Showing papers in "European Journal of Inorganic Chemistry in 2006"

Classical and Non-Classical Ruthenium-Based Anticancer Drugs: Towards Targeted Chemotherapy

Abstract: Ruthenium-based anticancer chemotherapies are making significant advances in clinical trials. Until recently, the focus has been on coordination complexes, and mechanisms such as "activation by reduction" and "transferrin-targeted delivery" have been proposed to account for the excellent cytotoxicity and low general toxicity of these complexes. More recently organoruthenium compounds, which to some extent appear not to follow the established rules, have started to be investigated. Despite such differences, similar activities between certain coordination and organometallic compounds suggest similar modes of action are present. DNA, the classic target, is believed to be the dominant mechanism for cytotoxicity with certain ruthenium drugs, while with others, non-classical targets are thought to be more important. In this article we describe these features and show how both ruthenium coordination complexes and organoruthenium compounds represent an ideal scaffold for further drug design and optimisation.

Supported Ionic Liquid Phase (SILP) Catalysis: An Innovative Concept for Homogeneous Catalysis in Continuous Fixed-Bed Reactors

Abstract: Applications of ionic liquids to replace conventional solvents in homogeneous transition-metal catalysis have increased significantly during the last decade. Biphasic ionic liquid/organic liquid systems offer advantages with regard to product separation, catalyst stability, and recycling but utilise in the case of fast chemical reactions only a small amount of expensive ionic liquid and catalyst. The novel Supported Ionic Liquid Phase (SILP) catalysis concept overcomes these drawbacks and allows the use of fixed-bed reactors for continuous reactions. In this Microreview the SILP catalysis concept is surveyed by presenting results for the continuous gas-phase hydroformylation of propene, as a reaction example. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Azide as a Bridging Ligand and Magnetic Coupler in Transition Metal Clusters

Abstract: The synthesis of transition metal spin-clusters has become an important sub-discipline of coordination chemistry, especially since the discovery of single-molecule magnets (SMMs) in the early nineties. In this context, complexes with high spin-numbers and large anisotropy are particularly desired. The use of the azide ligand to act as a bridge and magnetic coupler within cages of paramagnetic ions has become increasingly common in this field, especially during the last five years, mainly because of the coordination versatility of this ligand, which is capable of bridging several metals in a variety of coordination modes, and its ability to induce ferromagnetic interactions. Several high-spin 3d metal aggregates have been prepared in this manner, a significant number of which behave as SMMs. This review covers the rapid progress made with this relatively recent synthetic approach by describing the structures and summarising the magnetic properties of the systems prepared in this manner. Some of the trends identified could serve as a privileged starting point for the further development of this promising area. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Fe3GeTe2 and Ni3GeTe2 – Two New Layered Transition-Metal Compounds: Crystal Structures, HRTEM Investigations, and Magnetic and Electrical Properties

Abstract: Fe3GeTe2 and Ni3GeTe2 are two new air-stable, black-metallic solids. They were characterized by single-crystal X-ray crystallography, high resolution transmission electron microscopy (HRTEM), and preliminary magnetic measurements. Both compounds crystallize in the hexagonal system [P63/mmc, Z = 2; Fe3GeTe2: a = 399.1(1) pm, c = 1633(3) pm;Ni3GeTe2: a = 391.1(1) pm, c = 1602.0(3) pm], and represent a new structure type with a pronounced macroscopic and microscopic layer character. They show close structural relationships to iron/nickel germanium alloys. Each layer in the title compounds represents a sandwich structure with two layers of tellurium atoms covering a triple-layer Fe3Ge (Ni3Ge) substructure on both sides. Assuming full occupancies for the Fe and Ni sites, a mixed-valence formulation for the transition-metal atoms according to (M2+)(M3+)2(Ge4–)(Te2–)2 (M = Fe, Ni) may be concluded. A slightly reduced occupancy for one Fe/Ni position, however, indicates a more complicated local structural situation. This is confirmed by weak residual electron density in the van der Waals gap and by the results of detailed HRTEM and electron-diffraction experiments for Ni3GeTe2. The latter results show variations in the arrangement of Ni atoms, as well as vacancies and a misfit of in-plane disordered hexagonal layers. Fe3GeTe2 shows Curie–Weiss behavior above and ferromagnetism below 230 K, while Ni3GeTe2 exhibits temperature-independent paramagnetism in the measured temperature range and a metallic behavior of the electrical resistance. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Ligand variations in [ReX(diimine)(CO)3] complexes : Effects on photocatalytic CO2 reduction

