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Monomeric Complex (monomeric + complex)
Selected AbstractsMono-, Di- and Polymeric Calcium and Gadolinium Complexes of the Tripodal Ligand 2,2,,2,,-Nitrilotribenzoic AcidEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2005Stefan Wörl Abstract Three novel carboxylate-bridged complexes incorporating the tripodal N,O ligand 2,2,,2,,-nitrilotribenzoic acid H3L of formula [CaII(H2L)(OH2)4][(H2L)]·4H2O (1), [CaII(OH2)4]-[CaII(L)(OH2)2]2·7H2O (2) and [GdIII(L)(OH2)3]2[GdIII(L)-(OH2)4]2·13H2O (3) were synthesized and characterized by X-ray crystallography. In all three complexes, the ligand H3L binds to the metal centre only by its three carboxylate donors, leaving the bridgehead nitrogen atom nonbonding. The calcium(II) ion in the monomeric complex 1 is distorted pentagonal-bipyramidal coordinated, the +1 charge of the complex cation [CaII(H2L)(OH2)4]+ is balanced by an H2L, anion and both units are connected by hydrogen bonds. The polymeric compound 2 displays a one-dimensional chain structure, in which two [CaII(L)]2, units form a dimeric structure and are connected by hydrated CaII ions. 3 contains two different [GdIII(L)(OH2)n] dimers. In one of them the two GdIII ions are linked by two monoatomic carboxylate O-bridges showing a short Gd···Gd distance of 3.99 Å. In the second, a syn - anti carboxylate 1,3-bridge with a longer Gd···Gd distance of 4.96 Å is observed. Magnetic measurements of 3 show paramagnetic behaviour with weak antiferromagnetic coupling. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Molecular complementarity between tetracycline and the GTPase active site of elongation factor TuACTA CRYSTALLOGRAPHICA SECTION D, Issue 11 2006Susan E. Heffron Two crystal forms of a complex between trypsin-modified elongation factor Tu,MgGDP from Escherichia coli and the antibiotic tetracycline have been solved by X-ray diffraction analysis to resolutions of 2.8 and 2.1,Å, respectively. In the P21 form, cocrystals were grown from a solution mixture of the protein and tetracycline. Six copies of the trypsin-modified EF-Tu,MgGDP,tetracycline complex are arranged as three sets of dimers in the asymmetric unit. In the second crystal form, tetracycline was diffused into P43212 crystals, resulting in a monomeric complex in the asymmetric unit. Atomic coordinates have been refined to crystallographic R factors of 18.0% for the P21 form and 20.0% for the P43212 form. In both complexes, tetracycline makes significant interactions with the GTPase active site of EF-Tu. The phenoldiketone moiety of tetracycline interacts directly with the Mg2+, the ,-phosphate group of GDP and two amino acids, Thr25 and Asp80, which are conserved in the GX4GKS/T and DX2G sequence motifs found in all GTPases and many ATPases. The molecular complementarity, previously unrecognized between invariant groups present in all GTPase/ATPases and the active moiety of tetracycline, may have wide-ranging implications for all drugs containing the phenoldiketone moiety as well as for the design of new compounds targeted against a broad range of GTPases or ATPases. [source] Crystallization of a ZRANB2,RNA complexACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 12 2008Fionna E. Loughlin ZRANB2 is a zinc-finger protein that has been shown to influence alternative splice-site selection. The protein comprises a C-terminal arginine/serine-rich domain that interacts with spliceosomal proteins and two N-terminal RanBP2-type zinc fingers that have been implicated in RNA recognition. The second zinc finger bound to a six-nucleotide single-stranded RNA target sequence crystallized in the hexagonal space group P6522 or P6122, with unit-cell parameters a = 54.52, b = 54.52, c = 48.07,Å; the crystal contains one monomeric complex per asymmetric unit. This crystal form has a solvent content of 39% and diffracted to 1.4,Å resolution using synchrotron radiation. [source] Liquid-Injection MOCVD of ZrO2 Thin Films using Zirconium Bis(diethlyamido)-bis(di- tert -butylmalonato) as a Novel Precursor,CHEMICAL VAPOR DEPOSITION, Issue 5 2006R. Thomas Abstract The stabilization of highly reactive amide complexes of