Outer-sphere electron-transfer reactions with the participation of platinum(IV) haloammines

The kinetics of some outer-sphere electron-transfer reactions with the participation of the complexes [Pt(NH₃)_nX_6–n]² (n=6–0, X=Cl^–, Br^–) and dipyridyl complexes of Os(II), Ru(II), Ir(III), and Cr(II) have been investigated by means of luminescence-quenching measurements and flash photolysis. Estimates of the values of the Pt(IV)/Pt(III) one-electron potential and the change in the free energy of activation of electron self-exchange processes of the type Pt(IV) Pt(III) have been obtained on the basis of an analysis of the dependence of the rate constant on the change in the free energy accompanying the electrontransfer process.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 455–462, July–August, 1990.     

Heating and quenching of metastable superconducting compounds with a plasma jet

Superconducting compounds, such as cubic -MoC_1–x, cubic -WC_1–x, hexagonal MoB₂, and cubic -TaN, which are metastable at room temperature, have been formed by heating and quenching of their respective equilibrium phases, such as hexagonal -MoC_1–x, hexagonal WC, rhombohedral Mo₂B₅, and hexagonal -TaN in a plasma jet. From calculations based on a simple model, the quenching rate of particles has been estimated to be 10⁵ deg s^–1.     

Substitution of [Pt(terpy)H2O]2+ and [Pt(bpma)H2O]2+ with thiols in acidic aqueous solution. terpy = 2,2′:6′2″-terpyridine; bpma = bis(2-pyridylmethyl)amine

The substitution behaviour of [Pt(terpy)H₂O]²⁺ and [Pt(bpma)H₂O]²⁺, where terpy is 2,2:62-terpyridine and bpma is bis(2-pyridylmethyl)amine, was studied as a function of entering thiol concentration and temperature. The reactions between the Pt-complexes and DL-penicillamine, L-cysteine and glutathione were carried out in a 0.10 mol dm^–3 aqueous HClO₄ medium using stopped-flow and conventional u.v.–vis spectrophotometry. The observed pseudo-first-order rate constants for the substitutions are given by k _obs = k ₂[thiol] + k _–2. The k _–2 term represents the reverse solvolysis. This was found to be zero for Pt^II(terpy) which was the most reactive complex. The second-order rate constants, k ₂, for the three thiols varied between 0.107 ± 0.001 and 0.517 ± 0.025 M^–1 s^–1 for Pt^II(bpma) and 10.7 ± 0.7–711.9 ± 18.3 M^–1 S^–1 for Pt^II(terpy), whereas glutathione was found to be the strongest nucleophile. An analysis of the activation parameters, H and S , clearly shows that the substitution process is associative in nature.     

Physicochemical properties of electrode materials based on substituted yttrium manganite

Electrode materials Y_0.5Ca_0.5Mn_1–x (Co,Ni)_xO₃(x = 0–0.1) have an o-orthorhombic perovskite structure. Doping with transition metals raises the content of ions Mn⁴⁺ from 49% at x = 0 to 62% at x = 0.05 Ni. At 500–650 K there takes place an o-o-orthorhombic transition, with the thermal expansion coefficient rising from (7.1–8.1) × 10^–6 to (10.5–11) × 10^–6 K^–1. Composition Y_0.5Ca_0.5Mn_1–x (Co, Ni)_xO₃ is n-type semiconductor with a considerable oxygen constituent at >1000 K. Effect of the electrode material composition on the resistance parameter (/d) of an intermediate layer E/SE and on the polarization resistance (R ) of the triple-phase boundary E/SE/GP is similar. At 300–1100 K and 10²–10⁵ Pa, minimum values of these quantities are exhibited by samples with the Y_0.5Ca_0.5Mn_0.95Ni_0.05O₃ electrode layer 50 mg cm^–2 thick.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 291–297.Original Russian Text Copyright © 2005 by Tikhonova, Poluyan, Glushko, Vecher, Znosok.     

Properties of the products of CsxFeO2+0.5x thermal decomposition

It has been shown that cesium oxoferrate (VI) decomposes in oxygen at 500 °C giving solid Cs_xFe^IVO_2+0.5x (x1.0). The oxidation state of iron has been confirmed by Mössbauer spectroscopy data (single symmetrical resonance line with LW=0.4 (1) mm s^–1 and isomr shift of 0.15 (2) mm s^–1). Cesium oxoferrate (IV), Cs_xFeO_2+0.5x, crystallizes in the face-centered cubic system with the lattice parameter of a=8.36–8.46 Å and has a crystal structure derived from perovskite.     

