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European Journal of Inorganic Chemistry - Current Research Articles

Current research articles: Inorganic Chemistry

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European Journal of Inorganic Chemistry - published by Wiley-VCH

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.

Current articles of the journal:

Probing Solid-State Breathing and Structural Transformations in a Series of Silver(I) Porous Coordination Polymers

Key observations of the role anions and solvents play in the solid-state flexibility of a series of isostructural silver(I) porous coordination polymers (PCPs) are reported. Building upon earlier results for the perchlorate salt, the structural transformations of two new analogues of a 3D PCP [Ag(dpzm)]X (1) (dpzm = 2,2?-dipyrazinylmethane; X = PF6, ClO4, BF4), which contain either PF6 (1a) or BF4 (1c) counterions, are investigated. These materials undergo a remarkable guest-induced single-crystal to single-crystal (SC-SC) solid-state contraction and expansion, which is accurately elucidated by X-ray crystallography. The extent of breathing for PCPs 1a–1c is shown to relate to the type of anion contained within their 3D structures and the nature of the solvent guest. Using X-ray diffraction, further light is shed on structural transformations that take place upon desolvation for this group of materials. These investigations reveal that, while the as-synthesised forms (containing DMSO) undergo a transformation (porous 3D to close-packed 3D; porous 3D to 2D) upon desolvation, the solvent-exchanged forms are more stable. Herein two new examples of an AgI porous coordination polymer that display solid-state breathing are reported. Additional transformations of these materials to non-porous 2D and 3D structures are investigated.

Posted on 2 July 2015 | 1:30 pm

Insight into CaMgSi2O6:Eu2+,Mn2+,Dy3+ Nanoprobes: Influence of Chemical Composition and Crystallinity on Persistent Red Luminescence

Optical imaging in which photons are the information source seems to be a very important technique, less expensive and less harmful than more conventional diagnostic methods and suitable, for instance, for sensitive diagnosis capable of detecting cancer at an early stage. We have recently developed inorganic persistent luminescent nanoparticles (PLNPs) as nanoprobes useful for in vivo imaging that can master the difficulties of the biological environment such as tissue autofluorescence, absorption, or photobleaching because they are excited before injection into the animal. In this work, we have focused on silicate materials, CaMgSi2O6, that emit in the red/near-infrared range for several hours. With the aim of improving their luminescent properties and nanoparticle size, we have explored a new method of synthesis that allows a suitable yield of particles and studied the influence of chemical composition and crystalline structure on luminescence intensity. Adjusting the molar ratio of Ca/Mg/Si and crystallization temperature, very fine nanoparticles of PLNPs have been obtained with an improved luminescence and the high production yield necessary to promote the emergence of these nanoprobes in the field of optical imaging. Nanoparticles of CaxMgySi2O6 doped with Eu2+, Mn2+, and Dy3+ have been prepared with a high production yield by a sol–gel method inspired by the Stöber process with the aim of improving the luminescent properties and decreasing the size of silicate-based nanoprobes. Such a study is essential to promote the emergence of these nanoprobes in the field of optical imaging.

Posted on 2 July 2015 | 1:20 pm

Synthesis of Stable Magnetic Polyaniline Nanohybrids with Pyrene as a Cross-Linker for Simultaneous Diagnosis by Magnetic Resonance Imaging and Photothermal Therapy

We have developed pyrene-modified magnetic polyaniline nanoparticles (MPANs), a hybridization of MnFe2O4 magnetic nanoparticles (MNPs) and polyaniline (PANI) with pyrene as a cross-linker, for diagnosis by simultaneous magnetic resonance (MR) imaging and photothermal therapy. In general, the strong affinity between PANI molecules, owing to interchain hydrogen bonding and the ?–? interactions mediated by their aromatic composition, hinders the successful synthesis of complexes of PANI with inorganic materials. To overcome this obstacle, we used pyrene as a cross-linker to synthesize a stable complex of PANI with MNPs. We first modified the hydrophobic MNPs with pyrene through a hydrophobic interaction and then formed a complex with PANI. The pyrene-induced ?–? interactions between the pyrene molecules on the MNPs and PANI reduced the affinity between the PANI molecules, and the strong affinity between the PANI molecules and MNPs rendered stable nanocomplexes of MPANs. Finally, Cetuximab-conjugated MPANs were fully tested for simultaneous diagnosis by magnetic resonance imaging (MRI) from superparamagnetic MnFe2O4 and photothermal ablation therapy from the near-infrared absorbing characteristics of PANI in epidermal growth factor receptor (EGFR) overexpressed cancer cells (A-431 cells) in vitro. Magnetic polyaniline nanoparticles (MPANs) are synthesized and show evenly mixed magnetic nanoparticles (MNPs) and polyaniline (PANI) with increased colloidal stability owing to the hydrophobic and ?–? interactions between the PANI and pyrene molecules.

Posted on 2 July 2015 | 1:20 pm

Mercury Complexes with Tripodal Pseudopeptides Derived from D-Penicillamine Favour a HgS3 Coordination

The pseudopeptides L4 and L5 are built on a nitrilotriacetic scaffold and functionalized with three D-penicillamine (D-Pen) units. D-Pen is an interesting building block and a bulkier analogue of cysteine with the ?-methylene hydrogen atoms replaced by larger methyl groups. The two sulfur ligands L4 and L5 are studied here with the toxic HgII ion. The formation of the two mononuclear complexes HgL4 and HgL5 is demonstrated by 1H NMR spectroscopy and mass spectrometry and the tristhiolato coordination is unambiguously evidenced by the UV absorption signatures. An important feature is the stabilization of the HgS3 coordination mode at the expense of the generally preferred HgS2 linear coordination. It appears that the hindered D-Pen pseudopeptide L5 is capable of stabilizing the unusual HgS3 coordination over a large pH range in water, pH?> 5.5. This water-soluble compound can therefore be considered as a promising chelating agent for mercury detoxification. Tripodal pseudopeptides anchored on a nitrilotriacetic chemical scaffold and extended with three D-penicillamine units stabilize the unusual HgS3 coordination over a large pH range in a hindered coordination environment.

Posted on 1 July 2015 | 11:20 am

Off–On, Ratiometric, and On–Off Fluorescence Responses of Thioether-Linked Bisquinolines toward Hg2+ and Fe3+ Ions

Fifteen bisquinoline derivatives with a thioether linker have been prepared, and their Hg2+- and Fe3+-specific fluorescence responses have been investigated. Upon the addition of Hg2+ ions, unsubstituted 2-quinolylmethyl derivatives 1a–1c exhibit a fluorescence enhancement (off–on) response. On the other hand, ratiometric and fluorescence quenching (on–off) responses are accomplished for derivatives with monomethoxy (2a–2c) and trimethoxy (3a–3c) substituents on the aromatic ring, respectively. The 8-quinolylmethyl derivatives 4a–4c and 5a–5c exhibit a similar response pattern to those of 1 and 2 with enhanced Hg2+ ion selectivity. Increasing the number of sulfur atoms through the extension of the linker chain also improves the Hg2+ ion selectivity. The selectivity of fluorescent bisquinoline derivatives with thioether linkers for Hg2+ ions is improved by 8-quinolylmethyl tethering and increasing the number of sulfur atoms through the extension of the linker.

Posted on 1 July 2015 | 11:20 am

Redox-State Dependent Ligand Exchange in Manganese-Based Oxidation Catalysis

Manganese-based oxidation catalysis plays a central role both in nature, in the oxidation of water in photosystem II (PSII) and the control of reactive oxygen species, as well as in chemical processes, in the oxidation of organic substrates and bleaching applications. The focus of this review is on efforts made to explore and elucidate the redox-dependent coordination chemistry of these manganese-based systems in solution and the mechanisms by which their catalytic redox reactions proceed. We also examine the behaviour and activity of complexes that have been developed and used as models for the active sites of the corresponding enzymes, or used as catalysts in the oxidation of organic substrates. Given the current concern over the environmental and economic impact of chemical processes, manganese catalysts that use H2O2 as oxidant are the primary focus of this review. The role played by Mn-based complexes in controlling reactive oxygen species and in the water oxidation complex of photosystem II has inspired the design of catalysts for chemical processes such as the oxidation of organic substrates and bleaching applications. Here, the redox and pH dependence of the coordination chemistry of Mn complexes applied in oxidations with H2O2 is reviewed.

Posted on 30 June 2015 | 12:10 pm

Synthesis and Characterisation of Various Diester and Triester Adducts of TiCl4

Titanium(IV) chloride and the triester glycerol tribenzoate (gtb) were reacted under moisture-free conditions in order to investigate the use of triester-containing oils in the purification of TiCl4 in industrial processes. This resulted in the isolation of a chloro-bridged dimeric complex containing four titanium centres [{(TiCl4)2(gtb)}2] (1). Further novel coordination compounds of TiCl4 and the diesters; diisopropyl malonate, dibenzyl malonate and diethyl succinate were synthesised by direct reaction under moisture-free conditions, yielding [TiCl4{CH2(COOiPr)2}] (2), [TiCl4{CH2(COOCH2Ph)2}] (3) and [TiCl4{C2H4(COOEt)2}] (4) respectively. The structures of compounds 1–4 were determined by single-crystal X-ray diffraction. All structures assumed an octahedral geometry consisting of the titanium bound to four chloride ligands and the diester molecule acting as a bidentate ligand, through its two carbonyl oxygen atoms. Exposure of the isopropyl malonate reaction to trace amounts of water during synthesis resulted in the formation of an oxo-bridged dimeric structure [Ti2(?-O)Cl3{CH2(COOiPr)2}2] (2b), the structure of which was also obtained via single-crystal X-ray diffraction. The synthesis of novel titanium complexes with triesters and diesters was achieved using Schlenk techniques for the purpose of ellucidating the previously unknown mechanisms at play during the industrially used Chloride Process.

Posted on 30 June 2015 | 12:10 pm

Aerosol-Assisted Chemical-Vapour Deposition of Zinc Oxide from Single-Source ?-Iminoesterate Precursors

Single-source zinc ?-iminoesterate precursors have been used for the first time in the aerosol-assisted chemical-vapour deposition (AACVD) of ZnO thin films. Depositions at 450 °C on silica-coated glass substrates produced strongly adherent films with excellent coverage of the substrate. The zinc ?-iminoesterates [Zn(L1)2] (1) and [Zn(L2)2] (2) were synthesised by the reaction between ZnEt2 and 2 equiv. of a synthesised ?-iminoester ligand CH3C[NHCH(CH3)2]CHC(O)OCH2CH3 (L1) and CH3C(NHCH3)CHC(O)OCH2CH3 (L2). The synthesised complexes were isolated and characterised by 1H and 13C NMR spectroscopy, mass spectrometry and thermal gravitational analysis (TGA). The structures of the compounds were determined by single-crystal X-ray diffraction. The ZnO films deposited from 1 and 2 were analyzed by glancing-angle X-ray powder diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and their optical properties determined by UV/Vis/NIR transmission spectroscopy. These results reveal that the organic ligand attached to the N moiety of the zinc complex has a significant effect on the level of carbon incorporated into the deposited thin film. Upon annealing, highly transparent hexagonal wurtzite ZnO thin films were produced. The synthesis, isolation and characterisation of zinc ?-iminoesterate precursors of the type [Zn(CH3C(NR)CHC(O)OCH2CH3)] are described, as well as their use for the first time in the aerosol-assisted chemical-vapour deposition (AACVD) of ZnO thin films at 450 °C. Results show that changing the R group on the N moiety of the precursors has a significant effect on carbon contamination in the films.

Posted on 30 June 2015 | 12:10 pm

Origin of Projected Excellent Thermoelectric Transport Properties in d0-Electron AMN2 (A = Sr or Ba; M = Ti, Zr, Hf) Layered Complex Metal Nitrides

Layered materials have several properties that make them suitable as high-performance thermoelectric materials. In this study, we elucidated the potential of d0-electron layered complex metal nitrides, AMN2 (A = Sr or Ba; M = Ti, Zr, Hf), with KCoO2-type and ?-NaFeO2-type crystal structures. The detailed electronic structures and electronic transport coefficients for AMN2 compounds were calculated by using density-functional theory and Boltzmann theory, respectively. The KCoO2-type AMN2 compounds show highly anisotropic thermoelectric properties. The effective masses at the lowest conduction bands in both KCoO2-type and ?-NaFeO2-type AMN2 compounds were significantly smaller than that in three-dimensional perovskite SrTiO3, a well-known compound with good thermoelectric properties. The results suggest that the excellent thermoelectric transport properties arise from appropriate electronic structures and small effective masses in AMN2 layered complex metal nitrides. d0-Electron layered complex metal nitrides (AMN2) are expected to exhibit excellent thermoelectric properties that arise from their electronic structures and small effective masses.

Posted on 30 June 2015 | 12:10 pm

Mo-V-Phosphoric Heteropoly Acids and Their Salts: Aqueous Solution Preparation – Challenges and Perspectives

Vanadium-containing heteropoly acids (HPAs) are effective acidic and oxidizing catalysts in various reactions. The existing wide application of such catalysts requires their safe, waste-free, and easy preparation on a large scale. Unfortunately, the so-called ether method, first suggested more than 100 years ago, is still mainly used for the purpose, producing a lot of harmful waste material. Nowadays environmental safety requirements necessitate revision of such preparation processes and searching for alternative methods of synthesis. At present, there exist a range of new methods for preparing HPAs, with a so-called peroxide method seeming to be the most generally applicable one. For this reason, the aim of this review is to discuss some recent progress in obtaining aqueous solutions of Keggin and Wells–Dawson Mo-V-P HPAs and their salts. These solutions can be used as individual homogeneous oxidation catalysts, bifunctional catalysts for one-pot acidic and oxidizing transformations, or precursors for preparing their heterogeneous analogues. Preliminary V2O5 activation by addition of hydrogen peroxide H2O2 allows one to obtain vanadium-containing heteropoly acid (HPA) solutions directly from V2O5, MoO3, and H3PO4 without extraneous components. Such a synthetic pathway, named a peroxide route, offers a promising ecological method for preparing valuable Mo-V-P HPAs in short reaction times on a large scale.

