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Bridging Ligands (bridging + ligand)
Selected AbstractsDinuclear Iridium(III) Complexes Linked by a Bis(,-diketonato) Bridging Ligand: Energy Convergence versus Aggregation-Induced EmissionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2010Chang Hwan Shin Abstract Novel iridium(III)/iridium(III) and iridium(III)/platinum(II) dinuclear complexes, [{Ir(ppyFF)2}2(,2 - L)] (4) and [{Ir(ppyFF)2}(,2 - L){Pt(ppy)}] (5) [ppyFF = 2-(2,4-difluorophenyl)pyridine, ppy = 2-phenylpyridine, L = 1,3-bis(3-phenyl-3-oxopropanoyl)benzene], linked by an L bridging ligand were prepared, and their photophysical properties were investigated in solution and in the solid state. The photophysical properties of mononuclear iridium(III) and platinum(II) complexes, [Ir(ppyFF)2(dbm)] (1) and [Pt(ppy)(dbm)] (2) bearing a dibenzoylmethane (dbm) ligand were also compared. Whereas the UV/Vis absorption spectra of 4 and 5 show independent light absorption at each metal-centered moiety, the photoluminescence spectra of 4 and 5 display almost identical features, but very weak emissions in solution at both room temperature and 77 K. The weak emission in solution is found to mainly originate from a 3LX state of the L bridging ligand, which reflects the occurrence of efficient energy convergence from the triplet states of the Pt(ppy) and Ir(ppyFF) moieties to the 3LX state of L. By contrast, intense orange-red emission, that is, aggregation-induced emission, is produced in the solid state of 4 and 5. Inspection of the crystal-packing structures of 5 reveals that strong intermolecular ,,, interactions between the adjacent pyridine rings of ppyFF ligands in the Ir-centered moieties are responsible for the emissive metal-to-ligand,ligand charge-transfer [3M(LL)CT] state of the solid-state dinuclear systems. The electrochemical properties of 4 and 5 further indicate that the first two reductions occur at the dbm moieties of the L bridging ligand linked to each metal center, which is consistent with the fact that the lowest-energy excited state of the L bridging ligand dominates the excited-state properties of 4 and 5 in solution. [source] Mono- and Binuclear Arylnickel Complexes of the ,-Diimine Bridging Ligand 2,2,-Bipyrimidine (bpym)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2010Axel Klein Abstract The mono- and binuclear organometallic NiII complexes [(,-bpym){Ni(Mes)Br}n] (bpym = 2,2,-bipyrimidine; n = 1 or 2; Mes = mesityl = 2,4,6-trimethylphenyl) were prepared and characterised electrochemically and spectroscopically (NMR, UV/Vis/NIR) in detail. The long-wavelength absorptions for the binuclear complex reveal a marked electronic coupling of the two metal centres over the ligand bridge via their low-lying ,*-orbitals. While the mononuclear complex undergoes rapid dissociation of the bromido ligand after one-electron reduction the binuclear derivative exhibits reversible reductive electrochemistry and both of them yield stable radical anionic complexes with mainly bpym ligand centred spin density as shown by EPR spectroscopy of the free ligand bpym and the nickel complexes. The molecular structure of the binuclear bpym complex [(,-bpym){Ni(Mes)Br}2] was studied by EXAFS in comparison to the mononuclear analogue [(bpym)Ni(Mes)Br] revealing markedly increased Ni,C/N distance of the first coordination shell for the binuclear derivative suggesting an optimum overlap for the mononuclear complex, while two nickel complex fragments {Ni(Mes)Br} are seemingly too large to fit into the bis-chelate coordination site. [source] Synthesis of a Metallamacrocyclic Re(CO)3 Complex Using a Tridentate Bridging LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2004Thomas Brasey Abstract The reaction of [ReBr3(CO)3][NEt4]2 with 3-hydroxy-1,2,3-benzotriazine-4(3H)-one in the presence of base gave the ionic rhenium complex [ReBr(C7H4N3O2)(CO)3][NEt4] (2) which was crystallographically characterized. A neutral metallamacrocycle 3 was obtained upon abstraction of [NEt4]Br from complex 2. This complex cocrystallizes with an unusual C3 -symmetric [Ag(,2 -benzene)3(OH2)][BF4] complex as evidenced by single-crystal X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Novel RuII Complexes with Bispidine-Based Bridging Ligands: Luminescence Sensing and Photocatalytic PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2010Christoph Busche Abstract New ligands with a bidentate bipyridyl (bpy) and a tetradentate bispidine (bisp) subunit (bipyridyl = 2,2,-bipyridine derivative, bispidine = 3,7-diazabicyclo[3.3.1]nonane derivative) and their heterodinuclear {[Ru(bpy)3]2+ -[M(bisp)]2+} complexes (M = Cu2+, Fe2+) were prepared and characterized. The luminescence of the mononuclear RuII complexes (metal-free bisp subunit) is efficiently quenched in presence of CuII. An EPR spectroscopic study reveals thatvisible light irradiation does not alter the oxidation states of the two metal ions in {[Ru(bpy)3]2+ -[Cu(bisp)]2+}, i.e. there is energy rather than electron transfer. The heterodinuclear {[Ru(bpy)3]2+ -[Cu(bisp)]2+} complex shows a significantphotocatalytic activity in the aziridination of styrene. [source] Synthesis and Characterization of a Gold Complex Containing [SbPh]2, and [SbPh2], Anions as Bridging LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2007Dieter Fenske Abstract The synthesis and structural characterization of the gold antimony complex [Au8(SbPh)2(SbPh2)4(PEt3)6] (1) is reported. Complex 1 can be obtained by the reaction of [AuCl(PEt3)] with a mixture of PhSb(SiMe3)2 and Ph2(SbSiMe3) in presence of the bidentate phosphane ligand dppm [dppm = bis(diphenylphosphanyl)methane]. Complex 1 consists of a distorted heterocubic central [Au6Sb2] unit connected to two annulated five-membered rings on two opposite edges. The AuI ions show weak aurophilic interactions and are bridged by [SbPh]2, and [SbPh2], anions. Despite the high oxidation potential of AuI, the reaction mixtures and crystals are surprisingly stable. