Layer-by-layer self-assembly and electrocatalytic properties of poly(ethylenimine)-silicotungstate multilayer composite films

Hybrid multilayer films composed of poly(ethylenimine) and the Keggin-type polyoxometalates [ SiW₁₁O₃₉ ]^{8 -} ( SiW₁₁ ) {\left[ {{\hbox{Si}}{{\hbox{W}}_{{11}}}{{\hbox{O}}_{{39}}}} \right]^{{8} - }}\left( {{\hbox{Si}}{{\hbox{W}}_{{11}}}} \right) and [ SiW₁₁Co^II( H₂O )O₃₉ ]^{6 -} ( SiW₁₁Co ) {\left[ {{\hbox{Si}}{{\hbox{W}}_{{11}}}{\hbox{C}}{{\hbox{o}}^{\rm{II}}}\left( {{{\hbox{H}}_2}{\hbox{O}}} \right){{\hbox{O}}_{{39}}}} \right]^{{6} - }}\left( {{\hbox{Si}}{{\hbox{W}}_{{11}}}{\hbox{Co}}} \right) were prepared on glassy carbon electrodes by layer-by-layer self-assembly, and were characterized by cyclic voltammetry and scanning electron microscopy. UV-vis absorption spectroscopy of films deposited on quartz slides was used to monitor film growth, showing that the absorbance values at characteristic wavelengths of the multilayer films increase almost linearly with the number of bilayers. Cyclic voltammetry indicates that the electrochemical properties of the polyoxometalates are maintained in the multilayer films, and that the first tungsten reduction process for immobilized SiW₁₁ and SiW₁₁Co is a surface-confined process. Electron transfer to [ Fe( CN )₆ ]^{3 - /4 -} {\left[ {{\hbox{Fe}}{{\left( {\hbox{CN}} \right)}_6}} \right]^{{3} - /{4} - }} and [ Ru( NH₃ )₆ ]^{3 + /2 +} {\left[ {{\hbox{Ru}}{{\left( {{\hbox{N}}{{\hbox{H}}_3}} \right)}_6}} \right]^{{3} + /{2} + }} as electrochemical probes was also investigated by cyclic voltammetry. The (PEI/SiW₁₁Co)_n multilayer films showed excellent electrocatalytic reduction properties towards nitrite, bromate and iodate.     

Kinetics and mechanism of electron transfer reactions. Osmium(VIII) catalyzed oxidation of mannitol by hexacyanoferrate(III) in aqueous alkaline medium

The kinetics of electron transfer from mannitol to hexacyanoferrate(III), catalyzed by osmium(VIII), has been studied in alkaline medium. The substrate order is complex, whereas it is one with respect to the catalyst. The rate is independent of the concentration of oxidant. Also, the rate increases with increasing concentration of hydroxide ion in a complex manner. A kinetic rate law corresponding to the proposed mechanism has been suggested as follows:

Nickel(II) salophen-type complexes characterization and their thermodynamic studies with diorganotin(IV) dichlorides in chloroform

A u.v.–vis spectrophotometric study of the adduct formation of the nickel(II) Schiff base complexes,([NiL]) where L = [3-methoxysalophen, N,N′-bis(3-methoxysalicylidene)-1,2-phenylenediimine] (1), [4-methoxysalophen, N,N′-bis(4-methoxysalicylidene)-1,2-phenylenediimine] (2), [5-methoxysalophen, N,N′-bis(5-methoxysalicylidene)-1,2-phenylenediimine] (3) and [Salophen, [N,N′-bis(salicylaldehydo)-1,2-phenylenediimine] (4) as donors with R₂SnCl₂ (R = methyl, phenyl and n-butyl) as acceptors have been investigated in chloroform, as solvent. Adducts have been characterized by ¹H, ¹³C and ¹¹⁹Sn NMR, IR and electronic spectroscopy and CHN elemental microanalysis. The formation constants and the thermodynamic free energies were measured using u.v.–vis spectrophotometry titration for 1:1 adduct formation at various temperatures (T = 278 to 308 K). The trend of the adduct formation of the nickel Schiff base complexes with a given tin acceptor decreases as follows:

Thermolytic Transformation of Organometallic Polymers Containing the Cr(CO)<Subscript>5</Subscript> Precursor into Nanostructured Chromium Oxide

Thermal treatment in air of the organometallic polymer (1) results in the formation of nanometer-size metal oxide particles. Cr particles in the 35–85 nm range, mostly 54 nm, immersed in an phosphorus oxides matrix were found. ATG studies in air suggest that the formation of the nanostructures occurs in four steps, the first involving loss of the carbonyl groups of the Cr(CO)₅ fragment. The following steps involve the oxidation of the organic matter and finally the oxidation of the chromium to give the pyrolytic product. The use of these kinds of organometallic polymers as precursors for a general and potential new route to materials having metal/metal oxide nanostructures is discussed.     

The First Structurally Characterized Mn(III) Substituted Sandwich-type Polyoxotungstates

The new polyoxotungstates H₂O (1), · 28H₂O (2) and H₂O (3) were synthesized in aqueous solution and characterized by IR and Raman spectroscopy, energy dispersive X-ray fluorescence and single-crystal X-ray analysis. The anions in 1 and 2 are the first structurally characterized sandwich-type polyoxoanions which contain trivalent manganese atoms. The manganese atoms are coordinated by four oxygen atoms of two Keggin fragments and one water molecule, forming a square pyramid. The manganese(II) containing anions in 3 are linked via Mn–O–W-bonds, forming a two-dimensional network.Dedicated to Prof. M.T. Pope on the occasion of his retirement.     

Formation of hydrates from asymmetric and cyclic ketones in their oxidation by alkaline hexacyanoferrate(III)

Abstract  Alkaline hexacyanoferrate(III) oxidizes 2-methyl-3-pentanone and 2-methylcyclohexanone quite rapidly. Kinetic data show second-order kinetics with respect to hydroxide ion concentrations indicating the formation of hydrates by ketones in aqueous alkaline medium before their reaction with the oxidant. The rate follows direct proportionality with respect to the concentrations of hexacyanoferrate(III) and ketones. Externally added hexacyanoferrate(II) does not affect the reaction velocity indicating the reduction of oxidant takes place after the rate determining step. Orders with respect to various reactants were confirmed by various methods and the overall rate constant of the reaction was calculated by three different variations. Thermodynamic data suggest that 2-methyl-3-pentanone forms the activated complex more easily compared to 2-methylcyclohexanone. Graphical abstract  Second-order in [OH⁻] in the oxidation of 2-methyl-3-pentanone and methyl cyclohexanone by alkaline hexacyanoferrate (III) indicates that oxidation proceeds through the formation of hydrates. Rate constant and thermodynamic parameters at five temperatures were calculated. Mono and dicarboxylic acids were confirmedto be the final oxidation products. Rate law given was—

Relativistic effects in low-lying electronic states of iron

Excited electronic states of Fe I have been calculated using the MRCI Douglas?CKroll?CHess method. Average spin-free excitation energies of the eight lowest even electronic terms ( $\hbox{a}^5\hbox{D}, \hbox{a}^5\hbox{F}, \hbox{a}^3\hbox{F}, \hbox{a}^5\hbox{P}, \hbox{a}^3\hbox{P2}, \hbox{a}^3\hbox{H}, \hbox{b}^3\hbox{F2}, \hbox{and a}^3\hbox{G}$ ) are reported. The RASSI method was employed for calculation of individual J levels of the four lowest terms. All reported values are in good agreement with experiment. Our study pointed out significant relativistic effects even in relatively light element like iron.     

Cluster Oxalate Complexes [W3(μ3-Q)(μ2-Q)3 (C2O4)3(H2O)3]2? (Q=S, Se): Mechanochemical Synthesis and Crystal Structure

Mechanochemical reaction of cluster coordination polymers (Q=S, Se) with solid leads to the cluster core excision with the formation of anionic complexes . Extraction of the reaction mixture with water followed by crystallization gives crystalline (main product) and (1) (minor product). In the case of the Se cluster, the complex could not be isolated, and the treatment of the aqueous extract with PPh₃ gave (2) in a low yield. Alternatively, it was obtained from and in high yield. Both 1 and 2 were characterized by X-ray structure analysis. Dedicated to Academician I. I. Moiseev on the occasion of his 75th birthday and in recognition of his outstanding contribution to cluster chemistry.     

