZ(H)}(2-MMI){2-MMI(H)2}] (5) were synthesised from imidazole-, thiazole-, thiadiazole-, triazole-, tetrazole- and pyrimidine-based heterocyclic thiones. Four of these complexes 1–4 were synthesized from BiPh3, while complex 5 was obtained from Bi[4-(MeO)Ph]3. Complexes 1–5 were structurally characterised by XRD. Evaluation of the antibacterial properties against Mycobacterium smegmatis, Staphylococcus aureus, Methicillin-resistant S. aureus (MRSA), Vancomycin-resistant Enterococcus (VRE), Enterococcus faecalis and Escherichia coli showed that mixed thiolato complexes containing the anionic thiazole-based ligands MBT and 4-BrMTD are most effective. The mixed thiolato complexes [Bi(MBT)2(5-MMTD)] (3) having thiazole- and thiadiazole- and [Bi(4-BrMBT)3{2-MMI(H)}] (4) containing thiazole- and imidazole-based ligands proved to be more efficient, with low minimum inhibitory concentrations of 1.73 and 3.45 µM for 3 against VRE and E. faecalis, respectively, and 2.20 µM for 4 against M. smegmatis and E. faecalis. All complexes showed little or no toxicity towards mammalian COS-7 cell lines at 20 µg mL–1. Bismuth(III) mixed thiolato complexes [BiPh(5-MMTD)2{4-MMT(H)}] (1), [Bi(1-MMTZ)2{(PYM)(PYM(H))2}] (2), [Bi(MBT)2(5-MMTD)] (3), [Bi(4-BrMTD)3{2-MMI(H)}] (4) and [Bi(1-MMTZ)2{1-MMTZ(H)}(2-MMI){2-MMI(H)2}] (5) were synthesised, and their antibacterial activity was studied. Heteroleptic complexes seem to have improved activity.
Datum: 25.04.2016

A Convenient Route to Monoalkyl-Substituted Phosphanylboranes (HRP–BH2–NMe3): Prospective Precursors to Poly[(alkylphosphino)­boranes]

A simple method to access borylphosphonium iodides [RH2P–BH2·NMe3]I (1a: R = Me; 1b: R = Et; 1c: R = nPr) by the addition of iodoalkanes to PH2–BH2·NMe3 was developed. Complexes 1a–c were characterized by multinuclear NMR spectroscopy, and 1a and 1b additionally by single-crystal X-ray diffraction. It was possible to synthesize the Lewis-base-stabilized organosubstituted phosphanylborane MePH–BH2·NMe3 (2) from [MePH2–BH2·NMe3]I (1a). Thermolysis of 2 generated a soluble, low-molecular-mass poly(alkylphosphinoborane) consisting of at least 40 repeat units, as identified by ESI-MS. These results are promising for the future preparation of a wide range of Lewis-base-stabilized phosphanylboranes, which are of interest as precursors to poly[(alkylphosphino)boranes] and are otherwise difficult to access by conventional metal-catalyzed methods. A route for the synthesis of monoalkyl-substituted Lewis-base-stabilized phosphinoboranes via borylphosphonium precursors is presented. Mild thermolysis of the Lewis-base-stabilized methylphosphinoborane generates the corresponding polymer consisting of at least 40 repeat units, which exemplifies the applicability of this method.
Datum: 25.04.2016

Carboxylate–Hydrazone Mixed-Linker Metal–Organic Frameworks: Synthesis, Structure, and Selective Gas Adsorption

New mixed-linker metal–organic framework (MOF) materials incorporating both carboxylate and hydrazone linkers were prepared. The zinc-based 3D MOFs were obtained by utilizing a presynthesized aroylhydrazone [4-pyridinecarbaldehyde isonicotinoyl hydrazone (PCIH)] and para-dicarboxylic acids [1,4-benzenedicarboxylic acid (H2BDC) and 4,4′-biphenyldicarboxylic acid (H2BPDC)]. Single-crystal X-ray diffraction revealed the interpenetrated, pillar-layered structures of the MOFs, including layers formed by dicarboxylate-bridged Zn2 nodes as well as hydrazone pillars. The microporous [Zn2(dcx)2(hdz)2]·guests frameworks (dcx = linear dicarboxylate dianion; hdz = hydrazone) were found to adsorb CO2 selectively over N2 upon thermal activation. The frameworks represent rare MOFs of the type [Zn2(dcx)2(pil)2] (pil = neutral pillar), in which two pillars at each metallic site of the Zn2 node connect adjacent layers. Two metal–organic frameworks incorporating carboxylate and acylhydrazone moieties are constructed from 4-pyridinecarbaldehyde isonicotinoyl hydrazone (PCIH) and linear dicarboxylate [dcx = 1,4-benzene- (BDC) or 4,4′-biphenyldicarboxylate (BPDC)]. Interpenetrated pillar-layered [Zn2(dcx)2(PCIH)2] frameworks selectively adsorb CO2 over N2.
Datum: 21.04.2016

Synthesis, Characterization, Magnetic Properties, and Topological Aspects of Isoskeletal Heterometallic Hexanuclear CoII4LnIII2 Coordination Clusters Possessing 2,3,4M6–1 Topology

The reaction of (E)-2-(2-hydroxy-3-methoxybenzylideneamino)phenol (H2L1) with Co(NO3)2 6H2O and LnCl3 x(H2O) afforded a family of hexanuclear heterometallic coordination clusters (CCs) formulated as [CoII4LnIII2(µ3-OH)2(L1)4Cl2(NO3)2(MeOH)4] 3(Et2O) where Ln is Y (1), Gd (2), Dy (3), and Tb (4). All the compounds are stable in solution as confirmed by ESI-MS studies. The compounds can be described as twisted boat-like and possess a 2,3,4M6–1 topology. The reaction of (E)-2-(5-bromo-2-hydroxy-3-methoxybenzylideneamino)phenol (H2L2) with Co(NO3)2 6H2O and DyCl3 x(H2O) afforded [CoII4DyIII2(µ3-OH)2(L2)4Cl2(NO3)2(MeOH)4] (5), which is isoskeletal to compounds 1–4. Magnetic studies performed over the temperature range 1.8–300 K show that compound 3 undergoes slow magnetic relaxation. The use of a diprotic Schiff base ligand (H2L1) with Co(NO3)2 6H2O and LnCl3 x(H2O) afforded a family of hexanuclear coordination clusters formulated as [CoII4LnIII2(µ3-OH)2(L1)4Cl2(NO3)2(MeOH)4] 3(Et2O) where Ln is Y(1), Gd (2), Dy (3), and Tb (4). The topology of these compounds is 2,3,4M6–1. Compound 3 shows single molecule magnet (SMM) behavior.
Datum: 21.04.2016

Fe3O4@MIL-101 – A Selective and Regenerable Adsorbent for the Removal of As Species from Water

The chromium-based metal–organic framework MIL-101(Cr) served as a host for the in situ synthesis of Fe3O4 nanoparticles. This hybrid nanomaterial was tested as an adsorbent for arsenite and arsenate species in groundwater and surface water and showed excellent affinity towards AsIII and AsV species. The adsorption capacities of 121.5 and 80.0 mg g–1 for arsenite and arsenate species, respectively, are unprecedented. The presence of Ca2+, Mg2+, and phosphate ions and natural organic matter does not affect the removal efficiency or the selectivity. The structural integrity of the hybrid nanomaterial was maintained during the adsorption process and even after desorption through phosphate elution. Additionally, no significant leaching of Cr or Fe species was observed. MIL-101(Cr) serves as a host for the in situ synthesis of Fe3O4 nanoparticles. The resulting material shows excellent affinity towards AsIII and AsV species in water. Ca2+, Mg2+, and phosphate ions as well as natural organic matter do not affect the removal efficiency or selectivity. The structural integrity of the host is maintained during the adsorption and desorption process.
Datum: 21.04.2016

A Promising White-Light-Emitting Material Constructed from Encapsulating Eu3+/Tb3+ Hybrid Ions into a Robust Microporous Metal–Organic Framework

Metal–organic frameworks (MOFs) as extremely promising luminescent materials have become a hot area of research in recent years. Porous MOFs containing uncoordinated groups within the pores play a central role in the functional properties of the material and create a driving force for loading lanthanide(III) (Ln3+) ions. In this work, we report the fascinating {[Zn(H2thca)0.5(tib)]·5H2O}n [1; H6thca = p-terphenyl-3,3′,3″,5,5′,5″-hexacarboxylic acid; tib = 1,3,5-tris(imidazolyl)benzene] MOF, which has a permanently porous structure and uncoordinated carboxyl groups within the pores; it can emit blue light and can serve as a host for several guest Ln3+ ions. Strong red fluorescence and green fluorescence can be generated by introducing Eu3+ and Tb3+ ions into the pores of compound 1, respectively. Furthermore, the luminescence properties of Ln3+@1 can be easily modulated simply by adjusting the amounts of complexing Tb3+ and Eu3+ ions, and in this way the material exhibits broadband white emission with ideal CIE coordinates of (0.3438, 0.3547). This work provides a simple and practical strategy for the design and development of white-light emitters based on lanthanide-functionalized MOFs, which opens a new perspective for the development of white-light-emitting materials. A fascinating {[Zn(H2thca)0.5(tib)]·5H2O}n [H6thca = p-terphenyl-3,3′,3″,5,5′,5″-hexacarboxylic acid; tib = 1,3,5-tris(imidazolyl)benzene] metal–organic framework with a permanently porous structure and containing uncoordinated carboxyl groups within the pores is obtained. It emits blue light and can serve as a host for several guest Ln3+ cations; thus, it can exhibit broadband white emission by simple postmodification methods.
Datum: 21.04.2016

