European Journal of Inorganic Chemistry

Current research reports and chronological list of recent articles.

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

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

 - Dalton Transactions,

 - Inorganica Chimica Acta,

 - Inorganic Chemistry,

 - Inorganic Chemistry Communications,

 - European Journal of Inorganic Chemistry,

 - Russian Journal of Inorganic Chemistry.

European Journal of Inorganic Chemistry - Abstracts

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Datum: 26.04.2016

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

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

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

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

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

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

Double-Decker Coordination Cages

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Acyliridium(III) Complexes with PCN Terdentate Ligands Including Imino- or Iminium-Acyl Moieties or Formation of Hydrido from Hydroxyl (Eur. J. Inorg. Chem. 12/2016)

The cover picture shows an anionic dihydridoiridium species formed in methanol from a dihydridoirida-β-diketone in the presence of KOH and hydrogen release from the dihydrido species upon addition of 2-aminoalkylpyridines to the solution. Hydrogen is transferred from hydroxyl in the solvent to iridium to afford the final hydridoaminodiacyl species. In contrast, addition of 2-aminoalkylpyridines to a chloridohydridoirida-β-diketone in methanol affords acylhydridoiridium complexes containing terdentate PCN ligands with C(sp2)-iminium-acyl or -iminoacyl fragments. Details are discussed in the article by M. A. Garralda et al. on p. 1790 ff. For more on the story behind the cover research, see the Cover Profile.
Datum: 21.04.2016

Spotlights on our sister journals: Eur. J. Inorg. Chem. 12/2016

Datum: 21.04.2016

Acyliridium(III) Complexes with PCN Terdentate Ligands Including Imino- or Iminium-Acyl Moieties or Formation of Hydrido from Hydroxyl

Invited for the cover of this issue is the group of María A. Garralda at Universidad del País Vasco, San Sebastián, Spain. The cover image shows an anionic dihydridoiridium species formed in methanol from a dihydridoirida-β-diketone and hydrogen release from the dihydrido species upon addition of 2-aminoalkylpyridines to the solution. Hydrogen is transferred from hydroxyl in the solvent to iridium to afford the final hydridoaminodiacyl species. We find it most exciting that, in the presence of amines, a hydrido complex forms by transfer of the acidic proton in the alcohol solvent to the metal...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 1790 ff.
Datum: 21.04.2016

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Heterometallic Cube-Type Molecular Nitrides

Polynuclear transition-metal nitrido complexes constitute a class of molecular cage compounds with fascinating structures and interesting bonding properties. However, there is a lack of systematic strategies for the rational construction of aggregates with desired structures and compositions. This article provides a brief overview of the structure and bonding modes of polynuclear nitrido complexes, the most common synthetic approaches used to generate such aggregates, and a systematic review of the development of a family of heterometallic nitrido complexes with [MTi3N4] cube-type cores. The rational entry to those well-defined systems is based on the incorporation of transition metals, lanthanides, and main-group metals into the incomplete cube structure of the trinuclear titanium(IV) imido nitrido complex [{TiCp*(µ-NH)}3(µ3-N)] (Cp* = η5-C5Me5). The great versatility of [{TiCp*(µ-NH)}3(µ3-N)] as a preorganized metalloligand is also confirmed by the preparation of complexes with heterometals in low (e.g., Mo0, IrI, and Pt0) and high oxidation states (e.g., ZrIV, TaV, and PtIV). A wide family of heterometallic nitrido complexes with [MTi3N4] cube-type cores can be prepared by the incorporation of most of the metallic elements of the periodic table into the incomplete cube structure of [{TiCp*(µ-NH)}3(µ3-N)] (Cp* = η5-C5Me5).
Datum: 06.04.2016

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

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

Photoinduced Homolysis of Alkyl–Cobalt(III) Bonds in a Cyclodextrin Cage

Photodecomposition of methyl– and ethyl–CoIII complexes of meso-tetrakis(4-sulfonatophenyl)porphyrin (CH3– and C2H5–CoIIITPPSs) was used as a reaction probe to study the cage effect of cyclodextrin capsules formed by two per-O-methylated β-cyclodextrin (TMe-β-CD) molecules and their covalently linked dimer, Ph2CD. The photodecomposition of CH3–CoIIITPPS under aerobic conditions was markedly suppressed in the presence of TMe-β-CD and Ph2CD, while C2H5–CoIIITPPS was less affected. Alkyl–CoIIITPPS formed two types of inclusion complex with Ph2CD, the alkyl groups in Type 1 being located at the opposite side of the phenyl linker of Ph2CD and those in Type 2 being located at the same side. The photodecomposition of C2H5–CoIIITPPS in Type 1 proceeded via an ethylperoxo complex, while that in Type 2 occurred via a radical pair generated in a narrow, rigid cage to form ethylene and CoIITPPS. Photoinduced homolysis of the methyl–CoIIIL [L: meso-tetrakis(4-sulfonatophenyl)porphinato] bond was remarkably inhibited by including the porphyrin in per-O-methylated β-cyclodextrin capsules, which acted as a molecular cage that interfered with the contact of O2 with the methyl radical, leading to recombination of a photochemically generated radical pair.
Datum: 05.04.2016

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

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

A Rhenium-Functionalized Metal–Organic Framework as a Single-Site Catalyst for Photochemical Reduction of Carbon Dioxide

