Determination of the stability constant of cobalt-substituted mono-lacunary Keggin-type polyoxometalate and its electrocatalytic water oxidation performance

The anion form of a cobalt-substituted mono-lacunary Keggin-type polyoxometalate (POM) complex in aqueous solution was identified as [Co(H₂O)(H₃PW₁₁O₃₉)]^2? and its stability constant was determined to be 5.19 × 10⁴ by spectrophotometry. Additionally, the electrocatalytic performances toward water oxidation of different concentrations of [Co(H₂O)(H₃PW₁₁O₃₉)]^2? were investigated in the neutral phosphate buffer solution, and it was found that [Co(H₂O)(H₃PW₁₁O₃₉)]^2? anion itself has little activity; the activity of [Co(H₂O)(H₃PW₁₁O₃₉)]^2? solution actually results from dissociated [Co(H₂O)₆]²⁺. This work provides a simple way to understand the origin of catalytic water oxidation activity of a POM-based complex.     

Synthesis of palladium–polypyrrole nanocomposite and its electrocatalytic properties in the oxidation of formaldehyde

Three alternative methods were developed for the synthesis of modifying palladium–polypyrrole layers on the surface of an inert electrode. Their electrocatalytic activity toward formaldehyde under inert atmosphere was checked. All the suggested methods are one-stage and allow synthesis of a film on the electrode surface from a solution containing a palladium salt and pyrrole in the absence of other active reagents. The electrochemical methods (potentiodynamic and double cathodic and anodic pulses techniques) in an aqueous medium give films with poorly reproducible electrocatalytic properties, while the chemical redox synthesis affords films with reproducibly high electroactivity toward methylene glycolate.     

Synthesis and characterization of two binuclear nickel(II) complexes of thiophenol-based “end-off” compartmental ligands and their application as catalysts for selective oxidation of sulfides

Reaction of the binucleating S-protected ligand precursors 2-(N,N-dimethylthiocarbamato)-5-methylisophthalaldehyde di-2′-hydroxy anil (I) and 2-(N,N-dimethylthiocarbamato)-5-methylisophthalaldehyde di-2′-hydroxy 5′-methyl anil (II) with nickel(II) acetate tetrahydrate in the presence of pyrazole afforded the binuclear nickel(II) complexes [L^INi₂(pz)] (1) and [L^IINi₂(pz)] (2), respectively. The complexes have been characterized by routine physicochemical studies as well as by X-ray single crystal structure analysis. In both complexes, Ni(II) ions are doubly bridged by the thiophenolic sulfur of the pentadentate Schiff base ligand and a pyrazolate group. Efficient protocols for the oxidation of sulfides to sulfoxides with high selectivities, catalyzed by binuclear μ-thiophenolato-μ-pyrazolatonickel(II) in the presence of urea hydrogen peroxide (UHP) were explored. We obtained predominantly the monooxygenated product. The resulting products are obtained in good to excellent yields within a reasonable time.     

Surface oxidation and water desorption of CdS

The surface oxidation and HP desorption of powder CdS were studied by means of X-ray photoetectron spectroscopy (XPS), quadrupole mass spectrometry (QMS) and in-situ FTIR. The results show that with the changes of surface composition and the elongation of store time of CdS there are four types of H2O thermally desorbed at different temperatures. It has also been found that through high-temperature air treatment for a short time the oxidized surface layer of CdS can prevent O2 and H2O in air from further attacking the inner CdS molecules.     

Synthesis,structure and reactivity of complexes containing a transition metal–bismuth bond

The transition metal chemistry of bismuth has attracted significant interest since the 1970s. The low cost and high abundance of bismuth(III) reagents, such as the trihalides, makes them ideal starting materials and the size of the bismuth centre allows three- and higher-coordinate complexes to be synthesised, in which the bismuth atom is linked to one or more transition metal fragments. The ability to vary these metal fragments gives access to a plethora of available structures, with cyclopentadienylcarbonyl, metal carbonyl and sandwich compounds of bismuth in existence. Significant recent study has focused on applications in catalysis, where bismuth species can act as cross-coupling agents in carbon–carbon, carbon–nitrogen and carbon–oxygen bond forming reactions. Another striking feature is the variation in bonding situations that can be observed when studying the organometallic chemistry of bismuth. For example, dative and covalent interactions have been reported, in addition to cases of dibismuth acting as a two-, four- or six-electron donating ligand. This review aims to demonstrate the multi-faceted nature of the transition metal chemistry of bismuth and provide a detailed coverage of this topic.     