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis and Characterization of Heterotrinuclear Complexes of Nickel and Palladium with Pyridinecarboxylate as Bridging LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2005José Ruiz Abstract Heterotrinuclear pyridinecarboxylate complexes of nickel(II) and palladium(II) of the types [Ni(mcN3)(pyridinecarboxylate)]2{,-[Pd(C6F5)2]}(PF6)2 [mcN3 = 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene (Me3 -mcN3) or 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene (Me4 -mcN3)] have been prepared by two different routes. The corresponding monomeric pyridinecarboxylate complexes of nickel and the monomeric pyridinecarboxylic acid/ester complexes of palladium have also been prepared. The crystal structures of two precursors [Ni(Me4 -mcN3)(NC5H4 -3-COO)]PF6 and cis -[Pd(C6F5)2(NC5H4 -4-CH2COOCH3)2] have been established by X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] A Novel 3-D Self-Penetrating Topological Network Assembled by Mixed Bridging LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2004Xing Li Abstract The assembly of 5-sulfoisophthalic acid (H3sipa) and 4,4,-bipyridine (bpy) with Cd2+ ions gave rise to a new polymeric complex {[Cd3(sipa)2(bpy)4(H2O)2]·3H2O}n (1). X-ray diffraction analysis reveals that complex 1 has a 3-D self-penetrating network formed by the interlocking and interweaving of two types of one-dimensional chains comprising two kinds of Cd4(sipa)4 and Cd4(bpy)4 units, respectively. The sipa3, ligand serves as the connector and the Cd2+ ion as the node. Thermogravimetric analysis (TGA) and the luminescence property of 1 are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Dimeric 2,2,-Bipyridylruthenium(II) Complexes Containing 2,2,-Bis(1,2,4-triazin-3-yl)-4,4,-bipyridine-Like Bridging Ligands: Syntheses, Characterization and DNA BindingEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2004Cai-Wu Jiang Abstract Three new bridging ligands 2,2,-bis(1,2,4-triazin-3-yl)-4,4,-bipyridine (btb), 2,2,-bis(1,2,4-triazino[5,6-f]acenaphthylen-3-yl)-4,4,-bipyridine (btapb), 2,2,-bis(5,6-diphenyl-1,2,4-triazin-3-yl)-4,4,-bipyridine (bdptb) and their dimeric 2,2,-bipyridylruthenium(II) complexes [Ru(bpy)2(btb)Ru(bpy)2]4+ (1), [Ru(bpy)2(btapb)Ru(bpy)2]4+ (2), [Ru(bpy)2(bdptb)Ru(bpy)2]4+ (3) have been synthesized and characterized by elemental analysis, fast atom bombardment (FAB) mass spectrometry or electrospray mass spectrometry (ES-MS), 1H NMR and UV/Visible spectroscopy. The binding behavior of these dimeric complexes with calf thymus DNA (CT-DNA) was investigated by electronic absorption spectroscopy, viscosity measurements, and equilibrium dialysis experiments. The hypochromism of the metal-ligand charge transfer (MLCT) band in the electronic absorption spectra of the dinuclear complexes 1, 2, and 3 is 8.7%, 19% and 33%, respectively, with bathochromic shifts of 5, 5 and 14 nm, respectively. The binding constants are 7.5×104M,1, 4.8×105M,1 and 7.6×105M,1, respectively. Increasing the size of the plane of the bridging ligand increases the hydrophobicity of their complexes, leading to stronger binding by the complexes to calf thymus DNA. The effect of increasing concentrations of these novel dimeric ruthenium(II) complexes on the relative viscosities of CT-DNA is less notable than that of well-known intercalators such as [Ru(bpy)2(dppz)]2+. The equilibrium experiments showed that ,,,3 binding is stronger than ,,,3 binding to CT-DNA. This is the first example of a dinuclear complex binding enantioselectively to CT-DNA measured by equilibrium dialysis. The experiments suggest that the three complexes may be DNA groove binders. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Structures and Solvatochromic Phosphorescence of Dicationic Terpyridyl,Platinum(II) Complexes with Foldable Oligo(ortho -phenyleneethynylene) Bridging LigandsCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2008Ming-Xin Zhu Abstract A series of binuclear organoplatinum(II) complexes, [(tBu3tpy)Pt(CC1,2-C6H4)nCCPt(tBu3tpy)][ClO4]2 (1,7, n=1, 2, 3, 4, 5, 6, 8; tBu3tpy=4,4,,4,,-tri- tert -butyl-2,2,:6,,2,,-terpyridine) with foldable oligo(ortho -phenyleneethynylene) linkers were prepared and characterized by spectroscopic methods and/or X-ray crystallographic analyses. In the crystal structures of 3,2.5,CH3OH, 5,CH3CN, and 6,4,CH3CN, each of the bridging ortho -phenyleneethynylene ligands has a partially folded conformation. In aerated water/acetonitrile mixtures with water percentages larger than 40,%, the emission of complexes 3,7 are red-shifted and enhanced when compared to those recorded in acetonitrile. The red-shift in emission energy and enhanced