On the energy transfer at the radiolysis of CO-H2S gas mixture

The kinetics of hydrogen formation at various amounts of H₂S /1–60%/ in the radiolysis of CO–H₂S mixture has been studied. The ratio of the reaction rate constants for reactions CO^x+COproduct and CO^x+H₂SH+SH=CO, which amounts to 5×10^–2, has been estimated. The effective activation energy of hydrogen formation /E_eff/ has been determined at various amounts of H₂S in the temperature interval 323–573 K.     

Synthesis,spectroscopic and structural studies of tris(3-methyl-pyridinium)(3-ethylpyridinium)β-octamolybdate monohydrate

Summary Three isostructural compounds of general formula (3-MepyH) _x (3-EtpyH)_4–x [Mo₈O₂₆] (x=0, 2, 4) crystallize in the monoclinic system, space group P2₁/n, Z=2. Previously determined parameters for the compoundx=4 area=13.652(2),b=10.887(1),c=13.759(1) Å, =90.87(1)°,V=2044.8(4) ų,Dx=2.53,Do=2.54(1) mg m^–3,F(000)=1496. Slight differences in cell dimensions have been observed whenx=0 or 2. A nonisomorphous compound of formula (3-MepyH)₃(3-EtpyH)[Mo₈O₂₆]·H₂O crystallizes in the triclinic system, space group P2₁/n,Z=2,a=10.918(1),b=10.985(3),c=18.991(2) Å, =97.19(2), =91.45(2), =107.30(2)⁰,V=2152.8(7) ų,Dx=2.456,Do=2.456(5) mg m^–3,F(000)=1532. The distinguishing features of tris(3-methylpyridinium)(3-ethylpyridinium) -octamolybdate monohydrate are its non-centrosymmetric polyanion and its extensive hydrogen bonding. The asymmetric unit contains three independent 3-methylpyridinium and one 3-ethylpyridinium cations, one water molecule and the -octamolybdate anion. The planar cations are oriented to permit hydrogen bonds with either molybdate oxygen atoms or water oxygen atoms. Four different types of hydrogen bonds have been found: N–H...O (mono- and bifurcated); N–H...Ow (monofurcated); Ow–Hw...O (monofurcated); and C–H...O (monofurcated). The proposed hydrogen bonding interactions appear to stabilize the structure.     

The electron transfer reaction of [RuIII(edta)(pyz)]− with sulfite in aqueous solution

The reduction of [Ru^III(edta)(pyz)]^– (edta=ethylenediaminetetraacetate, pyz=pyrazine) with sulfite has been investigated spectrophotometrically in aqueous solution and found to be first order in both the complex and sulfite. The values of the observed rate constant depend on the pH, since it controls the spaciation of oxoanions of sulfur(IV). The effect of alkali cations (K⁺, Na⁺ and Li⁺) is attributed to triple-ion formation through an alkali cation bridging between two negatively charged reactants and facilitating the electron-transfer process. Kinetic data and activation parameters are interpreted in terms of an outer-sphere electron transfer mechanism. The reaction has also been analysed using the Marcus cross-section relationship for outer-sphere electron transfer reactions.     

An independent kinetic and mechanistic study of the secondary reactions in the substitution of [FeL(OH)](n−2)− (L= triethylenetetraaminehexaacetic acid) by cyanide ions

Summary The kinetics of reaction between [Fe(CN)₅OH]^3– and CN^– have been investigated spectrophotometrically at pH=11.00, I=0.25 M(NaClO₄) and temp.=25.0°C by disappearance of the absorption peak at 395 nm. The rate data for this reaction followed first order kinetics in both [Fe(CN)₅OH^3–] and [CN^–]. The second order rate constant (k_f) was found to be (3.44±0.08)×10^–3 M^–1 s^–1. The pH dependence of the reaction was also investigated in the range 9–12. The activation parameters were found to be H=36.4kJ mol^–1 and S=–168JK^–1 mol^–1.The reaction between [Fe(CN)₆]^3– and TTHA^6– (TTHA=triethylenetetraaminehexaacetic acid) has also been followed spectrophotometrically at 420 nm, pH=11.00, I=0.1M (NaClO₄) and temp.=25.0°C. This reaction also followed first order kinetics in both [Fe(CN) ₆ ^3– ] and [TTHA^6–]. The second order rate constant (k_f) was found to be (3.74±0.21)×10^–2 M^–1 s^–1. The rate of reaction was found to increase with pH in the range 9–11.5. The different reactive species of TTHA (L) are H₂L^4– HL^5– and L^6–. The rate constants for these species have been calculated and the pH profile is explained. The values of the activation parameters were found to be H= 30.9 kJmol^–1 and S=–167JK^–1 mol^–1. Electron transfer from [Fe(CN)₆]^3– to the substrate followed by decomposition of the latter is proposed. The oxidation products of TTHA have been investigated by g.l.c.     

