A novel dimer - Heteropolytungstate with a vanadium atom as the centre - Synthesis and structural characterization of (H3O)(4)[VW12O40Na (H2O)(4)](2)

A novel dimer-tungstovanadate, (H3O)(4)[VW12O40Na (H2O)(4)](2), was hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction, IR spectra, TGA-DSC thermal analysis and polarograpy. The yellowish crystal crystallized in the triclinic system, space group P1, a = 1.464 5(3) nm, b = 1.468 6(3) nm, c = 1.411 1(3) nm, alpha = 111.82(2)degrees, beta = 93.17(3)degrees, gamma = 117.47(3)degrees, V = 2.210 6(8) nm(3), Z = 1, D-c = 4.552 g . cm(-3), lambda (Mo K alpha) = 0.071 073 nm, mu = 31.402 mm(-1) F(000) = 2 6481 R = 0.078 0. The title compound consists of two Keggin structure units linked together with two hydrated sodium cations to form a dimer with a porous structure with the pore dimension of 0.766 nm X 0.778 5 nm.

Ion channel behavior of supported bilayer lipid membranes on a glassy carbon electrode

A new kind of solid substrate, a glassy carbon (GC) electrode, was selected to support lipid layer membranes. On the surface of the GC electrode, we made layers of didodecyldimethylammonium bromide (a synthetic lipid). From electrochemical impedance experiments, we demonstrated that the lipid layers on the GC electrode were bilayer lipid membranes. We studied the ion channel behavior of the supported bilayer lipid membrane. In the presence of perchlorate anions as the stimulus and ruthenium(II) complex cations as the marker ions, the lipid membrane channel was open and exhibited distinct channel current. The channel was in a closed state in the absence of perchlorate anions.

Renewable three-dimensional Prussian blue modified carbon ceramic electrode

Prussian blue (PB) supported on graphite powder was prepared by the chemical deposition technique and subsequently dispersed into methyltrimethoxysilane-derived gels to yield a conductive graphite organosilicate composite. The composite was used as the electrode material to fabricate a three-dimensional PB-modified electrode. PB acts as a catalyst, graphite powder ensures conductivity by percolation, the silicate provides a rigid porous backbone, and the methyl groups endow hydrophobicity and thus limit the wetting section of the modified electrode. The chemically modified electrode can electrocatalyze the oxidation of hydrazine, and exhibits a distinct advantage of polishing in the event of surface fouling, as well as simple preparation, good chemical and mechanical stability and good repeatability of surface-renewal. Hydrodynamic voltammetric experiments were performed to characterize the electrode as an amperometric sensor for the determination of hydrazine. (C) 2000 Elsevier Science B.V. All rights reserved.

Oriented polyoxometalate-polycation multilayers on a carbon substrate

In this paper, a new method of fabricating multilayers on a carbon substrate is presented. First, a uniformly charged carbon surface was prepared through molecular design. Then an ultrathin film consisting of layer-pairs of oppositely charged polymeric cationic poly(diallyldimethylammonium chloride) (PDDA) and silicotungstate, SiW12O404- (SiW12), was grown layer-by-layer onto the grafted carbon substrate using a molecular self-assembly technique and an electrochemical method. The technique allows one to prepare highly adherent, dense and smooth films of polyoxometalates with special properties. By combining cyclic voltammetry (CV) and X-ray (XR) reflectometry, it was determined that the average surface density of SiW12 was 2.10 x 10(-10) mol cm(-2), and the thickness increase per adsorption of PDDA-SiW12 was 1.7 +/- 0.2 nm, indicating that the amount of SiW12 anion per one layer adsorption corresponded to a monolayer coverage. Atomic force microscopy (AFM) was also used to examine the surface morphology and determine the grain size distribution and roughness for multilayer films. An increase in root-mean-square (RMS) surface roughness from 7 to 9 Angstrom was observed as the number of layer-pairs in the film increased from 2 to 6. FTIR results showed that the good stability of the multilayer films was due to Coulomb interactions between the SiW12 anion and the polymeric cations PDDA. Moreover, the multilayer films, in acidic aqueous solution, showed good electrocatalytic activity toward the reduction of NO2-, and the catalytic currents increased with increasing the layer numbers of SiW12 adsorption. These characteristics of the multilayer films might find potential applications in the field of sensors and microelectronics devices.

