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Bridging Group (bridging + group)
Selected AbstractsCopper Ion Selective Membrane Electrodes Based on Some Schiff Base DerivativesELECTROANALYSIS, Issue 15-16 2003S. Sadeghi Abstract A series of Schiff base derivatives were studied to characterize their abilities as a copper ion carrier in PVC membrane electrodes. The electrode based on 2,2,-[4,4,diphenyl-methanebis(nitrilomethylidyne)]-bisphenol exhibits a Nernstian response for copper ions over the activity range 8.0×10,6,1.0×10,1 mol L,1 with detection limit of about , mol L,1 of copper ion in comparison with two other Schiff bases. The response time, pH effect and other characteristics of the electrodes were studied in a static mode. The effect of the methyl group substitute on Schiff base structure with SO2 bridging group in different positions with respect to OH group was studied. The results show that behavior of the electrodes is not considerably influenced by the position of methyl substitute. The selectivity coefficients were determined with modified fixed interference method (FIM) and matched potential method (MPM). The proposed electrodes comparatively show good selectivity with respect to alkali, alkaline earth and some transition metal ions. The electrodes were used for the determination of copper in black tea, multivitamin and mineral capsule and as an indicator electrode in potentiometric titration of copper ion. [source] Structure,property correlations of sulfonated polyimides.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2004Abstract A series of six-membered sulfonated polyimides were synthesized using 1,4,5,8-naphthalenetetracarboxylic dianhydride, 4,4,-diaminobiphenyl 2,2,-disulfonic acid as the sulfonated diamine, and various nonsulfonated diamine monomers having different bridging groups. These bulky bridging groups have the capacity to increase hydrolytic stability and proton conductivity. Polyimides with bulky bridging groups showed increased solubility but exhibited lower thermal stability. The ion exchange capacity and water uptake reduced with increase in the bulkiness of the bridging group. This was attributed to the increase in the molecular weight of the repeating unit and hence effectively reduced the sulfonic acid content. In low temperatures, the conductivity was lower than Nafion®115 and, with increase in temperature, the conductivity rapidly increased and exhibited better conductivity than Nafion®115. Polyimides with bulky bridging groups 4-amino phenyl sulfone, and 2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane showed higher conductivity than other polyimides and Nafion®115 despite low ion exchange capacity. The hydrolytic stability of the polyimides with bulky bridging groups was higher than the polyimides with less bulky atoms because of the imparted flexibility. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3612,3620, 2004 [source] [{Cp2(tBuSe)Nb}2E] (E = O and Se) with bridging oxide or selenide ligandsACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2008Andrew L. Hector The title compounds, ,-oxido-bis[(tert -butylselenolato)bis(,5 -cyclopentadienyl)niobium(IV)] toluene solvate, [Nb2(C5H5)4(C4H9Se)2O]·C7H8, and ,-selenido-bis[(tert -butylselenolato)bis(,5 -cyclopentadienyl)niobium(IV)], [Nb2(C5H5)4(C4H9Se)2Se], consist of niobium(IV) centres each bonded to two ,5 -coordinated cyclopentadienyl groups and one tert -butylselenolate ligand and are the first organometallic niobium selenolates to be structurally characterized. A bridging oxide or selenide completes the niobium coordination spheres of the discrete dinuclear molecules. In the oxide, the O atom lies on an inversion centre, resulting in a linear Nb,O,Nb linkage, whereas the selenide has a bent bridging group [Nb,Se,Nb = 139.76,(2)°]. The difference is attributable to strong , bonding in the oxide case, although the effects on the Nb,C and Nb,SetBu bond lengths are small. [source] A novel bridged asymmetric binuclear manganese(II) complex with DTPB [DTPB is 1,1,4,7,7-pentakis(1H -benzimidazol-2-ylmethyl)-1,4,7-triazaheptane]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2004Xu-Xiu Yan The crystal structure of the title compound, tetrachloro[,-1,1,4,7,7-pentakis(1H -benzimidazol-2-ylmethyl)-1,4,7-triazaheptane]dimanganese(II) methanol