The Flexibility of P2O7 Dimers in Soft Structures: M2CdP2O7 (M = Rb, Cs)

Two new congruent-melting alkali metal diphosphates, Rb2CdP2O7 and Cs2CdP2O7, were synthesized by conventional solid-state reactions. Single-crystal X-ray structural analyses showed that M2CdP2O7 (M = Rb, Cs) feature two-dimensional [CdP2O7]2– layers that are composed of CdO5 pyramids and P2O7 dimers. The Rb+ and Cs+ cations ions fill the interlayers. The flexible P2O7 dimers could be bent and distorted if the Cs+ ion was substituted by the Rb+ ion, which led to crystallization of the Rb2CdP2O7 compound in the lower symmetry monoclinic space group P21/c (No. 14) and crystallization of the Cs2CdP2O7 compound in the high-symmetry orthorhombic space group Pnma (No. 53). Thermal analyses showed that the two compounds melt congruently and that the melting point of Rb2CdP2O7 compound is lower than that of the Cs2CdP2O7 compound owing to distortion of the P2O7 dimers. IR spectroscopy and UV/Vis–near-IR diffuse reflectance spectroscopy were performed on the reported compounds. Distortion of the P2O7 dimer in the Rb2CdP2O7 compound leads to a lower melting point than that of the Cs2CdP2O7 compound. It is found that the soft structures of Rb and Cs compounds can crystallize in different space groups.
Datum: 20.04.2016

Cyclopentadienyl–Silsesquioxane Titanium Catalysts: Factors Affecting Their Formation and Activity in Olefin Epoxidation with Aqueous Hydrogen Peroxide

The reaction of titanium chlorosilyl-substituted cyclopentadienyl (Cp) complexes, Ti(η5-C5H3R′SiMe2Cl)Cl3 (R′ = H, 1b; SiMe3, 1c), with 1 equiv. of various silsesquioxane trisilanols, R7Si7O9(OH)3 (R = iBu, 2a; Ph, 2b), affords either corner-capped Cp derivatives, Ti(η5-C5H3R′SiMe2Cl)(R7Si7O12-κ3O3) (R′ = H, R = iBu, 5a, Ph, 5b; R′ = SiMe3, R = iBu, 7a, Ph, 7b), or cyclopentadienyl–silsesquioxane complexes, Ti(η5-C5H4SiMe2OR7Si7O11-κ2O2)Cl (R′ = H, R = iBu, 6a, Ph, 6b; R′ = SiMe3, R = iBu, 8a, Ph, 8b), depending on the reaction conditions. In any case, upon heating, kinetic products 5 and 7 are transformed into the corresponding thermodynamic products 6 and 8, respectively. The electron-donating ability of the Cp ring is a relevant controlling parameter: a strong π-donor character facilitates the isomerization process. In addition, the nature of the silicon substituents in the silsesquioxane framework, the type of solvent, and the reaction temperature are also factors that significantly affect this process. Cyclopentadienyl–silsesquioxane complexes 6b and 8b are efficient and selective catalysts for epoxidation with aqueous hydrogen peroxide under mild conditions. Such a catalytic efficiency is attributed to the hydrophobic environment generated about the titanium atom by the Cp ring incorporated into the cyclopentadienyl–silsesquioxane ligand. A set of efficient catalysts based on titanium cyclopentadienyl–silsesquioxane derivatives for olefin epoxidation with aqueous hydrogen peroxide has been prepared. The modification of the electronic and steric properties of the Cp ring entails important differences in the chemical and catalytic behavior of such compounds
Datum: 20.04.2016

Hydrate Networks under Mechanical Stress – A Case Study for Co3(PO4)2·8H2O

The nature of the bound water in solids with hydrogen-bonded networks depends not only on temperature and pressure but also on the nature of the constituents. The collapse and reorientation of these network structures determines the stability of hydrated solids and transitions to other crystalline or amorphous phases. Here, we study the mechanochemically induced loss of bound water in Co3(PO4)2·8H2O and compare this process to the behavior under hydrostatic pressure. The associated phase transition and its kinetics were monitored by X-ray powder diffraction with synchrotron radiation and quantitative IR spectroscopy. High shearing forces are responsible for the degradation of the hydrogen-bonded network and the concomitant crystalline–amorphous transformation. UV/Vis spectroscopy, extended X-ray absorption spectroscopy (EXAFS), and X-ray absorption near-edge spectroscopy (XANES) provided information about the short-range order in the amorphous solid, and thermal analysis revealed its composition and showed that the moderate charge densities of the Co2+ and PO43– ions, which make the hydration enthalpy comparable to the binding energy of the counteranions, and the formation of hydrogen-bonded networks favor multistage crystallization processes associated with the release and uptake of coordinated water. The changes of the Co2+ coordination induce a color change from pink to blue; therefore, Co3(PO4)2·8H2O can be used as an overheat temperature indicator. The collapse and reorientation of a hydrate network induced by shear forces during ball milling is analyzed for Co3(PO4)2·8H2O and compared to the behavior under hydrostatic pressure. The release of bound water triggers a multistage amorphization process, associated with a color change from pink to blue, which makes Co3(PO4)2·8H2O potentially useful as an overheat temperature indicator.
Datum: 19.04.2016

Ce/Au(CN)2–-Based Coordination Polymers Containing and Lacking Aurophilic Interactions

New members of the Ln[Au(CN)2]3·3H2O and [nBu4N]2[Ln(NO3)4Au(CN)2] series Ln = Ce (CeAu3 and CeAu respectively) are reported herein where their synthesis, structure and photoluminescence properties are discussed. The first is a 3-D coordination polymer with aurophilic interactions of 3.35 Å and the latter is a 1-D coordination polymer that lacks them. At 293 K both CeAu3 and CeAu display characteristic CeIII-based emission at λmax = 393 nm (5d2FJ), however in CeAu3 AuI-based emission (λmax = 410, 1MLCT) dominates the spectrum. At 77 K however, the dominant emission is AuI-based with characteristic emissions of λmax = 430 nm (1MLCT) and 490 nm (3MLCT). The key difference in the luminescence of these two materials can be rationalized in terms of their respective structures, through either the aurophilic network and lack thereof and/or the rigidity offered in the 3-D structure of CeAu3. Cerium analogues of [nBu4N]2[Ln(NO3)4Au(CN)2] and Ln[Au(CN)2]3·3H2O systems have been synthesized and characterized with an emphasis on their luminescence properties at 293 and 77 K. These differ in the dominant emissive pathway and can be rationalized based on their respective structure.
Datum: 19.04.2016

Reactivity of a Monomeric Aluminium Hydrazide towards Isocyanates and Isothiocyanates: Active Lewis Pair Behaviour versus Classical Insertion Reactions

Hydroalumination of H10C5N–N=C(Ad) with HAliBu2 yielded the hydrazide H10C5N–N(AliBu2)Ad (4; Ad = adamantyl, NC5H10 = piperidinyl). Compound 4 is monomeric and contains a highly strained AlN2 heterocycle formed by a donor–acceptor interaction between the Al atom and the β-N atom of the hydrazine. Two equivalents of the hydride afforded an adduct with an HAliBu2 molecule coordinated to 4 by an Al–N and a 3c–2e Al–H–Al bond (5). tBuN=C=O did not insert into the relatively weak AlN donor–acceptor bond of 4; instead, insertion into the shorter Al–N(amide) bond yielded five-membered AlN3C heterocycle 6 with an exocyclic C=O group. PhN=C=O showed a similar reaction, but the product 7 was dimeric in the solid state with two Al–O bonds. Reaction in a 1:2 ratio afforded a unique linear dimer of phenyl isocyanate, which is stabilised by the aluminium hydrazide (8). Isothiocyanates gave thiosemicarbazides 9–11, which have Al atoms coordinated in a chelating manner by formation of AlSCN heterocycles and show fascinating differences in their bonding situation. A monomeric aluminium hydrazide with a strained AlN2 heterocycle was obtained by hydroalumination of a hydrazone. It shows interesting chemical behaviour and reacted as an active Lewis pair with the coordination of iBu2AlH or by insertion of one or two molecules of isocyanate into the Al–N polar covalent bond to afford a fascinating variety of structural motifs.
Datum: 19.04.2016

Helical CuICuII3 Metallocavitands with Sulfur-Containing Schiff Base Ligands Exhibiting Ferromagnetic or Antiferromagnetic Interactions

A unique example of self-assembly of chiral sulfur-containing Schiff base ligands (SBLs) into a mixed-valent metallocavitand is reported. A tetranuclear complex with one CuI and three CuII ions bridged by three sulfur-containing SBLs was obtained, in which connected CuIINO2S and CuIS3 planes form a CuICuII3 metallocavitand hosting a trialkylammonium cation in its chiral cavity. The ferro- or antiferromagnetic interactions in the complexes can be tuned by changing a substituent on the SBL. Helical CuICuII3 metallocavitands were created by the one-pot reaction of D-penicillamine, salicylaldehydes, R3N, and CuII. Each metallocavitand is composed of three CuII square planes that form a cyclic wall capped with a CuI trigonal plane, accommodating an R3NH+ ion in its cavity. The magnetic behavior of the metallocavitands was altered by changing a substituent on the ligand.
Datum: 19.04.2016

High Catalytic Performance of MIL-101-Immobilized NiRu Alloy Nanoparticles towards the Hydrolytic Dehydrogenation of Ammonia Borane