Synthesis,reactivity and electrochemical properties of substituted cyclopentadienyl cobalt (Ⅲ) complexes

Cyclopentadienyl cobalt complexes (n5-C5H4R)CoLI2 [L = CO,R=-COOCH2CH=CH2 (3); L=PPh3,R=-COOCH2-CH=CH2 (6); L= P(p-C6H4CH3)3,R=-COOC(CH3) = CH2 (7),-COOCH2C6H5(8),-COOCH2CH = CH2 (9)] were prepared and characterized by elemental analyses,1H NMR,IR and UV-vis spectra.The reaction of complexes (n5-C5H4R)CoLI2[L=CO,R=-COOC(CH3)=CH2 (1) ,-COOCH2C6H5(2):L=PPh3,R =-COOC(CH3)=CH2 (4),-COOCH2C6H5(5)] with Na-Hg resulted in the formation of their corresponding substituted cobaltocene (n5-C5H4R)2Co [R= -COOC(CH3) = CH2 (10),-COOCH2C6H5 (11) ].The electrochemical properties of these complexes 1-11 were studied by cyclic voltammetry.It was found that as the ligand (L) of the cobalt (Ⅲ) complexes changing from CO to PPh3 and P(p-tolyl)3,their oxidation potentials increased gradually.The cyclic voltammetry of α,α'-substituted cobaltocene showed reversible oxidation of one electron pro-     

Synthesis and reactivity of cationic niobium and tantalum methyl complexes supported by imido and β-diketiminato ligands

The synthesis and reactivity of the cationic niobium and tantalum monomethyl complexes [(BDI)MeM(N(t)Bu)][X] (BDI = [Ar]NC(CH(3))CHC(CH(3))N[Ar], Ar = 2,6-(i)Pr(2)C(6)H(3); M = Nb, Ta; X = MeB(C(6)F(5))(3), B(C(6)F(5))(4)] was investigated. The cationic alkyl complexes failed to irreversibly bind CO but formed phosphine-trapped acyl complexes [(BDI)(R(3)PC(O)Me)M(N(t)Bu)][B(C(6)F(5))(4)] (R = Et, Cy) in the presence of a combination of trialkylphosphines and CO. Treatment of the monoalkyl cationic Nb complex with XylNC (Xyl = 2,6-Me(2)-C(6)H(3)) resulted in irreversible formation of the iminoacyl complex [(BDI)(XylN[double bond, length as m-dash]C(Me))Nb(N(t)Bu)][B(C(6)F(5))(4)], which did not bind phosphines but would add a methide group to the iminoacyl carbon to provide the known ketimine complex (BDI)(XylNCMe(2))Nb(N(t)Bu). Further stoichiometric chemistry explored i) migratory insertion reactions to form new alkoxide, amidinate, and ketimide complexes; ii) protonolysis reactions with Ph(3)SiOH to form thermally robust cationic siloxide complexes; and iii) catalytic high-density polyethylene formation mediated by the cationic Nb methyl complex.     

Hydrogen evolution and oxidation—a prototype for an electrocatalytic reaction

Due to progress in the theory of electrocatalysis and in quantum chemistry, it has become possible to investigate the hydrogen reaction and perform quantitative calculations for the reaction rate. First, we demonstrate this with model calculations for the adsorption of hydrogen on Pt(111). In accordance with experimental data, we find hydrogen adsorption at a potential above the equilibrium potential and with an almost vanishing energy of activation. As a second example, we explain trends in the catalytic activity of palladium overlayers and clusters on Au(111) electrodes. Dedicated to J.O’M. Bockris on the occasion of his 85th birthday and in recognition of his contributions to electrochemistry.

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PtIr–WO3 nanostructured alloy for electrocatalytic oxidation of ethylene glycol and ethanol

In this article, we characterized tungsten oxide-decorated carbon-supported PtIr nanoparticles and tested it for the electrooxidation reactions of ethylene glycol and ethanol. Phase and morphological evaluation of the proposed electrocatalytic materials are investigated employing various characterization techniques including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Electrochemical diagnostic measurements such as cyclic voltammetry, chronoamperometry, and linear sweep voltammetry revealed that the tungsten oxide-modified PtIr/Vulcan nanoparticles have higher catalytic activity for ethylene glycol and ethanol electrooxidation than that of PtIr/Vulcan. A significant enhancement for electrooxidation of CO-adsorbate monolayers occurred in the presence of a transition metal oxide relative to that of pure PtIr/Vulcan electrocatalyst. The likely reasons for this are modification on the Pt center electronic structure and/or increasing the population of reactive oxo groups at the PtIr/Vulcan electrocatalytic interface in different potential regions.     

