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Coordinated Water (coordinated + water)
Terms modified by Coordinated Water Selected AbstractsNew Approaches to 12-Coordination: Structural Consequences of Steric Stress, Lanthanoid Contraction and Hydrogen BondingEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2010Anthony S. R. Chesman Abstract The anionic dinitrile ligand dicyanonitrosomethanide (dcnm), C(CN)2(NO),, and the anion resulting from its addition product with water, carbamoylcyanonitrosomethanide (ccnm), C(CN)(CONH2)(NO),, have been incorporated into lanthanoid complexes and display unusual ,2(N,O) nitroso coordination modes. (Et4N)3[Ln(ccnm)6] (1Ln; 1Ln = 1La, 1Ce, 1Pr, 1Nd, 1Sm) and (Me4N)3[Ln(ccnm)6] (2Ln; 2Ln = 2La, 2Ce, 2Pr, 2Nd) are systems containing 12-coordinate homoleptic trianionic lanthanoidate complexes. The nitroso groups of the ccnm ligands form three-membered ring chelates with the lanthanoid metal centre, with the asymmetry of the nitroso ,2 interactions dependent upon the intramolecular N,H···O=N hydrogen bonding. Additional intermolecular hydrogen bonding interactions exist between adjacent amide and nitrile groups giving rise to 3D ,-Po and 6,8-connected (412.63)(420.68) networks in 1Ln and 2Ln, respectively. The compounds (Me4N)3[Ln(dcnm)6] (3Ln; 3Ln = 3La, 3Ce, 3Nd, 3Sm) also contain a 12-coordinate trianionic lanthanoidate complex with the nitroso group exhibiting a highly symmetrical ,2 interaction. The sterically crowded environments of [Ln(18-crown-6)(dcnm)3] (4Ln; 4Ln = 4La, 4Ce, 4Pr, 4Nd) result in a shift towards a more asymmetric ,2 bonding of the nitroso group with decrease in the Ln3+ radius. There is a corresponding increase of the Ln,O,N angle, and one ligand is ,1(O) binding in 4Nd. The dcnm ligands in the discrete complexes [La(phen)3(dcnm)(3,x)Clx], x , 0.25 (5) (phen = 1,10-phenanthroline), (Et4N)[Ce(phen)2(dcnm)4] (6a/b, 6c) and [Ce(phen)2(dcnm)Cl2H2O] (7) display a variety of coordination modes. Complex 5 has 1D chains formed by ,,, stacking of adjacent phen co-ligands. Complexes 6 contain the monoanionic complex [Ce(phen)2(dcnm)4], with two geometric isomers present in the crystal structure of 6a/b. Complex 7 forms extended 1D chains via hydrogen bonding between coordinated water and chloride atoms and an extensive array of face-to-face , interactions. [source] Effect of water on zinc (II), cadmium (II) complexes with pyridylimidazole: Theoretical study of stability and electronic spectrumINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2006Yi Liao Abstract The geometry structures of complexes such as [Zn(PIm)2(H2O)] and [Cd(PIm)2(H2O)2] [PIm = (2-(2,-pyridyl) imidazole)] are optimized by density functional theory (DFT) B3LYP methods. On the basis of their stable structures, the stability of the coordinated water existing in the complexes is analyzed quantitatively in terms of the interaction between the central metal and the coordinated water. The interaction energy of the Zn pyridylimidazole complex increased obviously by considering the intermolecular hydrogen bond (OH,N). The theoretical calculation well explained penta- and hexa-coordinated conformation, respectively, in Zn and Cd pyridylimidazole complexes. The spectral properties of the Zn Cd complexes have been studied by time-dependent density functional theory (TD-DFT). The calculation results show that the coordinated waters in Cd complexes have little effect on their spectral properties. While the axially coordinated waters in Zn pyridylimidazole cause a red shift in the absorption wavelength and change the pattern of charge transfer as a result of the effect of polarization from intermolecular hydrogen bond. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Vibrational spectroscopic and force field studies of copper(II) chloride and bromide compounds, and crystal structure of KCuBr3JOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2008Liubov V. Stepakova Abstract Vibrational spectroscopic and force field studies have been performed of 15 related copper(II) chloride and copper(II) bromide compounds, including hydrated salts crystallizing in ternary aqueous systems with alkali and ammonium halides. For halocuprates with distorted octahedral coordination characteristic stretching Raman wavenumbers, corresponding to symmetric stretching CuIIX modes in the equatorial plane, were found in the ranges 247,288 cm,1 for X = Cl, and 173,189 cm,1 for X = Br, while the low-wavenumber stretching modes for the weaker axial CuX interactions varied considerably. The tetrahedral coordination for Cs2CuCl4 and Cs2CuBr4 leads to somewhat lower CuX symmetric stretching wavenumbers, 295 and 173 cm,1, respectively. The assignments of the copper,ligand stretching vibrations were performed with the aid of normal coordinate calculations. Correlations between force constants, averaged CuX stretching wavenumbers and bond distances have been evaluated considering the following aspects: (1) Jahn,Teller tetragonal distortion (axial elongation) of the octahedral copper(II) coordination environment, (2) differences between terminal and bridging halide ligands (3) effects of coordinated water and the influence of outer-sphere cations. Force constant ratios for terminal and bridging metal,halide bonds reveal characteristic differences between planar and