Singularity of proton transport in salts of orthoperiodic and orthotellurium acids: theoretical modeling using density functional calculations

Density functional B3LYP calculations have been performed to investigate proton transport in orthoperiodic and orthotellurium acids, their salts MIO(6)H(4)(M = Li, Rb, Cs) and CsH(5)TeO(6), dimers of the salt*acid type MIO(6)H(4)*H(5)IO(6)(M = Rb, Cs), CsIO(6)H(4)*H(6)TeO(6), CsHSO(4)*H(6)TeO(6), Cs(2)SO(4)*H(6)TeO(6), and also in double-substituted and binary salts Rb(2)H(3)IO(6) and Rb(4)H(2)I(2)O(10). It has been shown that the energy of salt dimerization is 33-35 kcal mol(-1) and the activation barrier for proton migration between the neighboring octahedrons of the salt*acid --> acid*salt type is calculated to be 3-13 kcal mol(-1). The activation energy of the proton migration along the octahedron, 20-30 kcal mol(-1), is comparable with the barrier for water molecule separation. Quantum-chemical calculations correlate with the results of X-ray and electrochemical studies.     

Manifestation of space-time electron delocalization in an x-ray study

We report a manifestation of the space-time electron delocalization in an x-ray diffraction structural analysis upon the condition that the relaxation time of the structure is less than the lifetime of the delocalized electron at any site, between which electron transfer occurs. In this case, the x-ray diffraction data may provide informative parameters characterizing the fraction of the time for the presence of an extra electron at each site. Such parameters are bond lengths in the coordination unit and mean square displacements of the atoms. The differences in the lengths of the bridging oxygen-iron bonds are explained for mixed-valence trinuclear iron carboxylates with the general formula [Fe₃O(COOR₁)₆3R₂]R₃. An expression was obtained, which gives the ratio of the lifetime of an electron at each of the sites using the bond lengths l = Fe–Ol₁:l₂:l₃ = ₁:₂:₃. The direction and magnitude of the displacement of the atoms upon rearrangement related to electron transfer (r) may be determined using this expression for the mean square atomic displacements u²=u₀ ²+(1–)·r² in the case of an experiment at two temperatures.Institute of Chemical Physics, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 5, pp. 90–95, September–October, 1989.     

Effect of adsorbed polymers on electrophoresis of dispersed particles in strong electric fields

In this study, the effect of adsorbed non-ionic polyethylenoxides (PEO) and polyvinil-pyrrolidones (PVP) of different molecular mass on the electrophoresis of polystyrene, graphite and aluminum oxide particles both in weak (5–20 V/cm) and strong (50–400 V/cm) electric fields has been studied. The measurements in strong fields have been performed in short electric pulses using image analyzing equipment in which we have determined the deviation of particles from their normal sedimentation trajectory. We have shown that the adsorption of PEO and PVP strongly decreases the electrophoretic velocity (V_ef) of particles in weak electric fields, and this decrease is bigger the adsorbed amount is higher. This is explained by the shift of the shear plane toward solution due to polymer adsorption. At the same time the polymer adsorption only slightly changes the V_ef of particles in strong fields. It means that the non-linear (“cubic”) electrophoresis is independent of the position of the shear plane, i.e. the zeta-potential value. It proves our idea that the electrophoretic velocity in strong electric fields is determined mainly by the surface conductivity of particles, i.e. it is not a function of the electrokinetic potential but rather the Dukhin number that characterizes the polarization of the electric double layer.     

Catalytic behavior of a polynuclear Mg-Mo complex and nitrogenase active site (FeMoco) isolated from the enzyme in reactions with C2H2, N2, and CO: A comparative study

In order to identify common and distinctive features in the catalytic behavior of natural and artificial nitrogen-fixation clusters, the kinetics of the catalytic reduction of C₂H₂ in the presence of Mg-Mo-cluster (1) was investigated and compared with the kinetics of acetylene reduction catalyzed by the cluster FeMoco (2) isolated from the enzyme nitrogenase we studied previously. The reactions were conducted in the presence of Zn/Hg and Eu/Hg as reducing agents and PhSH and C₆F₅SH as proton donors, i.e., under the same conditions as had been used in the case of 2. Both polynuclear Mg-Mo-complex and the europium amalgam-reduced FeMoco have multiple interdependent binding sites for substrates and/or inhibitors. Carbon monoxide inhibits the acetylene reduction much less efficiently in systems with cluster 1 than in systems with cluster 2, although the type of inhibition is mixed in both systems: CO binds to multiple sites of the cluster and affects both C₂H₂ complexation to the reduced cluster and decomposition of the catalyst-substrate complex to give the products. Unlike isolated FeMoco, the Mg-Mo-cluster efficiently catalyzes the reduction of molecular nitrogen. The reaction is greatly inhibited by acetylene, while no inhibiting effect of N₂ is observed in acetylene reduction, as was found earlier for a system with the natural cluster as the catalyst. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 766–774, May, 2006.     