Abstract: Two series of complexes MX(diimine)(CO)(3)] (M = Tc, Re) have been prepared, fully characterised and investigated for their ability to act as photocatalysts for the reduction of CO2 to CO. One series consists of complexes with different aromatic diimine ligands while keeping X = Br- constant. The second series describes complexes with diimine = 2,2-bipyridine and variations in the anionic ligand X-. Although numerous complexes of this type have been prepared and investigated before, a systematic study of their photocatalytic activity has not yet been carried out. Electrochemical and spectroscopic characterisation of these complexes has been performed with the objective of better understanding their respective activity in the photocatalytic CO2 reduction. Despite various modifications, catalytic activity is retained for all compounds exhibiting fluorescence, including (TcCl)-Tc-99(bipy)(CO)(3)], whereas nonfluorescing compounds did not convert CO2 to CO. The correlation of catalytic activity and spectroscopic or electrochemical properties such as absorption or emission wavelengths, redox potentials or Stern-Volmer constants for the reductive quenching of the excited complexes is difficult. Nevertheless, the study emphasises the possibility to obtain ReX(CO)(3)(diimine)] complexes with a wide range of physicochemical properties by ligand variations and the great potential of compounds of this class of complexes as inorganic photosensitisers.

Osmium‐ and Ruthenium‐Based Phosphorescent Materials: Design, Photophysics, and Utilization in OLED Fabrication

Abstract: Osmium(II) complexes possessing β-diketonate, quinolinate, diimine, and C-linked pyridyl azolate chelates reveal interesting structural and photophysical properties. Spectroscopic and dynamic measurements, in combination with theoretical analyses, have provided an important understanding of the electronically excited state properties of these complexes, such as the energy gap and nature of the lower lying states, rate for intersystem crossing, and the efficiency of corresponding radiative decay and nonradiative deactivation processes. This review also reports on the synthetic processes

σ‐Silane Ruthenium Complexes. The Crucial Role of Secondary Interactions

Abstract: The bonding coordination mode of various silanes to ruthenium complexes is discussed on the basis of a detailed analysis of NMR, IR, X-ray and DFT data. It is now more and more obvious that a continuum exists between the two extreme situations, i.e. formation of a σ-silane complex or Si–H bond breaking leading to oxidative addition. Within this continuum, secondary interactions involving Si and H play a significant role, in particular for the stabilization of unusual structures or as intermediates in exchange processes. Here, we highlight the criteria allowing the best description of the different bonding modes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Fe(Cu)‐Containing Coordination Polymers: Syntheses, Crystal Structures, and Applications as Benzyl Alcohol Oxidation Catalysts

Abstract: In this paper three coordination polymers, {[Fe(fcz)2Cl2]·2CH3OH}n (1), {[Cu(fcz)2(H2O)]·SO4·DMF·2CH3OH·2H2O}n (2), and {[Cu(fcz)2Cl2]·2CH3OH}n (3) {fcz = 1-(2,4-difluorophenyl)-1,1-bis[(1H-1,2,4-triazol-l-yl)methyl]ethanol}, were synthesized. Crystallographic analysis reveals that polymer 1 exhibits a 2-D rhombohedral grid structure with (4, 4) nets, while polymer 2 has a 1-D double-chain framework. The structure of polymer 3 is similar to that of 1. We found that polymers 1–3 could effectively catalyze the oxidation of benzyl alcohol to benzaldehyde with H2O2 (30 mass-%) as oxidant in aqueous medium. Various reaction conditions were studied, and optimal reaction conditions were obtained. Under the optimal conditions, the selectivity to benzaldehyde was almost up to 100 % and the conversion of benzyl alcohol was 87 % for 1, 79 % for 2, and 68 % for 3. The results of the recycling test showed that the catalytic activity decreased by only about 7 % after three consecutive reaction cycles. However, under similar conditions, when we used the corresponding metal salt instead of the polymer as catalyst, or replaced the water with acetonitrile as solvent, neither the selectivity nor the conversion was the same. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