Ultrafine NiRu alloy nanoparticles (NPs) were successfully immobilized on MIL-101 for the first time by the double-solvent method combined with the overwhelming reduction approach. The NPs were fully characterized by transmission electron microscopy, powder X-ray diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The MIL-101-immobilized NiRu alloy NPs exhibited much higher catalytic activity toward the hydrolytic dehydrogenation of ammonia borane than the pure NiRu alloy NPs and Ni@Ru core–shell NPs. Ultrafine NiRu alloy nanoparticles are successfully immobilized in the pores of MIL-101 by the double-solvent method combined with the overwhelming reduction approach. The immobilized nanoparticles show high catalytic performance towards the hydrolytic dehydrogenation of ammonia borane.
Datum: 19.04.2016

Introducing Tetrel Zintl Ions to N-Heterocyclic Carbenes – Synthesis of Coinage Metal NHC Complexes of [Ge9{Si(CH3)3}3]–

Reaction of the functionalized tetrel cluster [Ge9R3]– {R = Si(SiMe3)3} with coinage metal N-heterocyclic carbene (NHC) complexes affords the first Zintl cluster transition metal complexes coordinated by NHC molecules. In [(η3-Ge9R3)M(NHCDipp)], the D3d-symmetric cluster polyhedron coordinates with a triangular Ge3 face to the coinage metals M = Cu, Ag, Au, which themselves also bind to the NHC. The role of fine tuning of electronic properties by using an NHC ligand is discussed for the transformation reaction of [(η3-Ge9R3)Ag(NHCDipp)] to yield [Ag(η3-Ge9R3)2][Ag(NHCDipp)2]. All complexes are fully characterized including single-crystal X-ray structure analyses. Whereas intermetalloid cluster formation from ligand-free Zintl ions affords highly polar solvents, functionalized Zintl cluster anions allow for other solvents. Reactions with coinage metal N-heterocyclic carbene (NHC) complexes give a deep insight into the reactivity of Zintl clusters, as shown by the series [(η3-Ge9R3)M(NHCDipp)], M = Cu, Ag, Au and the subsequent transformation to [M(η3-Ge9R3)2][M(NHCDipp)2] for M = Ag.
Datum: 19.04.2016

Solvatochromic CuII-Containing Ionic Liquids with Ether Side Chains: Control of Solvent Response through Intramolecular Coordination

We reported previously that ionic liquids containing cationic solvatochromic metal–chelate complexes exhibit vapochromic and solvatochromic properties, changing color upon coordination of different solvents. To control the solvent response by intramolecular coordination, an ether side chain was introduced into the cation as an additional flexible coordination site, and ionic liquids of the formula [Cu(acac){Me2NCH2CH2NMe(CH2)nOMe}][Tf2N] {[1][Tf2N]: n = 3, [2][Tf2N]: n = 4; acac = acetylacetonato, Tf2N = (F3CSO2)2N–} were synthesized. The melting points of [1][Tf2N] and [2][Tf2N] were 44.1 °C and 49.8 °C, respectively. X-ray crystal-structure determination revealed intramolecular coordination of the side chain in [1][Tf2N] and its absence in [2][Tf2N] in the solid state. The addition of 1 and 2 mol-equiv. of dimethyl sulfoxide to [1][Tf2N] produced ionic liquids with Tm = 28.6 °C and –12.0 °C, respectively. To investigate the potential competition between side-chain coordination and solvent coordination, the solvatochromism of these salts was investigated in various solvents. Although the d–d transition energy of [2][Tf2N] varies linearly with the donor number (DN) of a solvent, that of [1][Tf2N] is nearly constant in solvents with a DN smaller than that of methanol owing to intramolecular coordination. This demonstrates the control of solvent response by intramolecular coordination sites. Ionic liquids containing solvatochromic metal–chelate complexes with a flexible ether side chain have been synthesized. These salts exhibit vapochromic and solvatochromic properties. The side-chain coordination is released when solvents with coordination abilities stronger than that of the ether side chain are added.
Datum: 13.04.2016

Zinc Scorpionate Complexes with a Hybrid (Thiopyridazinyl)(thio­methimidazolyl)borate Ligand

Zinc complexes with the mixed scorpionate ligand (6-tert-butyl-3-thiopyridazinyl)bis(2-thiomethimidazolyl)borate (PnBm) have been synthesized and characterized by NMR and IR spectroscopy. The complexes, with the general formula [(PnBm)ZnX]2 [X = Br (1a), I (1b)], are dimeric in the solid state, as determined by single-crystal X-ray diffraction analyses. The zinc atoms are tetrahedrally coordinated by the halogen atom, two sulfur atoms of PnBm, and one sulfur atom from a bridging PnBm ligand. Variable-temperature 1H NMR spectroscopy indicated dimeric structures also in solution. Upon abstraction of the bromine atom in 1a by thallium triflate, the zinc complex [(PnBm)Zn(OTf)]2 (2) was obtained and fully characterized by 1H and 13C NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction analysis. The mixed thiopyridazine/thiomethimidazole-containing soft scorpionate ligand (PnBm) was treated with zinc halide to form dimeric species. The bromine atoms can be abstracted with Tl(OTf) to form a triflate complex with a significantly short Zn–H–B distance.
Datum: 13.04.2016

Metal Complexes of Multitopic, Third Generation Poly(pyrazolyl)­methane Ligands: Multiple Coordination Arrangements

The structures of metal complexes of two classes of multitopic, “third generation” poly(pyrazolyl)methane ligands, ligands specifically functionalized at the non-coordinating “back” position, are discussed. For tris(pyrazolyl)methane based [(pz)3C–CH2–O–CH2]nC6H6–n (n = 2, 3, 4 and 6, pz = pyrazolyl ring) ligands, three bonding modes are observed depending on the metal, counterion and solvent: a) the κ3 (tripodal) mode, where all three pyrazolyl rings are coordinated to one metal; b) the κ2-κ0 mode, with only two pyrazolyl rings bonded to a metallic center while the third is not involved in a donor bond; and c) in a κ2-κ1 fashion, in which the tris(pyrazolyl)methane unit acts as a bridge between two metals. For bis(pyrazolyl)methane based [CH2–O–CH2–CH(pz)2]nC6H6–n ligands, the main structural arrangement is a mononuclear cationic unit in which two arms of the ligand bond a single silver(I) cation in a tetradentate fashion, giving rise to 16- or 17-member metallacyclic structures. Multitopic poly(pyrazolyl)methane ligands form metal complexes that show a variety of bonding modes and intricate overall structures.
Datum: 05.04.2016

Neutral 1,3,5-Triaza-7-phosphaadamantane-Ruthenium(II) Complexes as Precursors for the Preparation of Highly Water-Soluble Derivatives

The monodentate phosphane ligand 1,3,5-triaza-7-phosphaadamantane (PTA) imparts excellent water solubility to its complexes. We aimed to prepare precursors with one or more PTA coligands for solubility and one or more labile ligands for facile replacement by a linker. For this purpose, we investigated the reactivity of the neutral isomers trans- and cis-RuCl2(PTA)4 (1 and 2) towards 2,2′-bipyridine (bpy), as a model chelating diimine linker. The new derivatives mer-[Ru(bpy)Cl(PTA)3]Cl (9) and fac-[Ru(bpy)Cl(PTA)3]Cl (10) were prepared and characterized. We also found that PTA reacts rapidly with cis,fac-RuCl2(dmso-O)(dmso-S)3 (11) and trans-RuCl2(dmso-S)4 (13) under mild conditions through the replacement of pairs of mutually trans dmso ligands with high selectivity, even when in stoichiometric defect. Thus, 11 affords cis,cis,trans-RuCl2(dmso-S)2(PTA)2 (12), whereas 13 gives 1. The two dmso ligands of 12 can be replaced selectively by chelating diimines such as bpy to afford the less symmetrical all-cis product cis,cis-Ru(bpy)Cl2(PTA)2 (16). We prepared precursors with one or more 1,3,5-triaza-7-phosphaadamantane (PTA) coligands for solubility and one or more labile ligands for facile replacement. The reactivity of trans- and cis-RuCl2(PTA)4 (1 and 2) and cis,cis,trans-RuCl2(dmso-S)2(PTA)2 (12, dmso = dimethyl sulfoxide) towards 2,2′-bipyridine (bpy), as a model diamine linker, is reported.
Datum: 05.04.2016

Room-Temperature Synthesis of Mesoporous Sn/SnO2 Composite as Anode for Sodium-Ion Batteries

A mesoporous Sn/SnO2 composite has been synthesized by a self-templating pore formation process at room temperature without any external templates. When evaluated as an anode for sodium-ion batteries, the composite material exhibited stable performance and high Coulombic efficiency, in addition to excellent rate performance. Mesoporous Sn/SnO2 composite was synthesized via a self-templating pore formation process at room temperature. When evaluated as an anode for sodium-ion batteries, the material exhibited high capacity, cyclability, and rate-performance.
Datum: 30.03.2016

Long-Term Cycling Performance of Nitrogen-Doped Hollow Carbon Nanospheres as Anode Materials for Sodium-Ion Batteries

Nitrogen-doped hollow carbon nanospheres (N-HCSs) were prepared by a facile template method with dopamine as the precursor and subsequently used as the anode material for sodium-ion batteries. The N-HCSs demonstrated high reversible capacities with a retained capacity of 162.2 mA h g–1 over 100 cycles at 0.1 A g–1 and an excellent rate capability with an attainable capacity of 90 mA h g–1 at a high current density of 5 A g–1. Detailed characterization revealed that nitrogen doping introduces defects into the carbon wall structure and enables the storage of additional Na ions in the walls of the carbon spheres. We then show that the addition of an electrolyte additive [fluorinated ethylene carbonate (FEC)] also effectively enhances the cyclability of the N-HCSs anode; a capacity of 136.4 mA h g–1 was obtained after 2500 charge–discharge cycles at a current rate of 0.2 A g–1. Nitrogen-doped hollow carbon nanospheres (N-HCSs) are investigated as anode materials for sodium-ion batteries. A high reversible capacity of 162.2 mA h g–1 is retained over 100 cycles, and an excellent rate capability is achieved. The electrolyte additive fluorinated ethylene carbonate (FEC) enhances the cyclability, and a capacity of 136.4 mA h g–1 is obtained after 2500 cycles at 0.2 A g–1.
Datum: 11.03.2016