Chemical Processing of Potassium Substituted (Pb0.6Ba0.4)Nb2O6 Powders and Thin Films Through Metallo-Organics

Highly oriented tungsten bronze K_0.4(Pb_0.6Ba_0.4)_0.8Nb₂O₆ ferroelectric thin films have been prepared from metal alkoxides and metal acetate by chemical process. The formation of solid solution with potassium was found to be very effective to form the tungsten bronze phase at lower temperatures compared with (Pb_0.6Ba_0.4)Nb₂O₆. The amount of potassium in the composition of K_x(Pb_0.6Ba_0.4)_{1 – x/2}Nb₂O₆ [0 x 0.4] is also important to crystallize in the tungsten bronze phase. K_0.4(Pb_0.6Ba_0.4)_0.8Nb₂O₆ films with c-axis preferred orientation were successfully synthesized on MgO(1 0 0) and Pt(1 0 0)/MgO(1 0 0) substrates above 700°C. KPBN60 thin film on Pt(1 0 0)/MgO(1 0 0) showed a remnant polarization of 20 C/cm² and a coercive field of 140 kV/cm at –150°C.     

Simulation of donor-acceptor electron-transport systems in the example case of the oxidation of copper in media of organic solvents

The interaction of the onium salts [Me₂ Et=O]BF₄ ^–, [Me₂ =CH-OEt]BF₄ ^–, and [Me₃ =O]I^– with metallic copper in DMSO, DMF, and acetonitrile (AN) has been investigated. It has been shown that the reaction takes place with an intermediate step involving the formation of Cu(I) compounds. The complexes [Cu^I(AN)₄]BF₄, [Cu^II(DMSO)₅](BF₄)₂, [Cu^II(DMSO)₄(AN)₂](BF₄)₂, [Cu^II(DMSO)₂(DMF)(AN)](BF₄)₂, and [ME₃ ]₃Cu^II₄ · [Me₃ =O]I^– have been isolated and characterized. It has been established that dipolar onium compounds which simulate the intermediate products of the interaction of the components of donor-acceptor electron-transport systems are responsible for the oxidation of metals in organic complex-forming media.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1325–1330, June, 1991.     

Free Energy Relationships for the Outer-Sphere Anion–Anion and Anion–Cation Optical Electron Transitions Involving Common Cyanometalate (II) and (IV) Donors: Evidence for the Frequency-Distorted Reorganization Dynamics

This work is an extension of the research project on the outer-sphere optical charge transfer (CT) initiated by Prof. R.R. Dogonadze at the Laboratory founded by him in Tbilisi, Georgia. We report the band deconvolution procedures and accomplished free energy relationships for recently observed novel outer-sphere anion–anion and anion–cation optical electron transitions involving common cyanometalate II and IV ions, viz. [M(CN) _x ]^4–, M = Fe, Ru, Os (x = 6) and M = Mo, W (n = 8) as electron donors, and [Fe^III(CN)₆]^3– and [Ru^III(NH₃)₆]³⁺ as electron acceptors, respectively. The CT band maximum vs. the redox asymmetry free energy relationships, constructed through the consideration of spin-orbit splitting effects, exhibit linear character with slopes close to unity as predicted theoretically, and fully confirm the assignment of these transitions to outer-sphere optical electron transitions as outlined in the preceding works. The preliminary comparative analysis of presented relationships based on the contemporary charge transfer theory and recent differential DO-D stretching overtone data strongly suggests the essential redox asymmetry for the reorganization free energy increments attributed to first solvating shells of cyanometalate ions involved.     