Posted on 29 June 2015 | 10:10 am

Dye-Sensitized Solar Cells with Biferrocenyl Antennae Having Quinoxaline Spacers

Four biferrocene-based dyes with quinoxaline spacers possessing functional groups [H (2), Cl (3), NO2 (4) and COOH (5)] were successfully synthesized and characterized by elemental analyses, IR spectroscopy, electronic absorption, 1H NMR and 13C NMR spectroscopy, and mass spectrometry. The synthesized dyes as well as the starting diketenone (1), from which quinoxalines 2–5 were synthesized, were exploited as photosensitizers in TiO2-based dye-sensitized solar cells. The spectral responses of dyes 2–5 were extended into the visible region up to ? = 550 nm. Amongst all the ferrocenyl dyes with a quinoxaline spacer, dyes having Cl (3), NO2 (4), and COOH (5) substituents showed photovoltaic performance that was superior to that of starting material 1 and that of quinoxaline derivative 2. The superior performances of 3, 4, and 5 are probably because of the abilities of these systems to accept high loadings of the dye on the TiO2 surface and the long lifetime of electrons in the TiO2 conduction band. Dye 5 showed better thermal stability than the state-of-art dye N719 and has a comparable lifetime of electrons in the conduction band. Four biferrocenyl quinoxaline derivatives are synthesized and their light-harvesting properties are explored. Dyes having Cl, NO2, and COOH substituents on the spacers show the best photovoltaic performance, and this may be attributed to their ability to accept high loadings of the dye on the TiO2 surface and the long lifetime of electrons in the TiO2 conduction band.

Posted on 29 June 2015 | 10:10 am

High Turnover Catalase Activity of a Mixed-Valence MnIIMnIII Complex with Terminal Carboxylate Donors

The neutral dimanganese(II,III) complex [Mn2(BCPMP)(OAc)2] [1; BCPMP3– = 2,6-bis({(carboxymethyl)[(1-pyridyl)methyl]amino}methyl)-4-methylphenolato] has been synthesized and characterized. The complex contains two terminal carboxylate donors. Complex 1 was found to be an effective catalyst for the disproportionation of H2O2 with high catalytic rate and a turnover number of 7500, the highest turnover reported to date for a catalase mimic. The rates and TON were significantly higher than recorded for a dicationic dimanganese(II,III) counterpart ([Mn2(BPBP)(OAc)2]·(ClO4)2, 2; BPBP– = 2,6-bis{[bis(2-pyridylmethyl)amino]methyl}-4-butylphenolato), which lacks the terminal carboxylate donors, suggesting that introduction of a terminal carboxylate donor improves activity. A well-resolved 16-line pattern obtained upon addition of H2O2 to complex 1 suggests involvement of an MnIIIMnIV species in the catalytic cycle. The neutral dimanganese(II,III) complex [Mn2(BCPMP)(OAc)2] (1) has been synthesized and characterized. Complex 1 was found to be an effective catalyst for the disproportionation of H2O2 with high catalytic rate and a turnover number of 7500, the highest turnover reported to date for a catalase mimic.

Posted on 29 June 2015 | 10:10 am

Reversible Phase Transitions and Dielectric Properties in [(CH3)4P]2[Cr2O7] and ­[Et4P]2[Cr3O10]

Tetramethylphosphonium dichromate ([(CH3)4P]2[Cr2O7], 1) undergoes a reversible phase transition at around 221 K. The results of the variable-temperature single-crystal X-ray structural analyses and the rotational potential energy calculations suggest that the phase transition is probably related to the order–disorder transition of the [Cr2O7]2– anion. The change of the space group from Pa-3 at room temperature to Pbca at low temperature is reflected in the peak-like dielectric response. Tetraethylphosphonium trichromate ([Et4P]2[Cr3O10], 2) crystallizes in the monoclinic space group P21/c at room temperature. Upon cooling and heating, the step-like dielectric anomalies observed at around 270 K indicate a reversible phase transition. Moreover, the rotational potential energy calculations certify the potential motion of the [Cr3O10]2– anion, being related to the phase transition. These findings open a new approach to the design of complexes that show phase transitions coupled with unusual dielectric properties. Tetramethylphosphonium dichromate and tetraethylphosphonium trichromate undergo reversible phase transitions accompanied by peak- and step-like dielectric anomalies, respectively. The crystal structures and results of the rotational potential energy calculations indicate that the phase-transition mechanisms are closely related to the dynamics of the dichromate and trichromate anions.

Posted on 25 June 2015 | 1:24 pm

Trinuclear Heterobimetallic Complexes by Stepwise Metalation of a Macrocyclic Tetraimidazolium Salt

A series of trinuclear heterobimetallic AuI/M2 (M = RhIII, IrIII, RuII) complexes were prepared by the stepwise and selective metalation of a rigid cyclic tetraimidazolium salt. Reaction of the tetraimidazolium salt with exactly 1 equivalent of silver oxide and transmetalation of the dicarbene ligand to AuI yielded selectively a mononuclear AuI complex. This complex features an CNHC–Au–CNHC unit obtained by coordination of two N-heterocyclic carbene (NHC) donors placed in diagonal positions within the macrocycle and two non-metalated imidazolium moieties. Subsequent metalation of these imidazolium groups yielded heterobimetallic complexes (AuI/RhIII2, AuI/IrIII2, and AuI/RuII2) with Au···M separations shorter than 5.5 Å. The selective stepwise metalation of a rigid macrocyclic tetraimidazolium salt gives rise to trinuclear heterobimetallic tetracarbene complexes (AuI/RhIII2, AuI/IrIII2, AuI/RuII2) with M···M distances of less than 5.5 Å in the solid state.

Posted on 25 June 2015 | 1:24 pm

Azadipyrromethene-Based Near-Infrared Dyes: Effect of Thienylethynyl Substitution at the Distal and Proximal Phenyl Groups

Azadipyrromethene (ADP) ligands substituted with thienylethynyl substituents either at the distal phenyl groups H(CD1) or the proximal phenyl groups H(CD2) were synthesized and characterized. The thienyl groups have a hexyl group at the third position to improve solubility in organic solvents and prevent homocoupling of the ethynylthiophene reactants. To further tune the opto-electronic properties, the substituted ADPs were coordinated with BF2+ and ZnII. Absorption spectroscopy shows that the thienylethynyl substitutions redshift the absorption spectra of the dyes, with a larger shift when the substituents are added on the proximal phenyl groups. Cyclic voltammetry experiments show that the substitutions stabilize the anion and dianion. The reduction potentials for the modified ligands (or zinc chelates) were not affected by the placement of the thienylethynyl groups. Preliminary studies of blends of the new molecules with poly(3-hexylthiophene) (P3HT) suggest that the zinc(II) chelates have potential as electron acceptors for organic solar cells. Azadipyrromethene ligands substituted with thienylethynyl substituents at the distal or proximal phenyl groups were synthesized and coordinated with BF2+ and ZnII. Thienylethynyl substitutions redshift the absorption spectra of the dyes, with a larger shift for proximal substitution. Substitutions also stabilize the anions, and the placement of the thienylethynyl groups do not affect the reduction potentials.

Posted on 25 June 2015 | 1:24 pm

A Range of Nitrato Coordination Modes in NiII Complexes with the Versatile Ligand 1,8-Bis(2-pyridyl)-3,6-dithiaoctane: Structural, Spectroscopic, Electrochemical, and Theoretical Studies

We have synthesized a series of NiII-pdto complexes – [Ni(pdto)(NO3)]NO3·H2O (C1), [Ni(pdto)(H2O)2](NO3)2 (C2), and [Ni(pdto)(NO3)(H2O)]NO3 (C3), with pdto = 1,8-bis(2-pyridyl)-3,6-dithiaoctane – with different spectroscopic responses associated with the coordination modes of the nitrato moiety. Through UV/Vis spectroscopy and electrochemical experiments it was established that in acetonitrile solution the compounds C1, C2, and C3 are each transformed into the same chemical species [Ni(pdto)NO3]+. Cyclic voltammetry experiments gave evidence of two consecutive one-electron transfers associated with NiII-(pdto) + 1 e–??NiI-(pdto) and NiI-(pdto) + 1 e–??Ni0 + pdto processes, which are in agreement with the high flexibility of the pdto ligand with regard to accommodating the preferred geometry of the central atom. The complexation reaction between pdto and the starting salt Ni(NO)3·6?H2O in acetonitrile was also studied by UV/Vis spectroscopy and cyclic voltammetry. A linear relationship between the experimentally determined value of 10 Dq and the ?(EHOMO–LUMO) energy values obtained by computational methods was found. In this work we report a series of complexes of nickel with the ligand 1,8-bis(2-pyridyl)-3,6-dithiaoctane (pdto) and NO3– moieties coordinated or as counterion, with different electrochemical and spectroscopic responses. Theoretical studies were carried out to explain these changes.

Posted on 25 June 2015 | 1:12 pm

Ba2B6O11, a Member of the BaO-B2O3 Family, Featuring a Layer Framework

Ba2B6O11, a new member of the BaO-B2O3 family, has been found and features a layered structure. The single-crystal X-ray structural analysis revealed that Ba2B6O11 crystallizes in the monoclinic space group P21/c. The parameters of the monoclinic unit cell are a = 9.115(1), b = 7.773(1), c = 12.696(2) Å, ? = 100.325(9)°, and Z = 4. The new centrosymmetric alkaline earth metal borate, Ba2B6O11, is characterized by a 2D B–O framework composed of the basic building block (B6O14) with the Ba2+ cations filling the channels formed by the (B6O14) units or located between the (B6O10)? layers. Ba2B6O11 has a short cut-off edge of 240 nm. Based on a theoretical calculation, it has been proven that Ba2B6O11 has a birefringence of 0.04 and a relatively large indirect band gap of 4.94 eV, which is close to the experimental value of 5.17 eV. Its structure is discussed in terms of the B–O framework and dimensional reduction formalism together with the other structures reported in the BaO-B2O3 phase diagram. Ba2B6O11, a new centrosymmetric barium borate, features a layered structure and a wide transmission range from 240 to 2600 nm.

Posted on 24 June 2015 | 1:11 pm

Platinum Nanoparticles Stabilized by Glycerodendrimers: Synthesis and Application to the Hydrogenation of ?,?-Unsaturated Ketones under Mild Conditions

Air-stable platinum nanoparticles stabilized by glycerodendrimers were prepared in water and analyzed by TEM. These platinum nanoparticles showed good catalytic activity for the reduction of ?,?-unsaturated ketones to saturated ketones at room temperature in water or in water/THF (1:1) under H2 (101.3 kPa). The catalytic species was recovered and recycled several times. Pt nanoparticles are stabilized by glycerodendrimers (GD) and used (and recycled) for the reduction of ?,?-unsaturated ketones to saturated ketones at room temperature in water under H2 (101.3 kPa).

Posted on 24 June 2015 | 12:20 pm

Magnetofluorescent Nanoaggregates Incorporating Terbium(III) Complexes as Potential Bimodal Agents for Magnetic Resonance and Optical Imaging

Terbium(III) ions were coordinated to two diethylenetriaminepentaacetic acid (DTPA) amphiphilic bisamide ligands, and the complexes were assembled into micellar nanoaggregates. The magnetic and optical properties of the resulting nanoaggregates were examined in detail. Upon excitation into the ligand levels at 265 nm, the complexes show characteristic TbIII emission at 546 nm with quantum yields of up to 7.6?%. Nuclear magnetic relaxation dispersion (NMRD) measurements have shown that the transverse relaxivity r2 at 500 MHz and 310 K reaches a maximum value of 9.4 s–1?mM–1. The efficient T2 relaxivity at high magnetic field strengths is sustained by the increased rotational correlation time of the nanoaggregates and high magnetic moment of the terbium ion. Magnetofluorescent nanoaggregates incorporating amphiphilic terbium(III) complexes are created and their potential as bimodal agents for magnetic resonance and optical imaging are examined.

Posted on 23 June 2015 | 10:40 am

Spin-Crossover Nano- and Micrometric Rod-Shaped Particles Synthesized in Homogeneous Acid Media

Acidic conditions have been used for the elaboration of spin-crossover (SCO) nano- and microparticles of BF4 derivatives of a (triazole)iron complex. Modifying both the acid (HBF4) concentration and the synthetic method (reaction and evaporation rate), rods of various sizes ranging from 100 nm to ca. 50 ?m were obtained. The morphologies of the particles were probed by transmission electronic microscopy (TEM) and high-resolution transmission electronic microscopy coupled quantified energy-dispersive X-ray spectroscopy (HRTEM-EDX), elemental analysis, differential scanning calorimetry (DSC), NMR spectroscopy, and thermogravimetric analysis (TGA) were used to determine the fine compositions of the different samples. All these characterizations revealed a correlation between the size of the rod-shape particles and their composition, the smaller rods corresponding to the [Fe(Htrz)2(trz)](BF4) complex (form A; Htrz = 1,2,4-triazole and trz = 1,2,4-triazolato), and the larger ones to the [Fe(Htrz)3](BF4)2·3H2O derivative (form B). The SCO properties were investigated by optical, magnetic, and Mössbauer measurements. Various sizes of spin-crossover (SCO) nano- and micrometric rod-shaped particles have been synthesized in homogeneous acid media. The complete characterization of the samples revealed a correlation between the size of the particles and their composition. The SCO properties were investigated by optical, magnetic, and Mössbauer measurements.

Posted on 23 June 2015 | 9:50 am

Extremely Facile Transformations of Tris(3,5-dimethylpyrazolyl)borate: a Bidentate Nitrogen Ligand and a C2-Chiral Cation

Two novel transformations are reported for the well-known hydridotris(3,5-dimethylpyrazolyl)borate (Tp*–). The uncommon Lewis base abstractor aryldiazonium cation (ArN2+; Ar = p-Br-C6H4, p-MeO-C6H4) if used in equimolar amounts, removes a hydride from Tp*– in acetone to produce the formal acetone adduct of tris(3,5-dimethylpyrazolyl)borane (pz*3B·C3H6O, compound 1). Frustrated Lewis pair (FLP) like behavior is thus found for a tris(pyrazolyl)borane. If 2 equiv. of ArN2+ are used, 3,5-dimethylpyrazolate is now being abstracted from 1, and the resulting intermediate bifunctional borane adds another equivalent of acetone to form cation 2+ {[pz*2B·(C3H6O)2]+, obtained as 2-BF4}, a boronium cation that is the formal addition product of 2 equiv. of acetone to the bis(3,5-dimethylpyrazolyl)borinium cation. Compounds 1 and 2+ are characterized by 1H, 13C, and 11B NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. Compound 1 is potentially useful as a charge-neutral bidentate chelate ligand with controlled sterics, and 2+ is a C2-chiral cation. Although aryldiazonium cations have been known for a very long time, they are still good for surprises. Aryldiazonium cations ArN2+ react with hydridotris(3,5-dimethylpyrazolyl)borate (commonly used as a ligand) to remove a hydride and to form short-lived intermediate tris(3,5-dimethylpyrazolyl)borane, which is trapped as the acetone adduct. If 2 equiv. of ArN2+ are used, 3,5-dimethylpyrazolate will additionally be abstracted, followed by acetone trapping.