Electrocatalytic Reduction of O2 by a Cu(II)-Substituted Electron-Rich Wheel-Type Oxomolybdate Nanocluster

Catalysis of electron transfer by a Cu-substituted wheel-type oxomolybdate cluster–anion, , (1), is demonstrated. Data provided include aqueous-solution chemistry (stability) studies of 1 and , (2), derivatives of the “plenary” {Mo₁₅₄} anion, , (3). Combined use of cyclic voltammetry and UV–vis spectroscopy shows that, while both 1 and 2 appear to be stable in solution at pH 0.33 (0.5 M H₂SO₄), 1 is more stable than 2 at pH 3 (in 0.2 M Na₂SO₄). Cyclic voltammetric analysis in the presence of O₂ shows that 1 is an electrocatalyst for electron transfer to O₂. Bulk electrolysis of 1 in the presence of O₂ (ca. 1 mM) is used to assess catalyst stability under turnover conditions, and to demonstrate that the final product of electrocatalytic reduction is water, rather than H₂O₂. Finally, control experiments using 1, 2, and CuSO₄ (no oxomolybdate-cluster present), show that catalytic activity is due to specific interaction(s) between Cu ions and the Mo₁₄₂ type oxomolybdate structure of 1.     

Reactions of Unsaturated Quinoline Triosmium Clusters [Os3(CO)9(μ3-η2-C9H5(4-R)N)(μ-H)] (R=Me or H) with Tetramethylthiourea: X-ray Structures of [Os3(CO)8(μ-η2-C9H5(4-Me)N)(η2-SC(NMe2NCH2Me)(μ-H)2] and [Os3(CO)9(μ-η2-C9H6N)(η1-SC(NMe2)2)(μ-H)]

Treatment of the electronically unsaturated 4-methylquinoline triosmium cluster $[\hbox{Os}_{3}\hbox{(CO)}_{9}(\upmu_3\hbox{-}\upeta^{2}\hbox{-}\hbox{C}_{9}\hbox{H}_{5} \hbox{(4-Me)N})(\upmu\hbox{-H})]$ (1) with tetramethylthiourea in refluxing cyclohexane at 81°C gave $[\hbox{Os}_{3}\hbox{(CO)}_{8}(\upmu\hbox{-}\upeta^{2}\hbox{-C}_{9}\hbox{H}_{5} \hbox{(4-Me)N})(\upeta^2\hbox{-SC}(\hbox{NMe}_2\hbox{NCH}_2\hbox{Me})(\upmu \hbox{-H})_2]$ (2) and $[\hbox{Os}_{3}\hbox{(CO)}_{9}(\upmu\hbox{-}\upeta^{2}\hbox{-C}_{9}\hbox{H}_{5}\hbox{(4-Me)N})(\upeta^1\hbox{-SC}(\hbox{NMe}_2)_2)(\upmu\hbox{-H})]$ (3). In contrast, a similar reaction of the corresponding quinoline compound $[\hbox{Os}_{3}\hbox{(CO)}_{9}(\upmu_{3}\hbox{-}\upeta^{2}\hbox{-C}_{9}\hbox{H}_{6}\hbox{N})(\upmu\hbox{-H})]$ (4) with tetramethylthiourea afforded $[\hbox{Os}_{3}\hbox{(CO)}_{9}(\upmu\hbox{-}\upeta^{2}\hbox{-C}_{9}\hbox{H}_{6}\hbox{N})(\upeta^{1}\hbox{-SC(NMe}_{2})_{2})(\upmu\hbox{-H)}]$ (5) as the only product. Compound 2 contains a cyclometallated tetramethylthiourea ligand which is chelating at the rear osmium atom and a quinolyl ligand coordinated to the Os₃ triangle via the nitrogen lone pair and the C(8) atom of the carbocyclic ring. In 3 and 5, the tetramethylthiourea ligand is coordinated at an equatorial site of the osmium atom, which is also bound to the carbon atom of the quinolyl ligand. Compounds 3 and 5 react with PPh₃ at room temperature to give the previously reported phosphine substituted products $[\hbox{Os}_{3}\hbox{(CO)}_{9}(\upmu \hbox{-}\upeta^{2}\hbox{-C}_{9}\hbox{H}_{5}\hbox{(4-Me)N)(PPh}_{3})(\upmu\hbox{-H)}]$ (6) and $[\hbox{Os}_{3}\hbox{(CO}_{9}(\upmu \hbox{-}\upeta^{2}\hbox{-C}_{9}\hbox{H}_{6}\hbox{N)(PPh}_{3})(\upmu\hbox{-H)}]$ (7) by the displacement of the tetramethylthiourea ligand.     