A metal–organic framework (MOF) based on (bpy)Re(CO)3Cl-containing elongated dicarboxylate ligands and Zr6(µ3-O)4(µ3-OH)4 clusters was synthesized and used as an effective single-site catalyst to photochemically reduce carbon dioxide to carbon monoxide and formate and to provide mechanistic insights into the photocatalytic CO2 reduction process. A (bpy)Re(CO)3Cl-containing metal–organic framework (MOF) acts as an effective single-site catalyst to photochemically reduce carbon dioxide to carbon monoxide and formate. Mechanistic insights into the monomolecular pathway of the photocatalytic CO2 reduction have been obtained without interference from bimolecular pathways, thanks to site-isolation of the catalytic centers in MOFs.
Datum: 05.04.2016

Multiple-Metal (De-)Hydrogenation-Catalysed Processes

The use of different metals acting together in a synergistic way allows synthetic transformations that are not achievable by other means. Metal cooperation becomes important in catalytic processes for the synthesis of compounds with sophisticated structures or for difficult transformations. Rational design of multiple-metal-catalysed processes requires that the metal complexes and reaction conditions are compatible, which in general is not straightforward. A key feature for success found in all systems involving multimetallic processes is catalyst stability. The use of robust metal complexes increases the probability of success in the search for tandem catalytic processes. This microreview is based on the recent and most important findings of multiple-metal-catalysed processes that have involved (de-)hydrogenation reactions. The field constitutes a research area that is full of potential, and it can be foreseen that relevant applications will be described in the near future. Two or more metals acting together to accomplish difficult transformations. The unveiling of an old concept with modern potential applications in (de-)hydrogenation.
Datum: 04.04.2016

Face-Shared Octahedral Dimer In2O7S2 in the Non-Centrosymmetric Barium Indiumsilicate Oxysulfide Ba2In2Si3O10S

The first indiumsilicate oxysulfide Ba2In2Si3O10S (1) was obtained by an alkali polychalcogenide flux method through a high-temperature solid-state reaction. It crystallizes in the non-centrosymmetric space group Pca21 (No. 29), with a = 23.060(6), b = 5.2954(6), c = 8.779(2) Å, and Z = 4. Its three-dimensional (3D) framework is constructed from one-dimensional (1D) infinite ∞1[In2O7S2/2] double octahedral chains bridged by corner-sharing Si tetrahedral trimers [Si3O10]8–, yielding a 3D framework with the channels filled with Ba2+ cations along the b direction. It is unprecedented in that the two distorted indium octahedra in 1 face-share to form a [In2O7S2] dimer in indium oxides and oxide chalcogenides. The first indiumsilicate oxysulfide Ba2In2Si3O10S was obtained by an alkali polychalcogenide flux method. It is unprecedented in that the two distorted indium oxysulfide octahedra in this compound face-share to form a [In2O7S2] dimer in indium oxides and sulfides.
Datum: 04.04.2016

The Species of Fehling's Solution

A species model for the copper(II)/L-(+)-tartaric acid (LH2, tartH2) aqueous system between pH 1.9 and 12.3 has been established by potentiometric, UV/Vis spectroscopic, solubility and crystallographic studies. Eight species were detected, including the oligonuclear major species Cu8L6H–10 in the neutral region and the mononuclear major species CuL2H–4 in the alkaline region, the latter being associated with Fehling's solution. The octanuclear complex was isolated as its lithium salt Li7[Cu8(L-tartH–2)4(L-tartH–1)2(H2O)6]NO3·19H2O (1). The “Fehling species” CuL2H–4 was crystallized as its sodium, potassium and caesium salts, namely K2Na4[Cu(L-tartH–2)2]·12H2O (2), Na6[Cu(L-tartH–2)2]·9H2O (3), Na6[Cu(L-tartH–2)2]·14H2O (4), and Cs6[Cu(L-tartH–2)2]·8H2O (5). Each of them shows a distorted square-planar environment of copper(II), similar to the related non-chiral cuprate [Cu(rac-tartH–2-κ2O2,O3)2]6– (S. Albrecht, P. Klüfers, Z. Anorg. Allg. Chem. 2013, 639, 280–284). By comparing the components of the UV/Vis spectra of Fehling's solution and the solids, we confirmed the identity of the major solution species. [Cu(L-tartH–2)2]6– is the active species of Fehling' solution, a well-known probe in use for 170 years. The mononuclear bis(diolato) species needs a strongly alkaline medium. At around neutral pH, a persistent octanuclear tartrate cuprate has been structurally resolved.
Datum: 31.03.2016

Water-Soluble C-Scorpionate Complexes – Catalytic and Biological Applications

Recent advances in the synthesis of water-soluble homoscorpionates of the tris(pyrazol-1-yl)methane type as well as of their water-soluble metal complexes are reviewed. Moreover, the application of these tris(pyrazol-1-yl)methane metal complexes as catalysts for the oxidative functionalization of inexpensive and abundant alkanes to value-added products and other industrially significant reactions is addressed. We also focus on the main biological (antiproliferative and antimicrobial) applications of such C-scorpionate-type complexes. Water-soluble carbon homoscorpionates and their coordination chemistry are reviewed. Moreover, the application of the resulting water-soluble tris(pyrazol-1-yl)methane metal complexes as catalysts for C–C bond formation and oxidative functionalization as well as their use as antiproliferative and antimicrobial agents are addressed.
Datum: 31.03.2016