Posted on 23 June 2015 | 9:50 am

Quantum Chemical Investigation on Phosphine-Functionalized Charge-Neutral Osmium(II) Complexes Bearing Bidentate/Tetradentate Pyridylpyrazolate-Based Ligands

By altering the monodentate phosphine ligand (PR3), a series of charge-neutral OsII complexes 1a–5a [Os(fppz)2(PR3)2] and 1b–5b [Os(L-NPh)(PR3)2] [fppz = 3-(trifluoromethyl)-5-(2-pyridyl)pyrazole; PR3 = PMe3 (1a/1b), PPhMe2 (2a/2b), PPh2Me (3a/3b), PPh3 (4a/4b), P(OPh)3 (5a/5b); L-NPh is two bis(pyridylpyrazolate] fragments connected by a phenylamino bridge at the 6-position of the pyridyl rings] have been investigated by density functional theory (DFT) methods. The P(OPh)3 substitution in 5a (5b) rendered a considerable stabilization to the HOMO energy levels and an enlargement of the HOMO–LUMO energy gap compared with those of 1a–4a (1b–4b), which led to a clear blueshift in the emission spectra. With the enhancement of the electron-withdrawing strength of the phosphine ligands, the emissions are successively blueshifted from 1a/1b to 4a/4b. The results also revealed a general relationship between the variations of the emissions and changes to the Os–P bond lengths. The phenylamido bridge in 1b–5b redshifted the absorption and emission spectra compared with those of 1a–5a and decreased the Os(d) participation in the HOMOs, which led to dominant L-ligand-based 3?–?* character for their emissive states compared with dominant metal-to-ligand charge-transfer (3MLCT) characters for 1a–5a. A series of charge-neutral OsII complexes with bidentate/tetradentate pyridylpyrazolate-based ligands are investigated by changing the monodentate PR3 ligands. DFT and time-dependent DFT calculations show that the PR3 ligand plays an important role in controlling the photophysical and phosphorescence properties of these OsII complexes.

Posted on 22 June 2015 | 12:50 pm

Syntheses, Structures, and Characteristics of Six Coordination Polymers Based on 1,4-Bis(imidazol-1-yl)benzene and Isophthalates Containing Coordination-Inert Substituents

Hydrothermal reactions of 1,4-bis(imidazol-1-yl)benzene (bimb) and either 5-hydroxyisophthalic acid (HO-H2ip) or 5-methoxyisophthalic acid (MeO-H2ip), as well as transition metal salts, gave rise to six new coordination polymers: [Zn2(bimb)(H2O)(HO-ip)2]n (1), [Zn(bimb)(MeO-ip)]n·(H2O)n (2), [Mn2(bimb)2(HO-ip)2]n (3), [Mn2(bimb)2(H2O)2(MeO-ip)2]n (4), [Cu2(bimb)2(MeO-ip)2]n·(H2O)3n (5), and [Co(bimb)(H2O)(MeO-ip)]n·(DMF)0.5n·(H2O)n (6). Their structures have been defined by single-crystal X-ray diffraction analyses, IR spectra, elemental analyses and thermogravimetric analyses. Complex 1 is a 2D coordination network consisting of ?-oxygen-bridged dinuclear ZnII units, whereas 2 is an interdigitating 2D layer. ZnII ions in 1 and 2 have a distorted tetrahedral geometry, and two independent HO-ip and two bimb moieties in the dinuclear unit of 1 form ?···? stacking interactions. Complexes 3 and 4 are 2D layers consisting of dinuclear MnII carboxylate units; bimb in an anti conformation serves as an exo-bidentate ligand in 3, whereas in 4 it acts as a terminal ligand, filling void space. Bis-monodentate MeO-ip in 5 connects CuII ions into a 3D coordination network, whereas MeO-ip in 6 bridges between two CoII ions to form a 2D layer, with the strong hydrogen bonds between water molecules of the adjacent 2D layers generating a 2D supramolecular bilayer. The dinuclear MnII units in 3 and 4 are well separated by organic ligands, and make up the basic magnetic units. Temperature-dependent magnetic susceptibility analyses show the existence of antiferromagnetic interaction in 3 and 4. Six metal-organic coordination polymers have been constructed from 5-hydroxyisophthalate or 5-methoxyisophthalate and rigid 1,4-bis(imidazol-1-yl)benzene. The coordination-inert hydroxy and methoxy substituents of 5-substituted isophthalates and the directional hydrogen bonds exerted important effects on the structures and properties of the coordination polymers.

Posted on 22 June 2015 | 12:50 pm

Crystal Structure, Antioxidant Properties and Characteristics in Aqueous Solutions of the Oxidovanadium(IV) Complex [VO(IDA)phen]·2H2O

A new oxidovanadium(IV) complex was prepared by the reaction of vanadyl acetylacetonate [VO(acac)2], iminodiacetic acid (H2IDA) and 1,10-phenanthroline (phen) in aqueous solutions. The crystal structure of [VO(IDA)phen]·2H2O was determined by X-ray diffraction crystallographic analysis. The stability of the title compound in aqueous solution was investigated by using potentiometric titration methods. Moreover, the kinetics of substitution reactions of the VO(IDA) binary complex with 1,10-phenanthroline were investigated in aqueous solutions. These reactions were monitored spectrophotometrically at 249 nm by using stopped-flow methods. Kinetic measurements were performed in the 293–308 K temperature range, at different concentrations (0.1–0.5 mM) of the binary complex and at a constant concentration of phen (0.05 mmol/L). Moreover, the antioxidant properties of this complex against superoxide radicals were studied by nitrobluetetrazolium (NBT) and cyclic voltammetry (CV) and the antioxidant properties were also investigated against two organic radicals: the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH·) and the 2,2?-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical (ABTS·+) by using spectrophotometric methods. The results of the antioxidant tests show that VO(IDA)phen scavenges superoxide free radicals as well as organic radicals (ABTS·+ and DPPH·). The crystal structure of the oxidovanadium(IV) complex [VO(IDA)(phen)]·2H2O (IDA = iminodiacetate, phen = 1,10-phenanthroline) was determined. Potentiometric titrations and kinetic measurements based on stopped-flow methods allowed the stability of the complex to be determined in aqueous solution. The antioxidant activity of VO(IDA)phen towards superoxide and organic radicals was investigated.

Posted on 22 June 2015 | 12:50 pm

A Keggin-Type Structure Expanded by an Eight-Membered Ring of Alternating Edge-Sharing VO5 and VO6 Polyhedra: Solvothermal Synthesis, Crystal Structure, and Magnetic Properties

The new tungstovanadate (trenH)2(trenH2)2[W4V13O44]·ca.11H2O was prepared under solvothermal conditions in a basic solution at pH ? 12. The cluster core contains VIV/VV centers with delocalized spins exhibiting strong antiferromagnetic exchange interactions as evidenced by temperature-dependent magnetic susceptibility measurements pointing to an S = 1/2 magnetic ground state. The structure features an eight-membered ring composed of four alternating edge-sharing VO5 pyramids and VO6 octahedra encapsulating a central Keggin fragment. A mixed-valent polyoxidotungstovanadate featuring a central Keggin fragment encapsulated by an eight-membered ring consisting of edge-sharing VO5 and VO6 polyhedra was solvothermally synthesized at pH ? 12.

Posted on 22 June 2015 | 12:50 pm

Synthesis, Characterization, Stability, and Gas Adsorption Characteristics of a Highly Stable Zirconium Mesaconate Framework Material

A new ZrIV mesaconate framework material was synthesized by heating a mixture of ZrCl4, mesaconic acid, and acetic acid in a molar ratio of 1:1:30 in DMF at 150 °C for 24 h. The influence of the molar ratio of ZrCl4/acetic acid on the crystallinity of the compound was examined. The as-synthesized compound was Soxhlet-extracted with ethanol and subsequently heated under vacuum to remove guest solvent molecules from the pores. Both the as-synthesized sample and the thermally activated sample of this new material were characterized by X-ray powder diffraction (XRPD), FTIR spectroscopy, thermogravimetry, and elemental analysis. The compound is thermally stable up to 320 °C under air. XRPD experiments indicate that the compound maintains its crystallinity upon exposure to water, acetic acid, and 1 M HCl. According to the N2 sorption analyses, the compound possesses a BET surface area of 662 m2?g–1. Thus, the material is a promising candidate for gas storage and separation owing to its high physiochemical stability and considerable porosity. The modulated synthesis, complete characterization, thermal and chemical stability properties, as well as the gas adsorption behavior of a new ZrIV mesaconate material are presented.

Posted on 22 June 2015 | 12:50 pm

Determining the Electronic Structure of a Series of [(phen)3M]0 (M = Ti, V, Mo) and [(pdi)2M]n+ (M = Cr, Mo) Complexes: Coordination of Neutral Ligands vs. ?-Radical Anions

The molecular and electronic structures of newly synthesized complexes containing 2,6-bis[1-(4-methoxyphenylimino)ethyl]pyridine (pdi) ligands have been determined by high-resolution X-ray crystallography, electronic and electron-spin resonance spectroscopy, and temperature-dependent magnetic susceptibility measurements: [MoIV(pdi··)(pdi2–)]0 (S = 0) 1, [MoIV(pdi2–)(pdi·)](BF4) (S = 1/2) 2, [CrIII(pdi··)(pdi·)]0 (S = 0) 3, [CrIII(pdi·)(pdi0)](BF4)2 (S = 1) 4, [MIII(Mephen·)3]0 (M = Cr 5, Mo 6, Ti 7, and V 8). Complexes 5–8 contain ?-radical anions of 2,9-dimethyl-1,10-phenanthroline. Monoanionic radicals (SL = 1/2) are designated (pdi·)1– and (Mephen·)1–, whereas their neutral analogues are (pdi0) and (Mephen0) and the dianions are (pdi··)2– (SL = 1) and (pdi2–)2– (SL = 0). We show here that the oxidation level of these ligands can be determined experimentally in complexes 1–8 by high-quality single-crystal X-ray crystallography at low temperature (ca. 100 K). The appropriate oxidation levels of the tridentate ligands pyridine-2,6-diimine (pdi) and 2,9-dimethyl-1,10-phenanthroline (Mephen) as neutral species, monoanion ?-radical and dianion in “low valent” octahedral complexes [M(Mephen)3]0 (M = Ti, V, Cr, Mo) and [Mo(pdi)2]n (n = 0,1+) have been experimentally determined by X-ray crystallography and by UV/Vis and EPR spectroscopy.

Posted on 22 June 2015 | 12:50 pm

A Bis(tridentate)cobalt Polypyridine Complex as Mediator in Dye-Sensitized Solar Cells

Dye-sensitized solar cells equipped with cationic and neutral RuII-based sensitizers [Ru(ddpd){tpy(COOH)3}]2+ [12+; ddpd = N,N?-dimethyl-N,N?-di(pyridin-2-yl)pyridin-2,6-diamine, tpy(COOH)3 = 2,2?6?,2?-terpyridine-4,4?,4?-tricarboxylic acid] and [Ru(ddpd){tpy(COOH)(COO)2}] (2) with and without the coadsorbent chenodeoxycholic acid were constructed with I3–/I– or the CoIII/II-based redox mediators [Co(bpy)3]3+/2+ (33+/2+; bpy = 2,2?-bipyridine) and [Co(ddpd)2]3+/2+ (43+/2+) in the presence of LiClO4 and 4-tert-butylpyridine. The best photovoltaic performance was achieved by using the 43+/2+ shuttle and the neutral sensitizer 2 without coadsorbent. The higher short-circuit photocurrent density and higher electron recombination lifetimes obtained with this combination suggest slow electron recombination kinetics at the TiO2 surface with the CoIII complex 43+. The slow electron transfer to 43+ is tentatively ascribed to the high-lying ?* orbitals of the electron-rich ddpd ligands, which result in a weak electronic coupling. This contrasts with the faster recombination with 33+, which features the low-energy ?* orbitals of the bpy ligands. The depicted Co3+/2+ redox shuttle increases the short-circuit photocurrent density ISC relative to that of the standard I3–/I– mediator in dye-sensitized solar cells with Ru sensitizers. The higher ISC values and electron recombination lifetimes are ascribed to the high energy of the ?* orbitals of the polypyridine ligands of the mediator, which retard back electron transfer from TiO2 to the Co3+ species.

Posted on 22 June 2015 | 12:10 pm

Uniform Poly(acrylic acid)-Functionalized Lanthanide-Doped LaVO4 Nanophosphors with High Colloidal Stability and Biocompatibility

Ln-doped (Ln = Eu or Nd) LaVO4 nanoparticles functionalized with poly(acrylic acid) (PAA) were prepared from lanthanide and vanadate precursors in the presence of PAA by a simple one-pot method that consists of a homogeneous precipitation reaction in ethylene glycol/water at a moderate temperature (120 °C). The size of the nanoparticles could be modified in the 40–70 nm range by adjusting the amount of PAA added. The effects of the Eu and Nd contents of these nanomaterials on theirs optical properties (emission intensity and lifetime) were also analyzed to find the optimum nanophosphors. Finally, the nanoparticles showed negligible cytotoxicity for Vero cells at concentrations up to 0.05 mg?mL–1 and a high colloidal stability in physiological buffer solutions; therefore, they satisfy the most important requirements for in vitro biotechnological applications. Uniform lanthanide-doped LaVO4 nanospheres functionalized with poly(acrylic acid) are synthesized with a controllable size by a one-pot procedure. As these nanoparticles present strong red (Eu) or near-infrared (Nd) luminescence, are nontoxic for cells, and show high colloidal stability in physiological buffer, they are good candidates as optical biomarkers for in vitro applications.

Posted on 22 June 2015 | 12:10 pm

Stepwise Synthesis of Siloxane-Substituted Oligoarsanes and Structural Investigation of Alkaline Earth Metal Derivatives

The reaction between [Li(dme)AsH2] and (ClSiiPr2)2O gives a mixture of two products: the primary diarsanyldisiloxan (H2AsSiiPr2)2O (5) and the cyclic diarsanylsiloxane (HAsSiiPr2)2O (6). Through metallation of the mixture, the deprotonated species of both compounds could be obtained and isolated. Further reactions between the two metallated cyclic diarsanylsiloxanes (compounds 9 and 10) and (ClSiiPr2)2O both lead to the bicyclic compound As2[(iPr2Si)2O]2 (11). Subsequent oxidative coupling of 9 or 10 with C2H4Br2 as reagent leads to intermolecular As–As bond formation, yielding the quite remarkable compound As6[(iPr2Si)2O]3 (12), which features two siloxane-bridged As3 rings. Compounds 5–12 were characterized by NMR, elemental analysis and X-ray crystallography. Quantum chemical calculations were carried out to investigate the formation of the different products when arsenic (compound 12) is substituted by phosphorus (compound 4) in the final oxidation reaction of the cyclic compounds (HESiiPr2)2O. The calculations suggest a reaction path leading to 4 that is in agreement with experimental observations. The theoretical data also provide information that explains the experimental finding that two different products for E = P and E = As are formed under the same oxidative reaction conditions. A set of different arsane compounds based on siloxanes were synthesized and compared with their phosphorus analogues. After oxidative coupling of the cyclic compounds (HESiiPr2)2O, different product types were obtained for E = P and E = As. The courses of the different reactions are investigated in experimental and quantum chemical terms to explain the different outcomes for P and As.