Effect of Ni Incorporation into Malachite Precursors on the Catalytic Properties of the Resulting Nanostructured CuO/NiO Catalysts

Synthetic nickelian malachite nanopowders (Cu1–xNix)2(OH)2CO3 with x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1 were prepared by constant-pH coprecipitation. N2 sorption isotherms confirmed a steady increase of the BET surface area with increasing Ni content for the as-synthesized and calcined mesoporous materials. Powder XRD patterns for x ≤ 0.1 indicate the formation of single-phase materials with an anisotropic contraction of the unit cell. This is related to the gradual decrease of the Jahn–Teller distortion in the malachite structure. An XRD-amorphous hydroxide-rich phase is formed for x > 0.1, which appears as spongelike regions in SEM images. Thermogravimetric analysis showed that nickel lowers the onset of thermal decomposition. Powder XRD patterns of the calcined samples evidence the formation of a tenorite structure despite the presence of Ni. Heterogeneous Fenton-like decomposition of Bismarck Brown Y with H2O2 showed that a Cu/Ni ratio of 92:8 in the nanostructured oxide leads to the highest reaction rate constant derived from a pseudo-first-order kinetic rate law expression. Temperature-programmed CO oxidation experiments revealed that pure CuO achieved the highest activity. Similar performance was observed for the binary system obtained through calcination of the precursor prepared with a Cu/Ni ratio of 96:4. Partial substitution of Cu2+ by Ni2+ in (Cu,Ni)2CO3(OH)2 up to a Cu/Ni ratio of 90:10 leads to single-source precursors for nanostructured CuO/NiO catalysts. By Ni incorporation into the precursor, the specific surface area can be increased by a factor of three, leading to positive effects in the catalytic decomposition of dyes.
Datum: 10.03.2016

The Applications of Nano-Hetero-Junction in Optical and Thermal ­Catalysis

Semiconductors, metal oxides in particular, are usually regarded as key components in most industrial catalysts. It has been reported that the band structures of semiconductors can significantly influence their catalytic properties. As one of the most effective methods for tuning the band structure of semiconductors, the establishment of nano-hetero-junctions in catalysts is attracting increasing attention due to the use of rational design and the facile synthesis procedure. This Microreview covers the applications of nano-hetero-junctions in both photocatalytic and traditional thermal catalytic reactions. The applications of these reactions range from removal of pollutants to renewable energy production to new chemical synthesis routes, all of which are closely knitted into our daily lives. In photocatalysis, improvement is mainly attributed to the separation of photogenerated electrons and holes, which prolongs their lifetimes and eventually allows the occurrence of chemical reactions with adsorbed substrate molecules. Our research group were amongst the first to apply this concept in the design of metal/metal oxide catalysts in traditional thermal catalysis. It has been found that the establishment of electronic nano-hetero-junctions in support materials with use of two semiconducting metal oxides of different energy levels influences the catalytic properties of the dispersed metal particles from two perspectives: (i) the potential energy upon excitation, created by the charge separation on semiconducting oxide support in proximity to the overlying metal particles, and (ii) under H2, the accumulated electrons on one semiconducting oxide support can facilitate direct reduction of metal cations in this support to metal atoms, while the accumulated holes (activated oxygen) on the other semiconducting oxide are relaxed by water formation through hydrogen oxidation. The metallic atoms from the support surface thus act as modifiers to the primary metal particles through the formation of a bimetallic phase. As a result, the electronic configuration of the supported metal particles can be modified in a subtle manner that consequently influences the catalytic performance. It is believed that this concept of designing nano-hetero-junctions should empower scientists to approach new catalytic reactions in a systematic manner, allowing fine-tuning of catalysts with superior performance. Heterojunction of two semiconductor phases to prolong lifetimes for spatial charge separation is a well-established concept in photophysics and is widely explored in solar cell and photocatalytic devices. However, its applications in thermal catalysis are currently rather limited. This Microreview covers the applications of nano-hetero-junctions in thermal catalysis and photocatalysis.
Datum: 09.03.2016

Nanoparticulate TiO2-Supported Double Metal Cyanide Catalyst for the Copolymerization of CO2 with Propylene Oxide

A titanium oxide supported double metal cyanide (TiO2-DMC) was found to be a highly active catalyst for the reaction of CO2 with propylene oxide to polyethercarbonates, which are useful polymer building blocks for polyurethane applications. The catalyst was prepared by coprecipitation of potassium hexacyanocobaltate(III) and titanium(IV) ethoxide with an excess amount of ZnCl2 under slightly acidic conditions. The TiO2-DMC catalyst provided excellent selectivity to the polymer (>97 %) and outstanding productivity (>500 gpolymer/gcatalyst). The TiO2-support enhanced the Lewis acidity of the DMC catalyst, which facilitated activation of the epoxide and adjusted the binding strength of the polymer chain to the surface of the catalyst. CO2 is utilized as a renewable resource in the copolymerization with epoxides to polyethercarbonates. The excellent chemoselectivity of the nanoparticulate TiO2-supported double metal cyanide catalyst is rationalized by the Lewis acidity of the TiO2 support. The polyethercarbonate is characterized by a large fraction of carbonate linkages in segments with a nonalternating sequence of co-monomers.
Datum: 07.03.2016

Insight into the Role of Ligands in the Yellow Luminescence of Zinc Oxide Nanocrystals

The influence of the composition of the ligand shell on the yellow emission of ZnO nanocrystals (NCs) is reported. The ligand shell was modified either by a change of solvent or by the exchange of the primary alkylamine ligand with an alkylthiol ligand. The changes of the composition of the ligand shell were analyzed by NMR spectroscopy and isothermal titration calorimetry (ITC) and were related to the variation of the visible emission of the ZnO NCs. We demonstrate that the emission wavelength of ZnO is not affected by the medium or the type of ligand at the surface of the NCs; this suggests that the nature of the emitting site is not altered by the environment. However, the quantum yield of this emission is strongly dependent on the composition of the ligand shell, and this implies that the number of emitting sites or their lifetime is varied. This study highlights the possible modification of the optical properties of ZnO NCs through the modification of the surface with organic molecules and paves the way to the application of these ZnO NCs for optical sensors. This study highlights the possible modification of the optical properties of ZnO nanocrystals through the modification of the surface state with organic molecules.
Datum: 26.02.2016

Three-Dimensional Electrocatalysts for Sustainable Water Splitting Reactions

Development of catalysts with high activity and durability is essential for the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) of water splitting. Three-dimensional catalysts have large surface areas and good mechanical and antipoisoning properties and can directly act as working electrodes; these are especially important factors from the point of view of practical applications. Here we review recent significant progress in the field of three-dimensional catalysts for water splitting. Various three-dimensional catalysts that can be applied in electrocatalytic water splitting are presented. The fabricating methods, electrocatalytic performances, and the catalytic mechanisms of these catalysts are introduced. Lastly, the major challenges in this particular field and their prospective solutions are also discussed. Three-dimensional (3D) electrocatalysts have captured much attention in the field of water splitting due to their unique properties of high surface area and good mechanical strength. This review presents the general synthesis method and the electrocatalytic performances of different kinds of 3D catalysts in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER).
Datum: 10.02.2016

Mechanism and Kinetics of Oligosilsesquioxane Growth in the In Situ Water Production Sol–Gel Route: Dependence on Water Availability

Thiol-functionalized nanobuilding blocks (NBBs) were synthesized from 3-mercaptopropyltrimethoxysilane by using the in situ water production (ISWP) process in which the water needed to hydrolyze the precursor was provided by means of an esterification reaction. In the present study the reaction between 1-propanol and chloroacetic acid was used. Whereas the growth of the Si oligomers was followed at room temperature and 100 °C using 1D 29Si and 2D 1H–29Si heteronuclear single quantum correlation (HSQC) NMR spectroscopic experiments, the amount of water delivered along the process was followed by means of 1H NMR spectroscopy. The results show a good correlation between the evolution of the degree of condensation and the amount of water produced in situ. They also point to the preferential formation of cagelike structures and the narrowing of the species distribution over long reaction times. The average size of the growing oligomers was estimated from their diffusion coefficient, which was measured by means of 1H diffusion-ordered NMR spectroscopy (DOSY NMR). Like gel permeation chromatography, DOSY NNR showed a plateau between 70 to 100 hours in the growth of the oligomers, a time at which, according to 29Si NMR spectroscopy, the well-defined octakis(3-mercaptopropylsilsesquioxane) is the major species. Small thiol-functionalized oligosilsesquioxanes were prepared by the in situ water production (ISWP) process in which water was homogenously generated by an esterification reaction. Manipulation of the temperature allowed the water production kinetics to be controlled, which played a major role on the degree of condensation (DOC) of the formed nanobuilding blocks.
Datum: 05.02.2016

Synthesis of Bi–Fe–Sb–O Pyrochlore Nanoparticles with Visible-Light Photocatalytic Activity

