P-6(7/2)-excited-state decay mechanism and energy-transfer processes in KMgF3 : Eu2+ and KMgF3 : EuX (X = Gd, Ce, Cr)

A four-level decay model in KMgF3:Eu2+ is proposed. The decay profiles of the P-6(7/2) excited state of Eu2+ are biexponential, and the physical implication of each term in the fit equation responsible for the model is interpreted. The evidence obtained spectroscopically for supporting the model is presented. A new method to study energy transfer between Eu2+ and X3+ in KMgF3:Eu-X (X = Gd, Ce, Cr) is established on the basis of the proposed model.

Investigation of proton transfer across the water/1,2-dichloroethane interface by o-phenanthroline using glass micro/nano-pipets and cyclic voltammetry

Facilitated proton transfer across the water/1,2-dichloroethane (DCE) interface supported on the tips of micro- and nano-pipets by o-phenanthroline (Phen) was studied by using cyclic voltammetry. The formed micro- and nano-liquid/liquid interfaces functioned as micro- and nano-electrodes under certain experimental conditions. The dependence of the half-wave potentials on the aqueous solutions acidities was studied and the ratio of association constants between Phen and proton in the aqueous and DCE phases was calculated by the method proposed by Matsuda et al.. The standard rate constant (k(0)) and the transfer coefficient (alpha) evaluated by using nano-pipets were equal to 0.183 +/- 0.054 cm/s and 0.70 +/- 0.09, respectively.

Simple preparation method of multilayer polymer films containing Pd nanoparticles

A simple route to the fabrication of multilayer films containing Pd nanoparticles is described. Following layer-by-layer assembly of PdCl42- and polycation, QPVP-Os (a quaternized poly(4-vinylpyridine) complexed with [Os(bpy)(2)Cl](2+/+)), on 4-aminobenzoic acid-modified glassy carbon electrodes, the three-dimensional Pd nanoparticle multilayer films are directly formed on electrode surfaces via electrochemical reduction of PdCl42- sandwiched between polymers. The growth of PdCl42- is easy on electrode surfaces by electrostatic interaction, and the assembly processes are monitored by cyclic voltammetry and UV-vis spectroscopy. The depth profile analyses by X-ray photoelectron spectroscopy verify the constant composition of the Pd nanoparticle multilayer films. Atomic force microscopy proves that the as-prepared Pd nanoparticles are uniformly distributed with an average particle diameter of 3-7 mn. The resulting Pd nanoparticle multilayer-modified electrode possesses high catalytic activity for the reduction of dissolved oxygen and oxidation of hydrazine compounds in aqueous solution.

Hydrothermal synthesis and crystal structure of [{Cu(2,2 '-bpy)(2)}(2)Mo8O26]: a beta-octamolybdate cluster covalently bonded to two {Cu(2,2 '-bpy)(2)}(2+) coordination complexes via bridging oxo groups

An organic-inorganic hybrid solid, (Cu(2,2'-bpy)(2))(2)Mo8O26, has been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Dark green crystals crystallize in the orthorhombic system, space group Pna21, a = 24.164(5), b = 18.281(4), c = 11.877(2) Angstrom, alpha = 90 degrees, beta = 90 degrees, gamma = 90 degrees, V= 5247(2) Angstrom (3), Z = 4, lambda (MoK alpha) = 0.71073 Angstrom (R(F) = 0.0331 for 5353 reflections). Data were collected on a Siemens P4 four-circle diffractometer at 293 K in the range 1.69 degrees < theta < 25.04 degrees using the omega -scan technique. The structure was solved by the direct method and refined by full-matrix least squares on F-2 using SHELXL-93. The structure of this compound consists of discrete (Cu(2,2'-bpy)(2))(2)Mo8O26 clusters, constructed from beta -octamolybdate subunits ((Mo8O26)(4-)) covalently bonded to two (Cu(2,2'-bpy)(2))(2+) coordination complexes via bridging oxo groups that connect two adjacent molybdenum sites. (C) 2001 Academic Press.