A Facile Hydrothermal Route to Flower-Like Cobalt Hydroxide and Oxide

Abstract: Flower-like cobalt hydroxide [β-Co(OH)2] consisting of nanosheet networks has been synthesized by a hydrothermal method from Co(CH3COO)2·4H2O in mixtures of water and glycerol/ethylene glycol at 200 °C. The morphology and phase of the cobalt hydroxide can be controlled by adjusting the experimental parameters that include cobalt acetate concentration and the volume ratio of water to glycerol/ethylene glycol. The possible formation mechanism of flower-like cobalt hydroxide is discussed on the basis of experimental results. Cobalt oxide (Co3O4) flowers have also been obtained by thermal decomposition of cobalt hydroxide flowers in air at 400 °C. The products were characterized by powder XRD, TEM, selected-area electron diffraction (SAED), high resolution TEM (HRTEM), and field-emission SEM (FESEM). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Facile Synthesis of SnO2 Hollow Nanospheres and Applications in Gas Sensors and Electrocatalysts

Abstract: Tin oxide (SnO2) hollow nanospheres have been successfully synthesized from mixed ethanol and water systems containing the surfactants sodium dodecyl benzenesulfonate (SDBS) and terephthalic acid. Systematic studies reveal that terephthalic acid plays pivotal roles in the formation of hollow nanospheres. In the present work, the as-synthesized SnO2 hollow nanospheres exhibit excellent room-temperature ethanol sensitivity and potential catalytic ability towards the electrooxidation of ethanol, and thus are expected to be economical alternative catalysts and useful in industrial applications such as room-temperature gas sensors. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Two New CuII Coordination Polymers: Studies of Topological Networks and Water Clusters

Abstract: Two new Cull coordination polymers, namely [Cu-2(BDC)(2)(L)(4)(H2O)(2)]center dot 14H(2)O (1) and [Cu-1.5(BTC)(L)(1.5)(H2O)(0.5)]center dot 2H(2)O (2), where L = 1,1'-(1,4-butanediyl)bis(imidazole), BDC = 1,4-benzene dicarboxylate, and BTC = 1,3,5-benzenetricarboxylate, have been synthesized at room temperature. Complex 1 exhibits an unusual, square-planar, four-connected 2D (2)(6)4 net, which has been predicated by Wells. Interestingly, three types of water clusters, namely (H2O)(6), (H2O)(8), and (H2O)(10), are observed in the hydrogen-bonded layers constructed by the BDC ligands and water molecules. The BTC anion in compound 2 is coordinated to the Cu" cation as tetradentate ligand to form a (6(6))(2)(4(2)6(4)8(4))(2)(6(4)810) net containing three kinds of nonequivalent points, Thermogravimetric analyses (TGA) and IR spectra for 1 and 2 are also discussed in detail.

Block Copolymer Assemblies as Templates for the Generation of Mesoporous Inorganic Materials and Crystalline Films

Abstract: This Microreview presents the synthesis of mesoporous, crystalline inorganic materials using self-assembled block copolymer mesostructures as templates. The advances in this field are discussed in light of the progress in the development of suitable polymer templates. Particular emphasis is placed on the special conditions and demands to transform the primary sol–gel films into mesoporous, aligned crystalline films for functional applications. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

1,3,5-Triazine-Based Synthons in Supramolecular Chemistry

Abstract: Interest in supramolecular chemistry has grown significantly during the past two decades. In this context, hydrogen bonding and/or coordinative interactions have been extensively used to generate self-assembled one-, two- or three-dimensional polymeric networks. Crystal structure prediction has progressed tremendously, and the challenge for the contemporary supramolecular chemist is now to produce custom-made functional (and multifunctional) materials involving intermolecular interactions. Since the early 1990s, 1,3,5-triazine derivatives have shown their potential as building blocks for the preparation of such materials. In this microreview, a selection of outstanding examples of supramolecular networks involving the 1,3,5-triazine unit are discussed, illustrating the possibility of forming remarkable architectures by means of coordination and/or hydrogen bonds and their applications in host–guest chemistry, catalysis, anion recognition, sensoring, electronics and magnetism. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Structure and Function of Xanthine Oxidoreductase

Abstract: An overview of the current state of our understanding of the reaction mechanism of the molybdenum-containing enzyme xanthine oxidoreductase is presented, with an emphasis on work done in the past five years Recent studies of the biosynthesis of the pterin cofactor bound to the metal in the active site are also reviewed, as is crystallographic work that has clarified the coordination geometry of the molybdenum center This structural work provides the context in which to understand recent mechanistic studies of the enzyme, in particular those aimed at elucidating the role of specific amino acid residues in the active site of the enzyme(© Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2006)

Syntheses, Structures and Near‐IR Luminescent Studies on Ternary Lanthanide (ErIII, HoIII, YbIII, NdIII) Complexes Containing 4,4,5,5,6,6,6‐Heptafluoro‐1‐(2‐thienyl)hexane‐1,3‐dionate