Crystal and molecular structure of the simple cation-radical salt ethylenedithiopropylenedithiotetrathiafulvalene trichloromercurate (EPT)HgCl3

The new cation-radical salt (EPT)HgCl₃ is prepared. Its structure and electrical conductivity are studied. The crystal structure of (EPT)HgCl₃ contains (EPT)⁺ in the chair conformation and trigonal planar HgCl₃ ^– packed into organic and inorganic layers alternating along thea axis. Shortened intermolecular contacts join HgCl₃ ^– into infinite chains along the c axis (Hg...Cl, 3.289 and 3.387 Å), form stacks (S...S, 3.536 and 3.597 Å) and layers (S...S, 3.427–3.498 Å) of EPT⁺ cation-radicals, and create cation-anion interactions between neighboring layers in the crystal (Cl...S, 3.396–3.521 Å, Cl...C, 3.360 Å). The configuration of the bonds around Hg in HgCl₃ ^– is distorted trigonal planar: Hg-Cl, 2.342(3)–2.449(3) Å, Cl-Hg-Cl, 110.7(1)–137.4(1). The Hg atom lies out of the plane of the Cl atoms by 0.015 Å. The conductivity of (EPT)HgCl₃ at 20°C is ₃₀₀ 5·10^–2 (·cm)^–1. The dependence of conductivity on temperature is semiconducting in nature.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2055–2061, September, 1991.     

Effect of the potential of an external electron donor on C<Subscript>2</Subscript>H<Subscript>2</Subscript> reduction catalyzed by the nitrogenase active center (FeMoco) isolated from the enzyme

The effect of potential value and chemical properties of an external electron donor on C₂H₂ reduction catalyzed by nitrogenase active center (cluster [(₆-N)Fe₇MoS₉·homocitrate] FeMoco isolated from the enzyme) has been investigated in the presence of proton donors of different acidity. The temperature—reaction rate dependences of these reactions have been studied. It has been shown that the rate-limiting steps of the reactions differ depending on the proton donor used. When thiophenol or water are used as proton donors, and electrochemical step — the electron transfer from cathode to adsorbed catalytic cluster — has been found to be a rate-limiting one. The effective activation energy of ethane formation as a product of four-electron C₂H₂ reduction is found to be 1.5 times lower than that of ethylene, namely, 13 kcal mol^–1. When stronger acid, pentafluorothiophenol, is used as a proton donor, the chemical step of intramolecular rearrangement of the catalyst—substrate complex taking place in solution becomes a rate-limiting one. The effective activation energies of both ethylene and ethane become equal to 32 kcal mol^–1.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1583–1591, August, 2004.     

Volumetric Properties of Aqueous 2-Chloroethanol Solutions and Volumes of Transfer of Some Amino Acids and Peptides from Water to Aqueous 2-Chloroethanol Solutions

Densities and apparent molar volumes of aqueous 2-chloroethanol were determined at temperatures from 15.0 to 34.4°C using digital densimetry. The results of the volumetric measurements have been used to calculate the following thermodynamic quantites at 25°C: V ₂ ^o = 55.05 ± 0.02 cm³-mol^–1, (V ₂ ^o/T)_p = 0.01486 ± 0.00318 cm³-K^–1-mol^–1, and (² V ₂ ^o/T ²)_p = 0.02972 ± 0.00318 cm³-K^–2-mol^–1. Partial molar volumes of transfer from water to 1 mol-dm^–3 2-chloroethanol have also been determined for L-glycine, L-alanine, L-serine, L-glutamic acid, and L-aspartic acid at 35.0°C. The transfer results have been explained in terms of the nature of the interactions of the groups in the solute and solvent. Hydration numbers of L-glycine and L-alanine have also been calculated in aqueous 2-chloroethanol.     

On the linear mixed valence compounds obtained by partial oxidation ofcis-diamminedichloroplatinum(II)

Summary The partial oxidation products ofcis-[Pt(NH₃)₂Cl₂] (Cisplatin) by (NH₄)₂S₂O₈ and by K₂PtCl₆, as well as the recrystallization of the former product in various solutions (HClO₄, NaClO₄, NaBF₄, NaHSO₄, H₂SO₄) have been re-examined. Contrary to the conclusions of previous works, the general formulation of these compounds iscis-[Pt²⁺(NH₃)₂Cl₂]X_x·yH₂O ( = 0.3–0.4, X = SO ₄ ^2– , PtCl ₄ ^2– , ClO ₄ ^2– , BF ₄ ^2– , HSO ₄ ^2– , ..., 0y 1). These materials are all linear chain Pt—Pt compounds belonging to the class III of Robin-Day compounds with Pt—Pt distances in the range 3.00–3.06 Å. The oxidation of Cisplatin by persulphate gives two sulphate compounds of the same formulation (x = 0.2), which differ in aspect, metallic character and spectral properties. Structural information was obtained from polarized micro-Raman spectra of a needle-like sample of the perchlorate and from X-ray powder diffraction spectra. The cell of the perchlorate was orthorhombic while the two sulphate forms had a monoclinic cell with slightly different parameters. Expansion of the Cisplatin interchain distance occurred only along one crystallographic direction. The two sulphate forms differed in the degree of order along this direction. An approximate structure is proposed and discussed in relation to the Cisplatin precursor.     