An oxidation system for green chemistry – synthesis of bi-metallic schiff base complexes and oxidation of phenols in the presence of the complexes –

Bimetallic copper complexes were synthesized from the schiff bases which were obtained by the reaction between bis(3-aminophenyl) sulphone and salicylaldehyde and the derivatives in order to clarify the active site of the immobilized polymer catalyst. The complex-H₂O₂ system showed effective oxiation of phenols. The active site was elucidated by UV spectrum.     

Coordination chemistry of silones: Synthesis and reactivity of new silicon-disubstituted (η4-silole) complexes

The synthesis of some new silicon-disubstituted (η⁴-2,5-diphenylsilacyclopentadiene)tricarbonyliron complexes are described. Stable complexes with various functional groups attached at silicon have been isolated. The exo position shows an enhanced reactivity, and cleavage of an SiH bond at this position occurs selectively with retention.     

Covalent bonding photosensitizer–catalyst dyads of ruthenium-based complexes designed for enhanced visible-light-driven water oxidation performance

Transition Metal Chemistry - We have successfully prepared two ruthenium-based covalent bonding photosensitizer–catalyst dyads through a simple procedure. 1H NMR spectra of both dyads show...     

Synthesis and characterization of monomeric and dimeric palladium(II)–ammonium complexes: their use for the catalytic oxidation of alcohols

The addition of quaternary ammonium salts, R₄NX, to PdCl₂ leads to mononuclear anionic complexes: (R₄N)₂PdX₄. A dinuclear complex, (n-Bu₄N)₂Pd₂Cl₆, has been characterized from the crystallization of the corresponding monomeric species under controlled conditions. These complexes revealed a similar efficiency as mixtures of PdCl₂ and R₄NX for the catalytic oxidation of alcohols using 1,2-dichloroethane as both solvent and stoichiometric oxidant.     

Synthesis,crystal structure and properties of two terbium complexes with 2,2′-bipyridine

Two new complexes {[Tb(2-IBA)₃ · 2,2′-bipy]₂ · C₂H₅OH} (1) and [Tb(2-ClBA)₃ · 2,2′-bipy]₂ (2) (2-IBA = 2-iodobenzoate; 2-ClBA = 2-chlorobenzoate; 2,2′-bipy = 2,2′-bipyridine) were prepared and their crystal structures determined by X-ray diffraction. Complex 1 is composed of two types of binuclear molecules, [Tb(2-IBA)₃ · 2,2′-bipy]₂ (a) and [Tb(2-IBA)₃ · 2,2′-bipy]₂ (b), and an uncoordinated ethanol molecule. In molecule (a), two Tb³⁺ ions are linked by four 2-IBA groups, all bidentate-bridging. In molecule (b), two Tb³⁺ ions are held together by four 2-IBA groups in two coordination modes, bidentate-bridging and chelating-bridging. In the two molecules, each Tb³⁺ ion is further bonded to one chelating 2-IBA group and one chelating 2,2′-bipy molecule, resulting in coordination numbers of eight for (a) and nine for (b). The structural characteristics of 2 are similar to that of molecule (b) in 1. The two complexes, 1 and 2, both emit strong green fluorescence under ultraviolet light with the ⁵D₄ → ⁷F _j (j = 6–3) emission of Tb³⁺ ion observed.     

Synthesis, structures and reactivity of ruthenium nitrosyl complexes containing Kläui's oxygen tripodal ligand