Abstract: The ligand Hhfth [4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)hexane-1,3-dione], which contains a heptafluoropropyl group, has been used to synthesize several new ternary lanthanide complexes (Ln = Er, Ho, Yb, Nd) in which the synergistic ligand is 1,10-phenanthroline (phen) or 2,2'-bipyridine (bipy). The two series of complexes are [Ln(hfth)(3)phen] [abbreviated as (Ln)1, where Ln = Er, Ho, Yb] and [Ln(hfth)(3)bipy] [abbreviated as (Ln)2, where Ln = Er, Ho, Yb, Nd]. Members of the two series have been structurally characterized. The growth morphology, diffuse reflectance (DR) spectra, thermogravimetric analyses, and photophysical studies of these complexes are described in detail. After ligand-mediated excitation of the complexes, they all show the characteristic near-infrared (NIR) luminescence of the corresponding Ln(3+) ions (Ln = Er, Ho, Yb, Nd). This is attributed to efficient energy transfer from the ligands to the central Ln(3+) ions, i.e. an antenna effect. The heptafluorinated substituent in the main hfth sensitizer serves to reduce the degree of vibrational quenching. With these NIR-luminescent lanthanide complexes, the luminescent spectral region from 1300 to 1600 nm, which is of particular interest for telecommunication applications, can be covered completely.

Solvent-Induced Pore-Size Adjustment in the Metal-Organic Framework [Mg3(ndc)3(dmf)4] (ndc = naphthalenedicarboxylate)

Abstract: Two new compounds containing magnesium and the bidentate ligand 2,6-naphthalenedicarboxylate (ndc), namely [Mg(dmf)2(H2O)4]·ndc (1) (dmf = N,N-dimethylformamide) and [Mg3(ndc)3(dmf)4] (TUDMOF-2) (2), have been obtained from Mg(NO3)2·6H2O and the pure acid using a solvothermal route. According to single-crystal X-ray studies both compounds are monoclinic. Complex 1 crystallizes in the space group P21/c [a = 12.317(3), b = 12.582(2), c = 15.353(3) A, β = 110.96(3)°]. The compound consists of an isolated tetraaqua-bis-N,N-dimethylformamide cation and the deprotonated ligand with hydrogen bonds linking the cations and anions. The metal-organic framework 2 crystallizes in the space group C2/c [a = 13.451(3), b = 18.043(4), c = 20.937(5) A, β = 99.79(3)°] with trinuclear magnesium clusters connected to six dicarboxylate ligands that link the clusters into a three-dimensional network. In contrast to [Mg3(ndc)3(def)4] (def = N,N-diethylformamide; 3), the dmf molecules coordinated to magnesium in TUDMOF-2 (2) not only cause a distortion of the network but induce accessibility for the adsorption ofnitrogen. TUDMOF-2 has a Langmuir surface area of520 m2 g–1 and a hydrogen adsorption capacity of 0.78 wt.-% at 77 K and 760 Torr. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

A Hydrothermal Reduction Route to Single-Crystalline Hexagonal Cobalt Nanowires

Abstract: Hexagonal close-packed (hcp) cobalt nanowires with diameters of 150–300 nm and lengths of up to several hundreds of micrometers have been synthesized by a hydrothermal reduction method. These cobalt nanowires were generated by the reduction of cobalt(II) citrate complexes by hypophosphite (H2PO2–) in basic solution at 160 °C. High-resolution TEM and SAED reveal that the as-prepared Co nanowires have a single-crystalline structure with a [001] growth direction. The room-temperature hysteresis loop of these nanowires shows a ferromagnetic behavior with enhanced coercivity. A formation mechanism for these Co nanowires is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Atmospheric pressure chemical vapour deposition of NbSe2 thin films on glass

Abstract: Atmospheric pressure chemical vapour deposition (APCVD) of niobium selenide films on glass substrates was achieved by reaction of di-tert-butyl selenide with NbCl5 at 250600 degrees C. X-ray diffraction showed that the NbSe2 films were crystalline and of the 2H(a) poly-type with cell constants close to those expected (a = 3.44 angstrom; c = 12.58 angstrom). Marked preferred orientation along either (101) or (200) was noted at higher deposition temperature and this unexpectedly varied depending on distance from the reactor inlet. The films produced at 600 degrees C showed exactly the Nb/Se ratio expected for NbSe2 by energy dispersive analysis by X-rays. The films deposited at the substrate temperatures of 500 degrees C or less were selenium rich with a niobium to selenium ratio of 1:2.5. The films produced at 600 degrees C were da-rk-green, powdery and poorly adhesive. The films produced at 500 degrees C and below were dark-brown matte in appearance, they passed the Scotch tape test, but could be scratched with a steel scalpel. SEM showed that the films were composed of plate-like crystals, which become longer and thicker with increasing deposition temperature. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis, Structure and Magnetism of Metal-Organic Framework Materials with Doubly Pillared Layers