Posted on 22 June 2015 | 12:10 pm

Cyclometalation of Phosphanes at Iridium(I): Interplay with Intramolecular Reductive Elimination Induced by the Strong ?-Acceptor Ligands CO and NO+

Reaction of [{Ir(?-Cl)(coe)2}2] (1; coe = cis-cyclooctene) with 4 equiv. of PtBu2Ph in CH2Cl2 at ambient temperature resulted in oxidative addition of one phosphane ligand affording the known cyclometalated IrIII complex [IrCl(H)(PtBu2C6H4-?2P,C)(PtBu2Ph)] (2) in high yield. Compound 2 exhibits a coordinatively unsaturated five-coordinate 16 VE species, and its reactivity towards strong ?-acceptor ligands is investigated. Reaction of 2 with CO resulted in addition of the CO ligand and inversion of cyclometalation to give known IrI complex trans-[IrCl(CO)(PtBu2Ph)2] (3). In a similar manner, 1 reacted with nitrosonium tetrafluoridoborate affording the new complex salt [IrCl(NO)(PtBu2Ph)2][BF4] (4), which is isoelectronic with 3. Compounds 2 and 4 were characterized by spectroscopic methods as well as by X-ray crystallography confirming their molecular structures. The synthesis and crystal structure of the cyclometalated unsaturated complex [IrCl(H)(PtBu2C6H4-?2P,C)(PtBu2Ph)] (2) is reported. Whereas 2 is quickly formed by oxidative addition of one PtBu2Ph ligand, contrarily, also a facile inversion of the cyclometalation with simultaneous reductive elimination in reactions with strong ?-acceptor ligands such as CO or NO+ was observed.

Posted on 22 June 2015 | 12:10 pm

Ruthenium Carboxylate Complexes as Efficient Catalysts for the Addition of Carboxylic Acids to Propargylic Alcohols

Invited for the cover of this issue is the group of Heinrich Lang at the Technische Universität Chemnitz, Germany. The cover image shows the atom-economical and highly selective addition of carboxylic acids to propargylic alcohols to give ?-oxopropyl esters. This conversion is catalyzed by ruthenium complexes, represented by the skater in our picture. The kind of mononuclear ruthenium compounds presented in this work can be applied in many different fields of chemistry and materials science...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 2939 ff.

Posted on 19 June 2015 | 10:01 am

Masthead: Eur. J. Inorg. Chem. 18/2015

Posted on 19 June 2015 | 10:01 am

Graphical Abstract: Eur. J. Inorg. Chem. 18/2015

Posted on 19 June 2015 | 10:01 am

Ruthenium Carboxylate Complexes as Efficient Catalysts for the Addition of Carboxylic Acids to Propargylic Alcohols (Eur. J. Inorg. Chem. 18/2015)

The cover picture shows the atom-economical and highly selective addition of carboxylic acids to propargylic alcohols to give ?-oxopropyl esters. As background picture, one of the most famous sights of Chemnitz, the hometown of the authors, was chosen. It shows the bust of Karl Marx, in whose honor the city was named Karl-Marx-Stadt from 1953 to 1990. Today, this monument is not only a must-see for tourists but also the local meeting point for young skateboarders. One of these skateboarders represents the catalyst in our conversion. After coordinating the substrates, the ruthenium catalyst enhances the reaction by speeding it up and leading the substrates through the catalytic cycle, which is demonstrated by the dark-yellow loop. The pictures of the skaters are adopted from Fotolia (Copyright aroas/fotolia.com). We acknowledge graphic designer Jacob Müller from University Communications TU Chemnitz for graphic implementation of our concept into this picture. Details are discussed in the article by H. Lang et al. on p. 2939 ff. For more on the story behind the cover research, see the Cover Profile.

Posted on 19 June 2015 | 10:01 am

Synthesis, Characterization, and Thermal Properties of Chlorine-Containing 1,1,2,2-Tetraaminodisilanes and Their Potential as Chemical Vapor Deposition Precursors for Silicon Nitride Films

Three chlorine-containing aminodisilanes of the type Cl(RR?N)2Si–Si(NRR?)2Cl (with R = alkyl and R? = H or R) as potential chemical vapor deposition (CVD) precursors for silicon nitride (SiNx) films have been synthesized and characterized by X-ray diffraction; 1H, 13C, and 29Si NMR spectroscopy; and elemental analysis. They were obtained in high yields by the reactions of hexachlorodisilane (Si2Cl6) with excess liquid amines in diethyl ether through a general single-step procedure. Their thermal properties including stability, volatility, transport behavior, and vapor pressure were evaluated by thermogravimetric analysis (TGA) to confirm that they are suitable for the CVD procedure. The deposition of SiNx films was accomplished with a hot-wall CVD reactor system, which preliminarily verified the suitability of these compounds as CVD precursors. The aminodisilanes Cl(RR?N)2Si–Si(NRR?)2Cl (R = tBu and R? = H for 1, R = R? = nPr for 2, R = R? = allyl for 3) are synthesized and characterized. As they are potential chemical vapor deposition (CVD) precursors for silicon nitride (SiNx) films, their thermal properties including stability, volatility, transport behavior, and vapor pressure are evaluated by thermogravimetric analysis (TGA).

Posted on 18 June 2015 | 12:20 pm

Latest Developments in Metalloenzyme Design and Repurposing

In the past decade, artificial metalloenzymes (AMEs) have emerged as attractive alternatives to more traditional homogeneous catalysts and enzymes. This microreview presents a selection of recent achievements in the design of such hybrid catalysts. These include artificial zinc hydrolases and metathesases, the heme-protein repurposing for C–H, N–H, and S–H insertion reactions, novel light-driven redox hybrid catalysts, novel scaffold proteins, and metallocofactor anchoring techniques and metalloenzyme models. Artificial metalloenzymes (AMEs) combine homogeneous catalysis with enzymatic catalysis. In this microreview the authors describe recent developments in this fascinating field, ranging from artificial zinc hydrolases, metathesases, new heme protein reactions to light-driven redox reactions and enzyme models.

Posted on 18 June 2015 | 12:20 pm

Cyclometalated Diruthenium Complexes Bridged by 3,3?,5,5?-Tetra(pyrid-2-yl)biphenyl: Tuning of Electronic Properties and Intervalence Charge Transfer by Terminal Ligand Effects

Six cyclometalated diruthenium complexes bridged by 3,3?,5,5?-tetra(pyrid-2-yl)biphenyl have been prepared, in which 12+, 32+, and 52+ are symmetric complexes with different terminal ligands [2,6-bis(N-methylbenzimidazolyl)pyridine (Mebip), 4?-tolyl-2,2?:6?,2?-terpyridine (ttpy), and trimethyl-4,4?,4?-tricarboxylate-2,2?:6?,2?-terpyridine (Me3tctpy), respectively]. Three other complexes with mixed terminal ligands (Mebip-Me3tctpy for 62+; Mebip-ttpy for 72+; ttpy-Me3tctpy for 82+) are structurally nonsymmetric. These complexes display two consecutive Ru(III/II) redox couples between 0.20 and 0.90 V vs. Ag/AgCl, with the potential splitting ranging from 150 (for 52+) to 280 mV (for 62+). The mixed-valent states of these complexes have been generated by stepwise electrolysis. The symmetric complexes show intervalence charge transfer (IVCT) transitions at similar energy (Eop ? 5750 cm–1), with the electronic coupling parameter Vab of 1240, 1220, and 970 cm–1 for 13+, 33+, and 53+, respectively. The nonsymmetric series show significantly different Eop (7600, 5850, and 6650 cm–1 for 63+, 73+, and 83+, respectively) but Vab values that were comparable to that of 13+. DFT and TDDFT calculations have been performed to complement these experimental results. Three symmetric and three nonsymmetric cyclometalated diruthenium complexes bridged by 3,3?,5,5?-tetra(pyrid-2-yl)biphenyl have been prepared and studied. The electronic properties and intervalence charge transfer (IVCT) transitions can be effectively tuned by terminal ligand effects. DFT and TDDFT calculations give useful information on the spin density distributions and IVCT transitions.

Posted on 16 June 2015 | 1:20 pm

Synthesis, Spectroscopic Characterization, Crystal Structures, Energetics, and Thermal Stabilities of Li[AlX4] (X = Cl, Br): Investigation and Performance of Their Electrolyte Solutions

Lithium chloro- and bromoaluminates were prepared, fully characterized, and investigated as conducting salts for battery applications. In addition, thermodynamic investigations of their lattice enthalpies and other quantities were carried out. The Li[AlX4] salts also show very high conductivities in solvents of very low polarity, which makes them suitable candidates for conducting salts and battery systems working with voltages below ca. 3.5 V (X = Br) or ca. 4.4 V (X = Cl), such as lithium-sulfur batteries (LSBs). In particular, the bromoaluminates, with their Pearson-soft character, which prevents ion-pair formation with the Pearson-hard lithium ion, are promising for this purpose. An interesting alternative solvent for LSBs might be o-difluorobenzene, in which Li[AlBr4] shows very high solubility and conductivity. The carbonate solvents typically used for LIBs are not suitable for the bromoaluminates, and Li[AlCl4] also shows corrosive behavior towards aluminum at potentials higher than 2.5 V. This can be prevented by, for example, addition of Li[PF6]. Lithium salts of bromo- and chloroaluminates were tested and fully characterized for application as electrolytes for lithium-ion and -sulfur batteries in conventionally used solvents, as well as in o-difluorobenzene as a possible alternative. The lattice enthalpies of these salts were also investigated.

Posted on 16 June 2015 | 1:20 pm

Synthesis of an Iridium Peroxido Complex and Its Reactivity Towards Brønsted Acids

Treatment of the iridium(I) complex trans-[Ir(4-C5F4N)(CNtBu)(PiPr3)2] (2) with O2 or H2O2 gave the iridium(III) peroxido complex trans-[Ir(4-C5F4N)(O2)(CNtBu)(PiPr3)2] (3a). The peroxido complex 3a reacts with Brønsted acids to give the iridium(III) complexes cis-[Ir(4-C5F4N)(X)2(CNtBu)(L)(PiPr3)] (4: X = Cl, L = PiPr3, 5: X = CF3COO, L = H2O) and hydrogen peroxide. In the presence of formic acid, 3a yields the carbonato complex trans-[Ir{?2-OC(O)O}(4-C5F4N)(CNtBu)(PiPr3)2] (6) as the main product. Reactions between formic acid or dihydrogen and the iridium(I) complex 2 give the isomeric dihydrido complexes trans,trans-[Ir(4-C5F4N)(H)2(CNtBu)(PiPr3)2] (7a) and cis,trans-[Ir(4-C5F4N)(H)2(CNtBu)(PiPr3)2] (9a), respectively. The iridium peroxido complex trans-[Ir(4-C5F4N)(O2)(CNtBu)(PiPr3)2] was synthesized by treatment of the iridium(I) complex trans-[Ir(4-C5F4N)(CNtBu)(PiPr3)2] with O2 in the presence of [FeCp2]PF6. The peroxido complex reacts with CF3COOH to give H2O2 and the complex cis-[Ir(4-C5F4N)(CF3COO)2(CNtBu)(H2O)(PiPr3)].

Posted on 16 June 2015 | 1:20 pm

Water-Soluble, Monodisperse, Lanthanide-Doped Y(Gd)VO4 Nanocrystals as Promising Multimodal Bioprobe

Monodisperse and water-soluble lanthanide (Ln3+)-doped Y(Gd)VO4 nanocrystals (NCs) have been successfully synthesized by a fast, facile, and environmentally friendly microwave-assisted route with poly(acrylic acid) as the surfactant. The Y(Gd)VO4:5?%Ln3+ (Ln = Eu, Dy, Sm) NCs have unique fluorescence properties and polydimethylsiloxane (PDMS)-based white solid nanocomposites containing YVO4:5?%Eu3+ NCs show red emission upon UV irradiation. GdVO4 NCs can act as CT and MRI contrast agents as a result of their magnetic and X-ray absorption properties. A layer of SiO2 was coated onto the surfaces of the nanoparticles and MTT assays were carried out to test the cytotoxicity of the YVO4@SiO2 and GdVO4 NCs. The results indicate that the Y(Gd)VO4 NCs have potential in multimodal optical/MRI/CT bio-imaging. Monodisperse, water-dispersible, Ln3+-doped YVO4 nanocrystals have been synthesized by a microwave-assisted hydrothermal method. GdCl3 gradually replaced YCl3·6H2O from 0 to 100?% to yield GdVO4:Ln3+ nanocrystals. Y(Gd)VO4:Ln3+ nanocrystals have potential in 3D displays and fluorescent/magnetic/CT bio-imaging applications due to their excellent properties.

Posted on 15 June 2015 | 12:50 pm

NHC-Stabilized Bis(trimethylsilyl)phosphido Complexes of PdII and NiII

Halidometal complexes bearing monodentate N-heterocyclic carbenes [MX2(R2-bimy)2] {bimy = benzimidazole-2-ylidene; R = iPr, M = Pd or Ni, X = I; R = nBu, M = Pd, X = I and R = nBu, M = Ni, X = Br (1)} react under mild conditions with Li[P(SiMe3)2], in a 1:1 ratio, to provide the halido(silylphosphido)metal complexes [PdI(iPr2-bimy)2{P(SiMe3)2}] (2), [PdI(nBu2-bimy)2{P(SiMe3)2}] (3), [NiI(iPr2-bimy)2{P(SiMe3)2}] (4) and [NiBr(nBu2-bimy)2{P(SiMe3)2}] (5). Cleavage of the P–Si bonds in 3 and 5 with benzoyl chloride leads to the formation of the new (dibenzoylphosphido)halidometal complexes [PdI(iPr2-bimy)2P{C(O)Ph}2] (6) and [NiI(iPr2-bimy)2{P(C(O)Ph)2}] (7), respectively. NMR spectroscopy, X-ray crystallography and mass spectrometry are used to analyze these coordination complexes. N-Heterocyclic carbenes are employed to stabilize NiII and PdII metal centres containing bis(trimethylsilyl)phosphido ligands, including the square-planar complex [PdI(iPr2-bimy)2{P(SiMe3)2}] (2) illustrated (bimy = benzimidazole-2-ylidene).