emission intensity can be attributed to the inter- and/or intramolecular interactions induced by the addition of water to solutions of the platinum(II) complexes in acetonitrile. Data from dynamic light scattering and transmission electron microscopy studies revealed that these binuclear platinum(II) complexes aggregated into nanosized particles in acetonitrile/water mixtures. Hydrophobic folding of the ortho -phenyleneethynylene linkers in acetonitrile/water mixtures is postulated. [source] Dinuclear Iridium(III) Complexes Linked by a Bis(,-diketonato) Bridging Ligand: Energy Convergence versus Aggregation-Induced EmissionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2010Chang Hwan Shin Abstract Novel iridium(III)/iridium(III) and iridium(III)/platinum(II) dinuclear complexes, [{Ir(ppyFF)2}2(,2 - L)] (4) and [{Ir(ppyFF)2}(,2 - L){Pt(ppy)}] (5) [ppyFF = 2-(2,4-difluorophenyl)pyridine, ppy = 2-phenylpyridine, L = 1,3-bis(3-phenyl-3-oxopropanoyl)benzene], linked by an L bridging ligand were prepared, and their photophysical properties were investigated in solution and in the solid state. The photophysical properties of mononuclear iridium(III) and platinum(II) complexes, [Ir(ppyFF)2(dbm)] (1) and [Pt(ppy)(dbm)] (2) bearing a dibenzoylmethane (dbm) ligand were also compared. Whereas the UV/Vis absorption spectra of 4 and 5 show independent light absorption at each metal-centered moiety, the photoluminescence spectra of 4 and 5 display almost identical features, but very weak emissions in solution at both room temperature and 77 K. The weak emission in solution is found to mainly originate from a 3LX state of the L bridging ligand, which reflects the occurrence of efficient energy convergence from the triplet states of the Pt(ppy) and Ir(ppyFF) moieties to the 3LX state of L. By contrast, intense orange-red emission, that is, aggregation-induced emission, is produced in the solid state of 4 and 5. Inspection of the crystal-packing structures of 5 reveals that strong intermolecular ,,, interactions between the adjacent pyridine rings of ppyFF ligands in the Ir-centered moieties are responsible for the emissive metal-to-ligand,ligand charge-transfer [3M(LL)CT] state of the solid-state dinuclear systems. The electrochemical properties of 4 and 5 further indicate that the first two reductions occur at the dbm moieties of the L bridging ligand linked to each metal center, which is consistent with the fact that the lowest-energy excited state of the L bridging ligand dominates the excited-state properties of 4 and 5 in solution. [source] First Hexanuclear UIV and ThIV Formate Complexes , Structure and Stability Range in Aqueous SolutionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 32 2009Shinobu Takao Abstract The actinide(IV) hexanuclear [M6(,3 -O)4(,3 -OH)4(HCOO)12(LT)6] complexes were prepared (LT = H2O or CH3OH). Their structures were investigated by single-crystal X-ray analysis and XAFS spectroscopy. HCOO, acts as a bridging ligand, which prevents the formation of polynuclear hydrolysis species like UIV hydrous oxide colloids at least up to pH = 3.25, and stabilizes the nanosized clusters in solution. The charge of the hexamer is balanced by the O/OH ratio of the ,3 -bridges.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Inclusion Complexes for Use in Room-Temperature Gas-Sensor DesignEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 33 2007Liwei Mi Abstract The inclusion complex [{Co(bpy)(H2O)4}·(fcds)]n (1), which has been constructed using the guest molecule ferrocene-1,1,-disulfonate (fcds), the bridging ligand 4,4,-bipyridine (bpy) and d7 Co2+, contains an infinite zigzag chain formed by the central CoII ion and the bridging bpy ligand. Guest fcds molecules lie between two adjacent zigzag chains. The highly conjugated structure of complex 1 means that it can be used as a metal-organic semiconductor, and it also shows a high response to liquefied petroleum gas (LPG) and ethanol/petroleum ether (EP) at room temperature. The inclusion complexes [{Co(bpp)2(H2O)2}·(fcds)·4H2O]n [2; bpp = 1,3-bis(4-pyridyl)propane] and [{Zn(bpy)(H2O)4}·(fcds)]n (3), on the other hand, cannot be employed as room-temperature gas sensors because they are insulators. The electrical resistivity of inclusion complex [{Ni(bpy)(H2O)4}·(fcds)]n (4) is 621 M,, whereas that of [{Co(bpy)(H2O)4}SO4·(4-abaH)2·3H2O]n (5) (4-abaH = 4-aminobenzoic acid) is only 137 M,. This means that the semi-conducting properties of such inclusion complexes depend on both the conjugated structure and the central metal ions. Furthermore, conjugated inclusion complexes with an odd number of electrons could be useful for the design of highly selective room-temperature gas sensors.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Solid-State Anion,Guest Encapsulation by Metallosupramolecular Capsules Made from Two Tetranuclear Copper(II) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2007Emilio Pardo Abstract A new cationic tetranuclear copper(II) complex self-assembles from one 1,3-phenylenebis(oxamato) (mpba) bridging ligand and four CuII ions partially blocked with N,N,N,,N, -tetramethylethylenediamine (tmen) terminal ligands. In the solid state, two of these tetracopper(II) oxamato complexes of bowl-like shape and helical conformation then serve as a building block for the generation of either hetero- (MP) or homochiral (MM/PP) dimeric capsules depending on the nature of the encapsulated anion guest, perchlorate or hexafluorophosphate. The overall magnetic behaviour of these metallosupramolecular capsules does not depend on the nature of the encapsulated anion guest, but it is consistent with the dimer-of-dimer structure of the tetracopper(II) cation host, where the interdimer magnetic coupling through the meta -phenylenediamidate bridge is negligibly smallrelative to the reasonably strong intradimer one across the oxamato bridge.