Abstract: Two novel coordination polymers with a 3D pillared-layer framework, [MII(Tdc)(4,4′-Bpy)]n [M = Fe (1), Co (2); Tdc = thiophene-2,5-dicarboxylate; 4,4′-Bpy = 4,4′-bipyridine), have been hydrothermally synthesised and structurally characterised. A simultaneous reduction of iron(III) to iron(II) occurs under hydrothermal conditions in the self-assembly process of complex 1. The complexes are isostructural and, in each complex, the metal ions are linked by double μ2-carboxylate bridges in a syn-syn mode, giving rise to dinuclear units that are connected to each other by chelating carboxylate groups from the Tdc ligands in an approximately perpendicular orientation to form 2D rectangle-grid layers. The adjacent layers are held together through 4,4′-Bpy molecules in a double-pillar support fashion to give a 3D network with three intersecting perpendicular channels. Variable-temperature magnetic susceptibility measurements revealed weak antiferromagnetic coupling interactions in both complexes and a field-induced magnetic transition can be observed in 2.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Metalation chemistry of meso-aryl-substituted expanded porphyrins

Abstract: meso-Aryl-substituted expanded porphyrins are structural analogues of meso-aryl-substituted porphyrins. They exhibit rich and novel coordination behaviors, including multi-metal chelation due to the large cavities, spin–spin interaction arising from the proximity of metal centers, and large changes in their structural and electrochemical properties upon metalation. The recent discovery of a facile, one-pot synthesis of a series of meso-aryl-substituted expanded porphyrins enables us to investigate their metal-complexation chemistry. The aim of this Microreview is to highlight recent progress in the synthesis and characterization of metal complexes of meso-aryl-substituted expanded porphyrins. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Can the Clusters Zr6O4(OH)4(OOCR)12 and [Zr6O4(OH)4(OOCR)12]2 Be Converted into Each Other?

Abstract: Upon reaction of zirconium alkoxides, Zr(OR)4, with carboxylic acids, the clusters Zr6O4(OH)4(OOCR)12 (Zr6) or [Zr6O4(OH)4(OOCR)12]2 (Zr12) were obtained, depending on the employed carboxylic acid. The structures of Zr12 clusters with acetate, propionate, vinyl acetate or 3,3′-dimethylacrylate ligands were determined by single-crystal X-ray diffraction, as well as that of methacrylate/acetate and methacrylate/propionate mixed-ligand clusters. The structure of the hafnium cluster [Hf6O4(OH)4(acetate)12]2 is also reported for comparison. The Zr12 clusters are structurally related to the Zr6 clusters since they are composed of two Zr6 sub-units which are bridged by four carboxylate ligands. In each compound, carboxylic acid molecules interact with the cluster by hydrogen bonding to part of the μ3-OH ligands. The clusters are highly dynamic in solution, due to site exchange of the carboxylate ligands; low-temperature NMR spectra of the clusters correspond to the solid-state structures. The Zr6 and Zr12 clusters can be clearly distinguished by their solution NMR spectra. Reactions between selected Zr12 clusters and carboxylic acids led to the conclusion, that only part of the ligands is accessible for ligand exchange reactions. In contrast, all ligands were exchanged when the Zr6 cluster Zr6O4(OH)4(methacrylate)12 was treated with an excess of propionic acid, and Zr6O4(OH)4(propionate)12 was formed. However, the Zr12 cluster [Zr6O4(OH)4(propionate)12]2 was obtained from the reaction of Zr(OBu)4 with propionic acid. The Zr6 and Zr12 clusters thus do not interconvert at the given reaction conditions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Artificial Light-Harvesting Systems by Use of Metal Coordination