Ni3Cl2+x(OH)4–x·2H2O: Structural, Thermal, Spectral, and Magnetic Properties in Dependence of the Chloride Content

The previously unknown nickel chloride hydroxide phases Ni3Cl2+x(OH)4–x·2H2O (x = 0.26, 0.48, 0.82) have been synthesized in concentrated aqueous NiCl2 solutions and investigated in detail. Crystal structure determination from X-ray powder diffraction data revealed triple chains of distorted, edge-linked NiO6 and NiO3(O/Cl)3 octahedra as the main building blocks. The chains exhibit a layer-like configuration and therefore great structural similarity to nickel-layered hydroxy halides (Cl, Br, I) and β-Ni(OH)2. Increasing chloride content in Ni3Cl2+x(OH)4–x·2H2O leads to a reduction of the space group symmetry from C2/m (12) for x = 0.26 and 0.48 to P$\bar {1}$ (2) for x = 0.82 and to distinct shifts in their thermal, spectral, and magnetic properties. Each solid exhibits a maximum magnetic susceptibility in the range 5.9–9.7 K, which indicates antiferromagnetic ordering. Positive Curie–Weiss temperatures, θ, were found, which points to predominantly ferromagnetic spin-exchange interactions. In addition, broad maxima of the magnetic susceptibility evidence a low-dimensional magnetic character as the most prominent feature of the magnetic properties of the investigated phases. Three samples of Ni3Cl2+x(OH)4–x·2H2O (x = 0.26, 0.48, 0.82) have been synthesized. The varying chloride content affects the structural, spectral, thermal, and magnetic properties. Predominantly ferromagnetic spin-exchange interactions, despite a net antiferromagnetism, and most likely a low-dimensional magnetic character are the most prominent magnetic properties of Ni3Cl2+x(OH)4–x·2H2O.
Datum: 30.03.2016

Multi-Mode White Light Emission in a ZnII Coordination Polymer from Excited-State Intramolecular Proton Transfer (ESIPT) Ligands

Multi-mode photoluminescence, including enol-emission, keto-emission, and aggregate-related emission is achieved in a ZnII coordination polymer from excited-state intramolecular proton transfer (ESIPT) ligands. Single-phase white light emission (WLE) and tunable emitting colors can be obtained by varying the suspending/grinding solvent system or temperature, which brings a brand-new model in developing multi-stimuli-responsive WLE materials. ESIPT ligands were applied to assemble a ZnII coordination complex with solvent- and temperature-responsive single component white light emission.
Datum: 30.03.2016

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

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

Scorpionate Complexes as Models for Molybdenum Enzymes

Scorpionate ligands have supported the development of a number of important synthetic models for pterin-containing molybdenum enzymes. These ligands stabilize biologically relevant mononuclear oxido- and sulfido-Mo(VI,V,IV) complexes capable of sustaining a wide range of biomimetic reactions, including oxygen atom, sulfur atom and coupled electron-proton transfer reactions. Studies of scorpionate-Mo compounds have also provided key insights into the bonding in oxido-Mo dithiolene moieties, the orbital control of enzymatic reactions and the synthesis and behavior of biologically relevant Mo-pterindithiolene complexes. This microreview covers advances in the synthesis and study of scorpionate complexes as models for molybdenum enzymes in the second half of the field's 30-year history, i.e., from around 2000, the turn of the century, onwards. The study of molybdenum scorpionate complexes has greatly informed our understanding of the geometric and electronic structures, chemical and spectroscopic properties and mechanisms of action of Mo and W enzymes. This microreview focuses on the biologically relevant oxido- and sulfido-Mo(VI,V,IV) chemistry of hydrotris(R1/2-pyrazolyl)borate and related heteroscorpionate ligands.
Datum: 29.03.2016

Exposing the Excited-State Equilibrium in an IrIII Bichromophore: A Combined Time Resolved Spectroscopy and Computational Study

The electronic structure and photophysical properties of a luminescent IrIII bis-cyclometalated complex covalently attached to one 4-piperidinyl-1,8-naphthalimide (PNI) chromophore through a coordinated 1,10-phenanthroline, [Ir(ppy)2(phen-PNI)](PF6), is presented. This bichromophore represents a new class of visible light-harvesting IrIII complexes that exhibit markedly enhanced room-temperature excited-state lifetimes (τ = 8.8 ms) as a result of intervening ligand-centered triplet states present on the pendant naphthalimide chromophore. In this IrIII complex, the intense singlet fluorescence of the pendant PNI chromophore is nearly quantitatively quenched and was found to sensitize the IrIII metal/ligand-to-ligand charge-transfer (MLLCT) excited state. The excited state ultimately returns to the PNI chromophore as a long-lived excited triplet that disposes of its energy by equilibrating with the photoluminescent IrIII MLLCT excited state. Evidence of the excited-state equilibrium is provided through static and dynamic photoluminescence spectroscopy, transient absorption spectroscopy, and time-dependent density functional theory calculations. The electronic structure and photophysical properties of a luminescent IrIII bis-cyclometalated complex covalently attached to one 4-piperidinyl-1,8-naphthalimide (PNI) chromophore through a coordinated 1,10-phenanthroline, [Ir(ppy)2(phen-PNI)](PF6), is presented. This bichromophore represents a new class of visible light-harvesting IrIII complexes that exhibit enhanced excited-state lifetimes.
Datum: 29.03.2016