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Multicomponent Supramolecular Devices: Synthesis, Optical, and Electronic Properties of Bridged Bis-dirhodium and -diruthenium Complexes,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2006Anne Petitjean Abstract Four ruthenium- and rhodium-based metal,metal-bonded multicomponent systems have been synthesized, and their absorption, redox, spectroelectrochemical and structural properties have been studied. The absorption spectra of the four bis-dimetallic compounds M2LM2, where L is a bridging ligand and M is rhodium or ruthenium, exhibit very strong bands in the UV, visible and, for the diruthenium species, near-IR region. The low-energy absorption bands are assigned to charge-transfer transitions involving a metal,metal bonding orbital as the donor and an orbital centered on the bis-tetradentate aromatic ligands as the acceptor (metal,metal to ligand charge transfer, M2LCT). Each compound exhibits reversible bridging-ligand-centered reductions at mild potentials and several reversible oxidation processes. The oxidation signals of the two equivalent dimetallic centers of each bis-dimetallic compound are split, with the splitting , a measure of the electronic coupling , depending on both the metal and bridging ligand. The mixed-valence species of the dirhodium species was investigated, and the electronic coupling matrix element calculated from the experimental intervalence band parameters for one of them (86 cm,1) indicates a significant inter-component electronic interaction which compares well with good electron conducting anionic bridges such as cyanides. Although none of these compounds is luminescent, the M2LCT excited state of one of the bis-dirhodium complexes is relatively long-lived (about 6 ,s) in degassed acetonitrile at room temperature. The results presented here are promising for the development of linear poly-dimetallic complexes built on longer naphthyridine-based strands, with significant long-range electronic coupling and molecular-wire-like behavior. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Dimeric 2,2,-Bipyridylruthenium(II) Complexes Containing 2,2,-Bis(1,2,4-triazin-3-yl)-4,4,-bipyridine-Like Bridging Ligands: Syntheses, Characterization and DNA BindingEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2004Cai-Wu Jiang Abstract Three new bridging ligands 2,2,-bis(1,2,4-triazin-3-yl)-4,4,-bipyridine (btb), 2,2,-bis(1,2,4-triazino[5,6-f]acenaphthylen-3-yl)-4,4,-bipyridine (btapb), 2,2,-bis(5,6-diphenyl-1,2,4-triazin-3-yl)-4,4,-bipyridine (bdptb) and their dimeric 2,2,-bipyridylruthenium(II) complexes [Ru(bpy)2(btb)Ru(bpy)2]4+ (1), [Ru(bpy)2(btapb)Ru(bpy)2]4+ (2), [Ru(bpy)2(bdptb)Ru(bpy)2]4+ (3) have been synthesized and characterized by elemental analysis, fast atom bombardment (FAB) mass spectrometry or electrospray mass spectrometry (ES-MS), 1H NMR and UV/Visible spectroscopy. The binding behavior of these dimeric complexes with calf thymus DNA (CT-DNA) was investigated by electronic absorption spectroscopy, viscosity measurements, and equilibrium dialysis experiments. The hypochromism of the metal-ligand charge transfer (MLCT) band in the electronic absorption spectra of the dinuclear complexes 1, 2, and 3 is 8.7%, 19% and 33%, respectively, with bathochromic shifts of 5, 5 and 14 nm, respectively. The binding constants are 7.5×104M,1, 4.8×105M,1 and 7.6×105M,1, respectively. Increasing the size of the plane of the bridging ligand increases the hydrophobicity of their complexes, leading to stronger binding by the complexes to calf thymus DNA. The effect of increasing concentrations of these novel dimeric ruthenium(II) complexes on the relative viscosities of CT-DNA is less notable than that of well-known intercalators such as [Ru(bpy)2(dppz)]2+. The equilibrium experiments showed that ,,,3 binding is stronger than ,,,3 binding to CT-DNA. This is the first example of a dinuclear complex binding enantioselectively to CT-DNA measured by equilibrium dialysis. The experiments suggest that the three complexes may be DNA groove binders. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Dynamic structures of phosphodiesterase-5 active site by combined molecular dynamics simulations and hybrid quantum mechanical/molecular mechanical calculationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2008Ying Xiong Abstract Various quantum mechanical/molecular mechanical (QM/MM) geometry optimizations starting from an x-ray crystal structure and from the snapshot structures of constrained molecular dynamics (MD) simulations have been performed to characterize two dynamically stable active site structures of phosphodiesterase-5 (PDE5) in solution. The only difference between the two PDE5 structures exists in the catalytic, second bridging ligand (BL2) which is HO, or H2O. It has been shown that, whereas BL2 (i.e. HO,) in the PDE5(BL2 = HO,) structure can really bridge the two positively charged metal ions (Zn2+ and Mg2+), BL2 (i.e. H2O) in the PDE5(BL2 = H2O) structure can only coordinate Mg2+. It has been demonstrated that the results of the QM/MM geometry optimizations are remarkably affected by the solvent water molecules, the dynamics of the protein environment, and the electronic embedding charges of the MM region in the QM part of the QMM/MM calculation. The PDE5(BL2 = H2O) geometries optimized by using the QM/MM method in different ways show strong couplings between these important factors. It is interesting to note that the PDE5(BL2 = HO - ) and PDE5(BL2 = H2O) geometries determined by the QM/MM calculations neglecting these three factors are all consistent with the corresponding geometries determined by the QM/MM calculations that account for all of these three factors. These results suggest the overall effects of these three important factors on the optimized geometries can roughly cancel out. However, the QM/MM calculations that only account for some of these factors could lead to considerably different geometries. These results might be useful also in guiding future QM/MM geometry optimizations on other enzymes. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Structural-based mutational analysis of d -aminoacylase from Alcaligenes faecalis DA1PROTEIN SCIENCE, Issue 11 2002Cheng-Sheng Hsu Abstract d -Aminoacylase is an attractive candidate for commercial production of d -amino acids through its catalysis in the zinc-assistant hydrolysis of N -acyl- d -amino acids. We report here the cloning, expression, and structural-based mutation of the d -aminoacylase from Alcaligenes faecalis DA1. A 1,007-bp PCR product amplified with degenerate primers, was used to isolate a 4-kb genomic fragment, encoding a 484-residue d -aminoacylase. The enzyme amino-terminal segment shared significant homology within a variety of enzymes including urease. The structural fold was predicted by 3D-PSSM to be similar to urease and dihydroorotase, which have grouped into a novel ,/,-barrel amidohydrolase superfamily with a virtually indistinguishable binuclear metal centers containing six ligands, four histidines, one aspartate, and one carboxylated lysine. Three histidines, His-67, His-69, and His-250, putative metal ligands in d -aminoacylase, have been mutated previously, the remaining histidine (His-220) and aspartate (Asp-366) Asp-65, and four cysteines were then characterized. Substitution of Asp-65, Cys-96, His-220, and Asp-366 with alanine abolished the enzyme activity. The H220A mutant bound approximately half the normal complement of zinc ion as did H250N. However, the C96A mutant showed little zinc-binding ability, revealing that Cys-96 may replace the carboxylated lysine to serve as a bridging ligand. According to the urease structure, the conserved amino-terminal segment including Asp-65 may be responsible for structural stabilization. [source] A stair-like two-dimensional silver(I) coordination polymer of N,-(3-cyanobenzylidene)nicotinohydrazideACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009Cao-Yuan Niu The structure of the title compound, poly[[[,3 - N,-(3-cyanobenzylidene)nicotinohydrazide]silver(I)] hexafluoroarsenate], {[Ag(C14H10N4O)](AsF6)}n, at 173,K exhibits a novel stair-like two-dimensional layer and a three-dimensional supramolecular framework through C,H...Ag hydrogen bonds. The AgI cation is coordinated by three N atoms and one O atom from N,-(3-cyanobenzylidene)nicotinohydrazide (L) ligands, resulting in a distorted tetrahedral coordination geometry. The organic ligand acts as a ,3 -bridging ligand through the pyridyl and carbonitrile N atoms and deviates from planarity in order to adapt to the coordination geometry. Two ligands bridge two AgI cations to construct a small 2+2 Ag2L2 ring. Four ligands bridge one AgI cation from each of four of these small rings to form a large grid. An interesting stair-like two-dimensional (3,6)-net is formed through AgI metal centres acting as three-connection nodes and through L molecules as tri-linkage spacers. [source] catena -Poly[[[aqua(ethylenediamine-,2N,N,)(nitrato-,O)copper(II)]-,-4,4,-dithiodipyridine-,2N:N,] nitrate monohydrate]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009Rüdiger W. Seidel The title compound, {[Cu(NO3)(C2H4N2)(C10H8N2S2)(H2O)]NO3·H2O}n, is composed of a one-dimensional linear coordination polymer involving cis -protected copper(II) ions and a 4,4,-dithiodipyridine bridging ligand. The polymeric chains run along the c -axis direction. N,H...O and O,H...O hydrogen bonds involving the coordinating amine groups, nitrate ions and water molecules, as well as cocrystallized noncoordinating nitrate ions and water molecules, generate a three-dimensional structure. [source] Two bicyclic dinuclear complexes generated from 3,3,-[1,3,4-thiadiazole-2,5-diyldi(thiomethylene)]dibenzoic acid (L) and dimethylformamide (DMF): [Cu(L)(DMF)]2 and [Zn(L)(DMF)]2ACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Ping Wang A new 1,3,4-thiadiazole bridging ligand, namely 3,3,-[1,3,4-thiadiazole-2,5-diyldi(thiomethylene)]dibenzoic acid (L), has been used to create the novel isomorphous complexes bis{,-3,3,-[1,3,4-thiadiazole-2,5-diyldi(thiomethylene)]dibenzoato}bis[(N,N -dimethylformamide)copper(II)], [Cu2(C18H12N2O4S3)2(C3H7NO)2], (I), and bis{,-3,3,-[1,3,4-thiadiazole-2,5-diyldi(thiomethylene)]dibenzoato}bis[(N,N -dimethylformamide)zinc(II)], [Zn2(C18H12N2O4S3)2(C3H7NO)2], (II). Both exist as centrosymmetric bicyclic dimers constructed through the syn,syn bidentate bridging mode of the carboxylate groups. The two rings share a metal,metal bond and each of the metal atoms possesses a square-pyramidal geometry capped by the dimethylformamide molecule. The 1,3,4-thiadiazole rings play a critical role in the formation of a ,,, stacking system that expands the dimensionality of the structure from zero to one. The thermogravimetric analysis of (I) indicates decomposition of the coordinated ligands on heating. Compared with the fluorescence of L in the solid state, the fluorescence intensity of (II) is relatively enhanced with a slight redshift, while that of (I) is quenched. [source] A one-dimensional nickel(II) coordination polymer containing 2,6-dipicolinate and dipyrido[3,2- a:2,,3,- c]phenazineACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2007Yi Ma A new coordination polymer, catena -poly[[(dipyrido[3,2- a:2,,3,- c]phenazine-,2N,N,)nickel(II)]-,-2,6-dipicolinato-,4O2,N,O6:O2,], [Ni(C7H3NO4)(C18H10N4)]n, exhibits a one-dimensional structure in which 2,6-dipicolinate acts as a bridging ligand interconnecting adjacent nickel(II) centers to form a chain structure. The asymmetric unit contains one NiII center, one dipyrido[3,2- a:2,,3,- c]phenazine ligand and one 2,6-dipicolinate ligand. Each NiII center is six-coordinated and surrounded by three N atoms and three O atoms from one dipyrido[3,2- a:2,,3,- c]phenazine ligand and two different 2,6-dipicolinate ligands, leading to a distorted octahedral geometry. Adjacent chains are linked by ,,, stacking interactions and weak interactions to form a three-dimensional supramolecular network. [source] The first metalloporphyrin dimer linked by a bridging phenylenedicarbene ligandACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2006Hidetaka Yuge In the first bis[ruthenium(II),porphyrin],dicarbene complex, ,-[1,4-phenylenebis(phenylmethylidene-,C)]bis[(ethanol-,O)(5,10,15,20-tetra- p -tolylporphyrinato-,4N)ruthenium(II)] 1,2-dichloroethane trisolvate, [Ru2(C20H14)(C48H36N4)2(C2H6O)2]·3C2H4Cl2, an inversion center is located at the center of the ,-phenylene group, leading to a parallel arrangement for the pair of porphyrin ring systems. The bond lengths and angles compare favourably with literature values for ruthenium,porphyrin,monocarbene complexes; the Ru=C(carbene) bond length and the C(phenyl),C(carbene),C(phenylene) angle are 1.865,(3),Å and 112.3,(3)°, respectively. The RuII ion is displaced out of the C20N4 porphyrin least-squares plane (by 0.2373,Å) toward the bridging ligand of the Ci -symmetry dimer. The porphyrin ring systems of the dimer thus exhibit mildly domed conformations. [source] The twinned crystal structure of ,-2,2,-bipyrimidine-1,2N1,N1,:2,2N3,N3, -bis{tris[4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dionato-,2O,O,]terbium(III)} ethyl acetate solvateACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2006Kristin Kirschbaum The title compound, [Tb2(C24H12F9O6S3)2(C8H6N4)]·C4H8O2, has two terbium(III) centers bridged by the polyazine ligand 2,2,-bipyrimidine (bpm), which is distorted from planarity by 7.0,(2)°. The terminal ligand 4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dione (tta) is bidentate, coordinating through the two O atoms, while the bridging ligand is bis-bidentate, coordinating through four equivalent N atoms. Both the complex and the ethyl acetate solvent molecules are disordered. The structure was refined as a non-merohedral twin. [source] Synthesis, crystal structure and magnetic property of a two-dimensional herringbone-like network with praseodymium(III) nitrate and 1-bromo- 3,5-bis(imidazol-1-ylmethyl)benzene (bib)APPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2006Wen-Li Meng Abstract A new complex [Pr(bib)2(NO3)3] (1) was synthesized by reaction of bidentate imidazole-containing ligand 1-bromo-3,5-bis(imidazol-1-ylmethyl)benzene (bib) with Pr(NO3)·6H2O and characterized by X-ray crystallography. Complex 1 has a two-dimensional herringbone-like structure with the ligand bib serving as a bridging ligand using its two imidazolyl nitrogen atoms. Ligand bib adopts cis and trans two different conformations, and the Pr(III) atoms are bridged by bib in two different ways. Thermogravimetric analysis for complex 1 was carried out and the result shows that the complex is stable up to 180 °C. Variable-temperature magnetic susceptibility of complex 1 was measured between 1.8 and 300 K and the result shows that the ,MT value decreases continuously over the whole temperature range. Copyright © 2005 John Wiley & Sons, Ltd. [source] The Controlled Formation and Cleavage of an Intramolecular d8,d8 Pt,Pt Interaction in a Dinuclear Cycloplatinated Molecular "Pivot-Hinge"CHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2009Chi-Kin Koo Dr. Abstract The bis(diphenylphosphino)methane (dppm)-bridged dinuclear cycloplatinated complex {[Pt(L)]2(,-dppm)}2+ (Pt2,dppm; HL: 2-phenyl-6-(1H -pyrazol-3-yl)-pyridine) demonstrates interesting reversible "pivot-hinge"-like intramolecular motions in response to the protonation/deprotonation