Circular dichroism spectro electrochemical and voltammetric studies of vitamin B-2

Electroreduction of vitamin B-2 (VB2) was studied by in situ circular dichroism (CD) spectroelectrochemistry (SEC) with a long optical path length thin layer cell (LOPLTLC). The results showed that the electroreduction of VB2 in phosphate buffer solution (PBS) (PH 6.8) was a two-electron electrochemical process with weak adsorption of the reactant at the glassy carbon (GC) electrode surface. The CD spectra change of VB2 in the reduction process was explained with the theory of electronic states. We also treated the CD spectra with a singular value decomposition least square (SVDLS) method, and have found not only the number of components and their spectra, but also the fraction distribution of each component in the electroreduction process of VB2.

Electrochemical and spectroscopic study of vitamin D-2 by in situ thin layer CD spectroelectrochemistry

The electrooxidation of vitamin D-2 (VD2) was studied by cyclic voltammetry and in situ circular dichroic (CD) spectroelectrochemistry for the first time, The mechanism of electrooxidation and some useful kinetic and adsorption parameters were obtained. The results showed that the oxidation of VD2 in ethanol solution is an irreversible diffusion controlled process following a weak adsorption of the electroinactive product at a glassy carbon electrode, which blocks the electrochemical reaction. The electrooxidation occurs mainly at the triene moieties of the VD2 molecule. The CD spectroelectrochemical data were treated by the double logarithm method together with nonlinear regression, from which the formal potential E-0 = 1.08 V, alphan = 0.245, the standard electrochemical rate constant k(0) = 4.30( +/- 0.58) x 10(-4) cm s(-1) and the adsorption constant beta = 1.77(+/- 0.25) were obtained. (C) 2001 Elsevier Science B.V. All rights reserved.

Sol-gel synthesis and properties of Ce1-xGdxO2-x/2 solid solutions

A series of solid electrolytes Ce1-xGdxO2-x/2(x=0 similar to0.6) was prepared by sol-gel method. The structure, thermal expansion coefficient and electrical properties of the solid solutions were systematically studied. XRD data showed that a complete cubic fluorite structure was formed at 160 degreesC. The purity of the product prepared by the sol-gel method is higher, the grain size is uniformly smaller. They were easily sintered into highly dense ceramic pellets at 1 300 degreesC. The sintering temperature was significantly lower than that by traditionally high temperature solid phase reaction method. The thermal expansion coefficient of Ce0.8Gd0.2O1.9, determined from high- temperature XRD data, is 8. 125 X 10(-6) K-1. Impedance spectra analyses showed that the grain-boundary resistance of the solid electrolyte prepared by sol-gel method was reduced or even eliminated. The conductivity of Ce0.8Gd0.2O1.9 is 5.26 X 10(-3) S/cm at 600 degreesC. The activation energy (E-a) is 0.82 eV.

Photochemical synthesis and crystal structure of a charge transfer salt [HMDH2][(H2PMoMo11O40)-Mo-v]center dot 2AA center dot 3H(2)O center dot DMF

The title supramolecular compound, [HMDH2][(H2PMoMo11O40)-Mo-V] . 2AA . 3H(2)O . DMF (HMD = hexamethylene diamine; AA=acetaldehyde; DMF=N,N-dimethyl formamide), has been photochemically synthesized by using elemental analysis, IR, solid diffusion reflectance, electronic spectra, ESR spectra and X-ray single-crystal analysis. The crystallographic data: triclinic, P (1) over bar, a=14.092(2), b=14.347(3), c=14.358(3)Angstrom, alpha = 75.10(3), beta = 80.70(3), gamma = 80.73(3)degrees, V = 2746.6(10)Angstrom (3), Z = 2, M-r = 2081.68, D-c=2.517g/cm(3), F(000) =1970, mu (MoK alpha) =2.766mm(-1). The structure has been refined to R =0.0832 and wR=0.2638, by full-matrix least-squares method. The title compound is composed of hexamethylene diamine, two acetaldehyde molecules, three water molecules, one N,N-dimethylformamide and [(H2PMoMo11O40)-Mo-V](2-) heteropoly anion.