Hydrogen Photoevolution from a Green-Absorbing Iridium(III)–Cobalt­(III) Dyad

A bis-cyclometaling ligand afforded a novel IrIII–CoIII dinuclear complex with vectorial electron transfer that evolved hydrogen gas upon yellow-light irradiation. The supramolecular photosystem provided increased stability during photocatalysis with respect to that of classic bidentate systems. A supramolecular iridium(III)–cobalt(III) assembly bridged by a terdentate ligand photoevolves hydrogen. Besides showing broader absorption in the visible part of the spectrum, the robustness and efficiency of our system is significantly higher than that of systems containing bidentate ligands.
Datum: 29.03.2016

Synthesis, Crystal Structure and Magnetic Properties of Heteropolynuclear ReIVMII Complexes Based on the Robust [ReCl5(pyzCOO)]2– Unit (pyzCOO = 2-pyrazinecarboxylate)

The syntheses, crystal structures and magnetic properties of four rhenium(IV) compounds of formulae NBu4[ReCl5(pyzCOOH)]·H2O (1), [ReCl5(µ-pyzCOO)M(dmphen)2]·2CH3CN [M = Ni (2) and Co (3)] and {[ReCl5(µ3-pyzCOO)]2Mn2(dmphen)3}n (4) (NBu4 = tetra-n-butylammonium cation, pyzCOOH = 2-pyrazinecarboxylic acid, dmphen = 2,9-dimethyl-1,10-phenanthroline) are reported herein. Compound 1 was obtained by the reaction of NBu4[ReCl5(dmf)] (dmf = dimethylformamide) with pyzCOOH in acetone, whereas the other complexes were obtained by the reaction of 1 with M(ClO4)2·6H2O [M = Ni (2), Co (3), Mn (4)] and dmphen in acetonitrile. Complex 1 is a mononuclear compound, 2 and 3 are neutral heterodinuclear complexes and 4 is a neutral chain in which each pyzCOO– bridges one ReIV and two MnII in a very unusual µ3-binding mode. Compounds 2 and 3 behave as magnetically isolated species with intramolecular ferromagnetic coupling between ReIV and NiII or ReIV and CoII ions, respectively. In turn, weak antiferromagnetic coupling between the MnII ions through anti-syn-carboxylate bridges together with weak ferromagnetism below 3.1 K due to small spin canting is observed in 4. Three 2-pyrazinecarboxylate-bridged ReIVMII compounds [M = Ni (2), Co (3), Mn (4)] have been synthesized from the mononuclear complex NBu4[ReIVCl5(pyzCOOH)]·H2O (1). Ferromagnetic interactions between ReIV and MII occurs in 2 and 3 whereas spin canting and magnetic ordering is observed for 4 below 3.1 K.
Datum: 24.03.2016

Controlled Crystallization of Sodium Chloride Nanocrystals in Microdrop­lets Produced by Electrospray from an Ultra-Dilute Solution

Controlled crystallization is very important for crystal growth. The electrospray (ES) technique has attracted great interest thanks to its advantages of facile manipulation of micrometer droplets and the generation of fine and charged droplets with very narrow size dispersion. In this work, nanocrystals with cubic shapes with 32 nm edges were successfully grown from ultra-dilute NaCl solution (1 µg mL–1) on a millisecond timescale by an ES technique. Dispersed and charged microdroplets were created by ES. In the process, an increase in ion strength and built-in electric field in microdroplets promoted nucleation and growth. Moreover, solvent evaporation increased solute and charge concentration and decreased the size of the microdroplets, which had a further effect on nucleation and growth. The morphologies of crystals were the competitive results of ion strength and evaporation. Fortunately, these physicochemical properties can be controlled facilely by adjusting the ES parameters. This report suggests potential application of ES technology for controllable crystallization of pharmaceuticals, proteins, etc. Nanocrystals with cubic shapes with 32 nm edges were successfully grown from ultra-dilute NaCl solution (1 µg mL–1), without stabilizers and on a millisecond timescale, by an electrospray technique.
Datum: 24.03.2016

Mechanochemical Synthesis of SiO44–-Substituted Hydroxyapatite, Part III – Thermal Stability

Thermal stability of mechanochemically synthesized silicon-substituted hydroxyapatite containing 0.6, 0.8, 1.0, and 1.2 mol of silicon per mol of apatite unit cell has been studied for the first time. The powders of the silicon-substituted hydroxyapatite were annealed within the temperature range 700–1300 °C. It was found that the substituted hydroxyapatites remain single-phase after annealing at temperatures of up to 900 °C for all concentrations of added silicon. The second phase – silicocarnotite Ca5(PO4)2SiO4 – appears in the materials containing 1.0 and 1.2 mol of added silicon that have been annealed at 1000 °C. In the powder containing 0.8 mol of added silicon, silicocarnotite was detected after annealing at 1100 °C. The formation of silicocarnotite is likely to occur in the nanoparticles of the silicon-substituted hydroxyapatite with silicon concentrations much higher than the average value. It was found that the silicon-substituted hydroxyapatite containing 0.6 mol of silicon per mol of apatite unit cell has the highest thermal stability and remains single-phase up to a temperature of 1200 °C, similarly to pure hydroxyapatite obtained by the same synthesis method. Partial transformation of silicon-substituted hydroxyapatite to silicocarnotite (SCar) is facilitated at higher temperatures and higher concentrations of silicon. Within the studied concentration range of added silicon, the hydroxyapatite containing 0.6 mol of silicon per mol of apatite unit cell has the highest thermal stability.
Datum: 22.03.2016