Two new coordination polymers of Co(II) with 1,1 '-(1,4-butanediyl)bis(benzimidazole)

Two new compounds, [CoL2(H2O)(2)](NO3)(2). 8H(2)O (1) and [CoL(H2O)(2)(CH3CO2)(2)]. H2O (2), were obtained from self-assembly of the corresponding metal salts with 1,1'-(1,4-butanediyl)bis(benzimidazole) (L). In 1, each cobalt ion is coordinated to four nitrogen atoms from four molecules of L, and to two water molecules. Metal ions are bridged by L ligands to form infinite (4, 4) networks that contain 44-membered rings. The (4, 4) networks of 1 stack in a parallel fashion, resulting in the formation of large channels in the material. In 2, each cobalt ion is coordinated to two N atoms from two L molecules, two water molecules and two carboxylate O atoms from two acetate anions. Each L molecule is coordinated to two cobalt ions, acting as a bridging ligand as in 1. The bridged cobalt ions form an infinite zigzag chain structure.

Networks with hexagonal circuits in co-ordination polymers of metal ions (Zn-II, Cd-II) with 1,1 '-(1,4-butanediyl)bis(imidazole)

Three new compounds, [ZnL1.5(H2O)(SO4)]. 6H(2)O 1, [ZnL1.5(H2O)(2)][NO3](2). 2H(2)O 2 and [CdL1.5(H2O)(2)(SO4)]. 4H(2)O 3 were obtained from self-assembly of the corresponding metal salts with 1,1'-(1,4-butanediyl)bis(imidazole) (L). In both 1 and 2 zinc ion is five-co-ordinated, showing a less-common trigonal bipyramidal co-ordination polyhedron, while cadmium ion of 3 is six-co-ordinated with a common octahedral arrangement. The sulfate ions of 1 and 3 are co-ordinated, however the nitrate ions of 2 are not. Each of the three compounds is composed of a (6, 3) network with the hexagonal smallest circuit containing six metal ions and six L; each L is co-ordinated to two metal ions, acting as a bridging ligand. In 1 the 2-D sheet of (6, 3) networks is interpenetrated in an inclined mode by symmetry related, identical sheets to give an interlocked 3-D structure, while the (6, 3) networks of both 2 and 3 stack in a parallel fashion to construct frameworks having channels.

Advances in gas-phase electrophilic aromatic substitution reaction

Recent advances in the gas - phase reaction of aromatics with cationic electrophiles are reviewed. The overall substitution reaction is analyzed in terms of its elementary steps. Mechanistic studies have been focused on the structure and reactivity of covalent and non - covalent ionic intermediates, which display a rich chemistry and provide benchmark reactivity models. Particular attention has been devoted to proton transfer reactions, which may occur intra or intermolecularly in arenium intermediates.

Structure characteristics and valence state study for La1-xNaxTiO3 synthesized under high-pressure and high-temperature conditions

By using a novel high-pressure, high-temperature method, perovskite oxides of La1-xNaxTiO3 (x = 0.05, 0.1-0.8) with mixed valence state were synthesized. XRD analysis shows a cubic cell for the samples. Cell volumes of the samples with 0.1 less than or equal to x less than or equal to 0.5 decreases as x increases, and the cell Volume for x = 0.05 is smaller than that for x = 0.1. XPS of surface and EPR measurements indicate that Ti ions are of mixed valence of +3 and +4 and that A-cations vacancies exist in the samples. As x increases, the amount of Ti3+ ions decreases and the amount of A-cations vacancies increases. The valence state of Ti ions can be altered by changing both pressure and temperature. (C) 2000 Elsevier Science B.V. All rights reserved.

Gas-phase ion-molecule reactions of C-60 with the plasma of methyl acrylate

The gas-phase ion-molecule reactions of C-60 with the plasma generated from methyl acrylate under self-chemical ionization conditions were studied by use of a triple-quadrupole mass spectrometer. The adduct cation [C60C3H3O](+) and protonated molecular ion [C60H](+) were observed as the major product ions. The former adduct ion is formed by electrophilic reaction of C-60 with the ion [CH2=CHCO](+), a main fragment ion resulting from the methyl acrylate molecular ion [CH2=CHCOOCH3](+) through alpha cleavage. The latter ion is generated by proton transfer from protonated methyl acrylate to C-60. Semi-empirical quantum chemical calculations have been performed for the eight possible isomers of [C60C3H3O](+) at the Hartree-Fock level by use of the AMI method. The results show three types of cycloadducts as the most stable structures among the possible isomers.