Two Group 8 Carbonyl Clusters Containing a Naked {\varvec{\mu}}_5-Sb Atom

The synthesis and structural characterisation of two novel clusters, 2, and 3, are presented. They are the first examples of osmium and ruthenium clusters containing a naked atom.     

Transport, thermomechanical, and electrode properties of perovskite-type {\left( {{\hbox{L}}{{\hbox{a}}_{0.{75} - x}}{\hbox{S}}{{\hbox{r}}_{0.{25} + x}}} \right)_{0.{95}}}{\hbox{M}}{{\hbox{n}}_{0.{5}}}{\hbox{C}}{{\hbox{r}}_{0.{5} - x}}{\hbox{T}}{{\hbox{i}}_x}{{\hbox{O}}_{{3} - }}_\delta \left( {x = 0 - 0.{5}} \right)

Increasing Sr²⁺ and Ti⁴⁺ concentrations in perovskite-type $ {\left( {{\hbox{L}}{{\hbox{a}}_{0.{75} - x}}{\hbox{S}}{{\hbox{r}}_{0.{25} + x}}} \right)_{0.{95}}}{\hbox{M}}{{\hbox{n}}_{0.{5}}}{\hbox{C}}{{\hbox{r}}_{0.{5} - x}}{\hbox{T}}{{\hbox{i}}_x}{{\hbox{O}}_{{3} - }}_\delta \left( {x = 0 - 0.{5}} \right) $ results in slightly higher thermal and chemical expansion, whereas the total conductivity activation energy tends to decrease. The average thermal expansion coefficients determined by controlled-atmosphere dilatometry vary in the range (10.8?C14.5)?×?10^?6?K^?1 at 373?C1,373?K, being almost independent of the oxygen partial pressure. Variations of the conductivity and Seebeck coefficient, studied in the oxygen pressure range 10^?18?C0.5?atm, suggest that the electronic transport under oxidizing and moderately reducing conditions is dominated by p-type charge carriers and occurs via a small-polaron mechanism. Contrary to the hole concentration changes, the hole mobility decreases with increasing x. The oxygen permeation fluxes through dense ceramic membranes are quite similar for all compositions due to very low level of oxygen nonstoichiometry and are strongly affected by the grain-boundary diffusion and surface exchange kinetics. The porous electrodes applied onto lanthanum gallate-based solid electrolyte exhibit a considerably better electrochemical performance compared to the apatite-type La₁₀Si₅AlO_26.5 electrolyte at atmospheric oxygen pressure, while Sr²⁺ and Ti⁴⁺ additions have no essential influence on the polarization resistance. In H₂-containing gases where the electronic transport in $ {\left( {{\hbox{L}}{{\hbox{a}}_{0.{75} - x}}{\hbox{S}}{{\hbox{r}}_{0.{25} + x}}} \right)_{0.{95}}}{\hbox{M}}{{\hbox{n}}_{0.{5}}}{\hbox{C}}{{\hbox{r}}_{0.{5} - x}}{\hbox{T}}{{\hbox{i}}_x}{{\hbox{O}}_{{3} - }}_\delta $ perovskites becomes low, co-doping deteriorates the anode performance, which can be however improved by infiltrating Ni and $ {\hbox{Ce}}{{\hbox{O}}_{{\rm{2}} - }}_\delta $ v into the porous oxide electrode matrix.     