Posted on 15 June 2015 | 12:50 pm

Thiocyanato Coordination Polymers with Isomeric Coordination Networks – Synthesis, Structures, and Magnetic Properties

The reactions of M(NCS)2 (M = Mn, Fe, and Ni) with 4-acetylpyridine (4-Acpy) in water lead to the formation of discrete complexes of composition M(NCS)2(4-Acpy)2(H2O)2, in which the metal cations are coordinated only N-terminally to the thiocyanato anions. When heated, these precursors dehydrate, and some of them transform into compounds of composition [M(NCS)2(4-Acpy)2]n, in which the metal cations are linked by pairs of ?-1,3-bridging anionic ligands into chains (1D isomer). In contrast, the thermal decomposition of Ni(NCS)2(4-Acpy)4 or crystallization from solution leads to the formation of an isomeric 2D network of the same composition, which is thermodynamically more stable than the 1D isomer. Temperature-dependent magnetic measurements of the 1D isomer [Fe(NCS)2(4-Acpy)2]n at 200 Oe reveal antiferromagnetic ordering at TN = 4.5 K. Field-dependent measurements show a metamagnetic transition into a saturated paramagnetic phase at a critical field of ca. 700 Oe. In contrast, magnetic measurements of the 2D isomer [Ni(NCS)2(4-Acpy)2]n at 1000 Oe show a ferromagnetic transition at TC = 8.6 K, whereas only paramagnetic behavior is observed for the Ni 1D isomer. Thiocyanato coordination polymers of composition M(NCS)2(4-acetylpyridine)2 (M = Mn, Fe, and Ni) are prepared, and their magnetic properties are investigated. Depending on the synthesis conditions and the nature of the metal cation, compounds with 1D or 2D coordination networks are obtained.

Posted on 12 June 2015 | 12:10 pm

Ionic and Neutral Half-Sandwich Guanidinatoruthenium(II) Complexes and Their Solution Behavior

Ionic and neutral half-sandwich guanidinatoruthenium(II) complexes [(?6-C10H14)RuL(?2(N,N?){(ArN)2C-N(H)Ar})][OTf] [Ar = 4-MeC6H4, L = 2-methylimidazole (1); Ar = 2-MeC6H4, L = 1,3,5-triaza-7-phosphaadamantane (PTA; 2)], [(ArNH)3C][(?6-C10H14)RuCl3] [Ar = 2-ClC6H4 (3)] and [(?6-C10H14)RuCl(?2(N,N?){(ArN)2C-N(H)Ar})] [Ar = 2-ClC6H4 (4), 2-FC6H4 (5), 4-ClC6H4 (6), and 4-(NO2)C6H4 (7)] have been isolated and the molecular structures of all but 6 were determined by single-crystal X-ray diffraction. VT 31P{1H} NMR spectroscopy of complex 2 revealed the presence of a mixture of four isomers in a ratio of appproximately 1.4:11.0:1.6:0.1. Theoretical calculations were performed on the syn-syn, syn-anti, anti-syn, and anti-anti conformers of 2, which revealed syn-anti to be the most stable conformer, both in the gas phase and in solution. Furthermore, the energies relating to the interactions between the lone pairs of the nitrogen atoms of the CN3 unit and the antibonding orbital of the central carbon atom in the syn-anti conformer of 2 were investigated by NBO analysis. The 1H NMR spectrum of 3 reveals the presence of two species and their ratio is dependent upon the concentration of 3 in CDCl3 and on the amount of D2O in CD3CN. The two species have been ascribed to the presence of a monomer and a water-bridged dimer. The new complexes 1–7 were screened as pre-catalysts in the transfer hydrogenation of acetophenone and complex 3 was tested as a pre-catalyst in the transfer hydrogenation of a variety of ketones to explore the scope of the reaction. The guanidinate ligand in 2 adopts the syn-anti conformation in the solid state whereas in solution a mixture of syn-anti, syn-syn, anti-syn, and anti-anti conformations are observed, as detected by VT 31P{1H} NMR spectroscopy.

Posted on 12 June 2015 | 12:10 pm

Synthesis, Characterization, Crystal Structures, and Catalytic C–C Coupling and Hydrosilylation Reactions of Palladium(II) Complexes Derived from CNC Pincer-Type N-Heterocyclic Carbenes

A series of pyridine linker containing bis(benz)imidazolium salts serving as precursors to CNC pincer-type N-heterocyclic carbene (NHC) ligands were prepared by successive N-alkylation of the azole core. Binuclear NHC complexes of silver(I) were synthesized by in situ deprotonation of the corresponding (benz)imidazolium salt with silver(I) oxide in acetonitrile at elevated temperature in the dark. Subsequently, pincer-type palladium(II)–NHC complexes were prepared by transmetalation using silver(I)–NHC complexes in acetonitrile at elevated temperatures. All compounds were fully characterized by elemental analysis, FTIR spectroscopy, and 1H and 13C NMR spectroscopy. X-ray diffraction studies on single crystals of three compounds confirmed the distorted square-planar geometry around the palladium(II) center. All complexes are monomeric in nature, and the bis-NHC ligand chelates in the CNC mode. The effective catalytic potentials of the palladium complexes were demonstrated by their high activities in aqueous-phase Suzuki–Miyaura and Heck–Mizoroki cross-coupling reactions of phenylboronic acid and n-butyl acrylate with a range of functionalized bromobenzene derivatives. The former coupling reaction afforded biphenyls in yields of 71–99?%, whereas the latter reaction evidenced low yields of the n-butyl cinnamates. Further, all the palladium complexes were studied for their potential in a catalytic hydrosilylation reaction. A series of pincer-type Pd complexes are synthesized and their C–C and C–Si bond-forming properties are evaluated.

Posted on 12 June 2015 | 12:10 pm

N-Derivatives of peri-Substituted Dichalcogenide [FeFe]-Hydrogenase Mimics: Towards Photocatalytic Dyads for Hydrogen Production

Synthetic strategies towards molecular dyads based on peri-substituted dichalcogenide (S,Se) [FeFe]-hydrogenase synthetic mimics covalently linked to a ZnTPP photosensitizer are described. Dithiolate and diselenolate model systems 2–5 are prepared through condensation of 2-naphthaldehydes with p-methoxyaniline, reduction of the resulting Schiff base and oxidative insertion of Fe2(CO)6 into the dichalcogen bond of the imine or amine. Diselenolate-based [FeFe] complexes (imine 3 and amine 5) are more efficient in electrocatalysis of proton reduction than their sulfur analogues 2 and 4 with increasing concentrations of pTsOH. Molecular dyad 1 containing a peri-substituted naphthalene dithiolate Fe2(CO)6 cluster covalently linked via an amine to ZnTPP is prepared through sequential zinc insertion into the porphyrin followed by iron insertion into the disulfide bond. peri-Substituted naphthalenedithiolate and diselenolate-based mimics of [FeFe]-hydrogenase, appended at the 2-position with basic amine and imine functionalities, are electrocatalysts for the conversion of protons to diatomic hydrogen. The synthesis of a molecular dyad, consisting of a zinc tetraphenylporphyrin photosensitizer covalently linked via an amine in close proximity to the catalytically active site, is also reported.

Posted on 12 June 2015 | 12:10 pm

The Use of Malonate Coordination Polymers with CuII and BaII Atoms for Barium Cuprate Preparation

The reactions of CuSO4·5H2O and Ba(R2mal) [R2mal2– is the dianion of 1,1-cyclopropanedicarboxylic acid (H2Cpdc), 1,1-cyclobutanedicarboxylic acid (H2Cbdc), or butylmalonic (H2Bumal) acid] in water give crystals of the 3D coordination polymers [BaCu(Cpdc)2]n (1), [BaCu(Cbdc)2(H2O)]n (2) and [Ba3Cu3(Bumal)6(H2O)11]n·2n(H2O) (3). The heating of 2 in air to 200 °C for 60 min results in the removal of the coordinated water molecules to give anhydrous [BaCu(Cbdc)2]n (4). The structures of 1–3 were determined by single-crystal XRD, and that of 4 was derived from powder XRD (XPRD) data. It was assumed that the crystal structures of the polymer complexes that we isolated were determined, to a considerable extent, by the nature of the substituent of the dicarboxylic acid. For 2, the dicarboxylic acid contains closed cyclic moieties, which are retained during dehydration to give 4. A comparative study of the thermal decomposition processes and thermal kinetics of 1–3 showed that the dehydration proceeds by a single scheme, and the bonds between the structural moieties in the anhydrous intermediates become stronger. The thermal destruction of the anhydrous compounds 1, 4 and {3} [the dehydrated intermediate of the thermal decomposition of 3, as proved by thermogravimetric analysis (TGA) data] occurs above 170 °C. The phase compositions of their solid products are determined by the thermolysis conditions, and the formation of BaCuO2 from 3 can be realized under milder conditions than those for the formation from 1 and 2. Combinations of CuSO4 and barium salts of substituted malonic acids produce 3D coordination polymers with various new topologies. The solid-phase thermolysis of the anhydrous polymers under specially selected conditions results in the target BaCuO2 crystalline phase.

Posted on 12 June 2015 | 12:10 pm

A Family of Dinuclear Iron(II) SCO Compounds Based on a 1,3,4-Thiadiazole Bridging Ligand

A new family of dinuclear iron(II) spin-crossover (SCO) compounds with the formula [Fe2(?-L)2]X4, with three different counteranions [X = BF4– (1), ClO4– (2) and F3CSO3– (3)], was prepared and characterized by single-crystal X-ray diffraction, variable-temperature magnetic susceptibility and Mössbauer measurements. These are the first dinuclear iron(II) SCO complexes with a 1,3,4-thiadiazole bridging ligand L {with L = 2,5-bis[(2-pyridylmethyl)amino]methyl-1,3,4-thiadiazole}. The magnetic measurements reveal a gradual and incomplete SCO of the three compounds around room temperature, starting from a diamagnetic [LS–LS] state. The diamagnetic ground state is in agreement with the single-crystal X-ray diffraction and Mössbauer data. Herein we present a new 1,3,4-thiadiazole bridging ligand and three spin-crossover active dinuclear iron(II) compounds. The complexes show promising magnetic properties with a diamagnetic [LS–LS] ground state at low temperatures and represent a great starting point to explore this new family of dinuclear SCO compounds.

Posted on 12 June 2015 | 12:10 pm

Fe2+-Responsive Bimodal MRI and Fluorescent Imaging Probe Based on a Gadolinium(III) Complex

An Fe2+-responsive bimodal MRI and fluorescent imaging probe, Gd-DTTA-BPP (DTTA = diethylenetriamine-N,N,N?,N?-tetraacetate, BPP = 2-{4-[(2,2?-bipyridin)-5-ylethynyl]phenoxy}-N-ethylacetamide), has been synthesized and characterized and its relaxivity and fluorescence properties examined. Gd-DTTA-BPP displays a high relaxation efficiency (10.3 mM–1?s–1 at 23 MHz and 25 °C) as a result of its rigid ligand and two inner-sphere water molecules (q = 2). In the presence of 1.0 equiv. Fe2+, the relaxation efficiency increased from 10.3 to 13.6 mM–1?s–1 (23 MHz and 25 °C) due to the complexation of Gd-DTTA-BPP with Fe2+. The fluorescence emission of the Gd-DTTA-BPP complex is quenched by Fe2+ ions. The confocal fluorescence imaging experiments on living cells showed that the imaging probe is permeable to living cells and localizes in the cytoplasm. An Fe2+-responsive bimodal MRI and fluorescent imaging agent based on the gadolinium(III) complex Gd-DTTA-BPP exhibits clearly enhanced relaxivity and significant turn-off luminescence in response to Fe2+.

Posted on 9 June 2015 | 10:20 am

A Heterodinuclear FeIIIZnII Complex as a Mimic for Purple Acid Phosphatase with Site-Specific ZnII Binding

Purple acid phosphatases (PAPs) are the only dinuclear metallohydrolases for which the necessity for a heterovalent active site (FeIII–MII; M = Fe, Zn or Mn) for catalysis has been established. A major goal for the synthesis of PAP biomimetics is to design a ligand in which the two coordination sites exhibit discrimination between the trivalent and divalent metal ions. With this goal in mind the ligand 2-{[bis(2-methoxyethyl)amino]methyl}-6-{[(2-hydroxybenzyl)(2-pyridylmethyl)amino]methyl}-4-methylphenol (BMMHPH2), with two distinct coordination sites, N2O2 (?) and NO3 (?), has been prepared. Although not exactly mimicking the active site of PAP, the ligand facilitated the formation of the complex [FeIIIZnII(BMMHP)(CH3COO)2](BPh4), which exhibited regioselectivity in the two metal binding sites. The phosphoesterase-like activity of the complex in 50:50 acetonitrile/water was investigated by using the substrate bis(2,4-dinitrophenyl) phosphate (BDNPP) yielding kinetically relevant pKa values of 6.89, 7.37 and 9.00, a KM of 10.8?±?2.1 mM and a kcat of 3.20?±?0.38?×?10–3 s–1 (at pH = 7.5). Attempts to prepare a diiron analogue resulted in a centrosymmetric dimer, [FeIII2(BMMHPH)2(?-OH)2](BPh4)2, with one six-coordinate FeIII atom in each of the ?-sites, connected by two ?-hydroxido groups. In this Fe(?-OH)2Fe diamond core the FeIII ions are weakly antiferromagnetically coupled, with J = –1.76?±?0.03 cm–1. The ?-sites were vacant. Attempts to replace the ZnII ion with MgII resulted in the formation of a centrosymmetric trimer, i.e. [FeIII2MgII(BMMHPH)2(CH3COO)2(CH3O)2](BPh4)2. The ligand 2-{[bis(2-methoxyethyl)amino]methyl}-6-{[(2-hydroxybenzyl)(2-pyridylmethyl)amino]methyl}-4-methylphenol (BMMHPH2) with two distinct coordination sites, N2O2 (?) and NO3 (?), and the corresponding iron(III)–zinc(II) complex [FeZn(BMMHP)(CH3COO)2](BPh4) were prepared as a mimic for the active site of the plant enzyme purple acid phosphatase. The complex exhibits phosphoesterase-like activity. The centrosymmetric dimer [Fe2(BMMHPH)2(?-OH)2](BPh4)2 and the acentrosymmetric trimer [Fe2Mg(BMMHPH)2(CH3COO)2(CH3O)2](BPh4)2 were also characterized.