Metal ion and anion coordination in the thiamine-[Pt-II(NO2)(4)](2-) system. Structures of a metal complex, Pt(thiamine)(NO2)(3), and two salts, (H-thiamine)[Pt(NO2)(4)]center dot 2H(2)O and (thiamine monophosphate)(2)[Pt(NO2)(4)]center dot 2H(2)O

Reaction of thiamine or thiamine monophosphate (TMP) with K2Pt(NO2)(4) afforded a metal complex, Pt(thiamine)(NO2)(3) (1), and two salt-type compounds, (H-thiamine)[Pt(NO2)(4)]. 2H(2)O (2) and (TMP)(2)[Pt(NO2)(4)]. 2H(2)O (3), which were structurally characterized by X-ray diffraction. In 1, the square-planar Pt2+ ion is coordinated to the pyrimidine N(1'), a usual metal-binding site, and three NO2- groups. The thiamine molecule exists as a monovalent cation in 1 and a divalent cation in 2 while the TMP molecule is a monovalent cation in 3. In each compound, thiamine or TMP adopts the usual F conformation and forms two types of host-guest-like interactions with anions, which are of the bridging forms, C(2)-H . . . anion . . . pyrimidine-ring and N(4'1)-H(...)anion(...)thiazolium-ring. In 3, there is an additional anion-bridging interaction between the pyrimidine and thiazolium rings of TMP, being of the form C(6')-H . . . anion . . . thiazolium-ring. The salts 2 and 3 show similar hydrogen-bonded cyclic dimers of thiamine or TMP between which the anions are held. Results are compared with those of the other thiamine-platinum complexes. (C) 2001 Elsevier Science B.V. All rights reserved.

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.

Host-guest-like thiamine-anion complexation in thiaminium bis(tetrafluoroborate)

In the title compound, 3-[(4-amino-2-methyl-5-pyrimidin-1-io)methyl]-5-(2-hydroxyethyl)-4-methylthiazolium(2+) bis(tetrafluoroborate), C12H18N4OS2+. 2BF(4)(-), the divalent thiamine cation (in the F conformation) is associated with BF4- anions via two characteristic bridging interactions between the thiazolium and pyrimidinium rings, i.e. C-H . . . BF4- . . . pyrimidinium and N-H . . . BF4- . . . thiazolium interactions. Thiamine molecules are linked by N-H . . .O hydrogen bonds to form a helical chain structure.

Renewable manganous hexacyanoferrate-modified graphite organosilicate composite electrode and its electrocatalytic oxidation of L-cysteine

Manganous hexacyanoferrate (MnHCF) supported on graphite powder was dispersed into methyltrimethoxysilane-derived gels to yield a conductive composite, which was used as electrode material to construct a renewable three-dimensional MnHCF-modifed electrode. MnHCF acts as a catalyst, graphite powder ensures conductivity by percolation, the silicate provides a rigid porous backbone, and the methyl groups endow hydrophobicity and thus limit the wetting section of the modified electrode. Cyclic voltammetry was exploited to investigate the dependence of electrochemical behavior on supporting electrolytes containing various cations. The chemically modified electrode can electrocatalytically oxidize L-cysteine, and exhibits a distinct advantage of polishing in the event of surface fouling, as well as simple preparation, good chemical and mechanical stability, and good repeatability of surface renewal.

Four-level decay model of P-6(7/2) excited state of Eu2+ ion in KMgF3

A four-level model of P-6(7/2) excited state of Eu2+ ion in KMgF3: Eu2+ has been proposed. The decay profiles of the P-6(7/2) excited sstate of Eu2+ are two exponential and the physical implication of each term in the fit equation responsible for the model is interpreted. The data obtained spectroscopically are in good agreement with the fit results.

Gas-phase ion - Molecule reactions of neutral C-60 with the plasmas of alkyl methyl ethers and primary alcohols

The gas-phase ion-molecule reactions of C-60 with the methoxymethyl ion [CH3O=CH2](+) and the 1-hydroxyethyl ion [CH3CH=OH](+) generated under the self-chemical-ionization (self-CI) conditions of alkyl methyl ethers and primary alcohols were studied in the ion source of a mass spectrometer. The adduct ions [C60C2H5O](+) and protonated molecules [C60H](+) were observed as the major products of C-60 with the plasma of alkyl methyl ethers. On the contrary, the reactions of C-60 With the plasmas of primary alcohols produced few corresponding adduct ions. The AM1 semiempirical molecular orbital calculations were carried out on 14 possible structures. The calculated results showed that the most stable structure among the possible isomers of [C60C2H5O](+) is the [3+2] cycloadduct. According to experimental and theoretical results, the pathway for the formation of the adduct was presented.