zirconium diethylamide with malonates as chelating ligands leads to a stable six-coordinated monomeric complex which shows promise for CVD applications. This novel precursor, zirconium bis-(diethylamido)bis(di- tert -butylmalonato) zirconium, [Zr(NEt2)2(dbml)2], has been characterized and tested in a production-type MOCVD reactor for ZrO2 thin-film deposition. Up to 450,°C, the ZrO2 films are amorphous, and above 475,°C films they are crystalline. Atomic force microscopy (AFM) shows a lower roughness (,2.5Å) for as-deposited amorphous films compared to crystalline films (,6.0,Å); however, smooth crystalline films can be obtained by post-deposition annealing of amorphous films. Electrical properties are investigated for Pt/ZrO2/SiOx/Si capacitor structures. Relative dielectric permittivity reaches a bulk value of 24, and leakage currents for typically 4,nm thick films are below 10,4,A,cm,2 at a bias of ,1,V. Hence, the precursor shows promising properties for possible application in the deposition of high- k gate oxide (MIS) and high- k dielectric (MIM) structures. [source] Rationally Designed, Polymeric, Extended Metal,Ciprofloxacin ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2005Dong-Rong Xiao Dr. Abstract Reactions of the antimicrobial fluoroquinolone ciprofloxacin (cfH) with metal salts in the presence of aromatic polycarboxylate ligands or under basic conditions produce fourteen new metal,cfH complexes, namely, [Ba2(cf)2(1,4-bdc)(H2O)2],H2O (1), [Sr6(cf)6(1,4-bdc)3(H2O)6],2,H2O (2), [M2(cfH)2(bptc)(H2O)2],8,H2O (M = Mn(3) and Cd(4)), [M(cfH)(1,3-bdc)] (M = Mn(5), Co(6), and Zn(7)), [Zn2(cfH)4(1,4-bdc)](1,4-bdc),13,H2O (8), [Ca(cfH)2(1,2-Hbdc)2],2,H2O (9) and [M(cf)2],2.5,H2O (M = Mn(10), Co(11), Zn(12), Cd(13), and Mg(14)) (1,4-bdc = 1,4-benzenedicarboxylate, bptc = 3,3,,4,4,-benzophenonetetracarboxylate, 1,3-bdc = 1,3-benzenedicarboxylate, 1,2-bdc = 1,2-benzenedicarboxylate). Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric analyses. The structures of 1 and 2 consist of unique two-dimensional arm-shaped layers. Compounds 3 and 4 are isostructural and feature one-dimensional structures formed from the interconnection of [M2(cfH)2(H2O)2] dimers with bptc ligands. Compounds 5,7 are isostructural and contain double-chain-like ribbons constructed from [M2(cfH)2(CO2)2] dimers and 1,3-bdc. Compound 8 consists of a pair of [Zn(cfH)2]2+ fragments bridged by a 1,4-bdc into a dinuclear dumbbell structure. Compound 9 is a neutral monomeric complex. To the best of our knowledge, compounds 1,9 are the first examples of metal-quinolone complexes that contain aromatic polycarboxylate ligands. Compounds 10,14 are isostructural and exhibit interesting two-dimensional rhombic grids featuring large cavities with dimensions of 13.6×13.6 Å. Up to now, polymeric extended metal,cfH complexes have never been reported. [source] Variable Coordination Modes of Benzaldehyde Thiosemicarbazones , Synthesis, Structure, and Electrochemical Properties of Some Ruthenium ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2008Swati Dutta Abstract Reaction of benzaldehyde thiosemicarbazones [H2LR, where H2 stands for the two protons, the hydrazinic proton, and the phenyl proton at the ortho position, with respect to the imine function and R (R = OCH3, CH3, H, Cl, and NO2) for the para substituent] with [Ru(PPh3)2(CO)2Cl2], carried out in refluxing ethanol, afforded monomeric complexes of type [Ru(PPh3)2(CO)(HLR)(H)]. The crystal structure of the [Ru(PPh3)2(CO)(HLNO2)(H)] complex was determined. The thiosemicarbazone ligand is coordinated to the ruthenium center as a bidentate N,S-donor ligand forming a four-membered chelate ring. When the reaction of the thiosemicarbazones with [Ru(PPh3)2(CO)2Cl2] was carried out in refluxing toluene, a family of dimeric complexes of type [Ru2(PPh3)2(CO)2(LR)2] were obtained. The crystal structure of [Ru2(PPh3)2(CO)2(LCl)2] was determined. Each thiosemicarbazone ligand is coordinated to one ruthenium atom, by dissociation of the two protons, as a dianionic tridentate C,N,S-donor ligand, and at the same time the sulfur atom is also bonded to the second ruthenium center. 