Posted on 9 June 2015 | 10:20 am

Synthesis of Vinylnickel and Nickelacyclopropane Complexes Containing a Chelate [P,Se]-Ligand

The reaction of 2-(diphenylphosphanyl)benzeneselenol with Ni(PMe3)4 yielded the hydridonickel(II) complex [Ph2P(C6H4)Se]NiH(PMe3)2 (1). The insertion reactions of 1 with alkynes have been investigated. The vinylnickel complexes [Ph2P(C6H4)Se]Ni(CPh=CH2)(PMe3) (2) and [Ph2P(C6H4)Se]Ni(CCH3=CHPh)(PMe3) (3) were obtained by reacting phenylacetylene and 1-phenyl-1-propyne with 1. The nickelacyclopropane complexes [Ph2P(C6H4)Se]Ni[Ph(PMe3)C–CHPh] (4), [Ph2P(C6H4)Se]Ni[(SiMe3)(PMe3)C–CH2] (5) and 6 (6A and 6B) containing an ylidic ligand were obtained by reacting diphenylacetylene, (trimethylsilyl)acetylene, and 1-phenyl-2-(trimethylsilyl)acetylene with 1. The molecular structures of 1–5 were determined by single-crystal X-ray diffraction. The treatment of 2-(diphenylphosphanyl)benzeneselenol with Ni(PMe3)4 affords the hydridonickel(II) complex 1. The insertion reactions of 1 with phenylacetylene and 1-phenyl-1-propyne afford the vinylnickel(II) complexes 2 and 3, and the combination of 1 with diphenylacetylene, (trimethylsilyl)acetylene, and 1-phenyl-2-(trimethylsilyl)acetylene deliver nickelacyclopropane complexes 4–6.

Posted on 9 June 2015 | 10:20 am

A Computational Comparison of Oxygen Atom Transfer Catalyzed by Dimethyl Sulf­oxide Reductase with Mo and W

A thorough computational study has been performed to investigate oxygen atom transfer (OAT) reactions catalyzed by dimethyl sulfoxide reductase (DMSOR) with a catalytic molybdenum or tungsten ion. Thirteen different density functional theory (DFT) methods have been employed to obtain structural parameters along the reaction pathway, and single-point energies were computed with local correlation coupled-cluster methods [LCCSD(T0)]. For both Mo and W, most DFT methods indicate that the enzyme follows a two-step mechanism with a stable intermediate in which a DMSO molecule coordinates to the metal ion in the +IV oxidation state, and this is also confirmed by the LCCSD(T0) energies. The W-substituted models have a 26–30 kJ/mol lower activation barrier for the OAT reaction, and the reaction is 63–70 kJ/mol more exothermic than that with Mo. Different DFT methods give widely different activation and reaction energies, which roughly depend on the amount of exact exchange in the method; these differences are also reflected in the structures, especially for the rate-limiting transition state. Consequently, there is quite a large variation in energies and various energy corrections (thermal, solvation, dispersion, and relativistic; up to 39 kJ/mol) depending on which DFT method is used to obtain the geometries. Therefore, a mechanism predicted by a single method should be viewed with caution. The dimethyl sulfoxide (DMSO) reductase reaction with Mo and W was studied by using 13 different DFT methods calibrated to accurate LCCSD(T0)/CBS energies. A two-step reaction was found, the second barrier being rate limiting. This barrier is about 28 kJ/mol lower for W than for Mo owing to a ca. 67 kJ/mol more exothermic reaction energy. The experimental activation enthalpy for Mo is reproduced within 5–9 kJ/mol.

Posted on 9 June 2015 | 10:20 am

Synthesis, Structure, and Properties of Coordination Polymers with Layered Transition-Metal Thiocyanato Networks

Reaction of 4-tert-butylpyridine (tBP) with transition-metal thiocyanates leads to the formation of compounds of composition [M(NCS)2(tBP)4] [M = Mn (1-Mn), Fe (1-Fe), Co (1-Co), Ni (1-Ni)] that consist of discrete complexes, in which the metal centers are octahedrally coordinated by two terminal thiocyanato anions and four tBP ligands. If less tBP is used in the synthesis, two compounds of composition [M(NCS)2(tBP)2]n with M = Co (2-Co) and Ni (2-Ni) are obtained, in which the metal centers are linked into a 2D network by single thiocyanato anions. Thermal decomposition of 1-Co leads to the formation of an additional modification of [Co(NCS)2(tBP)2] (3-Co). Magnetic measurements of 2-Ni and 2-Co reveal that 2-Ni shows a ferromagnetic phase transition at Tc = (14.8?±?0.1) K and 2-Co shows a transition to the magnetic state with uncompensated magnetic moment at (3.15?±?0.03) K. New layered thiocyanato coordination polymers of composition [M(NCS)2(4-tert-butylpyridine)2]n (M = Ni, Co) were prepared and investigated for their magnetic properties. The Ni compound shows a ferromagnetic transition whereas the Co compound shows a transition to a magnetic state with uncompensated magnetic moment.

Posted on 9 June 2015 | 10:20 am

Electrochemically Exfoliated Black Phosphorus Nanosheets – Prospective Field Emitters

Herein we report field emission (FE) investigations on an electrochemically exfoliated few-layered black phosphorus nanosheet emitter at a base pressure of approximately 1?×?10–8 mbar. The turn-on electric field required to draw an emission current density of approximately 10 ?A/cm2 is found to be about 4.2 V/?m. Furthermore, few-layered black phosphorus nanosheet emitters deliver an emission current density of about 170 ?A/cm2 at an applied field of about 7.5 V/?m. The emission current vs. time plot measured at preset current values of about 5 ?A shows emission current fluctuations within ±10?% of the average value, indicating the highly stable nature of the black phosphorus field emitter. Thus, the 2D black phosphorus nanosheets synthesized using the simple electrochemical exfoliation method can be utilized for micro/nanoelectronics and flat panel FE display applications. 2D black phosphorus nanosheets, synthesized by electrochemical exfoliation, have the potential to be utilized for field emission (FE) display applications.

Posted on 5 June 2015 | 1:10 pm

Zn-MOFs Containing Pyridine and Bi­pyridine Carboxylate Organic Linkers and Open Zn2+ Sites

Two Zn-based metal-organic frameworks (Zn-MOFs) were solvothermally synthesized using two pyridine-based carboxylate linkers to generate unique pore topologies, as evidenced by single-crystal XRD analysis. These Zn-MOFs provided coordinatively unsaturated Zn2+ sites with square-pyramidal geometry, leading to an enhanced interaction with CO2, as demonstrated by sub-atmospheric pressure isotherms. The presence of open Zn2+ sites in these MOFs was validated by Raman spectroscopy under atmospheric CO2, revealing the presence of CO2 chemisorbed on surface sites. Additionally, in situ DRIFT spectra of chemisorbed acetic acid provided evidence for the formation of acetate-Zn2+ species after adsorption compared to IRMOF-1, which showed only physisorbed acetic acid species. Zn-based MOFs with unique pore structures were solvothermally synthesized, while imparting open Zn2+ centers that can interact with CO2 molecules.

Posted on 3 June 2015 | 1:10 pm

Synthesis and Characterization of a Dinuclear Copper Complex Bearing a Hydrophobic Cavity as a Model for Copper-Containing Monooxygenases

The synthesis and characterization of a dinuclear copper complex as a model of mononuclear copper-containing monooxygenases [dopamine ?-monooxygenase (D?M), tyramine ?-monooxygenase (T?M), and peptidylglycine ?-hydroxylating monooxygenase (PHM)] are described. This model is based on a cyclophane moiety bearing two bis(picolylamine) ligands for the complexation of two copper atoms and exhibits macroscopic features equivalent to those of the enzymes: (1) the two copper centers are 11.5 Å apart (11 Å for the enzymes) and (2) there is a hydrophobic pocket consisting of a cyclophane moiety in which substrates can bind near the two copper centers. The synthesis and characterization of a dinuclear copper complex as a model of mononuclear Cu-containing monooxygenases are described. This model exhibits features equivalent to those of the enzymes: (1) the two Cu centers are 11.5 Å apart and (2) there is a hydrophobic pocket consisting of a cyclophane moiety in which substrates can bind near the two Cu centers.

Posted on 3 June 2015 | 12:40 pm

Coordination of Ln3+ Ions to Perhydroxycucurbit[5]uril and the Formation of Supramolecular Self-Assemblies in the Presence of [SiW12O40]4– Anions and Transition Metal Salts – Potential Application in the Isolation of Light Lanthanides

The coordination and supramolecular assemblies of lanthanide cations and perhydroxycucurbit[5]uril {(HO)10Q[5]} in the presence of [SiW12O40]4– anions and transition metal salts show significant differences as the lanthanide atomic number increases. The molecular capsule (HO)10Q[5] coordinates with the light lanthanide cations Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, and Tb3+ but does not coordinate with heavier Ln3+ cations. However, (HO)10Q[5]/Na+-based molecular capsules form in the presence of the heavier lanthanide cations Ho3+, Er3+, Tm3+, Yb3+, and Lu3+ under the same synthetic conditions. These differences could be key in establishing a strategy for the isolation of light lanthanides from their heavier counterparts. The coordination and supramolecular assemblies of lanthanide cations and the sodium salt of perhydroxycucurbit[5]uril {(HO)10Q[5]} in the presence of [SiW12O40]4– anions and transition metal salts show significant differences as the lanthanide atomic number increases.

Posted on 3 June 2015 | 12:40 pm

Synthesis and Crystal Structure of the First Selenonyl Bis(carboxylate) SeO2(O2CCH3)2

Analytically pure selenonyl bis(acetate) SeO2(O2CCH3)2 was prepared by the reaction of SeO3 with a stoichiometric amount of acetic anhydride in nitromethane; it crystallizes in the monoclinic P21/n space group with one molecule in the asymmetric unit and a = 5.2044(1) Å, b = 21.6580(5) Å, c = 6.7074(2) Å, and ? = 93.628(2)°. The selenium atom binds to two oxo groups and two acetate anions in a distorted tetrahedral geometry. Analysis of the Hirschfeld surface indicated the presence of numerous C–H···O interactions. The selenonyl bis(acetate) SeO2(O2CCH3)2 can be prepared from the reaction of SeO3 with acetic anhydride and represents the first case of a selenonyl carboxylate. The compound is characterized by multinuclear NMR and Raman spectroscopy, and its molecular structure is determined by single-crystal X-ray diffraction.

Posted on 3 June 2015 | 12:40 pm

Unexpected Reactivity of Red Phosphorus in Ionic Liquids

Red phosphorus is far less reactive than the white allotrope. On the other hand, it is easier to handle and not as toxic as white phosphorus. In the Lewis-acidic ionic liquid (IL) [BMIm]Cl·2AlCl3 ([BMIm] = 1-butyl-3-methylimidazolium), red phosphorus and elemental iodine form several iodides at moderate temperature. 31P liquid- and solid-state NMR spectroscopy was used to rationalize the reaction at various temperatures and ratios of the starting materials. Monitoring of the reaction revealed nanoscale red-phosphorus particles. In addition to this top-down formation, phosphorus nanoparticles were also obtained in a bottom-up synthesis by dissociation of P2I4 in the IL. Depending on the ratio of red phosphorus and iodine, as well as the reaction temperature, P2I4, PI3, or P2I5+ dominate. Red phosphorus readily reacts with iodine in a Lewis-acidic ionic liquid at moderate temperature. Besides iodides, phosphorus nanoparticles are formed. The latter are also obtained in a bottom-up process starting from P2I4. In situ liquid- and solid-state NMR spectroscopy reveals details of the reactions.

Posted on 3 June 2015 | 12:40 pm

A Kumada Coupling Catalyst, [Ni{(Ph2­P)2N(CH2)3Si(OCH3)3-P,P?}Cl2], Bearing a Ligand for Direct Immobilization Onto Siliceous Mesoporous Molecular Sieves

The ligand-exchange reaction between [Ni(PPh3)2Cl2] and (Ph2P)2N(CH2)3Si(OCH3)3 afforded the novel NiII complex [Ni{(Ph2P)2N(CH2)3Si(OCH3)3-P,P?}Cl2] (1) in which the square-planar NiP2Cl2 coordination sphere contains a four-membered Ni–P–N–P ring. Comparison of the structure of 1 and related NiII square-planar or Ni0 tetrahedral complexes containing similar P–N–P ligands shows that the magnitude of the P–Ni–P angle is controlled by the presence of the Ni–P–N–P ring, irrespective of the geometry of the nickel coordination sphere. Direct anchoring of 1 onto SBA-15 molecular sieves through the trimethoxysilyl end-group of the ligand afforded heterogeneous catalyst 1/SBA-15. Both 1 and 1/SBA-15 catalyze Kumada cross-coupling reactions, exhibiting similar activity and a slightly higher product selectivity than the [Ni{Ph2P(CH2)3PPh2-P,P?}Cl2] and [Ni{(Ph2P)2N-(S)-CHMePh-P,P?}X2] (X = Cl, Br) complexes described in the literature. The Grignard reagent employed is likely to induce leaching of the catalyst, which retains its activity in solution. The structurally and spectroscopically characterized [Ni{(Ph2P)2N(CH2)3Si(OMe)3-P,P?}Cl2] complex (1) has been anchored onto SBA-15 siliceous mesoporous sieves, affording a heterogeneous catalyst. Both 1 and 1/SBA-15 catalyze Kumada coupling reactions.

Posted on 2 June 2015 | 11:50 am

Reactions of Laser-Ablated U Atoms with HCN: Infrared Spectra in Solid Argon and Quantum Chemical Calculations for HUNC

Reactions of laser-ablated U atoms with HCN produce HUNC, which is identified from its argon matrix infrared spectrum of strong N–C and U–H stretching modes at 2028 and 1417 cm–1. B3LYP calculations show that the unobserved HUCN isomer has a 6.3 kcal/mol higher energy, and its C–N stretching mode is about 125 cm–1 higher with more than an order of magnitude weaker intensity. Complementary experiments were done with thorium and group 4 metal atoms to form the analogous HMNC species for comparison and to demonstrate metal dependence for these new metal-bearing product absorptions. Laser-ablated U atoms react with HCN to produce HUNC, which is identified from its argon matrix infrared spectrum of strong N–C and U–H stretching modes. B3LYP density functional calculations show that the unobserved HUCN isomer has a 6.3 kcal/mol higher energy. Experiments with thorium atoms form the analogous HThNC species.