Computational Insights into the Mechanisms of H2 Activation and H2/D2 Isotope Exchange by Dimolybdenum Tetrasulfide Complexes

The mechanisms for H2 activation by [Cp*Mo]2(µ-S)2(µ-S2) (1-a, Cp* = pentamethylcyclopentadienyl) and its reaction product [Cp*Mo]2(µ-S)2(µ-SH)2 (2) have been investigated by DFT methods. The reaction of 1-a involves the homolytic addition of H2 to its µ-S ligands, followed by the cleavage of the S–S bond of the µ-S2 ligand in a subsequent step. Complex 2 can adopt five conformations that only differ in the stereochemistry of the µ-SH and µ-S ligands; although an isomer with adjacent µ-S ligands (2-a) is formed initially, it then isomerises into the experimentally observed 2-d. This species promotes H/D scrambling in H2/D2 mixtures, and the mechanism of the process has also been studied. Notably, all of the computed pathways for the addition of D2 to 2-d present prohibitive barriers; instead, only those isomers with adjacent µ-S ligands are able to react further. The homolytic activation of D2 by these leads to isomers of [Cp2Mo2(µ-SH)2(µ-SD)2], the interconversion of which is the rate-determining step. A DFT study of the possible mechanistic pathways for H2 activation by [Cp*Mo]2(µ-S)2(µ-S2) and [Cp*Mo]2(µ-S)2(µ-SH)2 (Cp* = pentamethylcyclopentadienyl) shows that homolytic activation at the bridging sulfur centres is preferred in both cases. The latter compound promotes H/D scrambling in H2/D2 mixtures, and the mechanism of the process is also analysed.
Datum: 21.03.2016

11B NMR Probes of Copper(II): Finding and Implications of the Cu2+-Promoted Decomposition of ortho-Carborane Derivatives

The development of noninvasive methodologies for the detection of d-block metal ions such as copper (Cu2+), zinc (Zn2+), and manganese (Mn2+) is important for understanding their biological roles and relationship with diseases. We have been interested in the use of 11B NMR probes for the detection of d-block metal ions, because 11B is an ultratrace element in living systems. o-Carboranes, which consist of ten boron and two carbon atoms, have been applied to numerous drugs and biological active agents. In this work, we found that the o-carborane-pendant cyclens (L3–L5) (cyclen = 1,4,7,10-tetraazacyclododecane) are decomposed in the presence of Mn2+ or Cu2+ in aqueous solution at neutral pH, accompanied by the release of 4–9 equiv. of B(OH)3. Furthermore, it was found that o-carborane derivatives that contain hydroxyl groups instead of a cyclen unit also undergo decomposition in the presence of Cu2+ and the corresponding complexes such as Cu(bpy) to afford 10 equiv. of B(OH)3, as confirmed by 11B NMR spectroscopic analysis and an azomethine-H assay. These reactions are applied to 11B MRI (magnetic resonance imaging) probes for Cu2+. It is found that copper(II) ion promotes full decomposition reactions of o-carborane derivatives in aqueous solution to release 10 equiv. of B(OH)3. The application of this discovery to 11B NMR/MRI detection of Cu2+ is also presented.
Datum: 21.03.2016

Oxygen Atom Transfer Catalysis with Homogenous and Polymer-Supported N,N- and N,N,O-Heteroscorpionate Dioxidomolybdenum(VI) Complexes

The N,N-chelate ligand bis(3,5-dimethyl-4-vinylpyrazol-1-yl)methane (bdmvpzm) and the N,N,O-heteroscorpionate ligand bis(3,5-dimethyl-4-vinylpyrazol-1-yl)acetic acid (Hbdmvpza), both with vinyl linkers suitable for copolymerisation, were synthesised under Vilsmeier–Haack conditions. The reactions of these ligands with [MoO2Cl2] yielded the corresponding molybdenum(VI) complexes [MoO2Cl2(bdmvpzm)] and [MoO2Cl(bdmvpza)], which were applied in oxygen atom transfer studies as mimics of dimethyl sulfoxide reductase (DMSO reductase). The catalytic properties of the homogeneous complexes and copolymers with embedded complexes were evaluated. The N,N-chelate ligand bdmvpzm and the N,N,O-heteroscorpionate ligand Hbdmvpza, both with vinyl linkers suitable for copolymerisation, are treated with [MoO2Cl2] to yield the molybdenum(VI) complexes [MoO2Cl2(bdmvpzm)] and [MoO2Cl(bdmvpza)]. The complexes and polymers with incorporated complexes are applied in oxygen-transfer studies.
Datum: 21.03.2016

Photophysical Properties of Oligo­(phenylene ethynylene) Iridium(III) Complexes Functionalized with Metal-Anchoring Groups