of L. In its protonated "closed" configuration, the two platinum(II) centers are held in position by intramolecular d8,d8 Pt,Pt interaction. In its deprotonated "open" configuration, such Pt,Pt interaction is cleaved. To further understand the mechanism behind this hingelike motion, an analogous dinuclear cycloplatinated complex, {[Pt(L)]2(,-dchpm)}2+ (Pt2,dchpm) with bis(dicyclohexylphosphino)methane (dchpm) as the bridging ligand, was synthesized. From its protonation/deprotonation responses, it was revealed that aromatic ,,, interactions between the phenyl moieties of the ,-dppm and the deprotonated pyrazolyl rings of L was essential to the reversible cleavage of the intramolecular Pt,Pt interaction in Pt2,dppm. In the case of Pt2,dchpm, spectroscopic and spectrofluorometric titrations as well as X-ray crystallography indicated that the distance between the two platinum(II) centers shrank upon deprotonation, thus causing a redshift in its room-temperature triplet metal,metal-to-ligand charge-transfer emission from 614 to 625,nm. Ab initio calculations revealed the presence of intramolecular hydrogen bonding between the deprotonated and negatively charged 1-pyrazolyl-N moiety and the methylene CH and phenyl C,H of the ,-dppm. The "open" configuration of the deprotonated Pt2,dppm was estimated to be 19,kcal,mol,1 more stable than its alternative "closed" configuration. On the other hand, the open configuration of the deprotonated Pt2,dchpm was 6,kcal,mol,1 less stable than its alternative closed configuration. [source] Structural and Magnetic Resolution of a Two-Step Full Spin-Crossover Transition in a Dinuclear Iron(II) Pyridyl-Bridged CompoundCHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2006Jarrod J. M. Amoore Abstract A dinuclear iron(II) complex containing the new pyridyl bridging ligand, 2,5-di(2,,2,,-dipyridylamino)pyridine (ddpp) has been synthesised and characterised by single-crystal X-ray diffraction, magnetic susceptibility and Mössbauer spectral methods. This compound, [Fe2(ddpp)2(NCS)4],4,CH2Cl2, undergoes a two-step full spin crossover. Structural analysis at each of the three plateau temperatures has revealed a dinuclear molecule with spin states HS,HS, HS,LS and LS,LS (HS: high spin, LS: low spin) for the two iron(II) centres. This is the first time that resolution of the metal centres in a HS,LS ordered state has been achieved in a two-step dinuclear iron(II) spin-crossover compound. Thermogravimetric data show that the dichloromethane solvate molecules can be removed in two distinct steps at 120,°C and 200,°C. The partially de-solvated clathrate, [Fe2(ddpp)2(NCS)4],CH2Cl2, undergoes a one-step transition with an increased transition temperature with respect to the as synthesised material. Structural characterisation of this material reveals subtle changes to the coordination geometries at each of the iron(II) centres and striking changes to the local environment of the dinuclear complex. The fully de-solvated material remains high spin over all temperatures. Interestingly, the solvent can be re-introduced into the monosolvated solid to achieve complete conversion back to the original two-step crossover material, [Fe2(ddpp)2(NCS)4],4,CH2Cl2. [source] In Situ Synthesis of Trisubstituted Methanol Ligands and Their Potential as One-Pot Generators of Cubane-like Metal ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2006Brendan F. Abrahams Dr. Abstract Two different one pot routes to a variety of metal cubane compounds are reported; one route is based on an in situ benzilic acid type rearrangement and the other involves in situ nucleophilic attack at a ketone. Diketosuccinic acid in basic solution in the presence of certain divalent metal ions undergoes a benzilic acid type rearrangement to generate the carbon oxyanion, C(CO2,)3O,, which serves as a cubane-forming bridging ligand in a series of octanuclear complexes of composition [M8{C(CO2)3O}4](H2O)12 (M=Mg, Mn, Fe, Co, Ni, Zn). At the heart of each of these highly symmetrical aggregates is an M4O4 cubane core, each oxygen component of which is provided by the alkoxo centre of a C(CO2,)3O, ligand. Reaction of 2,2,-pyridil, (2-C5H4N)COCO(2-C5H4N), and calcium nitrate in basic alcoholic solution, which proceeds by a similar benzilic acid type rearrangement, gives the cubane compounds, [Ca4L4(NO3)4] in which L=(2-C5H4N)2C(COOR)O, (R=Me or Et). Nucleophilic attack by bisulfite ion at the carbonyl carbon atom of 2,2,-dipyridyl ketone in the presence of certain divalent metals generates the electrically neutral complexes, [{(C5H4N)2SO3C(OH)}2M] (M=Mn, Fe, Co, Ni, Zn and Cd). Cubane-like complexes [M4{(C5H4N)2SO3C(O)}4] (M=Zn, Mn) can be obtained directly from 2,2,-dipyridyl ketone in one-pot reaction systems (sealed tube, 120,°C) if a base as weak as acetate ion is present to deprotonate the OH group of the initial [(C5H4N)2SO3C(OH)], bisulfite addition compound; the [(C5H4N)2SO3C(O)]2, ligand in this case plays the same cubane-forming role as the ligands C(COO,)3O, and (2-C5H4N)2C(COOR)O, above. When excess sodium sulfite is used in similar one-pot reaction mixtures, the monoanionic complexes, [M3Na{(C5H4N)2SO3C(O)}4], (M=Zn, Mn, Co) with an M3NaO4 cubane core, are formed directly from 2,2,-dipyridyl ketone. [source] Heteropolynuclear Palladium Complexes with Pyrazolate and Its 3- tert -Butyl Derivatives: The Effect of Heterometal Ions on the Rate of IsomerizationCHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2006Keisuke Umakoshi Prof. Dr. Abstract The heteropolynuclear complexes [Pd2M,2(,-pz)6] (M,=Ag (1), Au (2); pzH=pyrazole), HT -[Pd2M,2(,-3- tBupz)6] (M,=Ag (3,a), Au (4,a); 3- tBupzH=3- tert -butylpyrazole), and HH -[Pd2Au2(,-3- tBupz)6] (4,b) have been prepared and some of them were structurally characterized. When 3- tert -butylpyrazolate was employed as a bridging ligand, two linkage isomers (head-to-tail (HT) and head-to-head (HH)) arise from the difference in orientation of the substituent groups on the pyrazolate bridges between the two Pd atoms. 