1H NMR spectra of the complexes of both types are in excellent agreement with their compositions. All the dimeric and monomeric complexes are diamagnetic (low-spin d6, S = 0) and show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry of the [Ru(PPh3)2(CO)(HLR)(H)] and [Ru2(PPh3)2(CO)2(LR)2] complexes show the ruthenium(II),ruthenium(III) oxidation within 0.48,0.73 V vs. SCE followed by a ruthenium(III),ruthenium(IV) oxidation within 1.09,1.47 V vs. SCE. Potentials of both the oxidations are found to correlate linearly with the electron-withdrawing character of the substituent R. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Tripyrrinatocadmium Complexes: Enforcing Supramolecular Aggregation by a Large IonEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2007Martin Bröring Abstract A newly developed method for the preparation of free base tripyrrin ligands HTrpy by cyanide-promoted demetalation of nickel chelates TrpyNiNCO was used in order to explore the chemistry of cadmium tripyrrins TrpyCdX with a variety of anionic co-ligands X. The introduction of the large CdII ion into the tripyrrin N3 coordination site was accomplished by the use of cadmium acetate as the metal precursor. Ligand exchange experiments using sodium salts of different anions disclose a marked tendency for pentacoordination, which is achieved either by the formation of chelates or of 1D coordination polymers that form as a consequence of the size of the central metal. The attempted introduction of chlorido, iodido, or cyanato ligands thus leads mainly to decomposed material, while the use of 1,1,1-trifluoracetylacetonate, salicylate, and acetate ligands results in stable, pentacoordinate and monomeric complexes with the external ligand bound as a four- or six-membered O,O -chelate ring. With the pseudohalogenido ligands thiocyanate, selenocyanate, and azide as well as with the weakly coordinating trifluoroacetate 1D coordination polymers with a variety of chain structures were obtained and investigated by X-ray diffraction studies. Interestingly TrpyCdN3 is present in the crystal as a coordinatively and hydrogen-bonded methanol adduct with a dimeric repeating subunit. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] First Example of a Gold(I) N -Heterocyclic-Carbene-Based Initiator for the Bulk Ring-Opening Polymerization of L -LactideEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2006Lipika Ray 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) [source] Titanium Imido Complexes of Cyclooctatetraenyl LigandsCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2005Simon C. Dunn Dr. Abstract Reaction of [Ti(NR)Cl2(py)3] (R=tBu or 2,6- iPr2C6H3) with K2[COT] (COT=C8H8) or Li2[COT,,] (COT,,=1,4-C8H6(SiMe3)2) gave the monomeric complexes [Ti(NR)(,8 -COT)] or [Ti(NR)(,8 -COT,,)], respectively. The pseudo-two coordinate, ,pogo stick, geometry for these complexes is unique in both early transition-metal and cyclooctatetraenyl ligand chemistry. In contrast, reaction of [Ti(N-2,6-Me2C6H3)Cl2(py)3] with K2[COT] gave the ,-imido-bridged dimer [Ti2(,-N-2,6-Me2C6H3)2(,8 -COT)2]. It appears that as the steric bulk of the imido and C8 ring substituents are decreased, dimerisation becomes more favourable. Aryl imido COT complexes were also prepared by imido ligand exchange reactions between anilines and [Ti(NtBu)(,8 -COT)] or [Ti(NtBu)(,8 -COT,,)]. The complexes [Ti(NtBu)(,8 -COT)], [Ti(N-2,6- iPr2C6H3)2(,8 -COT)] and [Ti2(,-N-2,6-Me2C6H3)2(,8 -COT)2] have been crystallographically characterised. The electronic structures of both the monomeric and dimeric complexes have been investigated by using density functional theory (DFT) calculations and gas-phase photoelectron spectroscopy. The most striking aspect of the bonding is that binding to the imido nitrogen atom is primarily through , and , interactions, whereas that to the COT or COT,, ring is almost exclusively through , symmetry orbitals. A DFT-based comparison between the bonding in [Ti(NtBu)(,8 -COT)] and the bonding in the previously reported late transition-metal ,pogo-stick, complexes [Os(NtBu)(,6 -C6Me6)], [Ir(NtBu)(,5 -C5Me5)] and [Ni(NO)(,5 -C5H5)] has also been undertaken. [source] | ||||||||||