Abstract: Construction of artificial light-harvesting systems by metal coordination is reviewed. Light absorbing dyes include porphyrin, phthalocyanine, perylenebisimide and polypyridyl metal complexes. The supramolecular assemblies are obtained by ligand coordination to metal ions in the center or exterior of the chromophores. Supermolecules of discrete structures even in the solution phase are focused on, and methodologies to acquire large association constants are discussed. Complementary or multitopic coordination to the Zn2+ ion gives satisfactory results in obtaining stable and discrete supramolecular structures while maintaining the singlet excited state. Fast energy transfers among the chromophore units are analyzed satisfactorily to examine the properties of light-harvesting antennae. Use of transition-metal ions provides strong coordination, but intersystem crossing of the singlet excited state to the triplet becomes significant. Photophysical properties of such triplet excited species are reported in a limited number of cases and their properties are discussed in view of the light-harvesting antenna function. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Kinetics and Thermodynamics of Halide and Nitrite Oxidation by Mammalian Heme Peroxidases

Abstract: The human heme peroxidases myeloperoxidase (MPO),eosinophil peroxidase (EPO) and lactoperoxidase (LPO) are able to oxidise (pseudo)halides and nitrite to reactive species that participate in host defence against foreign microorganisms as well as in immunomodulation and tissue degradation in certain pathologies. The heme in EPO and LPO is covalently linked to the apoprotein by two ester bonds, whereas in MPO it is additionally linked by a unique sulfonium ion bond to a methionine residue. As a consequence, the prosthetic group in MPO is significantly distorted from a planar conformation. These structural differences are reflected by distinct spectral and redox properties as well as reactivities toward chloride, bromide, iodide, thiocyanate and nitrite, which function as endogenous two- and one-electron donors for these enzymes in vivo. Standard reduction potentials at pH 7 have been determined for all redox couples involved in the halogenation and peroxidase cycle of MPO and LPO and partially of EPO. A detailed thermodynamic analysis of the formation of reactive halide species by MPO and EPO was also performed. Thus, for the first time, a comprehensive analysis of reactions catalysed by human heme peroxidases is presented that allows a better understanding of their role in physiological and pathophysiological processes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

2D and 3D Cadmium(II) Coordination Polymers from a Flexible Tripodal Ligand of 1,3,5-Tris(carboxymethoxy)benzene and Bidentate Pyridyl-Containing Ligands with Three-, Eight- and Ten-Connected Topologies

Abstract: Four novel cadmium(II) coordination polymers, [Cd3(TCMB)2(4,4-bipy)(H2O)16]n (1), [Cd3(TCMB)2(bpe)(H2O)13]n (2), [Cd3(TCMB)2(bpe)2(H2O)4]n (3), and [Cd3(TCMB)2(dpp)2(H2O)3]n (4), [TCMB = 1,3,5-tris(carboxymethoxy)benzene, 4,4-bipy = (4,4-bipyridine), bpe = 1,2-bis(4-pyridyl)ethane, dpp = 1,3-bis(4-pyridyl)propane] have been hydrothermally synthesized by the self-assembly of the flexible tripodal acid TCMB and Cd(OAc)2·2H2O with pyridyl-containing ligands possessing different flexibilities. Single-crystal X-ray diffraction analysis reveals that the four polymers exhibit novel frameworks due to diverse coordination modes and different conformations of the flexible TCMB as well as pyridyl-containing ligands. Complex 1 shows a unique twofold parallel interpenetrating 2D honeycomb network structure with an unusual 63 topology, in which two different large hexagonal rings are arranged alternately, with extraordinarydimensions of ca. 22.172(6) × 12.947(2) A (A) and 17.233(2) × 12.947(2) A (B) based on the distances of the atoms at the opposite positions of the rings. Complex 2 is almost isostructural to complex 1, except that the bidentate bpe ligands bridge the cadmium centers in an anti conformation, rendering the network more flexible. Complex 3 features a 3D network with one of the scarce eight-connected (46, 614, 88)(43)2 topologies based on the rare CdI2-type layer constructed from secondary building units (SBUs) of rare [Cd3(CO2)4]2- isosceles triangle cadmium clusters. Complex 4 possesses distorted CdI2-type layers constructed from unprecedented ten-connected Cd3 clusters which are linked by more flexible dpp ligands in a trans-gauche (TG) conformation in (4,4) networks, leading to another 3D framework of the unusual (418, 624, 83)(43)2 topology. Such an arrangement represents the highest connected topology presently known for the frameworks. Among them, complex 1 displays photoluminescent properties at 460 nm due to the ligand-to-metal charge transfer (LMCT).