The electrochemical and photophysical properties of a family of conjugated ligands and their iridium(III) cyclometallated complexes are described. They consist of a series of monocationic IrIII bis-2-phenylpyridine complexes with p-phenylethynyl-1,10-phenanthroline ligands of different length. The structure of these ligands includes terminal acetylthiol or pyridine groups, which can provide good electrical contacts between metal electrodes. Cyclic voltammetry, absorption and emission spectroscopy, laser flash photolysis and density functional theory calculations reveal that the high conjugation of the diimine ligand affords small energy gaps between the frontier orbitals. Nevertheless, the nature of the terminal substituents and the extent of the conjugation in the diimine ligand have little influence on the photophysical features at room temperature. The spectroscopic data and theoretical calculations agree that the charge-transfer nature of the emitting excited state is maintained along the series at room temperature, whereas in rigid matrices ligand-centred states also contribute to the low-temperature emission. The good conducting features of the diimine ligands, the small dependence of the HOMO–LUMO (HOMO = highest occupied molecular orbital, LUMO = lowest unoccupied molecular orbital) gaps of these complexes on the ligands and the charge-transfer nature of the emitting excited state make these complexes promising test beds for the study of photoconducting phenomena in molecular junctions. The charge-transfer nature of the emitting excited state, the small dependence of the HOMO–LUMO gap on the molecular length, the presence of metal-anchoring groups, and the good conducting features of the diimine ligands make our iridium(III) complexes promising test beds for the study of photoconducting phenomena in molecular junctions.
Datum: 21.03.2016

SALE-Ing a MOF-Based “Ship of Theseus.” Sequential Building-Block Replacement for Complete Reformulation of a Pillared-Paddlewheel Metal-Organic Framework

A complete structure and composition evolution of a pillared-paddlewheel metal-organic framework was achieved using a combination of solvent-assisted linker exchange (SALE) and node transmetalation. In this example, each building unit – the di-topic carboxylate strut, the di-topic nitrogen-based pillar, and the di-zinc node – of the original metal-organic framework is replaced in sequential fashion to produce a nickel-based daughter metal-organic framework with entirely different components. Text for Table of Contents: Interchange of a non-interpenetrating Zn based pillared-paddlewheel MOF into an entirely different Ni-based pillared-paddlewheel MOF has been achieved through the combination of solvent assisted linker exchange and transmetalation.
Datum: 18.03.2016

Pyridylborates as a New Type of Robust Scorpionate Ligand: From Metal Complexes to Polymeric Materials

The importance of scorpionate ligands in modern coordination chemistry continues to increase, because of their outstanding versatility, tunability and user-friendliness. Herein, we provide a short overview of recent developments in the classes of scorpionate ligands, derived from pyrazoles, triazoles, imidazoles, oxazolines, thioimidazoles and other similar systems, followed by an in-depth discussion of a new type of robust and tunable scorpionate ligand, tris(2-pyridyl)borates. The structure and synthesis of tris(2-pyridyl)borate (Tpyb) ligands are discussed, and key features of coordination of Tpyb ligands with metal ions, as well as supramolecular crystal packing, transmetallation and applications in metallo-supramolecular polymer chemistry are addressed. An overview of the different classes of scorpionate ligands is provided, and an in-depth discussion of a new type of robust and tunable ligand, the tris(2-pyridyl)borates. The structure and synthesis of the ligands, key features of coordination with metal ions, the supramolecular crystal packing, transmetallation and applications in metallo-supramolecular polymer chemistry are addressed.
Datum: 17.03.2016

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

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

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

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

A Family of Homo- and Heteroscorpionate Ligands: Applications to Bioinorganic Chemistry

In this brief review we focus on a few examples of how a family of homo- and heteroscorpionate ligands allow us to examine how changes in reactivity, structure, or physical/chemical properties around biologically interesting N2X coordinated metal centers vary as a function of donor atom, charge, hydrophobicity, hydrogen bonding, etc., in a way previously unavailable. Such a family of ligands is the bioinorganic chemists answer to site-directed mutagenesis. Here we focus on two bioinorganic examples i.e. models for molybdoenzymes and zinc metalloproteins. A family of heteroscorpionate ligands of the form N2X is presented where X can be interchanged between a thiolate sulfur, a pyrazole nitrogen, or a carboxylate, alkoxy or phenoxy oxygen in a series of isostructural isoelectronic metal complexes gives the bioinorganic chemist the ability to do the equivalent of “site directed mutagenesis”.
Datum: 09.03.2016

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

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

Copper(I) Complexes of Naphthyl-Substituted Fluorinated Trispyr­azolylborate Ligands with Ethene and Carbon Monoxide