Posted on 2 June 2015 | 11:50 am

Structural and Magnetic Analysis of Retrosynthetically Designed Architectures Built from a Triply Bridged Heterometallic (CuL)2Co Node and Benzenedicarboxylates

The flexible trinuclear metallatecton {(CuL)2Co}2+ [H2L = N,N?-bis(salicylidene)-1,3-propanediamine] has been used as a building block, and its coordinative interaction with ortho-, meta-, and para-benzenedicarboxylates (BDCs) has been investigated to evaluate the positional isomeric effect of these carboxylate ligands on the resulting compounds. Structural characterization reveals that o-H2BDC produces a discrete trinuclear complex, namely [(CuL)2Co(o-HBDC)2]·H2O (1). As expected from the retrosynthetic design, one-dimensional (1D) coordination polymers, i.e., [{(CuL)2Co(m-BDC)}·CH3OH]? (2) and [{(CuL)2Co(p-BDC)}·2CH3OH]? (3), are obtained with m-BDC and p-BDC linkers, respectively. In all three complexes, the triply bridged bimetallic trinuclear coordination clusters are linear and solely a syn-syn bridging mode is observed for the carboxylates. In 2, the nodes are connected sidewise and are inclined toward each other to be accommodated by the 120°-angular m-BDC units, whereas in 3, the linear p-BDC linkers connect the parallel nodes diagonally. These differences in connectivity give rise to one-dimensional “great wall”-like chains for 2 and to quasi-linear coordination chains for 3. These distinct one-dimensional propagations induced by the different BDC isomers influence the three-dimensional columnar packing of 2 and 3. Magnetic susceptibility measurements and fitting of the results confirm that these three compounds are made by analogous magnetic building blocks, with very similar antiferromagnetic intramolecular magnetic exchange (with J in the –16.96 to –11.80 cm–1 range, using the –2JS1S2 convention). The structural homogeneity of the magnetic fragment within this family of compounds has allowed magnetostructural correlations to be explored, which has not previously been attempted. Rationally designed connectivity between triply bridged bimetallic trinuclear nodes has been made from a trans-[(CuIIL)2CoII]2+ tecton. The design distinguishes between the carboxylate functionalities of the three isomeric benzyldicarboxylates and permits solely a syn–syn bridging mode of ligation. Antiferromagnetic exchange interactions are associated with these complexes.

Posted on 2 June 2015 | 10:10 am

Patent Blue Derivatized Dendronized Iron Oxide Nanoparticles for Multimodal Imaging

Dendronized nanoparticles were designed for the bimodal (optical and magnetic) detection of lymph nodes with a hand-held probe during surgery. Patent Blue VF dye and iron oxide nanoparticles with 20 nm diameter, displaying high magnetization and located at the superparamagnetic/blocked monodomain boundary, were associated through a dendritic PEGylated coating to obtain stable water suspensions. Conjugation procedures (the sulfonamide link formed between the PEGylated dendron and the dye, together with the phosphonate anchoring on the iron oxide surface) were shown to be strong enough to survive in vivo conditions when the prepared nanohybrids were tested in an inflammatory node model. Moreover, magnetization of 20 nm nanoparticles increased when dendrons were grafted onto the surface, showing that they are good candidates for magnetic particle imaging, which requires high magnetization values. Preliminary lymphatic node uptake experiments performed in an inflammatory animal model showed higher uptake of the 10 nm nanoparticles relative to that of 20 nm nanoparticles. The highest probe concentration was reached 2 d after injection. Iron oxide particles of 10 and 20 nm diameter, dendronized and derivatized with Patent Blue VF dye, survived subcutaneous injection for bimodal lymph node detection with a hand-held probe during surgery.

Posted on 2 June 2015 | 10:10 am

Gas Sorption Properties of Isostructural Co-MOFs Containing Dipyridylporphyrin Linkers with Different Substituents at the 10,20-meso-Positions

Two new isostructural 3D dipyridylporphyrin-based MOFs, [Co(DpyDClP)]6·18H2O (I) and [Co(DpyDCNP)]6·18H2O (II), were prepared and structurally characterized by X-ray crystallography [DpyDClP: 5,15-di(4-pyridyl)-10,20-di(4-chlorophenyl)porphyrin; DpyDCNP: 5,15-di(4-pyridyl)-10,20-di(4-cyanophenyl)porphyrin]. They display exactly the same framework structures, notwithstanding different substituents at the 10,20-meso-positions of the dipyridylporphyrin backbones. Both substituents, –Cl for I and –CN for II, are completely exposed to the open space of solvent-free I and II. Therefore, the two MOFs have the same framework structures with distinct pore functionalities. Solvent-free I and II have solvent-accessible void volumes of 17.3 and 14.9?%, respectively. The thermal properties of I and II are very similar, but the gas sorption properties strongly depend on the pore dimensions and functionalities. Compound I has a higher uptake of CO2 compared with that of II due to its larger void volume. Particularly, CO2 sorption isotherms at 196 K indicate dramatically different patterns depending on the meso-substituents. Whereas I shows S-shape isotherms for CO2 adsorption/desorption at 196 K, II does not. The sorption of N2, H2, and CH4 by the two MOFs was also investigated. Two new isostructural 3D Co–porphyrin MOFs, [Co(L)]6·18H2O (L = DpyDClP and DpyDCNP), possess well-defined hexagonally arranged micropores, and the pore dimensions and functionalities inside the micropores can be varied systematically.

Posted on 2 June 2015 | 10:10 am

Long-Term Stability and Reproducibility of Magnetic Colloids are Key Issues for Steady Values of Specific Power Absorption Over Time

Virtually all clinical applications of magnetic nanoparticles (MNPs) require the formulation of biocompatible, water-based magnetic colloids. For magnetic hyperthermia, the requirements also include a high colloidal stability against precipitation and agglomeration of the constituent MNPs to maintain the heating efficiency of the ferrofluid in the long term. Agglomeration can change the heating efficiency by forming MNP clusters that modify the magnetic dipolar interactions between particles. Additionally, precipitation of the MNPs (i.e., the heating sources within the liquid) can change the measured heating rates of a colloid by altering the heat flow dynamics as the particles plunge to the precipitate. The specific power absorption (SPA) of single-domain MNPs depends critically on the average particle size and size distribution width and therefore first-rate reproducibility of different batches with respect to these parameters is also needed. We have studied the evolution of the SPA of highly reproducible and stable water-based colloids composed of polymer-coated Fe3O4 magnetic nanoparticles. By measuring the specific power absorption (SPA) values for 1 year as a function of field amplitude and frequency (H ? 24 kA/m; 260 ? f ? 830 kHz), we have demonstrated that the SPA values of these samples can be reproduced in successive synthetic batches and stable for several months due to the in situ polymer coating that provides colloidal stability and keeps dipolar interactions negligible. The poly(ethyleneimine)-coated magnetic nanoparticles (PEI-MNPs) prepared in this work by oxidative hydrolysis show good reproducibility of size and size distribution. In addition, these PEI-MNPs show only a moderate decrease in the specific power absorption when they aggregate over time. These results render these particles suitable for applications in magnetic hyperthermia.

Posted on 2 June 2015 | 10:10 am

Synthesis of Thorium(IV) and Uranium(IV) Salicylaldiminate Pseudo-Halide Complexes

To explore the coordination chemistry of salicylaldiminate ligands as a non-cyclopentadienyl ligand framework, we report the synthesis of their ThIV and UIV complexes. Deprotonation of (NC5H4)N=C(H)(3,5-tBu2C6H2)OH (1), (NC9H6)N=C(H)(3,5-tBu2C6H2)OH (2), and (CH3SC6H4)N=C(H)(3,5-tBu2C6H2)OH (3) with sodium hydride and the subsequent addition of 0.5 equivalents of [UI4(1,4-dioxane)2] yielded [{(NC5H4)N=C(H)(3,5-tBu2C6H2)O-?3(O,N,N?)}2UI2] (4), [{(NC9H6)N=C(H)(3,5-tBu2C6H2)O-?3(O,N,N?)}2UI2] (5), and [{(CH3SC6H4)N=C(H)(3,5-tBu2C6H2)O-?3(O,N,S)}2UI2] (6), respectively. The reaction of 3 equivalents of the sodium salt of 1 afforded [{(NC5H4)N=C(H)(3,5-tBu2C6H2)O-?3(O,N,N?)}3U]I3 (7). By using [ThCl4(dme)2], [{(NC5H4)N=C(H)(3,5-tBu2C6H2)O-?3(O,N,N?)}2ThCl2] (8) and [{(NC9H6)N=C(H)(3,5-tBu2C6H2)O-?3(O,N,N?)}2ThCl2] (9) were isolated. The metathesis of both chloride ligands in 9 with NaN3 led to a rare thorium azide product, [{(NC9H6)N=C(H)(3,5-tBu2C6H2)O-?3(O,N,N?)}2Th(N3)2] (10). The reaction of 5 with AgOTf (OTf = O3SCF3) afforded [{(NC9H6)N=C(H)(3,5-tBu2C6H2)O-?3(O,N,N?)}2U(OTf)2] (11), and the subsequent reaction of 11 with 2 equivalents of NaN3 provided [{(NC9H6)N=C(H)(3,5-tBu2C6H2)O-?3(O,N,N?)}2U(N3)2] (12). The reaction of 5 with 2 equivalents of AgNO3 produced [{(NC9H6)N=C(H)(3,5-tBu2C6H2)O-?3(O,N,N?)}2U{NO3-?2(O,O)}2] (13). Each complex was characterized by 1H NMR and IR spectroscopy and, with the exception of 11, their structures were determined by X-ray crystallographic analysis. The synthesis and characterization of non-cyclopentadienyl thorium(IV) and uranium(IV) complexes with pseudo-halide ligands is described. Rare examples of bis(azido) as well as a UIV nitrate species have been structurally and spectroscopically determined.

Posted on 2 June 2015 | 10:10 am

The Syntheses and Crystal Structures of the First Disiloxane–1,3-Dithiol and Its Cadmium Complex

The silicon–sulfur compound bis-1,3-[di(2,6-diisopropylphenoxy)]disiloxane–1,3-dithiol was obtained from silicon disulfide and 2,6-diisopropylphenol in a reaction catalyzed by imidazole or 4-(dimethylamino)pyridine (DMAP). The disiloxane–1,3-dithiol is produced in a low yield but in a repeatable manner and can be isolated as colorless crystals. The X-ray crystal structure of the compound reveals a linear or close-to-linear Si–O–Si angle and a mutual trans position of the two hydrosulfido groups. The compound forms a chelating mononuclear complex with cadmium ions. In the complex, the sulfido groups adopt a cis conformation, and the Si–O–Siangle deviates from linearity. The molecular structure of the compound is discussed on the basis of DFT calculations. The silicon–sulfur compound bis-1,3-[di(2,6-diisopropylphenoxy)]disiloxane–1,3-dithiol is produced in a low yield but in a repeatable manner from silicon disulfide and 2,6-diisopropylphenol in a reaction catalyzed by imidazole or 4-(dimethylamino)pyridine (DMAP). The exchange of the aryloxy substituent for an alkoxy one strongly influences the Si–O–Si angle.

Posted on 2 June 2015 | 10:10 am

Pd-Catalyzed Functionalization of the Thenoyltrifluoroacetone Coligands by Aromatic Dyes in Bis(cyclometallated) IrIII Complexes: From Phosphorescence to Fluorescence?­

The synthesis, characterization and photophysical properties of a series of neutral Ir(CN-Meppy)2(OO-tta-Ar) (MeppyH = 4-methyl-2-phenylpyridine; tta = thenoyltrifluoroacetonate) complexes containing new functionalized tta-Ar ligands in which the incorporated Ar group is an aromatic dye such as naphthalene, pyrene, naphthalimide or coumarin, are reported. The arylated proligands ttaH-Ar are readily obtained in two steps through Pd-catalyzed C–H bond activation of 2-acetylthiophene. In contrast to the parent Ir(CN)2(OO) complexes, which are phosphorescent in solution at room temperature, all of the arylated complexes display fluorescence, and the phosphorescence emission is quenched. Thus, this work shows that the incorporation of such aromatic dyes in the tta ligand has a dramatic influence on the photophysical properties of the resulting Ir complexes. Bis(cyclometallated) IrIII complexes featuring acetylacetonate-type ligands directly conjugated to dyes are prepared by an original synthesis. The introduction of an aromatic pendant promotes fluorescence from the singlet state of the functionalized OO unit.

Posted on 2 June 2015 | 9:50 am

Modelling Binuclear Metallobiosites: Insights from Pyrazole-Supported Biomimetic and Bioinspired Complexes

Numerous enzymes use two closely spaced metal ions to activate and transform small molecules. This allows these biocatalysts to perform diverse physiological functions, achieving impressive chemistry under remarkably mild conditions. Model studies of these metalloenzymes contribute to furthering our understanding of the unusual mechanistic aspects and interplay of cooperative effects used by Nature, and help provide clues as to how such reactivity might be harnessed for applications outside of the natural systems. This microreview describes synthetic models of binuclear metalloenzymes, focusing on complexes which are bridged by pyrazole ligand scaffolds. Structural and functional models of iron, nickel, copper and zinc binuclear active sites are discussed, in addition to several cobalt complexes possessing biologically relevant features. Metal separation and secondary-coordination-sphere interactions are recurring themes which aid in highlighting aspects of common importance in the native enzymes. Metalloenzymes with binuclear active sites are widespread in Nature. Synthetic modelling of these active sites has helped to highlight important structural and functional aspects which can dictate reactivity, providing blueprints for the development of new bioinspired catalysts. This microreview focuses on biologically relevant insights provided by complexes of 3,5-disubstitued pyrazole ligands.