Ruthenium nitrosyl complexes containing the Kl?ui's oxgyen tripodal ligand L(OEt)(-) ([CpCo{P(O)(OEt)(2)}(3)](-) where Cp = η(5)-C(5)H(5)) were synthesized and their photolysis studied. The treatment of [Ru(N^N)(NO)Cl(3)] with [AgL(OEt)] and Ag(OTf) afforded [L(OEt)Ru(N^N)(NO)][OTf](2) where N^N = 4,4'-di-tert-butyl-2,2'-bipyridyl (dtbpy) (2·[OTf](2)), 2,2'-bipyridyl (bpy) (3·[OTf](2)), N,N,N'N'-tetramethylethylenediamine (4·[OTf](2)). Anion metathesis of 3·[OTf](2) with HPF(6) and HBF(4) gave 3·[PF(6)](2) and 3·[BF(4)](2), respectively. Similarly, the PF(6)(-) salt 4·[PF(6)](2) was prepared by the reaction of 4·[OTf](2) with HPF(6). The irradiation of [L(OEt)Ru(NO)Cl(2)] (1) with UV light in CH(2)Cl(2)-MeCN and tetrahydrofuran (thf)-H(2)O afforded [L(OEt)RuCl(2)(MeCN)] (5) and the chloro-bridged dimer [L(OEt)RuCl](2)(μ-Cl)(2) (6), respectively. The photolysis of complex [2][OTf](2) in MeCN gave [L(OEt)Ru(dtbpy)(MeCN)][OTf](2) (7). Refluxing complex 5 with RNH(2) in thf gave [L(OEt)RuCl(2)(NH(2)R)] (R = tBu (8), p-tol (9), Ph (10)). The oxidation of complex 6 with PhICl(2) gave [L(OEt)RuCl(3)] (11), whereas the reduction of complex 6 with Zn and NH(4)PF(6) in MeCN yielded [L(OEt)Ru(MeCN)(3)][PF(6)] (12). The reaction of 3·[BF(4)](2) with benzylamine afforded the μ-dinitrogen complex [{L(OEt)Ru(bpy)}(2)(μ-N(2))][BF(4)](2) (13) that was oxidized by [Cp(2)Fe]PF(6) to a mixed valence Ru(II,III) species. The formal potentials of the RuL(OEt) complexes have been determined by cyclic voltammetry. The structures of complexes 5,6,10,11 and 13 have been established by X-ray crystallography.     

Synthesis and thermal decomposition kinetics of two lanthanide complexes with cinnamic acid and 2,2′-Bipyridine

The two complexes of [Ln(CA)₃bipy]₂ (Ln = Tb and Dy; CA = cinnamate; bipy = 2,2′-bipyridine) were prepared and characterized by elemental analysis, infrared spectra, ultraviolet spectra, thermogravimetry and differential thermogravimetry techniques. The thermal decomposition behaviors of the two complexes under a static air atmosphere can be discussed by thermogravimetry and differential thermogravimetry and infrared spectra techniques. The non-isothermal kinetics was investigated by using a double equal-double steps method, the nonlinear integral isoconversional method and the Starink method. The mechanism functions of the first decomposition step of the two complexes were determined. The thermodynamic parameters (ΔH ^≠ , ΔG ^≠ and ΔS ^≠ ) and kinetic parameters (activation energy E and the pre-exponential factor A) of the two complexes were also calculated.     

Synthesis and reactivity studies of α,α-difluoromethylphosphinates

The preparation and reactivity of some α,α-difluorophosphinates are investigated. Alkylation of H-phosphinates with LiHMDS and ClCF₂H gives the corresponding α,α-difluorophosphinates in good yield. Deprotonation of these reagents with alkyllithium or LDA is then studied. Subtle electronic effects translate into significant differences in the deprotonation/alkylation of the two ‘Ciba-Geigy reagents’ (EtO)₂CRP(O)(OEt)H (R=H, Me). On the other hand, attempted methylation of difluoromethyl-octyl-phosphinic acid butyl ester resulted in the exclusive alkylation of the octyl chain. Finally, reaction with carbonyl compounds results in the formation of 1,1-difluoro-2-phosphinoyl compounds.     

Synthesis and co-crystallisation behaviour of copper(II) complexes of two isomeric p -tolyl-terpyridines§

Copper(II) complexes incorporating the isomeric tolyl-derivatised terpyridine ligands, 4′-p-tolyl-2,2′:6′,2′′-terpyridine (L¹) and 6′-p-tolyl-2,2′:2′′,4′-terpyridine (L²) have been prepared and characterised by X-ray diffraction. The first of these is a co-crystal of type [Cu(L¹)(NO₃)₂]·[Cu(L¹)(NO₃)(EtOH)]NO₃·MeOH while the second is a single complex of type [Cu(L²)₂(NO₃)]NO₃·0.5MeOH·1.5H₂O. Crystallisation of a mixture of both products from ethanol/methanol (1:1) yields an unusual co-crystalline product of stoichiometry [Cu(L²)₂NO₃]₂[Cu(L¹)(NO₃)₂](NO₃)₂ whose structure was also confirmed by an X-ray stucture determination.