Influence of Fixed Charge Distribution on Ion Mobility: Small Deviations of Equilibrium Potential from Donnan Value

The influence of the electrostatic interaction on the diffusion coefficients of ions is estimated in the approximation of the slightly varying equilibrium potential. Various assumptions have been considered for the fixed charge distribution, namely, the discrete charge distributed in the bulk, the surface charge, and the linear charge distributed around a macroion. Both the random and regular distributions of the fixed charge groups are being separately analyzed as applied to each assumption. Obtained dependencies show in some measure various types of the fixed charge heterogeneity contribute to the effect of the diffusion coefficient decrease.     

Synthesis and crystal structure of bis(μ-periodato-<Emphasis Type="Italic">O,O′,O″</Emphasis>)bis(18-crown-6)dirubidium

A new binuclear complex, bis(μ-periodato-O,O′,O″)bis(18-crown-6)dirubidium [Rb₂(IO₄)₂(18-crown-6)₂] (I), is synthesized. Its crystal structure is studied by single-crystal X-ray diffraction analysis (space group P2₁/n, a = 11.942 Å, b = 8.394 Å, c = 19.664 Å, β = 101.08°, Z = 4, direct method, anisotropic full-matrix least-squares approximation, R = 0.030 for 2823 independent reflections, CAD-4 automated diffractometer, λMoK _α radiation). Complex I is binuclear and centrosymmetric, consisting of two cationic monomers [Rb(18-crown-6)]⁺ of the host-guest type linked through two tridentate IO ₄ ^? bridging ligands. The coordination polyhedron of the Rb⁺ cation (coordination number 9) can be described as a distorted hexagonal pyramid with a base of six O atoms of one 18-crown-6 ligand and one threefold vertex at three O atoms of the two IO ₄ ^? bridging ligands. The 18-crown-6 ligand has a usual crown conformation.     

Synthesis and structure of 2-ethoxy- and 2-aminomethylidene-3-fluoroalkyl-3-oxopropionates

Condensation of ethyl 3-polyfluoroalkyl-3-oxopropionates with excess triethyl orthoformate gave ethyl 3-polyfluoroalkyl-2-ethoxymethylidene-3-oxopropionates which reacted with primary aliphatic, aromatic, and heterocyclic amines to form ethyl 2-alkyl(aryl, hetaryl)aminomethylidene-3-polyfluoroalkyl-3-oxopropionates. According to the X-ray diffraction and IR data, the latter exist in the crystalline state as the corresponding E isomers, while in solution (NMR data), as mixtures of Z and E isomers. Condensation of ethyl 2-ethoxymethylidene-3-oxopropionates with secondary heterocyclic amines (morpholine and pyrrolidine) led to the formation of 2-morpholino(pyrrolidin-1-yl)methylidene-3-fluoroalkyl-3-oxopropionates which were shown to exist as Z isomers both in the crystalline state and in solution.     

Condensation of fluoroalkyl-containing 1,2,3-trione 2-arylhydrazones with methylamine

Fluoroalkyl-containing 1,2,3-trione 2-arylhydrazones react with methylamine in different ways, depending on the substrate structure. Arylhydrazones having a short fluoroalkyl substituent (R_F = CF₃, HCF₂CF₂) react at the carbonyl group adjacent to the nonfluorinated substituent to give 3-alkyl(aryl)-2-aryldiazenyl-3-methylamino-1-polyfluoroalkylprop-2-en-1-ones. Arylhydrazones with a long-chain fluoroalkyl group (R_F = C₃F₇ and longer) and a bulky nonfluorinated group take up methylamine molecule at the carbonyl group linked to the fluorinated substituent, and the subsequent haloform reaction yields N-methyl-2-arylhydrazono-3-oxobutanamides. Both types of products are formed in reactions of methylamine with 1,2,3-triketone 2-arylhydrazones having a long fluoroalkyl group and methyl group at the other carbonyl group. Template condensation of fluoroalkyl-containing 1,2,3-trione 2-arylhydrazones with methylamine over Ni(II) template gives bis[3-alkyl(aryl)-1-polyfluoroalkyl-3-methylamino-2-aryldiazenylprop-2-en-1-onato-N,N′]-nickel(II), regardless of the size of the fluoroalkyl substituent. The same complexes and their copper analogs can be obtained by treatment of 3-alkyl(aryl)-2-aryldiazenyl-3-methylamino-1-polyfluoroalkylprop-2-en-1-ones with the corresponding metal salts.     

Synthesis and structure of 2,2′-spirobi(1,3-benzodioxole) derivative prepared from 3,5-di(<Emphasis Type="Italic">tert</Emphasis>-butyl)-1,2-benzoquinone

3,5-Di(tert-butyl)-1,2-benzoquinone reacted with 1,2,3-trimethylbenzimidazolium iodide led to the formation of 2,2′-spirobi[4,6-di(tert-butyl)-1,3-benzodioxole]. The reaction mechanism was suggested. The structure of 2,2′-spirobi[4,6-di(tert-butyl)-1,3-benzodioxole] was established by means of X-ray diffraction analysis.