A method has been developed for the preparation of Bi–Fe–Sb–O pyrochlore nanoparticles by microwave hydrothermal treatment. Experiments revealed that the preparation procedure for the precursors is an important factor that affects the phase composition of the product. The morphology of the pyrochlore particles was investigated by SEM, HRTEM, and selected-area electron diffraction (SAED) methods. The samples consist of numerous spherical agglomerates from 100 to 200 nm formed from 20 nm mutually oriented nanocrystallites. A mechanism for the formation of the particles is proposed, and the magnetic and photocatalytic properties of the Bi–Fe–Sb–O pyrochlore nanocrystallites are reported. Bi–Fe–Sb–O pyrochlore nanoparticles are synthesized by microwave hydrothermal treatment. The samples consist of 100–200 nm spherical agglomerates formed from 20 nm mutually oriented nanocrystallites. Some of the spheres are hollow. The photocatalytic activity of the pyrochlore nanoparticles is higher than that of TiO2.
Datum: 01.02.2016

Pseudomorphic Transformation of Layered Simple Hydroxides into Prussian Blue Analogue Nanoplatelets

The reactivity of potassium or sodium hexacyanoferrate(II) with transition-metal layered simple hydroxides (LSHs) has been investigated to evaluate the possibility of inserting Prussian Blue analogues (PBAs) into magnetic copper(II) LSHs. This report shows how such a reaction led, unexpectedly, to the direct formation of PBA nanoparticles, the layered hydroxide serving as a metal-ion reservoir. The lamellar structure of the starting LSH collapses and copper–iron PBA nanoparticles were obtained as well-defined cubic structures stacked in layers. In addition to structural and magnetic characterization, the reaction mechanism was investigated by 57Fe Mössbauer spectrometry and X-ray photoemission spectroscopy. The layered copper hydroxide acetate turns out to be a smart precursor of well-shaped PBA nanoparticle layers through pseudomorphic replication. Prussian Blue analogue nanoplatelets have been produced by pseudomorphic replication of layered Cu2(OH)3(OAc) in the presence of K4[Fe(CN)6]. A transformation mechanism is proposed. Our results demonstrate that lamellar simple hydroxides can be used as precursors of molecular-based networks and that the lamellar nature of the Cu reservoir favours the organization of crystallites into sheets.
Datum: 01.02.2016

Structural and Magnetic Properties of 57Fe-Doped TiO2 and 57Fe/Sn-Codoped TiO2 Prepared by a Soft-Chemical Process

A series of 57Fe-doped TiO2 and 57Fe/Sn-codoped TiO2 materials were prepared by a soft-chemical solution process with various 57Fe concentrations from 0.1 to 1.0 at.-% and a fixed Sn concentration of 2.0 at.-%. In this process, an aqueous H2O2 solution reacts with iron and titanium or iron, tin, and titanium precursor compounds to produce peroxopolymetallic acids. The structures and magnetic properties of the products were characterized by magnetic-moment measurements, X-ray diffraction, and Raman and Mössbauer spectroscopy. The results showed that all samples consisted of a rutile phase (and a trace amount of anatase in 57Fe-TiO2). All samples exhibited hysteresis loops in the M–H curves, which demonstrated the presence of room-temperature ferromagnetism. In addition, their magnetic properties decreased with increasing degree of 57Fe doping. Oxygen vacancies were considered to be responsible for the presence of ferromagnetism. Room-temperature ferromagnetism (RTFM) was found in 57Fe-TiO2 and 57Fe/Sn-TiO2 materials prepared by a soft-chemical solution method. Their magnetic properties were found to decrease with increasing degree of 57Fe doping. Fe3+–oxygen vacancy (VO)–Fe3+ centers are responsible for the observed RTFM.
Datum: 27.01.2016

Multiple Modes of Motion: Realizing the Dynamics of CO Adsorbed in M-MOF-74 (M = Mg, Zn) by Using Solid-State NMR Spectroscopy

Metal–organic frameworks (MOFs) often exhibit high porosities and surface areas, making them ideal media for gas storage and carbon capture. MOF-74 is an intriguing porous MOF featuring one-dimensional honeycomb-shaped channels and open metal sites, and is able to adsorb poisonous CO. Variable-temperature (VT) 13C solid-state NMR (SSNMR) experiments focusing on 13CO adsorbed within M-MOF-74 (M = Mg, Zn) are a sensitive probe of guest motion, revealing valuable details regarding the dynamics of adsorbed CO within the MOF channels. 13C SSNMR experiments recorded at temperatures ranging from 153 to 373 K, along with accompanying simulations, unambiguously indicate that two types of dynamic CO motion are present in MOF-74: a localized wobbling of CO on the open metal site, and a non-localized hopping of CO molecules between adjacent open metal sites. The fine details of these motions, including the motional angles and rates, are revealed and discussed. The CO dynamics in MOF-74 are then compared and contrasted with those of CO2, illustrating the similarities and differences in motion between the two types of guest molecules across the experimental temperature range. CO dynamics in M-MOF-74 (M = Mg, Zn) are comprehensively described. There are two types of CO motion: a localized sixfold wobbling and a non-localized sixfold hopping. The wobbling angles are inversely proportional to CO heats of adsorption. CO and CO2 motional data in MOF-74 confirm that the wobbling angle of these guests is very sensitive to several factors.
Datum: 19.01.2016

Amino Acid Interleaved Layered Double Hydroxides as Promising Hybrid Materials for AA2024 Corrosion Inhibition

Various α-amino acid (αAA) molecules were screened for their ability to retard the corrosion of AA2024 aluminum alloy substrate. The αAAs screened were L-arginine (L-Arg), L-asparagine (L-Asn), L-cysteine (L-Cys), L-cystine, L-histidine (L-His), L-methionine (L-Met), L-phenylalanine (L-Phe), L-serine (L-ser), L-tryptophan (L-Trp), and L-tyrosine (L-Tyr). From their performances compared with that of the reference additives chromate and 2-mercaptobenzothiazolate (MBT), L-Cys and L-Phe were selected, and their layered double hydroxide (LDH) interleaved derivatives were further scrutinized. Different LDH phases, namely, LiAl2, Mg2Al, MgZnAl, and Zn2Al, were tested as hosts for the inhibitor αAA substances, and the materials were characterized by XRD, FTIR spectroscopy, and SEM. The efficiencies and durable performances of the hybrid materials as an anticorrosion agents for aluminum alloy 2024 (AA2024) were demonstrated through direct current (DC) polarization measurements, and the evolution of the polarization resistance was recorded. The mechanism of inhibition focused on the most promising hybrid material LDH/L-Cys and was tentatively explained as anion exchange and dissolution of the inorganic framework at the cathodic and anodic corrosion zones, respectively, with the particular occurrence of Cu-rich intermetallic zones. The obtained results evidence that the LDH/L-CYS assembly embedded in the polymer coating retards the corrosion process of the AA2024 substrate after a prolonged immersion time. An assembly composed of L-cysteine (L-Cys) intercalated into a layered double hydroxide (LDH) is used as an ion-exchange inorganic functionalized filler dispersed in an epoxy-based primer layer. Upon corrosion, L-Cys molecules are released from the LDH container either by anion exchange or platelet dissolution and retard the corrosion of aluminum alloy AA2024 efficiently.
Datum: 19.01.2016

Facile Synthesis of Cooperative Acid–Base Catalysts by Clicking Cysteine and Cysteamine on an Ethylene-Bridged Periodic Mesoporous Organosilica

A periodic mesoporous organosilica (PMO) that contains ethylene bridges was functionalized to obtain a series of cooperative acid–base catalysts. A straightforward, single-step procedure was devised to immobilize cysteine and cysteamine on the support material by means of a photoinitiated thiol-ene click reaction. Likewise, PMO materials capped with hexamethyldisilazane (HMDS) were used to support both compounds. This resulted in different materials in which the amine site was promoted by carboxylic acid groups, surface silanol groups, or both. The catalysts were tested in the aldol reaction of 4-nitrobenzaldehyde and acetone. It was found that silanol groups have a stronger promoting effect on the amine than the carboxylic acid group. The highest turnover frequency (TOF) was obtained for an amine-functionalized material that contained only silanol promoting sites. The loading of the active sites also had a significant effect on the activity of the catalysts, which was rationalized on the basis of a computational study. An ethylene-bridged periodic mesoporous organosilica was functionalized with cysteine and cysteamine by means of thiol-ene click chemistry. The resulting cooperative acid–base catalysts were tested for their activity in an aldol reaction. The influence of the acid promoting sites as well as the loading of the active centers is discussed herein.
Datum: 15.01.2016

Optimized Design of Pt-Doped Bi2WO6 Nanoparticle Synthesis for Enhanced Photocatalytic Properties

The preparation of photocatalytic heterostructures of platinum on Bi2WO6 nanoparticles by a wet reduction method is described in this report and compared with other preparation methods. The as-obtained photocatalysts were characterized by XPS and TEM, the results of which confirmed the presence of solely zero-valent metal nanoparticles on the surface of Bi2WO6. The photocatalytic activity of these heterostructures was evaluated by the degradation of Rhodamine B under blue light (λmax = 445 nm). The deposited noble metal nanoparticles were shown to significantly improve the photocatalytic performance of the bismuth-based material under visible light. Both the preparation mode and the metal loading may impact on the efficiency. The observed photocatalytic enhancement has been attributed to an electron transfer from the semiconductor to the metal, which prevents fast electron/hole recombination. The electrons trapped in the metals may then participate in the multi-electron reduction of O2. We discuss the way to prepare optimized metal/oxide nanoheterostructures for photocatalytic applications. The characteristics of the materials are linked to both the mode of metal reduction and the amount deposited. The Rhodamine B photodegradation mechanism and overall rate of degradation are directly impacted by the mode of preparation.
Datum: 15.01.2016