Posted on 2 June 2015 | 9:50 am

The Role of the Ligand-to-Metal Charge-Transfer State in the Dipivaloylmethanate-Lanthanide Intramolecular Energy Transfer Process

Two new bis(dipivaloylmethanate)nitrato-bis(triphenylphosphine oxide)lanthanide(III) complexes [Eu(dpm)2(NO3)(tppo)2] (1) and [Tb(dpm)2(NO3)(tppo)2] have been prepared in monomeric form. The structural behavior of these coordination compounds is significantly different from those of [Eu2(dpm)6] and [Tb2(dpm)6] dimeric complexes. The photoluminescent properties of the monomeric and dimeric complexes are dependent on the energy positions of the low-lying ligand-to-metal charge-transfer (LMCT) state, which may be correlated with the chelating and chelate bridging coordination modes of the dpm ligand, respectively. The monomeric complex presents higher luminescence intensity than the dimeric complex due to the higher energy of the LMCT state in this system. Although the excited energy levels of the EuIII ion in complex 1 undergo efficient depopulation by LMCT, the same is not observed for the 5D0 emitting level, which presents values of the emitting lifetime that are almost temperature independent. The triboluminescence phenomenon of the [Ln(dpm)2(NO3)(tppo)2] complex is also discussed. New EuIII and TbIII compounds containing the dipivaloylmethanate (dpm) ligand have been synthesized and characterized. Ligand-to-metal energy transfer and the role of the charge transfer state on the luminescent properties have been investigated. The luminescent properties have been compared with those of dimeric complexes containing the dpm ligand

Posted on 2 June 2015 | 9:50 am

Versatile Reactivity of CH3CN-Coordinated Nickel-Iron Heterodimetallic Complexes with Cp* Ligand on Diazadithiolate (N2S2) or Dithiadithiolate (S4) Platforms

By using 3,7-dithianonane-1,9-dithiol (S4) and N,N?-dimethyl-N,N?-bis(2-mercaptoethyl)ethylenediamine (N2S2) as ligands, two CH3CN-coordinated nickel-iron heterodimetallic complexes, [NiS4Fe(CH3CN)Cp*][PF6] (1a) and [NiN2S2Fe(CH3CN)Cp*][PF6] (1b) (Cp* = ?5-C5Me5), were synthesized and characterized spectroscopically and crystallographically. Reactivities of 1a and 1b towards CO, CH2Cl2, HBF4, and NOPF6 have also been investigated. A series of complexes coordinated with small molecules [NiS4Fe(L)Cp*][PF6]n [n = 1, L = Cl (2a), CO (3a); n = 2, L = NO (4a)], [NiN2S2Fe(L)Cp*][PF6] [L = Cl (2b), CO (3b)] were obtained. We also studied the redox properties of 2a, 2b, 3a, and 3b by cyclic voltammetry in CH2Cl2 and in CH3CN solution. Complex 3a was found to be an excellent electrocatalyst for proton reduction from HBF4. CH3CN-coordinated nickel-iron heterodimetallic complexes [NiS4Fe(CH3CN)Cp*][PF6] and [NiN2S2Fe(CH3CN)Cp*][PF6], and complexes with small molecules coordinated [NiS4Fe(L)Cp*][PF6]n (n = 1, L = Cl, CO; n = 2, L = NO) and [NiN2S2Fe(L)Cp*][PF6] (L = Cl, CO) were synthesized and characterized crystallographically. One of the complexes is an excellent electrocatalyst for proton reduction.

Posted on 28 May 2015 | 1:10 pm

Facile Synthesis of Bimodal Mesoporous Fe3O4@SiO2 Composite for Efficient Removal of Methylene Blue

A facile self-assembly synthetic procedure was exploited to fabricate mesoporous-silica-capped Fe3O4 mesoporous clusters, so-called bimodal mesoporous Fe3O4@SiO2 composites. Structural characterization demonstrated that the core of the Fe3O4 clusters is coated with a mesoporous silica shell of uniform size distribution. Moreover, unprecedentedly good tunability of the core size (180–1700 nm) and the shell thickness (20–75 nm) is achievable by changing the synthetic parameters. Application of the composite in the removal of the organic dye methylene blue (MB) from aqueous solution was examined. The composite exhibits excellent adsorption of methylene blue from aqueous solution (33.12 mg?g–1) within 5 min and is easily regenerated by the photo-Fenton degradation reaction as a result of its high specific surface area, accessible pore channels, and good magnetic separation properties. This novel adsorbent promises extensive application in the practical removal of organic dyes. A bimodal mesoporous Fe3O4@SiO2 composite was fabricated through a facile self-assembly route. Unprecedentedly good tunability of the core size (180–1700 nm) and the shell thickness (20–75 nm) has been achieved. The composite exhibits excellent performance in organic pollutant removal through adsorption and photo-Fenton degradation.

Posted on 28 May 2015 | 1:10 pm

Acyclic Amido-Containing Silanechalcogenones

Reactions of the amidinate-stabilized silicon(II) bis(trimethylsilyl)amide [LSiN(SiMe3)2], {L = PhC(NtBu)2, 1} with a stiochiometric amount of elemental sulfur, selenium and tellurium afforded the first stable silanechalcogenones comprising an acyclic amido substituent [L{N(SiMe3)2}Si=E] {E = S (2), Se (3) or Te (4)}. All compounds were characterized by X-ray crystallography and multinuclear NMR spectroscopy. The results illustrate that these compounds possess some silicon–chalcogen double bond character. Reactions of the amidinate-stabilized silicon(II) bis(trimethylsilyl)amide [LSiN(SiMe3)2], {L = PhC(NtBu)2, 1} with a stiochiometric amount of elemental sulfur, selenium and tellurium afforded the first stable silanechalcogenones comprising an acyclic amido substituent, [L{N(SiMe3)2}Si=E] {E = S (2), Se (3) or Te (4)}.

Posted on 27 May 2015 | 11:30 am

Synthesis of BINAM-Based Chiral Di-1,2,3-triazolylidene Complexes and Application of the Di-NHC RhI Catalyst in Enantioselective Hydrosilylation

Despite the prolific use of (di-)NHC complexes in homogeneous catalysis, there are relatively few reports on their successful application in asymmetric transformations. In this work the atropisomeric binaphthyl backbone was combined with readily obtainable 1,2,3-triazolylidenes to develop a strongly electron-donating C2-symmetric ligand. The ligand was efficiently synthesized in a three-step procedure in an overall yield of 91?% starting from commercially available materials. Strategies for the synthesis of the corresponding di-NHC silver(I), palladium(II), rhodium(I), and iridium(I) complexes have been developed. The rhodium(I) complex was employed in the catalytic asymmetric hydrosilylation of ketones, providing good conversions at catalyst loadings as low as 0.2 mol-% and giving chiral inductions of up to 51?% ee. A convenient synthetic (“click”) route to a chiral di-1,2,3-triazolylidene ligand has been developed and its coordination to Ag, Pd, Ir, and Rh was established. The latter complex has been studied in the asymmetric hydrosilylation of ketones.

Posted on 27 May 2015 | 11:30 am

Synthesis and Characterization of Frustrated Spin Ladders SrFe2S2O and SrFe2Se2O

Chemical pressure was introduced by replacing Ba atoms with Sr atoms in the spin-ladder compounds AEFe2Ch2O (AE = Ba, Sr; Ch = S, Se). Powders and small single crystals of SrFe2S2O and SrFe2Se2O were synthesized from SrO, Fe, and Ch (S, Se). X-ray diffraction data were used to determine the crystal structures, which showed prominent magnetic ladderlike sublattices. The Mössbauer spectra of SrFe2S2O and SrFe2Se2O suggest the presence of localized divalent Fe ions in the FeCh3O structural units (distorted e3t23 configuration, S = 2). Single sharp hyperfine patterns at 5 K indicate the formation of simple antiferromagnetic ground states. The spin-ordering transitions (TN) were determined by magnetic, resistivity, and specific heat data to be 216 and 228 K for SrFe2S2O and SrFe2Se2O, respectively. At ca. 540 K, both compounds exhibit a similar broad maximum in ? (T?max). In comparison with BaFe2S2O and BaFe2Se2O, the Sr homologues have higher T?max values, which suggest stronger intersite exchange interactions in accordance with the chemical pressure from the replacement of Sr atoms with Ba atoms. However, the lower Néel temperatures for the Sr homologues supports the idea that magnetic frustration is present, and it clearly has to be considered for this group of compounds. SrFe2Ch2O (Ch = S, Se) contain ladder lattices of high-spin Fe2+ (d6) ions that exhibit strong magnetic coupling. Geometrical frustration prevents long-range spin order above TN = 216 (Ch = S) and 228 K (Ch = Se). The Mössbauer spectroscopy data require a more complex description because of the special local Fe coordination: a tetrahedron of one oxygen ion and three heavier chalcogenide ions.

Posted on 27 May 2015 | 11:30 am

Discrete Polymetallic Arrangements of AgI and CuI Ions Based on Multiple Bridging Phosphane Ligands and ?–? Interactions

A simple and straightforward approach to new polymetallic AgI and CuI supramolecules is presented. The reaction of N,P,N,P,N ligand 2 with AgI ions affords a trimetallic complex bearing a triangular Ag3 core; metallophilic interactions are stabilized by ligands that display a multiple bridging coordination mode as 10-electron donors. Heteroleptic polymetallic AgI and CuI complexes based on ligand 2 and the 1,12-diazaperylene (dape) ligand are obtained by an alternative molecular organization of the polymetallic arrays compared to that in homoleptic complexes of ligand 2. Reaction of an N,P,N,P,N ligand with AgI ions affords a stereoselective Ag3 triangular macrocyclic complex composed of multiple bridging phosphane ligands acting as unprecedented 10-electron donors. N,P,N,P,N and N,N 1,12-diazaperylene (dape) ligands with AgI or CuI ions lead to Ag3 and Cu5 heteroleptic columnar complexes revealing polymetallic linear structures with extended ?–? interactions.

Posted on 27 May 2015 | 10:53 am

Bio-Inspired Formation of Silica Thin Films: From Solid Substrates to Cellular Interfaces

Silica formation in biological systems (biosilicification) has been intensively studied for synthesizing inorganic materials such as silica and titania under biocompatible conditions. Inspired by biosilicification, biocompatible strategies have been developed to fabricate silica thin films on the surfaces of solid substrates such as flat wafers and micro/nanoparticles. In the search for biological applications, these strategies have been applied to cellular surfaces to coat living cells with silica or titania thin films while maintaining cell viability, and it was found that the inorganic coat is beneficial for the protection of living cells and to control cell division. This Microreview focuses on bio-inspired approaches to the formation of silica thin films on solid substrates and cellular surfaces, and includes the bio-inspired formation of other inorganic thin films that have been formed by bio-inspired silicification. The current status and future prospects of this field are also discussed. The bio-inspired formation of silica thin films on the surfaces of flat solids, microparticles, nanoparticles, and living cells is reviewed.

Posted on 19 May 2015 | 4:40 pm

Too Many Cooks Spoil the Broth – Variable Potencies of Oxidizing Mn Complexes of a Hexadentate Carboxylato Ligand

Given the hexadenticity of the monoanionic ligand in the procatalyst [Mn(tpena)(H2O)](ClO4) {tpena– = N,N,N?-tris(2-pyridylmethyl)ethylenediamine-N?-acetate}, it is perhaps surprising that this complex can catalyze the epoxidation of alkenes. When peracetic acid is used as terminal oxidant, the selectivity and rates of reactions are comparable with those reported for the manganese complexes of the commonly employed neutral tetradentate N4 ligands under analogous conditions. Cyclooctene conversion rates are similar when tert-butyl hydroperoxide (TBHP) is used; however, the selectivity is greatly diminished. In the absence of organic substrates, [MnII(tpena)]+ catalyzes water oxidation by TBHP (initial rate ca. 23 mmol/h when [Mn] = 0.1 mM, at room temp.). To explain the variations in the selectivity of catalytic epoxidations and the observation of competing water oxidation, we propose that several metal-based oxidants (the “cooks”) can be generated from [MnII(tpena)]+. These embody different potencies. The most powerful, and hence least selective, is proposed to be the isobaric isomer of [MnIV2(O)2(tpena)2]2+, namely an oxylic radical complex, [(tpena)MnIII(?2-O)MnIV(O·)(tpena)]2+. The formation of this species depends on the catalyst concentration, and it is favoured when TBHP is used as the terminal oxidant. The generation of the less potent [MnIV(O)(tpena)]+, which we propose as the direct oxidant in epoxidation reactions, is favoured in non-aqueous solutions when peracetic acid is used as the terminal oxidant. A manganese(II) complex of a hexadentate ligand catalyzes epoxidation. However, reaction conditions are critical since several metal-based oxidants with varying potencies can be generated. This observation is probably general for related catalysts, and consequences include decreased selectivity and competing water oxidation.

Posted on 29 April 2015 | 3:10 pm

Regioselective Cleavage of Electron-Rich Double Bonds in Dienes to Carbonyl Compounds with [Fe(OTf)2(mix-BPBP)] and a Combination of H2O2 and NaIO4

A method for the regioselective transformation of dienes to carbonyl compounds has been developed. Electron-rich olefins react selectively to yield valuable aldehydes and ketones. The method is based on the catalyst [Fe(OTf)2(mix-BPBP)] with an oxidant combination of H2O2 (1.0 equiv.) and NaIO4 (1.5 equiv.); it uses mild conditions and short reaction times, and it outperforms other olefin cleavage methodologies. The combination of an Fe-based catalyst, [Fe(OTf)2(mix-BPBP)], and the oxidants H2O2 and NaIO4 can discriminate between electronically different double bonds and oxidatively cleave the electron-rich bond in dienes to yield aldehydes and ketones in a regioselective manner. The reaction requires mild conditions (0–50 °C) and short reaction times (70 min).

Posted on 27 April 2015 | 9:50 pm

Ruthenium Carboxylate Complexes as Efficient Catalysts for the Addition of Carboxylic Acids to Propargylic Alcohols

Ruthenium complexes [Ru(CO)2(PPh3)2(O2CR)2] – 3a (R = CH2OCH3), 3b (R = iPr), 3c (R = tBu), 3d (R = 2-cC4H3O), and 3e (R = Ph) – were synthesized by treatment of Ru(CO)3(PPh3)2 with the corresponding carboxylic acids. The molecular structures of the newly synthesized complexes in the solid state are discussed. Compounds 3a–e were successfully applied as catalysts in the addition of carboxylic acids to propargylic alcohols to give the corresponding ?-oxo esters in good to excellent yields even in air. The different carboxylate ligands do not have an influence on the productivities, because the carboxylates exchange rapidly under the applied reaction conditions, as was confirmed by 31P{1H} NMR spectroscopic studies. The addition of catalytic amounts of Na2CO3 resulted in an increase in ?-oxo ester formation. The reaction is tolerant to the use of versatile functional groups on the propargylic alcohols and carboxylic acids, revealing a broad substrate generality. In contrast to most other known catalytic systems, even sterically hindered substrates, including 2,4,6-trimethylbenzoic acid, 1,1-diphenylprop-2-yn-1-ol, or the biologically active steroid ethisterone, were successfully converted. Ruthenium carboxylate complexes were applied in the synthesis of diverse ?-oxo esters by the addition of carboxylic acids to propargylic alcohols. The catalytic system tolerates a broad range of functional groups and even facilitates the successful conversion of challenging substrates such as sterically demanding steroids.

Posted on 27 April 2015 | 12:13 pm

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