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Optical and electronic properties of a novel zinc complex bis[bis(N-octylsalicylideneamineto) zinc(II)] (1) encapsulated in the nanocavities of Mobile Catalytic Material 41 (MCM-41) have been investigated by both experimental measurement and theoretical analysis. Ultraviolet-visible absorption and emission spectra and excited-state lifetimes of 1 in ethanol solution and nanoporous MCM-41 have been recorded. The bathochromic shift of the 0–0 transitions and the shortening of the excited-state lifetimes have been correlated with the reduction of the band gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital accompanying by the increased energies of the frontier molecular orbitals. The variations of the electronic states and band gaps are correlated with the increase of Coulomb integral α and the resonance integral β, which has been confirmed by the theoretical calculations. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Steady-state and dynamic spectroscopic studies have been given in support of the electronic confinement of Zn(phen)[sub 2](NO[sub 3])[sub 2], 1 (phen = 1, 10-phenanthroline), within nanoporous MCM-41. The bathochromic shift of the 0-0 transitions, together with the shortening of the excited state lifetimes have been correlated with the reduction of the HOMO-LUMO band gap accompanying by the increased energies of the frontier orbitals. This trend indicates that the electronic confinement of organic molecules is indeed realized in larger cavities, such as nanocavities of MCM-41. The variations in the 0-0 transitions observed here have also been confirmed by theoretical calculations. [ABSTRACT FROM AUTHOR]

Two inhibitor-containing ‘half-sandwich’ cobalt(II) complexes [(TpPh)Co(X)(CH3OH)m]·nCH3OH ((TpPh)=hydrotris(3-phenylpyrazolyl)borate; 1: X−=N3−, m=1, n=2; 2: X−=NCS−, m=0, n=0) have been synthesized and used as the catalysts in the bicarbonate dehydration reaction. The structures of 1 and 2 were determined by X-ray diffraction analysis, which shows that N3− and NCS− coordinate to the Co(II) ions of 1 and 2, respectively, with the Co&z.sbnd;N bond lengths of 1.992(6) A˚ and 1.901(3) A˚. The coordination geometries of the Co(II) complexes in solution are five-coordinated trigonal bipyramid as revealed by the spectroscopic measurements. The dehydration kinetic measurements of HCO3− are performed by the stopped-flow techniques at pH<7.9. The apparent dehydration rate constant kobs varies linearly with Co(II) complex and H+ concentrations, respectively, and the catalytic activity of 2 is lower than that of 1. The aqua Co(II) complex must be the reactive catalytic species in the catalyzed dehydration reaction and the rate-determining step is the substitution of the labile water molecule by HCO3−. The kobs values increase with increasing reaction temperature, and the large negative entropy of activation also indicates the associative activation mode. The inhibition ability of NCS− is stronger than that of N3−, which can be rationalized by the decreases in the Co&z.sbnd;N(N3−/NCS−) bond lengths and effective atomic charges of the Co(II) ions based on the X-ray crystallographic data and theoretical calculations in this work. [Copyright &y& Elsevier]

This communication reports the dehydration kinetic measurements of HCO3− catalyzed by three inhibitor-containing half-sandwich nickel(II) complexes [TpMe]NiX ([TpMe]=hydrotris(3,5-dimethylpyrazolyl)borate; X−=η2-NO2− (1), N3− (2), NCS− (3)) by employing the stopped-flow techniques at pH <7.9. The five- or six-coordinated aqua complexes must be the reactive catalytic species in the catalyzed bicarbonate dehydration reaction and the rate-determining step is the substitution of the labile water molecule by HCO3−. The dehydration rate constants k of the rate-determining step decrease in the order: 1 (186 M−1 s−1) > 2 (169 M−1 s−1) > 3 (120 M−1 s−1), which is correlated with an increase of the activation energy barrier heights, this being the origin of the variation in the inhibition abilities among the different inorganic anions. [Copyright &y& Elsevier]

The preparation and characterization of the half-sandwich zinc complexes [TpPh]ZnX ([TpPh] = hydrotris(3-phenylpyrazolyl)borate; X− = OH− (1), N3− (2), NCS− (3)) have been described. The bicarbonate dehydration kinetic measurements are performed by the stopped-flow techniques at pH < 7.9. The apparent dehydration rate constant kobsd varies linearly with the total Zn(II) concentration, and the catalytic activity of the model complexes decreases in the order 1>2>3. The catalytic activity decreases with increasing pH, which indicates that the aqua model complex must be the reactive catalytic species in the catalyzed dehydration reaction and the rate-determining step is the substitution of the labile water molecule by HCO3−. The kobsd values increase with increasing reaction temperature, and the apparent activation energies of the model complexes with small inorganic ions are remarkably higher, this being the origin of inhibition. The large negative entropy of activation also indicates an associative mode of activation in the rate-determining step. The inhibition ability of NCS− is strong than that of N3−, which can be rationalized by the decrease in effective atomic charges of the Zn(II) ions as revealed by the theoretical calculations. [Copyright &y& Elsevier]