Molecular and Electronic Structures of Homoleptic Nickel and Cobalt Complexes with Non‐Innocent Bulky Diimine Ligands Derived from Fluorinated 1,4‐Diaza‐1,3‐butadiene (DAD) and Bis(arylimino)acenaphthene (BIAN)

Abstract: The diimine complexes with bulky fluorinated N-substituents [NiII(FDAD)2] 1 and [CoII(FDAD)2] 2 [FDAD = N,N′-bis(pentafluorophenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene]as well as diimine complexes with extended π system [NiII(FBIAN)2] 3 and [CoI(FBIAN)3] 4 (FBIAN = bis[N-{3,5-bis(trifluoromethyl)phenyl}imino]acenaphthene) were synthesized. Compound 4 represents the first complex with three bis(imino)acenaphthene ligands synthesized so far. The molecular structures of the complexes 1–4 were determined by X-ray crystallography at 193 K. Complexes 1, 2 and 3 comprise the divalent metal ions with pairs of radical monoanionic ligands, whereas 4 is best described as a cobalt(I) complex with two neutral (FBIAN)0 and one (FBIAN)1– ligand in the radical monoanionic form. The electronic structures of the paramagnetic cobalt complexes 2 and 4 were investigated by SQUID measurements and X-band EPR spectroscopy. Both complexes possess a doublet ground state, with electron density located mostly in the metal d-orbitals. The doublet–quartet energy gap for 4 was established to be 159 cm–1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

A Cationic (N‐Heterocyclic carbene)silver Complex as Catalyst for Bulk Ring‐Opening Polymerization of L‐Lactides

Abstract: catalysis / Silver Synthetic, theoretical, and catalysis studies of a cationic functionalized N-heterocyclic carbene complex of silver, namely [{1-isopropyl-3-(N-phenylacetamido)imidazol-2-ylidene}2Ag] + Cl – (1b), is reported. Specifically, 1b was synthesized by the reaction of 1-isopropyl-3-(N-phenylacetamido)imidazolium chloride (1a) with Ag2O in 64 % yield; 1a was synthesized by the alkylation reaction of 1-isopropylimidazole with N-phenyl chloroacetamide in 90 % yield. The molecular structure of 1b was determined by X-ray diffraction studies and was found to be active for polymerization of L-lactide at elevated temperatures under solvent-free melt conditions to give polylactide of moderate molecular weight with narrow molecular weight distribution. Density functional theory studies of the cationic species 2b, derived from NHC silver complex 1b, were employed to obtain an understanding of the structure, bonding, and electronic features of the mole

Multielectron Storage and Photo-Induced Electron Transfer in Oligonuclear Complexes Containing Ruthenium(II) Terpyridine and Ferrocene Building Blocks

Abstract: The heteroleptic complex [(HOOC-tpy)Ru(tpy-NH2)](PF6)2 (tpy = 2,2′;6′,2″-terpyridine) has been incorporated into a multicomponent system with ferrocene moieties attached on either the N-terminal end or the C-terminal end and on both ends of the ruthenium complex. Electrochemical studies reveal almost noninteracting subunits in the oligonuclear systems, whereas ground-state and excited-state optical properties are shown to strongly depend on the site of ferrocene attachment. Interpretation of the experimental results is supported by DFT calculations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis, Crystal Structures, and Photophysical Properties of Two Novel Lead(II)–SIP Coordination Polymers (NaH2SIP = 5-Sulfoisophthalic Acid Monosodium Salt) Containing Tetranuclear Lead(II) Units

Abstract: Two new PbII–SIP coordination polymers, {[Pb4(OH)2(SIP)2(H2O)](H2O)5}n (1) and [Pb3(SIP)2(H2O)5]n (2), have been synthesized by hydrothermal reactions of Pb(OH)2 or Pb(NO3)2 and 5-sulfoisophthalic acid monosodium salt (NaH2SIP) at 160 °C, respectively. Single-crystal X-ray diffraction reveals that compound 1 has a 2D brick-wall-like architecture constructed from 1D tapes containing the basketlike tetranuclear [Pb4(μ3-OH)2(COO)2]. Compound 2 has a 2D-layered structure, which is constructed from a 1D-ladder structure composed of the cyclic [Pb4(SIP)2(COO)2] grid with the four Pb atoms nearly coplanar. In the solid state, compound 1 exhibits blue photoluminescence with the maximum emission intensity at 436 nm upon excitation at 335 nm. Compound 2 shows phosphorescence with the maximum emission intensity at 603 nm upon excitation at 426 nm. Both compounds have also been characterized by elemental analysis, IR spectra, TG analysis, and powder X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis, Structures and Catecholase Activity of a New Series of Dicopper(II) Complexes of Reduced Schiff Base Ligands