Kinetics of iron(III)-catalyzed autoxidation of sulfur(IV) in acetate buffered medium

The kinetics of the environmentally important oxidation of sulfur(IV) by oxygen in acetate buffered medium in the presence of Fe(III) and the pH range 5.27–5.70 has been studied. The results were in agreement with the rate law:

Charge transfer interaction and electrical conductivity of poly(vinyl acetals) containing dispersed TCNQ radical anion salts

Charge transfer (CT) interaction is described in semiconducting dispersions of TCNQ complex salt \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Et}_3 {\rm NH}^+ ({\rm TCNQ})_2^{\cdot^{\hskip-3.7pt\hbox{--}}}$\end{document} with and without added TCNQ°, in poly(vinyl acetal) matrices in which the electron-donor moiety is varied. The extent of CT interaction was determined in films and in solution (DMF, acetonitrile, or methylene chloride) through the absorbances at 398 nm (\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm TCNQ}{\ }^{\cdot^{\hskip-3.7pt\hbox{--}}}$\end{document} and TCNQ°) and 857 nm \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm TCNQ}{\ }^{\cdot^{\hskip-3.7pt\hbox{--}}}$\end{document}. Resistivity of the conductive films was related to the stoichiometry of TCNQ species in the films and found to have a minimum at \documentclass{article}\pagestyle{empty}\begin{document}$[{\rm TCNQ}^\circ]/[{\rm TCNQ}{\ }^{\cdot^{\hskip-3.7pt\hbox{--}}}]\simeq 1$\end{document}. Lower resistivities were attained with films having a uniform, densely packed dispersion of microcrystallites which were obtained at a relatively slow solvent removal rate. With this particular complex salt, strong electron-donor polymers are found to be better matrices for semiconductivity.     

Pd(PBu 3 t ) Adducts of Os3(CO)12. Synthesis and Structures of Pd2Os3(CO)12(PBu 3 t )2 and Pd3Os3(CO)12 (PBu 3 t )3

Two new compounds Pd₂Os₃(CO)₁₂ , 13 and Pd₃Os₃(CO)₁₂ , 14 have been obtained from the reaction of with Os₃(CO)₁₂ at room temperature. The products were formed by the addition of two and three groups to the Os–Os bonds of Os₃(CO)₁₂. Compounds 13 and 14 interconvert between themselves by intermolecular exchange of the groups in solution. Compounds 13 and 14 have been characterized by single crystal X-ray diffraction analyses.Dedicated to Professor Brian F. G. Johnson on the occasion of his retirement – 2005.     

Synthesis, characterization and redox properties of macrocyclic Schiff base by reaction of 2,6-diaminopyridine and 1,3- bis (2-carboxyaldehyde phenoxy)propane and its CuII, NiII, PbII, CoIII and LaIII complexes

A new macrocyclic ligand, 1,3,5-triaza-2,4:7,8:,14,15-tribenzo-9,13-dioxacyclohexadeca-1,5-diene (L) was synthesized by reaction of 2,6-diaminopyridine and 1,3-bis(2-carboxyaldehyde phenoxy)propane. Then, its Cu^II, Ni^II, Pb^II, Co^III and La^III complexes were synthesized by a template effect by reaction of 2,6-diaminopyridine and 1,3-bis (2-carboxyaldehyde phenoxy)propane and Cu O, Ni O, Co O, La O, respectively. The ligand and its metal complexes have been characterized by elemental analysis, IR, ¹H- and ¹³C-NMR-, UV-vis spectra, magnetic susceptibility, conductivity measurements, mass spectra and cyclic voltammetry. All complexes are diamagnetic and the Cu^II complex is binuclear. The diamagnetic behaviour of the binuclear complex may be explained by a very strong anti-ferromagnetic interaction in the Cu–Cu pair. The Co^II was oxidised to Co^III.     

Optimal descriptors as a tool to predict the thermal decomposition of polymers

Quantitative structure-property relationship for the thermal decomposition of polymers is suggested. The data on architecture of monomers is used to represent polymers. The structures of monomers are represented by simplified molecular input-line entry system. The average statistical quality of the suggested quantitative structure-property relationships for prediction of molar thermal decomposition function $\hbox {Y}_{\mathrm{d},1/2}$ is the following: $\hbox {r}^{2}=0.970 \pm 0.01$ and $\hbox {RMSE}=4.71\pm 1.01\,(\hbox {K}\times \hbox {kg}\times \hbox {mol}^{-1})$ .