A series of half-sandwich copper(Il) complexes [Tp[sup Ph]]CuX ([Tp[sup Ph]] = hydrotris(3-phenyl-pyrazolyl)borate; X[sup -] = OH[sup -] (l), N[sub 3, sup -] (2), NCS[sup -] (3)) have been synthesized as models for carbonic anhydrase. The structure of 3 was determined by X-ray diffraction analysis. Crystals of 3 (C[sub 37]H[sub 30]BCuN[sub 9]S) are triclinic, space group P&1macr; with a = 11.997(3) Å, b = 12.116(3) Å, c = 13.384(4) Å, α = 81.088(5)°, β = 79.289(6)°, γ = 68.668(5)°, V = 1772.4(8) ų , 3, and Z = 2. The dehydration kinetic measurements of HCO[sub 3, sup -] are performed by the stopped-flow techniques at pH < 7.9. The apparent dehydration rate constant k[sup d, sub obs] varies linearly with total Cu(ll) concentration, and the catalytic activity of the model complexes decreases in the order 1 > 2 > 3. The catalytic activity decreases with increasing pH indicating that the aqua model complex must be the reactive catalytic species in the catalyzed dehydration reaction and the rate-determining step is the substitution of the labile water molecule by HCO[sup 3, sub -]. The k[sup d, sub obs] values increase with increasing reaction temperature, and the apparent activation energies of the model complexes with inhibitors are remarkably higher than that of the complex with no inhibitors, this being the origin of inhibition. The large negative entropy of activation also indicates an associative mode of activation in the rate-determining step. The inhibition ability of the inhibitor NCS[sup -] is stronger than that of the inhibitor N[sub 3, sub -], which can be rationalized by the decrease in effective atomic charges of the Cu(ll) ions as revealed by the theoretical calculations. [ABSTRACT FROM AUTHOR]

A novel coordination polymer [Zn(BDC)(H2O)2]n 1 (where BDC = 1,4-benzenedicarboxylate), has been synthesized and characterized by X-ray diffraction. 1 crystallizes in the monoclinic space group C2/c, a=15.09(2) A˚, b=5.058(7) A˚, c=12.196(16) A˚, β=103.62(2)°, V=904(2) A˚3, Z=4. The most striking feature of 1 is that it consists of a high-dimensional network structure constructed from BDC-bridged 1-D chains via interchain hydrogen bonds. The coordination sphere of the zinc(II) ion is a distorted tetrahedron completed by four oxygen atoms from two water molecules and two BDC ligands. BDC adopts the bis-monodentated (syn–anti) coordination mode linking two adjacent zinc(II) ions. 1 shows strong blue photoluminescence as the result of the fluorescence from the intraligand emission excited state. [Copyright &y& Elsevier]

A novel heteronuclear compound, [Na8Zn4(CH3CO2)16·2H2O]n 1, with an unusual two-dimensional condensed polymeric structure was successfully synthesized. 1 crystallizes in the triclinic space group P-1, a=9.3332(19) A˚, b=10.511(2) A˚, c=16.152(3) A˚, α=79.78(3)°, β=83.82(3)°, γ=64.85(3)°, V=1410.6(5) A˚3, Z=2. The most striking feature of 1 is that the bridging acetate ligands show four coordination modes within one compound. The luminescence studies show strong blue photoluminescence as the result of the fluorescence from the intraligand emission excited state. [Copyright &y& Elsevier]

In the title compound, [Cu(C15H22NO)2], the CuII cation lies on a centre of symmetry. The coordination geometry about the CuII ion is a parallelogram, formed by the N2O2 donor set of the two bidentate long alkane chain Schiff base imine-phenol ligands. The Cu-N and Cu-O distances are 2.009 (3) and 1.888 (3) Å, respectively. [ABSTRACT FROM AUTHOR]

A series of half-sandwich copper(II) complexes [TpPh]CuX ([TpPh] = hydrotris(3-phenyl-pyrazolyl)borate; X- = OH- (1), N3- (2), NCS- (3)) have been synthesized as models for carbonic anhydrase. The structure of 3 was determined by X-ray diffraction analysis. Crystals of 3 (C37H30BCuN9S) are triclinic, space group P1 with a = 11.997(3) A, b = 12.116(3) A, c = 13.384(4) A, alpha = 81.088(5) degrees, beta = 79.289(6) degrees, gamma = 68.668(5) degrees, V = 1772.4(8) A3, and Z = 2. The dehydration kinetic measurements of HCO3- are performed by the stopped-flow techniques at pH < 7.9. The apparent dehydration rate constant kdobs varies linearly with total Cu(II) concentration, and the catalytic activity of the model complexes decreases in the order 1 > 2 > 3. The catalytic activity decreases with increasing pH indicating that the aqua model complex must be the reactive catalytic species in the catalyzed dehydration reaction and the rate-determining step is the substitution of the labile water molecule by HCO3-. The kdobs values increase with increasing reaction temperature, and the apparent activation energies of the model complexes with inhibitors are remarkably higher than that of the complex with no inhibitors, this being the origin of inhibition. The large negative entropy of activation also indicates an associative mode of activation in the rate-determining step. The inhibition ability of the inhibitor NCS- is stronger than that of the inhibitor N3-, which can be rationalized by the decrease in effective atomic charges of the Cu(II) ions as revealed by the theoretical calculations.