Four CuI complexes of the two new hydridotrispyrazolylborate ligands hydridotris[3-trifluoromethyl-5-(1-naphthyl)pyrazol-1-yl]borate (= [TpCF3,1Nt]–) and hydridotris[3-trifluoromethyl-5-(2-naphthyl)pyrazol-1-yl]borate (= [TpCF3,2Nt]–) have been synthesized by reaction of the sodium salts of the ligands with CuI under either ethene or carbon monoxide atmosphere. Single crystal X-ray diffraction analyses yielded the molecular structures of the three compounds [Na2(TpCF3,1Nt)2(µ-acetone)2], [Cu(TpCF3,1Nt)(C2H4)] and [Cu(TpCF3,2Nt)(C2H4)]. The CuI ions are in approximate tetrahedral geometries comprising the three nitrogen donors of the tridentate ligand and the η2-coordinated ethene ligands. The sodium ion in [Na2(TpCF3,1Nt)2(µ-acetone)2] is found in a distorted octahedral coordination geometry formed by three N-donors of the facially coordinating tridentate ligand, two O-donors of bridging acetone ligands and a fluoride of a bridging –CF3 group with a particularly short Na···F distance. The chemical shifts of the ethene ligands in [Cu(TpCF3,1Nt)(C2H4)] and [Cu(TpCF3,2Nt)(C2H4)] are 5.00 ppm and 4.96 ppm respectively on 1H-NMR and 85.9 ppm and 85.8 ppm on 13C-NMR spectroscopy. The CO stretching frequencies in the IR spectra of [Cu(TpCF3,1Nt)(CO)] and [Cu(TpCF3,2Nt)(CO)] are found at 2103 and 2109 cm–1, respectively. The structures of the CuI complexes of the two new ligands hydridotris[3-trifluoromethyl-5-(n-naphthyl)pyrazol-1-yl]borate (n = 1, [TpCF3,1Nt]–; n = 2, [TpCF3,2Nt]–) show essentially equal binding pockets. The surprising differences in the electron density on the CuI ions must therefore be the result of different conformations of the 1- and 2-naphthyl groups.
Datum: 09.03.2016

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

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

Acyliridium(III) Complexes with PCN Terdentate Ligands Including Imino- or Iminium-Acyl Moieties or Formation of Hydrido from Hydroxyl

2-Aminoalkylpyridines [H2N(CH2)nC5H4N] (n = 1 or 2) react with [IrHCl{(PPh2(o-C6H4CO))2H}] (1a) in THF to afford hydridoirida-β-ketoimines [IrHCl{(PPh2(o-C6H4CO))(PPh2(o-C6H4CN(CH2)nC5H4N))H}] (2, n = 1; 3, n = 2) with intramolecular N-H···O hydrogen bonding and a dangling pyridine. In protic media 2–3 transform into [IrH(PPh2(o-C6H4CO))(PPh2(o-C6H4C=N(CH2)nC5H4N))] (4, n = 1; 5, n = 2) containing new terdentate PCN ligands in a facial disposition with the phosphorus atom trans to H and an iminoacyl fragment trans to the other phosphorus atom. The formation of 4–5 requires breaking of the hydrogen bond, isomerization, and dehydrochlorination of an intermediate iminium-acyl species to allow the coordination of the nitrogen atom of pyridine to iridium. The reaction of 1a with the N-substituted N-methylaminomethylpyridine allows the synthesis of [IrH(PPh2(o-C6H4CO))(PPh2(o-C6H4C=N(CH3)CH2C5H4N))]ClO4 (6) containing a PCN ligand with an iminium-acyl moiety trans to phosphorus. The reaction of [IrH2{(PPh2(o-C6H4CO))2H}] (1b) with 2-(aminoalkyl)pyridines [H2N(CH2)nC5H4N] (n = 1 or 2) in MeOH requires the presence of KOH to afford the hydrido derivatives [IrH(PPh2(o-C6H4CO))2(NH2(CH2)nC5H4N,κNH2)] (7, n = 1; 8, n = 2) were the ligands are amino-coordinated with a dangling pyridine. The reaction occurs with hydrogen evolution and transfer of hydrogen from a hydroxyl in the solvent to iridium. Single-crystal X-ray diffraction analysis was performed on 3, 4, 6, and 8. Acylhydridoiridium(III) complexes containing PCN ligands with a C(sp2)-iminoacyl motif (a) can be obtained by the imination reaction of the hydridochloridoirida-β-diketone with 2-(aminoalkyl)pyridines (L) followed by isomerization and loss of HCl from the intermediate iminium-acyl (b). Dihydridoirida-β-diketones require MeOH/KOH to release H2 and afford (c) by H transfer from hydroxyl to Ir.
Datum: 04.03.2016

The Original CoII Heteroscorpion­ates Revisited: On the EPR of Pseudotetrahedral CoII

An examination of the solution spectroscopy of a series of tetrahedral bis-bispyrazolylborate complexes of CoII is presented. This includes a re-examination of the UV/Vis-NIR of the three stable derivatives, Bp2Co, Bp3,5Me2Co and (Ph2Bp)2Co, which showed two transitions previously unobserved, one arising from splitting of the near-infrared d-d transition and one arising from a ligand-based or charge-transfer mechanism; a reevaluation of Δ and B led to values more in line with similar complexes. Frozen solution EPR of the series of complexes suggests all are under the influence of a non-negligible, negative zero-field splitting. This is in contrast to previous powder measurements, which we show observed only a subset of the available transitions, leading to a mis-assignment of the parent complex's electronic structure. We present a proposal, based on the EPR of this closely related set of complexes, that the 59Co hyperfine coupling that is only sometimes observed in the EPR of pseudotetrahedral CoII at X-band is in fact indicative of an MS = ± 3/2 ground level (D < 0), with the hyperfine coupling originating in the nominally forbidden ΔMS = 3 transition along g∥. Solution spectroscopy of a series of five (RBpx)2Co complexes is reported. A frozen solution EPR study shows that all of the complexes have MS = 3/2 ground states, and offer insight into the complex EPR of pseudotetrahedral CoII.
Datum: 02.03.2016