Solvent Influence on the Magnetic Properties of Iron(II) Spin-Crossover Coordination Compounds with 4,4′-Dipyridylethyne as Linker

New iron(II) coordination polymers with solvent-dependent spin-crossover behaviour have been synthesised by using an N2O2 Schiff base like ligand and 4,4′-dipyridylethyne as the bridging axial ligand in different solvents. The effects of different solvents and preparation methods (temperature, concentration) on the magnetic properties have been investigated. Annealing the coordination polymers prepared by the same method but in different solvents led to the same compound exhibiting the same three-step spin crossover independent of the magnetic properties of the solvated species. The X-ray structures of the axial ligand, an iron(II) dimer and one of the iron(II) coordination polymers are discussed. Powder X-ray diffraction analysis was additionally used for further comparison of the compounds. Different solvates of an iron(II) coordination polymer have been prepared. Although the spin-crossover properties of the different solvated forms are different, after removal of the solvent the same three-step spin transition is observed.
Datum: 15.01.2016

A Systematic Study on the Prep­aration and Hydrogen Storage of Zeolite 13X-Templated Microporous Carbons

A systematic study on chemical vapour deposition (CVD)-based synthesis strategies (single CVD process, double CVD process and a combination of liquid impregnation and a CVD process) for the nanocasting of zeolite-templated porous carbon materials with commercially available zeolite 13X as hard template and ethylene, furfuryl alcohol, acetonitrile and/or vinyl cyanide as carbon precursor is presented. The results indicated that the combination of liquid impregnation and CVD is superior to the single or the double CVD processes in producing carbon materials with high surface area, high pore volume and high microporosity. The combination of liquid impregnation with furfuryl alcohol and CVD with ethylene generates carbon materials with the highest surface area of 2841 m2/g, a pore volume of 1.54 cm3/g and a hydrogen-uptake capacity of 6.3 wt.-% (at –196 °C and 20 bar). Under the studied conditions, the porous carbon materials exhibit variable structural ordering and tuneable textural properties with surface areas of 1600–2850 m2/g, pore volumes of 1.0–1.8 cm3/g and hydrogen-uptake capacities in the range of 3.4–6.3 wt.-% (at –196 °C and 20 bar). Notably, linear relationships between the hydrogen-uptake capacity and the total surface area, the micropore volume and the micropore surface area were found for the studied porous carbons, and this implies an important role of the total surface area, the micropore volume and the micropore surface area in the hydrogen adsorption. A systematic study on CVD-based strategies for the nanocasting of porous carbon materials with zeolite 13X as template is presented. The resulting carbon materials exhibit hydrogen-uptake capacities of up to 6.3 wt.-%. Linear relationships between the uptake capacity and the total surface area, the micropore volume, and the micropore surface area were found.
Datum: 12.01.2016

Fluorescence Quenching of Sulfo­rhodamine Dye over Graphene Oxide and Boron Nitride Nanosheets

We report the fluorescence quenching of sulforhodamine 640 (SR 640) supported on graphene oxide (GO) and boron nitride (BN) nanosheets (NSs). The synthesis and characterization of both materials are described. X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), transmission and scanning electron microscopy (TEM and SEM), and the Brunauer–Emmett–Teller (BET) method were used. The photophysical properties, such as the fluorescence lifetime and anisotropy of the SR dye over the synthesized materials, are reported. The observed fluorescence quenching of the SR dye over GO and BN occurs through an electron-transfer process. Fluorescence decay analysis of SR revealed different behavior in the presence of GO and BN NSs. Adsorption of the dye on GO NSs leads to a non-fluorescent complex, whereas adsorption of the dye on BN NSs results in quenching induced by a decrease in the fluorescence lifetime of the dye. We report the fluorescence quenching properties of sulforhodamine 640 (SR 640) supported on graphene oxide (GO) and boron nitride (BN) nanosheets (NSs). For GO, the adsorption of dye leads to a non-fluorescent complex, whereas for BN NSs the observed quenching is induced by a decrease in the fluorescence lifetime of the dye.
Datum: 12.01.2016

Hybrid Hierarchical Porous Silica Templated in Nanoemulsions for Drug Release

A new nanocarrier for loading and releasing drugs is reported, and ketoprofen was used as a model drug. More precisely, the carrier is a hybrid material prepared by combining oil-in-water (O/W) nanoemulsions, into which the drug has been solubilized, with mesostructured silica. This organic–inorganic hybrid material shows a controlled release of the drug that is pH dependent. If the drug is impregnated into the bare hierarchical meso-/macroporous dual silica material, obtained after the removal of the organic components by extraction, only 8 wt.-% of ketoprofen is released in a phosphate buffer medium (pH 7.4), probably owing to its low solubility in the aqueous phase. The drug solubility and release are increased strongly by the addition of Pluronic micelles to the receptor phase; this suggests a micelle-promoted and -assisted release mechanism. Whatever the vehicle, the release profiles of ketoprofen always follow the Korsmeyer–Peppas model with a diffusional release exponent value lower than 0.5, characteristic of a pseudo-Fickian release mechanism. Moreover, the release of ketoprofen is better controlled from the hybrid nanocarrier than from the hierarchical bare porous silica. A nanocarrier for loading and releasing ketoprofen combines nanoemulsions with mesostructured silica. The release of the drug is pH responsive. By contrast, for the impregnation of ketoprofen in the bare macro-/mesoporous silica, a micelle-assisted release is observed. The modeling of the release profiles with the Korsmeyer–Peppas equation evidences a pseudo-Fickian release mechanism.
Datum: 12.01.2016

Cryogenic Nanothermometer Based on the MIL-103(Tb,Eu) Metal–Organic Framework

The microporous metal–organic framework MIL-103 doped with Tb3+ and Eu3+, formulated as [(Tb0.95Eu0.05)(btb)(H2O)]·(solv)x [H3btb = 1,3,5-tris(4-carboxyphenyl)benzene; solv = H2O, CH3OH] has been shown to be a good platform for luminescent ratiometric thermometry. Although operative over a wide range of temperatures (10–320 K), this material exhibits, in the cryogenic range (<100 K), one of the best performances of metal–organic frameworks, with a relative thermal sensitivity of 2.85 % K–1 at 14 K. The material exists in the form of nanoparticles, suitable for nanothermometry applications (e.g., microfluidics). Moreover, as MIL-103 is nanoporous, its use as a multisensing platform deserves further consideration in the near future. Nanoparticles of MIL-103 doped with Tb3+ and Eu3+ are among the best metal–organic framework luminescent (ratiometric) thermometers functioning in the cryogenic range (<100 K), with a relative thermal sensitivity of 2.85 % K–1 at 14 K. Being also microporous, these lanthanide-bearing MIL-103 nanoparticles are, potentially, an excellent multisensing platform.
Datum: 05.01.2016

The Spin-Crossover Phenomenon at the Coherent-Domains Scale in 1D Polymeric Powders: Evidence for Structural Fatigability

The coherent-domain morphology was determined for a crystalline powder of the 1D polymeric spin-crossover [Fe(Htrz)2(trz)](BF4) {Htrz = 1H-1,2,4-triazole, trz = deprotonated triazolato(–) ligand} compound. This morphology is in adequacy with the crystal packing and proved that the long axis of the domain corresponds to the iron–triazole chains axis, which gives information on the crystal-growth process. Furthermore, thermal cycling clearly demonstrated that the coherent-domain length strongly and continuously decreased as a function of the number of spin-crossover cycles undergone. The degradation in the crystalline quality corresponds to a break in the [Fe(Htrz)2(trz)]+ chains. This structural fatigability was confirmed by similar observations on a close spin-crossover compound, [Fe(NH2trz)3](NO3)2·H2O, showing that a few hundreds of thermal spin-crossover cycles could destroy the crystalline aspect of the sample. The coherent-domain morphology is determined in 1D polymeric spin-crossover iron(II)-based triazole materials. A break in the chains over a large number of thermal spin crossover cycles is demonstrated.
Datum: 30.12.2015

Thermal and Light-Induced Spin Transitions of FeII Complexes with 4- and 5-(Phenylazo)-2,2′-bipyridine Ligands: Intra- vs. Intermolecular Effects

Five new spin crossover complexes with 4- and 5-(phenylazo)-2,2-bipyridine (4-/5-PAbipy) ligands were synthesized and investigated with respect to their spin crossover (SCO) behavior. The results are compared to the thermal and light-induced spin transition properties of the parent SCO complexes [Fe(bpz)2(bipy)] (1) and [Fe(bipy)2(NCS)2] (2). [Fe(bpz)2(4-PAbipy)] (1a) undergoes a stepwise spin transition whereas [Fe(bpz)2(5-PAbipy)] (1b) exhibits a one-step transition with a 6 K-wide hysteresis. For [Fe(bpz)2(tBu5-PAbipy)] (1c) the spin transition to the low-spin state is incomplete. Qualitatively similar changes of the SCO behavior are observed for the complexes [Fe(4-PAbipy)2(NCS)2] (2a) and [Fe(5-PAbipy)2(NCS)2] (2b). In comparison to the parent system 2, a strengthening of intermolecular interactions leads to a stabilization of the low-spin state. Evidence for the LIESST behavior could be obtained for all new compounds by means of magnetic susceptibility measurements as well as UV/Vis and resonance Raman spectroscopy. Attachment of a phenylazo unit in 4- and 5-position to 2,2′-bipyridine leads to characteristic changes in the spin crossover properties of FeII complexes with bipy ligands
Datum: 23.12.2015