1H NMR spectroscopy has been used to identify and to follow the reversible stereochemical rearrangement of the HH isomer of [Pd2Ag2(,-3- tBupz)6] (3,b) to form the HT isomer 3,a in CDCl3 and the HT isomer of [Pd2Au2(,-3- tBupz)6] (4,a) to form the HH isomer 4,b in C6D6. Kinetic studies of the reaction have established the rate law to be ,d(HH)/dt=d(HT)/dt=k2[HH],k1[HT] for 3,b and ,d(HT)/dt=d(HH)/dt=k1[HT],k2[HH] for 4,a, where k1 and k2 denote the rate of isomerization from the HT to the HH isomer and that from the HH to the HT isomer, respectively. For typical runs at 50,°C in C6D6, k1=13.8×10,5 s,1, k2=18.6×10,5 s,1, and Keq=k2/k1=1.24 for 3,b, and k1=1.26×10,5 s,1, k2=3.52×10,5 s,1, and Keq=k1/k2=0.36 for 4,a. Temperature-dependent rate measurements reveal ,H, and ,S, to be 100(1) kJ,mol,1 and 0(3) J,mol,1,K,1 for 3,b and 112(5) kJ,mol,1 and 20(17) J,mol,1,K,1 for 4,a, respectively. The rate of isomerization is essentially unaffected by the concentration of the complex or by the presence of neutral bridging ligands. These data and observations imply that the isomerization involves an intramolecular exchange process. [source] A Nonanuclear Copper(II) Polyoxometalate Assembled Around a ,-1,1,1,3,3,3-Azido Ligand and Its Parent Tetranuclear ComplexCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2005Pierre Mialane Dr. Abstract Reaction of CuII, [,-SiW10O36]8,, and N3, affords three azido polyoxotungstate complexes. Two of them have been characterized by single-crystal X-ray diffraction. Complex KNaCs10[{,-SiW10O36Cu2(H2O)(N3)2}2],26,H2O (1) is obtained as crystals in few hours after addition of CsCl. This linear tetranuclear CuII complex consists in two [,-SiW10O36Cu2(H2O)(N3)2]6, units connected through two WO bridges. When the filtrate is left to stand for one night, a new complex is obtained. From both elemental analysis and IR spectroscopy, it has been postulated that this compound could be formulated K1.5Cs5.5[SiW10O37Cu2(H2O)2(N3)],14,H2O (1,a), showing the loss of one azido ligand per polyoxometalate unit. Finally, when no cesium salt is added to the reaction medium, the nonanuclear complex K12Na7[{SiW8O31Cu3(OH)(H2O)2(N3)}3(N3)],24,H2O (2) is obtained after three days. Compound 2 crystallizes in the R3c space group and consists in three {Cu3} units related by a C3 axis passing through the exceptional ,-1,1,1,3,3,3-azido bridging ligand. Each trinuclear CuII unit is embedded in the [,-SiW8O31]10, ligand, an unprecedented tetravacant polyoxometalate, showing that partial decomposition of the [,-SiW10O36]8, precursor occurs with time in such experimental conditions. Magnetically, complex 1 behaves as two isolated {Cu2(,1,1 -N3)2} pairs in which the metal centers are strongly ferromagnetically coupled (J=+224 cm,1, g=2.20), the coupling through the WO bridges being negligible. The magnetic behavior of complex 2 has also been studied. Relatively weak ferromagnetic couplings (J1=+1.0 cm,1, J2= +20.0 cm,1, g=2.17) have been found inside the {Cu3} units, while the intertrimeric magnetic interactions occurring through the hexadentate azido ligand have been found to be antiferromagnetic (J3=,5.4 cm,1) and ferromagnetic (J4=+1.3 cm,1) with respect to the end-to-end and end-on azido-bridged CuII pairs, respectively. [source] Titanium-Based Molecular Squares and Rectangles: Syntheses by Self-Assembly Reactions of Titanocene Fragments and Aromatic N-HeterocyclesCHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2005Susanne Kraft Dr. Abstract This paper reports on the potential of titanium compounds as building blocks for supramolecular polygons. Self-assembly reactions of low-valent titanocene units and N-heterocyclic bridging ligands lead to novel titanium-based supramolecular squares. Pyrazine (3), 4,4,-bipyridine (4), and tetrazine (5) were used as bridging ligands, and the acetylene complexes [Cp2Ti{,2 -C2(SiMe3)2}] (1) and [(tBuCp)2Ti{,2 -C2(SiMe3)2}] (2) as sources of titanocene fragments. Molecular rectangles can be synthesized by stepwise reduction of the titanocene dichlorides [Cp2TiCl2] and [(tBuCp)2TiCl2] and consecutive coordination of two different bridging ligands. The resulting complexes are the first examples of molecular rectangles containing bent metallocene corner units. Single-crystal X-ray analyses of the tetranuclear compounds revealed the geometric properties of the molecular polygons in the solid state. Comparison of bond lengths and angles in coordinated and free ligands reveals the reduced state of the bridging ligand in the low-valent titanium compounds. The syntheses and properties of these novel, highly air- and moisture-sensitive compounds are discussed. [source] | ||||||||||