FeII and CoII Complexes with Click-Derived Tripodal Ligands: Influence of the Peripheral Substituents on Geometric Structures and Magnetic Properties

Tuning of the geometric and electronic properties of a transition metal center through manipulation of the secondary coordination sphere is an important topic in contemporary chemistry. In this contribution we present mononuclear iron(II) and cobalt(II) complexes that contain “click”-derived tripodal ligands with peripheral phenyl substituents on the backbone. A comparison of the complexes presented here with those of previously reported complexes shows that the substituents at the ligand backbone dictate the first coordination environment at the metal center, and hence, its geometric structure. The substituents also have a decisive influence on the spin state of the metal centers. Apart from synthesis and characterization, single-crystal X-ray diffraction studies and magnetometric measurements have been performed to investigate the properties of these complexes. We show here how the modification of the peripheral substituents in these increasingly popular tripodal ligands can influence the geometric and electronic structures of the reported metal complexes. These results are likely to have an impact in the field of magnetism related to such complexes, as well as in the study of spin state dependent reactivity in related iron(II) and cobalt(II) complexes. In FeII and CoII complexes with click-derived tripodal ligands, the geometric structures around the metal centers, as well as their spin states are shown to be dictated by the peripheral substituents (phenyl vs. benzyl) on the tripodal ligands.
Datum: 01.03.2016

The First Structurally Characterised Example of Silicon in an S6 Coordination Sphere

The reaction of sodium hydro-tris(phenylthioimidazolyl)borate (NaTmPh) with silicon tetraiodide gives rise to the first crystallographically characterised molecular silicon compounds, [Si(TmPh)2] 2X (X = I– and I3–), in which the silicon is found in a regular S6 environment. The [Si(TmPh)2]2+ cation is subjected to analysis using DFT methods to explain why an S6 coordination motif is preferred to an S4 coordination motif. Reaction of NaTmPh with SiI4 results in an octahedral Silicon complex in an S6 ligand environment. The resulting compound has been characterised crystallographically and been the subject of DFT calculations.
Datum: 01.03.2016

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

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

Variable Borohydride Hapticity in Nickel(II) Scorpionate Complexes [(TpR,Me)Ni(ηn-BH4)]: TpR,Me = hydro­tris­{3-R-5-methyl-1-pyrazolyl}­borate; R = Ph, n = 3 vs. R = Me, n = 4

A “second-generation” scorpionate ligand was utilized to prepare the nickel(II) borohydride complex [(TpPh,Me)Ni(η3-BH4)], wherein the borohydride was coordinated through two bridging B–H bonds, leaving two terminal B–H bonds uncoordinated as determined by X-ray crystallography. The distorted square-pyramidal complex is paramagnetic (S = 1), with 18 valence electrons, and contrasts with a previously reported 20-electron pseudo-octahedral “first-generation” analogue, [(TpMe,Me)Ni(η4-BH4)] (P. J. Desrochers, et al. Inorg. Chem. 2003, 42, 7945–7950). These distinct borohydride coordination modes were distinguished by FTIR spectroscopy, and rationalized by DFT calculations on simplified models, [(Tp)Ni(ηn-BH4)] (n = 3, 4). The difference in borohydride hapticities is attributed to the steric effect of the scorpionate 3-pyrazole phenyl substituents disposed proximally to the metal, thus demonstrating the subtle versatility of Trofimenko's scorpionate ligands in controlling ligand field geometries. The precursor complex [(TpPh,Me)Ni(κ2-NO3)] was also prepared and characterized. [(TpPh,Me)Ni(BH4)] exhibits η3-BH4 coordination with two bridging and two terminal hydrides on boron. This contrasts with [(TpMe,Me)Ni(BH4)], previously shown to have an η4-BH4 ligand. The borohydride hapticities diverge as a result of the different 3-pyrazole substituents on the scorpionate co-ligands, and can be distinguished by FTIR spectroscopy.
Datum: 24.02.2016

On the Stability of Trimeric Beryllium Hydroxide Scorpionate Complexes

The controlled hydrolysis of TpBeCl {Tp = trispyrazolylborate [HB(C3N2H3)3]–} with H2O and D2O in the presence of N,N-diisopropylethylamine (DIPEA) yields the trimeric beryllium hydroxide scorpionate complexes [Be3(µ-OX)3(Tp)3] (X = H: 1, D: 2) quantitatively. The complexes contain six-membered Be3O3 rings according to single-crystal X-ray diffraction studies and theoretical calculations. Temperature-dependent 1H and 9Be NMR spectroscopy established that 1 has a dynamic structure in solution. In addition, the structure of [Be3(µ-OH)3(Br)3(thf)6], which was obtained from hydrolysis of a solution of BeBr2 in tetrahydrofuran and CHCl3, is reported. Two trimeric beryllium hydroxide scorpionate complexes [Be3(µ-OX)3(Tp)3] (X = H: 1, D: 2) and [BeBr3(µ-OH)3(Br)3(thf)6] were structurally characterized. The six-membered Be3O3 ring of 1 is stable in both solution and the gas phase as was shown by temperature-dependent 1H and 9Be NMR spectroscopy and theoretical calculations.
Datum: 22.02.2016

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