Hierarchical Meso-Mesoporous and Macro-Mesoporous Silica Templated by Mixtures of Polyoxyethylene ­Fluoroalkyl Ether and Triblock Copolymer

We report here the synthesis of different kinds of hierarchical porous silica materials by using mixtures of an amphiphilic block copolymer (Pluronic P123) and a nonionic fluorinated surfactant. In particular, we have taken advantage of the difference in polarities between the two compounds to design dual-mesoporous materials through the cooperative templating mechanism (CTM). We have undertaken a complete study of this system by varying the composition of the mixed micelles and the synthesis conditions. We have shown that both the dual-mesoporosity and the mesopore ordering are favored when materials are prepared with fluorine-rich and P123-rich micelles. However, when the P123-rich micelles predominate, the mesostructure is less organized and the dual-porosity depends on the P123 content. In addition, concentrated emulsions were formed by incorporating perfluorodecalin (PFD) in the surfactant mixture, and hierarchical macro-mesoporous materials were prepared by combining the CTM and the emulsion templating mechanism. Mixtures of polyoxyethylene fluoroalkyl ether and triblock copolymer were used to prepare hierarchical porous silica materials. Dual-mesoporous materials were obtained from the coexistence of two types of micelles through the cooperative templating mechanism (CTM), and macro-mesoporous silica materials were templated by concentrated emulsions.
Datum: 23.12.2015

Influence of Reinforcing Nonagglomerated Nanodiamond Particles on Metal Matrix Nanocomposite Structure Stability in the Course of Heat­ing

We show that the use of mechanical alloying makes it possible to produce metal matrix composites with uniformly distributed nonagglomerated nanodiamond (ND) reinforcing particles. An aluminium matrix has been used for this study. X-ray analysis shows that a composite structure containing uniformly distributed nanoparticles of 4–6 nm can significantly slow down the process of recrystallization during heating, which becomes evident only when the material is heated above 350 °C. Higher volume fractions of diamond nanoparticles lead to higher starting recrystallization temperatures. Aluminium matrix composites with different volume fractions of nonagglomerated nanodiamond reinforcing particles are developed. The uniform distribution of nonagglomerated nano-reinforcements in an aluminium matrix can significantly slow down the recrystallization of the matrix material during heating, which becomes evident only when it is heated above 350 °C.
Datum: 23.12.2015

Solids Go Bio: Inorganic Nanoparticles as Enzyme Mimics

A longstanding goal of biomimetic chemistry is the design and synthesis of functional enzyme mimics. The past three decades have seen a wide variety of materials, including metal complexes, polymers and other biomolecules, that mimic the structures and functions of naturally occurring enzymes. Among these, inorganic nanoparticles offer huge potential, because they are more stable than their natural counterparts, while having large surface areas and sizes comparable to those of natural enzymes. Therefore, a considerable number of “artificial enzymes” derived from inorganic nanomaterials have been reported. This microreview highlights the recent progress in the field of enzymatically active inorganic nanomaterials, including mimics of peroxidases, haloperoxidases, superoxide dismutases and sulfite oxidases, along with selected biotechnological applications and their future prospects. This microreview highlights the recent progress in the field of nanoparticles possessing enzyme-like activities, including peroxidase, haloperoxidase, superoxide dismutase and sulfite oxidase mimics. Inorganic nanoparticles are more stable and cost-efficient in synthesis than their natural counterparts, while exhibiting equally high enzymatic activities.
Datum: 23.12.2015

Robust Room Temperature Hysteresis in an FeIII Spin Crossover Metallomesogen

The high temperature magnetic and structural properties of an amphiphilic iron(III) spin crossover complex are reported. Thermal cycling reveals a scan rate-dependent 20 K thermal hysteresis in the mT vs. T data close to room temperature. A fast scan rate is essential for the hysteresis but it is robust and reproducible after multiple thermal cycles. Differential scanning calorimetry and cross polarized microscopy are used to show that the magnetic switching aligns with a material state change from solid to ordered liquid phase on warming. The high temperature magnetic and structural properties of an amphiphilic iron(III) spin crossover complex are reported. Thermal cycling reveals a scan rate-dependent 20 K thermal hysteresis close to room temperature. Differential scanning calorimetry and cross polarized microscopy are used to show that the magnetic switching aligns with a material change from solid to ordered liquid phase on warming.
Datum: 16.12.2015

Directional Energy Transfer in Nanocrystals of [Ru(2,2′-bipyridine)3]­[NaCr(oxalate)3]

Size-controlled nanocrystals (140 and 670 nm) and microcrystals (2.5 μm) of the three-dimensional oxalate network [Ru(bpy)3][NaCr(ox)3] (ox = oxalate, bpy = 2,2′-bipyridine) were prepared by the reverse micelle technique. The photophysical properties of the [Cr(ox)3]3– chromophores in the nanocrystals at low temperatures are significantly different from those of the same chromophore in 4 μm crystallites prepared by fast precipitation. For the latter, the absorption in the region of the R lines of the 4A22E transition is characterized by a sharp doublet. For the nanocrystals, the inhomogeneous broadening of the two lines is considerably larger and they have tails on the low-energy side. The 4 μm crystallites at low temperatures show equally sharp emission from the R1 line, whereas the emission intensity from the nanocrystallites is shifted into the low-energy tail. Time-resolved fluorescence line-narrowing spectra and luminescence decay curves demonstrate that this is due to efficient directional energy migration from the center of the nanocrystals towards the surface. The complex sequence of events from the first energy-transfer step in [Ru(bpy)3][NaCr(ox)3] (bpy = 2,2-bipyridine, ox = oxalate) nanocrystals after the initial excitation of [Ru(bpy)3]2+ as sensitizer to [Cr(ox)3]3– in the core of nanocrystals to directional energy migration within the 2E state to the surface chromophores is elucidated.
Datum: 14.12.2015

Framework Isomerism: Highly Augmented Copper(II)-Paddlewheel-­Based MOF with Unusual (3,4)-Net Topology

The synthesis and structure of a new, highly augmented {Cu2}-“paddlewheel”-based metal–organic framework (MOF) that is stabilized by tritopic benzoate ligands is reported. The structure adopts an uncommon, less symmetrical, (3,4)-connected net topology and represents a rare framework isomer of the extensively studied {Cu2}-based pto and tbo analogues related to the purely inorganic, solid-state structures of platinum oxide or the twisted boracite. The concomitant formation of three isomeric forms by using {Cu}2-“paddlewheel” complexes and a single triangular, trifunctional ligand is unique and stems from the rotational flexibility of the benzoate moieties. Computational analyses support the structural studies and underline that this observed net topology can give rise to an exceptionally high surface area (greater than 3500 m2/g) despite the triple-interpenetrated nature of the compound. An uncommon, less symmetrical, (3,4)-connected net topology that represents a rare framework isomer of the extensively studied {Cu2}-based pto and tbo (platinum oxide or twisted boracite) analogues is reported. Computational analyses suggest that the observed structure gives rise to a surface area that is greater than 3500 m2/g despite the triple-interpenetrated nature of the compound.
Datum: 14.12.2015

The First 1,3,4-Oxadiazole Based Dinuclear Iron(II) Complexes Showing Spin Crossover Behavior with Hysteresis

Three new dinuclear complexes [FeII2(μ-L)2]X4 (L is the bis-tridentate ligand 2,5-bis{[(2-pyridylmethyl)amino]methyl}-1,3,4-oxadiazole and X = ClO4–, BF4– and CF3SO3–) have been synthesized and fully characterized by single-crystal X-ray diffraction, Mössbauer spectroscopy and magnetic susceptibility measurements. Upon cooling, a trapped [high-spin–low-spin] state of the iron(II) centres is detected. Depending on the counterion, a pronounced thermal hysteresis is found. In one case, it was possible to observe a space group change that accompanies the spin transition. This is the first system showing spin crossover based on an oxadiazole ligand. Herein we present a new 1,3,4-oxadiazole bridging ligand and three spin-crossover active dinuclear iron(II) compounds. For two of the complexes a trapped high-spin/low-spin state at temperatures below 170 K was proven. Moreover, the spin state switching could be monitored crystallographically for one complex. The other compound shows a 26 K wide hysteresis in the region of 150–175 K.
Datum: 10.12.2015

Comparative Synthesis of Cu and Cu2O Nanoparticles from Different Copper Precursors in an Ionic Liquid or Propylene Carbonate

Copper metal and copper(I) oxide (cuprite, cuprous oxide) nanoparticles (Cu-NPs and Cu2O-NPs) were prepared from different readily available copper salts by means of microwave irradiation in propylene carbonate (PC) or in the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) without addition of extra reducing agents. The nanostructures were studied by high-angle annular dark field-scanning transmission electron microscopy, TEM, SEM, and powder XRD. Star-shaped agglomerated Cu-NPs with about 45 nm diameter were formed from Cu(BF4)2 in PC. Cu-NPs with smaller size distributions of 3.1 ± 0.7 nm and 3.7 ± 1.4 nm were obtained when copper(II) bis[1-(dimethylamino)propan-2-olate], Cu[OCH(Me)CH2NMe2]2, was decomposed in PC and in [BMIm][BF4]. Small Cu-NPs were also obtained from copper(II) acetylacetonate in [BMIm][BF4] with a diameter distribution of 3.3 ± 0.9 nm. Cubic Cu2O nanocubes (Cu2O-NCs) of 43 ± 15 nm in size could be prepared by using Cu(OAc)2·H2O with [BMIm][BF4]. The size of the Cu2O-NCs increased on isolation from the neat IL by addition of acetonitrile, which gave NCs of 0.1–0.5 μm in size. Copper metal nanoparticles and copper(I) oxide (cuprite) nanocubes can be easily and reproducibly synthesized under microwave irradiation in an ionic liquid (IL) or propylene carbonate (PC).
Datum: 07.12.2015