pentasolvate tetrahydrate, [Mn2Cl4(C44H43N13)]·5CH4O·4H2O, contains an asymmetric dinuclear MnII,DTPB [DTPB is 1,1,4,7,7-pentakis(1H -benzimidazol-2-ylmethyl)-1,4,7-triazaheptane] complex with an intra-ligand bridging group (,NCH2CH2N,), as well as several solvate molecules (methanol and water). Both MnII cations have similar distorted octahedral coordination geometries. One MnII cation is coordinated by a Cl, anion and five N atoms from the ligand, and the other is coordinated by three Cl, anions and three N atoms of the same ligand. The Mn,Mn distance is 7.94,Å. A Cl,H,O,H,O,H,N hydrogen-bond chain is also observed, connecting the two parts of the complex. [source] Effect of Cyanato, Azido, Carboxylato, and Carbonato Ligands on the Formation of Cobalt(II) Polyoxometalates: Characterization, Magnetic, and Electrochemical Studies of Multinuclear Cobalt ClustersCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2007Laurent Lisnard Dr. Abstract Five CoII silicotungstate complexes are reported. The centrosymmetric heptanuclear compound K20[{(B-,-SiW9O33(OH))(,-SiW8O29(OH)2)Co3(H2O)}2Co(H2O)2],47,H2O (1) consists of two {(B-,-SiW9O33(OH))(,-SiW8O29(OH)2)Co3(H2O)} units connected by a {CoO4(H2O)2} group. In the chiral species K7[Co1.5(H2O)7)][(,-SiW10O36)(,-SiW8O30(OH))Co4(OH)(H2O)7],36,H2O (2), a {,-SiW10O36} and a {,-SiW8O30(OH)} unit enclose a mononuclear {CoO4(H2O)2} group and a {Co3O7(OH)(H2O)5} fragment. The two trinuclear CoII clusters present in 1 enclose a ,4 -O atom, while in 2 a ,3 -OH bridging group connects the three paramagnetic centers of the trinuclear unit, inducing significantly larger Co-L-Co (L=,4 -O (1), ,3 -OH (2)) bridging angles in 2 (,av(Co-L-Co)=99.1°) than in 1 (,av(Co-L-Co)=92.8°). Weaker ferromagnetic interactions were found in 2 than in 1, in agreement with larger Co-L-Co angles in 2. The electrochemistry of 1 was studied in detail. The two chemically reversible redox couples observed in the positive potential domain were attributed to the redox processes of CoII centers, and indicated that two types of CoII centers in the structure were oxidized in separate waves. Redox activity of the seventh CoII center was not detected. Preliminary experiments indicated that 1 catalyzes the reduction of nitrite and NO. Remarkably, a reversible interaction exists with NO or related species. The hybrid tetranuclear complexes K5Na3[(A-,-SiW9O34)Co4(OH)3(CH3COO)3],18,H2O (3) and K5Na3[(A-,-SiW9O34)Co4(OH)(N3)2(CH3COO)3],18,H2O (4) were characterized: in both, a tetrahedral {Co4(L1)(L2)2(CH3COO)3} (3: L1=L2=OH; 4: L1=OH, L2=N3) unit capped the [A-,-SiW9O34]10, trivacant polyanion. The octanuclear complex K8Na8[(A-,-SiW9O34)2Co8(OH)6(H2O)2(CO3)3],52,H2O (5), containing two {Co4O9(OH)3(H2O)} units, was also obtained. Compounds 2, 3, 4, and 5 were less stable than 1, but their partial electrochemical characterization was possible; the electronic effect expected for 3 and 4 was observed. [source] Evaluation of the Efficiency of the Photocatalytic One-Electron Oxidation Reaction of Aromatic Compounds Adsorbed on a TiO2 SurfaceCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2004Takashi Tachikawa Dr. Abstract The TiO2 photocatalytic one-electron oxidation mechanism of aromatic sulfides with a methylene bridging group (-(CH2)n -, n=0,4) between the 4-(methylthio)phenyl chromophore and the carboxylate binding group on the surface of a TiO2 powder slurried in acetonitrile (MeCN) has been investigated by time-resolved diffuse reflectance (TDR) spectroscopy. The electronic coupling element (HDA) between the hole donor and acceptor, which was estimated from the spectroscopic characteristics of the charge transfer (CT) complexes of the substrates (S) and the TiO2 surface, exhibited an exponential decline with the increasing of the methylene number of S. The determined decay factor (,) of 9 nm,1 also supports the fact that the 4-(methylthio)phenyl chromophore is separated from the TiO2 surface. The efficiency of the one-electron oxidation of S adsorbed on the TiO2 surface, which was determined from the relationship between the amount of adsorbates and the concentration of the generated radical cations, significantly depended on the HDA value, but not on the oxidation potential of S determined in homogeneous solution. [source] | ||||||||||