tetrahedrally coordinated M2X6 species. In the hydrated copper(II) halide complexes, the halide ligands are more strongly bound than coordinated water molecules. The crystal structure of KCuBr3 (K2Cu2Br6), which was determined to provide structural information for the force field analyses, contains stacks of planar dimeric [Cu2Br6]2, complexes held together by weak axial CuBr interactions. Copyright © 2007 John Wiley & Sons, Ltd. [source] Tetraaquabis(2-methoxybenzaldehyde isonicotinoylhydrazone)cadmium(II) dinitrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2007Zhongwu Fu The CdII centre in the title complex, [Cd(C14H13N3O2)2(H2O)4](NO3)2, occupies a crystallographic inversion centre and is coordinated by two donor N atoms from two 2-methoxybenzldehyde isonicotinoylhydrazone ligands and by four O atoms from four coordinated water molecules, giving a slightly distorted octahedral geometry. There is an extended three-dimensional network structure resulting from O,H...O hydrogen bonds between coordinated water and nitrate anions, and between coordinated water and carbonyl O atoms, and from N,H...O hydrogen bonds between NH groups and nitrate O atoms. [source] Unexpected Aggregation of Neutral, Xylene-Cored Dinuclear GdIII Chelates in Aqueous SolutionCHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2006Jérôme Costa Dr. Abstract We have synthesized ditopic ligands L1, L2, and L3 that contain two DO3A3, metal-chelating units with a xylene core as a noncoordinating linker (DO3A3, = 1,4,7,10-tetraazacyclododecane-1,4,7-triacetate; L1 = 1,4-bis{[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-1-yl]methyl}benzene; L2 = 1,3-bis{[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-1-yl]methyl}benzene; L3 = 3,5-bis{[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-1-yl]methyl}benzoic acid). Aqueous solutions of the dinuclear GdIII complexes formed with the three ligands have been investigated in a variable-temperature, multiple-field 17O NMR and 1H relaxivity study. The 17O longitudinal relaxation rates measured for the [Gd2L1,3(H2O)2] complexes show strong field dependence (2.35,9.4 T), which unambiguously proves the presence of slowly tumbling entities in solution. The proton relaxivities of the complexes, which are unexpectedly high for their molecular weight, and in particular the relaxivity peaks observed at 40,50 MHz also constitute experimental evidences of slow rotational motion. This was explained in terms of self-aggregation related to hydrophobic interactions, , stacking between the aromatic linkers, or possible hydrogen bonding between the chelates. The longitudinal 17O relaxation rates of the [Gd2L1,3(H2O)2] complexes have been analysed with the Lipari,Szabo approach, leading to local rotational correlation times of 150,250 ps and global rotational correlation times of 1.6,3.4 ns (cGd: 20,50 mM), where is attributed to local motions of the Gd segments, while describes the overall motion of the aggregates. The aggregates can be partially disrupted by phosphate addition; however, at high concentrations phosphate interferes in the first coordination sphere by replacing the coordinated water. In contrast to the parent [Gd(DO3A)(H2O)1.9], which presents a hydration equilibrium between mono- and dihydrated species, a hydration number of q = 1 was established for the [Ln2L1,3(H2O)2] chelates by 17O chemical shift measurements on Ln = Gd and UV/Vis spectrophotometry for Ln = Eu. The exchange rate of the coordinated water is higher for [Gd2L1,3(H2O)2] complexes ( = 7.5,12.0×106 s,1) than for [Gd(DOTA)(H2O)],. The proton relaxivity of the [Gd2L1,3(H2O)2] complexes strongly decreases with increasing pH. This is related to the deprotonation of the inner-sphere water, which has also been characterized by pH potentiometry. The protonation constants determined for this process are logKOH = 9.50 and 10.37 for [Gd2L1(H2O)2] and [Gd2L3(H2O)2], respectively. [source] Effect of water on zinc (II), cadmium (II) complexes with pyridylimidazole: Theoretical study of stability and electronic spectrumINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2006Yi Liao Abstract The geometry structures of complexes such as [Zn(PIm)2(H2O)] and [Cd(PIm)2(H2O)2] [PIm = (2-(2,-pyridyl) imidazole)] are optimized by density functional theory (DFT) B3LYP methods. On the basis of their stable structures, the stability of the coordinated water existing in the complexes is analyzed quantitatively in terms of the interaction between the central metal and the coordinated water. The interaction energy of the Zn pyridylimidazole complex increased obviously by considering the intermolecular hydrogen bond (OH,N). The theoretical calculation well explained penta- and hexa-coordinated conformation, respectively, in Zn and Cd pyridylimidazole complexes. The spectral properties of the Zn Cd complexes have been studied by time-dependent density functional theory (TD-DFT). The calculation results show that the coordinated waters in Cd complexes have little effect on their spectral properties. While the axially coordinated waters in Zn pyridylimidazole cause a red shift in the absorption wavelength and change the pattern of charge transfer as a result of the effect of polarization from intermolecular hydrogen bond. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] | ||||||||||