Salt-Acid-Surfactant Lyotropic Liquid Crystalline Mesophases: Synthesis of Highly Transparent Mesoporous Calcium Hydroxyapatite Thin Films

Even though calcium hydroxyapatite [Ca10(PO4)6(OH)2, HAp] is one of the most investigated materials in the literature, the synthesis of mesoporous transparent thin film of HAp has not yet been reported. We show herein that mixtures of phosphoric acid (H3PO4·H2O, PA), calcium nitrate tetrahydrate [Ca(NO3)2·4H2O, CaN] and non-ionic surfactant [C12H25(OCH2CH2)10OH, C12E10] can self-assemble into stable lyotropic liquid crystalline (LLC) mesophases. The clear aqueous solutions of the mixtures can be spin-coated over any substrate and then calcined to form highly transparent mesoporous HAp (mHAp) thin films. From among the compositions studied, three molar ratios of CaN/PA/C12E10 [3.3:2:1 (low), 5.8:3.5:1 (intermediate) and 8.4:5:1 (high)] were chosen for large-scale preparation to investigate their structural and thermal properties. The mHAp films form at around 300 °C and fully crystalize at 500 °C, retaining their transparency, uniformity and porosity in all compositions with few differences. The surface area and pore volume decrease, and the pore size and pore size distribution increase with increasing annealing temperature for all compositions. Phosphoric acid and calcium nitrate self-assemble into lyotropic liquid crystalline mesophases that can be calcined into sponge-like transparent mesoporous thin films of calcium hydroxyapatite.
Datum: 02.12.2015

Dysprosium- and Ytterbium-Based Complexes Involving Tetrathiafulvalene Derivatives Functionalised with 2,2′-Bipyridine or 2,6-Di(pyrazol-1-yl)-4-pyridine

Two new tetrathiafulvalene-based ligands {L1 = 4,5-bis[2,6-di(pyrazol-1-yl)-4-pyridylmethylthio]-4′,5′-bis(methylthio)tetrathiafulvene, L3 = 4-(4′-methyl-2,2′-bypiridin-4-ylmethylthio)-5-(2-cyanoethylthio)-4′,5′-ethylenedithiotetrathiafulvene} have been elaborated and four new lanthanide coordination complexes, namely [Dy2(hfac)6(L1)]·C6H14 (1; hfac– = 1,1,1,5,5,5-hexafluoroacetylacetonate), [Ln(hfac)3(L2)]·CH2Cl2 {Ln = Dy (2) and Yb (3); L2 = 4,5-bis[2,6-di(pyrazol-1-yl)-4-pyridylmethylthio]-4′,5′-ethylenedithiotetrathiafulvene} and [Yb(hfac)3(L3)] (4) were isolated as single crystals. The lanthanide ions adopt an N3O6 nine-coordination with either a spherical tricapped trigonal prism (D3h) or spherical capped square antiprism (C4v) as coordination polyhedra in complexes 1–3. In 4, the YbIII ion adopts an N2O6 eight-coordination with a square antiprism (D4d) coordination sphere. The photophysical properties of the ligands L1 and L3 were studied in both solution and solid state and rationalised by time-dependent density functional theory. Complex 2, in which the DyIII ion has the most regular C4v symmetry, behaves as a field-induced single-molecule magnet. DyIII and YbIII ions adopt spherical tricapped trigonal prism (D3h), spherical capped square antiprism (C4v) and square antiprism (D4d) coordination polyhedra when linked to tetrathiafulvalene-based ligands involving 2,6-di(pyrazol-1-yl)pyridine or 2,2′-bipyridine acceptors. The complex in which the DyIII ion has the most regular C4v symmetry behaves as a field-induced single-molecule magnet.
Datum: 19.11.2015

Phosphorous–Nitrogen-Codoped Carbon Materials Derived from Metal–Organic Frameworks as Efficient Electrocatalysts for Oxygen Reduction Reactions

Despite the impressive progress in the development of doped carbon catalysts for the oxygen reduction reaction (ORR), the current mono-heteroatom-doped carbon-based catalysts are still far from satisfactory for large-scale applications in fuel cells. The development of dual-heteroatom-doped nanoporous carbon electrocatalysts for the ORR is particularly attractive as a feasible solution for the commercialization of fuel-cell technology. Herein, a series of UiO-66-NH2-derived phosphorus–nitrogen-codoped porous carbon materials (P–N-carbons) are prepared from phosphorus-doped UiO-66-NH2 through postsynthetic modification (PSM) followed by one-step pyrolysis at various temperatures. The newly developed P–N-carbons exhibit high catalytic activity that is nearly equal to those of commercial Pt/C catalysts along with superior long-term stability and excellent methanol tolerance. This work shows not only that UiO-66-NH2 can be considered as a self-sacrificial precursor and nitrogen source but also that metal–organic frameworks (MOFs) with active functional groups may be developed as efficient alternative precursors. Owing to the versatility of MOF structures, the MOF-derived porous carbon materials would broaden the family of nanoporous carbon materials significantly and provide new structures and multifunctional properties for use in electrocatalysts, sensors, supercapacitors, and batteries, for example. Newly developed P–N carbon materials, derived from modified Uio-66-NH2 by a postsynthetic method, exhibit a high catalytic activity for the oxygen reduction reaction that is close to that of commercial Pt/C catalysts along with superior long-term stability and excellent methanol tolerance.
Datum: 18.11.2015

A Modular Approach towards Meso­porous Silica Monoliths with Organically Modified Pore Walls: Nucleophilic Addition, Olefin Metathesis, and Cycloaddition

We have synthesized mesoporous silica (monoliths) with defined surface chemistry by means of a number of addition reactions: (i) coupling of an isocyanate to a surface-immobilized thiol, (ii) addition of an epoxide to a surface-immobilized thiol, (iii) cross-metathesis between two olefins, and (iv) Huisgen [2+3] cycloaddition of an alkyne-functionalized silica monolith with an azide. Functionalization of the mesopores was observed, but there are significant differences between individual approaches. Isocyanate and epoxide additions lead to high degrees of functionalization, whereas olefin metathesis and [2+3] cycloaddition are less effective. We further show that the efficiency of the modification is about twice as high in mesoporous silica particles than in macroscopic silica monoliths. Mesoporous silica monoliths with defined surface chemistry were synthesized by a number of reactions: (i) coupling of an isocyanate to a surface-immobilized thiol, (ii) addition of an epoxide to a surface-immobilized thiol, (iii) cross-metathesis between two olefins, and (iv) Huisgen [2+3] cycloaddition of an alkyne-functionalized silica monolith with an azide.
Datum: 13.11.2015

Insertion of a [FeII(pyimH)3]2+ [pyimH = 2-(1H-Imidazol-2-yl)pyridine] Spin-Crossover Complex Inside a Ferromagnetic Lattice Based on a Chiral 3D Bimetallic Ox­alate Network

The insertion of the [FeII(pyimH)3]2+ [pyimH = 2-(1H-imidazol-2-yl)pyridine] spin-crossover complex into a ferromagnetic bimetallic oxalate network affords the hybrid compound [FeII(pyimH)3][MnIICrIII(ox)3]2·X (ox = C2O42–). This spin-crossover complex templates the growth of crystals formed by a chiral 3D oxalate network. The magnetic properties of this hybrid magnet show the coexistence of long-range ferromagnetic ordering at 4.5 K and a spin crossover of the intercalated [FeII(pyimH)3]2+ complex above 250 K. The compound presents a light-induced excited spin-state trapping (LIESST) effect below 60 K although with limited photoconversion (less than 8 %). The [FeII(pyimH)3]2+ spin-crossover complex has been inserted into a chiral 3D ferromagnetic bimetallic oxalate network in the compound [FeII(pyimH)3][MnIICrIII(ox)3]2·X. It shows the coexistence of long-range ferromagnetic ordering at 4.5 K, thermal spin crossover above 250 K and a light-induced excited spin-state trapping (LIESST) effect with a small photoconversion below 60 K.
Datum: 23.10.2015

Synthesis of the Single-Crystalline Form and First-Principles Calculations of Photomagnetic Copper(II) Octacyanidomolybdate(IV)

A gel crystallization technique was successfully applied in the pioneering preparation of a single-crystalline form of the three-dimensional copper(II) octacyanidomolybdate(IV) network, which is a photomagnetic material. This assembly crystallizes with the formula {[CuII(H2O)]2[MoIV(CN)8]}·2H2O in the tetragonal crystal system and reveals a three-dimensional cyanido-bridged framework constructed of five-coordinate square-pyramidal [CuII(H2O)(NC)4]2– complexes and [MoIV(CN)8]4– ions of square-antiprismatic geometry. First-principles calculations by the GGA + U method indicate that the visible-light absorption band, crucial for the observation of a photomagnetic effect, is interpreted in terms of MoIV to CuII charge transfer, which is enabled owing to the accompanying pz  spx transition of the nitrogen atoms of the bridging cyanido ligands. The optical transitions in the visible range are anisotropic, and the most efficient light absorption along the [111] direction corresponds to the alignment of the cyanide bridges. A single-crystalline form of three-dimensional copper(II) octacyanidomolybdate(IV) photomagnetic material is prepared. First-principles calculations indicate that an optical transition in the visible range is a charge transfer from MoIV to CuII, and the most efficient light absorption along the [111] direction corresponds to the alignment of the cyanide bridges.
Datum: 06.10.2015

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