Study of the conductivity and side chain mobility of a comb-like polymer electrolyte using the dynamic mechanical method

Using poly(styrene-co-maleic anhydride) as a backbone and poly(ethylene glycol) methyl ether (PEGME) with different molecular weights as side chains, three comb-like polymers and their Li salt complexes were synthesized. The dynamic mechanical properties and conductivities were investigated. Results showed that the polymer electrolytes possess two glass transitions: alpha -transition and beta -transition, and the temperature dependence of the ionic conductivity shows WLF (Williams-Landel-Ferry) behavior. Based on the time-temperature equivalence principle, a master curve was constructed by selecting T-beta as reference temperature. The values of the WLF parameters (C-1 and C-2) were obtained and were found to be almost independent of the length of the PEGME side chain and the content of Li salt. By reference to T-0 = 50 degreesC. the relation between log tau (c) and c was found to be linear. The master curves are displaced progressively to higher frequencies as the molecular weight of the side chain is increased. The relation between log tau (n) and the molecular weight of the side chain is also linear. (C) 2001 Elsevier Science B.V. All rights reserved.

Two dimensional nuclear magnetic resonance analysis of ruthenium-(4,4'-dimethyl-2,2'-bipyridine)(2) (2,2'-bipyridine-4,4'-dicarboxylic acid) (PF6)(2)

The (1) H and C-13 NMR spectra are reported for Ru(4, 4'-dimethyl-2,2'-bipyridene)(2) (2,2'-bipyridine-4,4'-dicarboxylic acid) (PF6)(2) that can be used as a new electrochemiluminescent probe in immunoasssay and nucleic acid hybridization assay. Because of the effect ol:Ru atom ligands and complex steric configuration, it is difficult to attribute spectra of the title molecular, By using 2D (1) H-(1) H COSY and (1) H-C-13 HETCOR method, the proton and C-13 NMR spectra are assigned completely, which provides a satisfactory method to quantitative and qualitative, analysis of the title moleculer in the further study.

Syntheses and crystalline structures of clusters Co-3(CO)(7)(mu(3)-S)(mu, eta(2)-SCNR2)

Through the reaction of Co-2(CO)(8) with four thiuram [R2NC(S)S](2), four new sulfur-capped trinuclear cobalt carbonyl clusters Co-3 (CO)(7) (mu(3)-S) (mu, eta(2)-S* C* NR2) ( I : R = Me; I : R = Et; II : R = i-Pr; IV : NR= -N [GRAPHICS] were prepared and characterized by elementary analysis, IR,H-1 NMR and MS spectroscopy. The crystal structure of the cluster Co-3(CO)(7)(mu(3)-S)[mu, eta(2)-S*C*N (i-Pr)(2)]( III) was determined by X-ray single crystal diffraction method. The crystal of m is monoclinic, belonging to space group P2(1)/n, and the cell parameters are as follows: a = 1, 145 2(2) nm, b = 1. 502 8(3) nm, c = 1, 214 4(2) nmj alpha = 90 degrees, beta = 92, 15(3)degrees, gamma = 90 degrees; V = 2. 088 5(7) nm(3) , Z = 4, F (000) = 1 096, D-c = 1. 747 mg . m(-3), mu = 2. 588 mm(-1), R=0. 040 7, R-w=0. 062 4, The structural analysis shows that cluster II has a pyrimidal Co3S framework and contains a heterocylic bridging bidentate ligand [mu, eta(2)-S* C* N (i-Pr)(2)] linked to the Co2 and Co3 atoms of the cluster by a cobalt-carbon and a cobalt-sulfur bond respectively.

Synthesis, crystal structure and properties of H-8[P4W14O58Na4 (H2O)(20)] center dot 16H(2)O

A novel heteropoly tungstophosphates, H-8[P4W14O58Na4(H2O)(20)] . 16H(2)O, was synthesized by hydrothermal method and characterized by elemental analysis, IR spectrum and single-crystal X-ray structure analysis. The thermal stability of the compound was investigated by using TG-DTA. The crystal is triclinic system with space group P (1) over bar, a = 1. 137 9(2) nm, b=1. 363 2(3) nm, c=1. 627 1(3) nm; alpha=78. 20(3)degrees, beta=71, 20(3)degrees, gamma= 71. 62(3)degrees; V = 2. 252 5(8) nm(3), Z=1, M-r= 4 374. 38, D-c = 3. 225 mg/cm(3), mu = 18. 007 mm(-1), F(000)=1 972, R=0. 074 2, R-w=0. 200 4. The result of structure analysis shows that the anion of the compound consists of two PW7O29Na2(H2O)(10) subunits and two linked phosphorous atoms. A kind of microporous with size of 0. 661 4 nm X 0. 318 9 nm was formed in the crystal structure.