Rapid radiochemical separation and determination of chlorine,bromine and iodine in water samples using ion exchange

On the basis of tracer experiments, a simple and rapid radiochemical separation method for simultaneous determination of I^–, Br^– and Cl^– in one aliquot of a water sample (only 2–4 ml) has been developed. The method is based on short irradiation of the water sample and separation of the halogens using sequential ion exchange columns filled with Dowex 1×8, 100–200 mesh anionic resin prepared in I^–/I₂, Br^–/Br₂ and Cl^– form. After washing the columns with an appropriate volume of 2% NaCl solution, the resins were transferred to vials and activities of the isolated radionuclides¹²⁸I,⁸²Br and³⁸Cl measured together with standards in a well type or on a coaxial Ge detector connected to a Canberra 90 multichannel analyzer. Besides high chemical yields, from the -spectra of the isolated radionuclides, it is evident that high decontamination fac-The paper was presented at the MTAA-8, Vienna, September 1991.     

New Ion Conductor of (Ba1−xLax)2In2O5+x

The structural characterization, thermogravimetric analysis and electrical properties for solid solution system, (Ba_1–xLa_x)₂In₂O_5+x with perovskite-type structure were investigated. X-ray diffraction showed that the orthorhombic phase was in the range of 0.0<x0.3, the tetragonal phase 0.3<x0.5, and the cubic phase 0.5<x. The sharp transition of electrical conductivity shifted to a lower temperature with increasing x and disappeared at the phase boundary between the orthorhombic and tetragonal phases. This perovskite-related oxide exhibited a pure oxide-ion conduction over the oxygen partial pressure range of 1 atm to 10^–3.5 atm, and the electrical conductivity reached the value of 1.610^–1 (S cm^–1) at 1073 K, which was nearly equal to that of the yttria stabilized zirconia. These properties were successfully explained in terms of disordered oxygen ions.This revised version was published online in November 2005 with corrections to the Cover Date.     

Structural Features of Grafted Phosphates in Mesopores of Si-MCM-41 and Ti,Si-MCM-41 Molecular Sieves

We have used ³¹P NMR (MAS) and IR spectroscopy and also chemical analysis to show that when Si- and Ti,Si-MCM-41 mesoporous molecular sieves are treated with phosphorus oxychloride, surface-anchored silicophosphate and titanophosphate compounds are formed of the type (Si—O) _x —{PO(OH)_3–x } and (Ti—O) _x —{PO(OH)_3–x } (x = 1, 2), and also compounds with the structure of titanium hydrophosphate and pyrophosphate.     

Platinum and rhodium complexes with isoleucinol-based bi- and tricyclic hydrophosphoranes

The complex formation of bi- and tricyclic hydrophosphorane derivatives of isoleucinol with [Pt(COD)Cl₂], [Rh(CO)₂Cl]₂, and [Rh(THF)₂(COD)]⁺BF₄ ^– (COD is cycloocta-1,5-diene) was investigated. In all cases, bicyclic hydrospirophosphorane selectively forms the metal chelates [M(²-PN)(X)Cl] (M = Pt, X = Cl; M = Rh, X = CO) and [Rh(²-PN)(COD)]⁺BF₄ ^–. («» denotes the residue of the hydrospirophosphorane ligand, which does not contain the P and N atoms). In addition, tricyclic hydrophosphorane (L) generates the phosphoranide complexes [Pt(¹-L)(COD)Cl]⁺Y^– (Y = Cl or BF₄). The structures of the new compounds were established by IR spectroscopy, ³¹P, ¹³C, ¹H, ²H, ¹¹B, ¹⁹F, and ¹⁹⁵Pt NMR spectroscopy, and plasma-desorption and electrospray ionization mass spectrometry. The possible mechanism of coordination of hydrophosphoranes is discussed.