Abstract: A series of dinuclear Cu II complexes of reduced Schiff bases from substituted salicylaldehydes and amino acids have been synthesized and characterized. They are: [Cu 2 (Rscp11) 2 -(H 2 O) 2 ) {H 2 RScp11 = 1-[(2-hydroxy-5-R-benzyl)amino]cyclopentane-1-carboxylic acid; R = H (1), Cl (2), CH 3 (3), OH (4)), [Cu 2 (Rsch11) 2 (H 2 O) x ] {H 2 RSch11 = 1-[(2-hydroxy-5-R-benzyl)amino]cyclohexane-1-carboxyhc acid; R = H and x = 1 (5), R = Cl and x = 2 (6), R = CH 3 and x = 2 (7)), [Cu 2 (RSch12) 2 -(H 2 O) 2 ] {H 2 RSch12 = 2-[(2-hydroxy-5-R-benzyl)amino]cyclo-hexane-1-carboxylic acid; R = H (8), CH 3 (10) and [Cu 2 (ClSch12) 2 ]·2H 2 O (9)}, [Cu 2 (Diala5) 2 (H 2 O) 2 ]·H 2 O [H 3 -Diala5 = N-(2,5-dihydroxybenzyl)-L-alanine] (11), [Cu 2 -(Diala4) 2 (H 2 O) 2 ]·H 2 P [H 3 Diala4 = N-(2,4-dihydroxybenzyl)-L-alanine] (12), and (Cu 2 (Diala3) 2 (H 2 O) 2 ]·H 2 O [H 3 Diala3 = N-(2,3-dihydroxybenzyl)-L-alanine] (13). They were isolated and characterized by chemical and spectroscopic methods. Single crystal X-ray crystallographic studies have revealed that [Cu 2 (Scp11) 2 (MeOH) 2 ] (la), [Cu 2 (ClScp11) 2 (DMF)-(H 2 O)]·MeCN (2a), [Cu 2 (MeScpll) 2 (MeOH) 2 ]·2MeOH (3a), [Cu 2 (ClSchll) 2 (MeOH) 2 ]·2MeOH (6a), [Cu 2 (ClSch12) 2 ]· 2MeOH (9a), and [Cu 2 (Diala4) 2 (DMSO) 2 ]·2DMSO·2 acetone (12a) have 1D hydrogen-bonded polymeric structures while 4 has a 3D hydrogen-bonded network structure. Complex 8 displays a 2D coordination polymeric network structure. The complexes 1-13 have been investigated as functional models for the catechol oxidase by employing 3,5-di-tert-butylcatechol as a model substrate. Electron-withdrawing substituents reduced the activity while electron-donating substituents enhanced the activity. Variable-temperature magnetic studies conducted on compound 8 suggest the presence of strong inter-dimer antiferromagnetic coupling.

First Example of a Gold(I) N‐Heterocyclic‐Carbene‐Based Initiator for the Bulk Ring‐Opening Polymerization of L‐Lactide

Abstract: Synthesis, structure, and catalysis studies of two Au- and Ag-based initiators, namely, [3-(N-tert-butylacetamido)-1-(2-hydroxycyclohexyl)imidazol-2-ylidene]AuCl (1c) and [3-(N-tert-butylacetamido)-1-(2-hydroxycyclohexyl)imidazol-2-ylidene]AgCl (1b), for the bulk ring-opening polymerization of L-lactide are reported. Specifically, gold complex 1c was obtained from silver complex 1b by the transmetalation reaction with (SMe2)AuCl. Silver complex 1b was synthesized by the treatment of 3-(N-tert-butylacetamido)-1-(2-hydroxycyclohexyl)imidazolium chloride (1a) with Ag2O. Compound 1a was synthesized directly from the reaction of N-tert-butyl-2-chloroacetamide, cyclohexene oxide, and imidazole. The molecular structures of 1a, 1b, and 1c have been determined by X-ray diffraction studies. The formation of neutral monomeric complexes with linear geometries at the metal centers was observed for both 1b and 1c. The Au and Ag complexes 1c and 1b successfully catalyzed the bulk ring-opening polymerization of L-lactide at elevated temperatures under solvent-free melt conditions to produce moderate to low molecular weight polylactide polymers with narrow molecular weight distributions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)