Determination of surface pK(a) of SAM using an electrochemical titration method

A self-assembled monolayer (SAM) of 3-mercaptopropionic acid (HSCH2CH2COOH) was formed on a gold electrode. The effect of the charge of the end group on the electrochemical response of Fe(CN)(6)(3-) at the SAM modified electrode was studied by using cyclic voltammetry. At high pH, when the -COOH groups are dissociated, Fe(CN)(6)(3-) current is suppressed; as the solution pH is lowered, Fe(CN)(6)(3-) current increases. The electrochemical titration curve was obtained by correlating the currents to the different electrolyte pH values, from which the surface pK(a) was obtained to be 5.2+/-0.1. Furthermore, a calculation equation was presented to simulate the electrochemical titration. As comparison, the surface pK(a) was also measured by contact angle titration as 5.6+/-0.1. The surface pK(a) values determined by the two methods in our work are consistent and accurate.

Electrochemiluminescent determination of perchlorate by solvent extraction in the presence of Ru(bpy)(3)(2+)

A novel method for the highly sensitive determination of perchlorate was proposed. It was based on solvent extraction in the presence of Ru(bpy)(3)(2+) followed by Ru(bpy)(3)(2+) electrochemiluminescent determination. A linear calibration was obtained over the range of 0.1 to 10 mu mol l(-1) with a correlation coefficient of 0.998. The detection limit (S/N = 3) was 5.0 x 10(-8) mol l(-1). The relative standard deviation for 10 replicates of 1 mu mol l(-1) perchlorate was 1.6%. Interference studies suggest that this method is selective for the determination of perchlorate. Application of this method to the highly sensitive determination of other anions is suggested. (C) 1999 Elsevier Science S.A. All rights reserved.

A nickel molybdenum phosphate with tunnel: Hydrothermal synthesis and structure of (NH3CH2CH2NH3)(4)center dot(NH3CH2CH2NH2)center dot Na center dot[Ni2Mo12O30(PO4)(HPO4)(4)(H2PO4)(3)]center dot 6H(2)O

A nickel molybdenum phosphate, (NH3CH2CH2NH3)(4).(NH3CH2CH2NH2). Na .[Ni2Mo12O30(PO4)(HPO4)(4)(H2PO4)(3)]. 6H(2)O, invoicing molybdenum present in V oxidation, has been hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction. Deep brown-red crystals are formed in the triclinic system, space group P (1) over bar, a = 12,011(2), b = 14,612(3), c = 21.252(4) Angstrom, alpha = 80.54(2)degrees, beta = 83.10(2)degrees, gamma = 76.29(2)degrees, V = 3561.4(12) Angstrom(3), Z = 2, lambda(MoK alpha) = 0.71073 Angstrom (R(F) = 0.0529 for 9880 reflections), Data mere collected on a Siemens P4 diffractometer at 20 degrees C in the range of 1.75 degrees < theta < 23.02 degrees using the omega-scan technique. The structure was solved by direct methods using the program SHELXTL-93 and refined with the method of fun-matrix least-squares on F-2. The structure of the title compound may be considered to be two [Mo6O15(HPO4)(H2PO4)(3)](5-) units bonded together with a nickel atom, although several P-O groups are not protonated on account of coordination with a Na+ cation, The one-dimensional tunnels were formed in the solid of the title compound. A probe reaction of the oxidation of acetaldehyde with H2O2 using the title compound as catalyst was carried out in a liquid- solid system, showing that the title compound had high catalytic activity in the reaction, (C) 1999 Academic Press.