Isomerism in OBe3F3 + cation: anab initio study

Ab initio MP2/6-31G^*//HF/6-31G^*+ZPE(HF/6-31G^*) calculations of the potential energy surface in the vicinity of stationary points and the pathways of intramolecular rearrangements between low-lying structures of the OBe₃F₃ ⁺ cation detected in the mass spectra of μ₄-Be₄O(CF₃COO)₆ were carried out. Ten stable isomers with di- and tricoordinate oxygen atoms were localized. The relative energies of six structures lie in the range 0–8 kcal mol⁻¹ and those of the remaining four structures lie in the range 20–40 kcal mol⁻¹. Two most favorable isomers, aC _2v isomer with a dicoordinate oxygen atom, planar six-membered cycle, and one terminal fluorine atom and a pyramidalC _3v isomer with a tricoordinate oxygen atom and three bridging fluorine atoms, are almost degenerate in energy. The barriers to rearrangements with the breaking of one fluorine bridge are no higher than 4 kcal mol⁻¹, except for the pyramidalC _3v isomer (∼16 kcal mol⁻¹). On the contrary, rearrangements with the breaking of the O−Be bond occur with overcoming of a high energy barrier (∼24 kcal mol⁻¹). A planarD _3h isomer with a tricoordinate oxygen atom and linear O−Be−H fragments was found to be the most favorable for the OBe₃H₃ ⁺ cation, a hydride analog of the OBe₃F₃ ⁺ ion; the energies of the remaining five isomers are more than 25 kcal mol⁻¹ higher. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 420–430, March, 1999.     

Synthesis of diblock copolymers with cellulose derivatives. 3. Cellulose derivatives carrying a single pyrene group at the reducing-end and fluorescent studies of their self-assembly systems in aqueous NaOH solutions

Novel cellobiose and cellulose (DP _n =ca. 30) derivatives, N-(1-pyrenebutyloyl)-4-O-(β-d-glucopyranosyl)-β-d-glucopyranosylamine (6), N-(15-(1-pyrenebutyloylamino)-pentadecanoyl)-4-O-(β-d-glucopyranosyl)-β-d-glucopyranosylamine (7), N-(1-pyrenebutyloyl)-β-cellulosylamine (13), N-(15-(1-pyrenebutyloylamino)-pentadecanoyl)-β-cellulosylamine (14) carrying a pyrene group as a single fluorescent probe at the reducing end, were prepared in order to investigate their self-assembly systems in solutions. The relative intensity of the excimer emission at ca. 480 nm due to dimerized pyrenes (intensity I _E) to the monomer emission at ca. 380 nm due to isolated pyrene (intensity I _M), i.e., I _E/I _M, was monitored in various solutions. In water/dimethyl sulfoxide (DMSO) mixed solvent (0–98%, v/v), the ratio I _E/I _M remained low (0.04) for compound 6 over the range of water concentrations, indicating that pyrenes at C-1 position of compound 6 were diffused. On the other hand, the ratio I _E/I _M increased (0.04–4.96) for compound 7 with the increase in water concentration, indicating that pyrenes at C-1 position were associated. In aqueous NaOH solutions (4.4–17.5%, w/w), compound 14 showed a large increase in the ratio I _E/I _M (0.84–8.14) with the increase in NaOH concentration, compared to compound 13 (0.06–0.41). It was found that the association of hydrophobic groups at the reducing-end of cellulose could be controlled by the hydrophilic–hydrophobic balance of compounds and the solvent polarity.     

Multiple bond migration with participation of a protophilic agent

The pathways of migration of the multiple bond in propene and propyne molecules involving the hydroxide ion were investigated by theab initio (RHF/6-31+G^* and MP2/6-31+G^*) methods. Stationary points corresponding to stable complexes between the molecules under study and the hydroxide ion and between corresponding carbanions and water molecule were found on the potential energy surfaces of the proton transfer reactions. In the presence of hydroxide ion, migration of the multiple bond can occur by an “intramolecular” mechanism of the proton transfer involving the proton of hydroxide ion bound in the complex with propene or propyne molecule. For the propene system, such a mechanism seems to be quite realistic and more preferable energetically than a traditional two-stage mechanism with a passage of the proton into the medium. For the system with the triple bond, an equal expenditure of energy is required to follow any mechanism (without taking into account the effects of solvation and the interaction with a cation), whereas the formation of the stable [H₂C=C=CH·H₂O]⁻ complex can prevent further transformations. For Part 1, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 35–41, January, 1999.     

Structural and spectroscopic characterization of Al2−x Cr x O3 powders obtained by polymeric precursor method

Al₂O₃ and Al_2−x Cr _x O₃ (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL^*a^*b^* color data). The obtained results allow to identify the γ-Al₂O₃ to α-Al₂O₃ phase transition. The single-phase α-Al₂O₃ powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al_2−x Cr _x O₃ are related to the γ to α-Al₂O₃ phase transition and the temperature and time range for such transition depends on the chromium content.     

Theoretical refinements of theendo and theexo structures of tetraborane(8) carbonyl

The molecular structures of theendo (1a) andexo (1b) isomers of B₄H₈CO have been optimized at the ab initio MP2(Full)/6-31G^* level of theory. The agreement of the computed geometrical parameters with the recently published electron-diffraction (GED) data is very good, even though a number of geometrical constraints were applied in the experimental determination. The IGLO (individual gauge for localized orbitals)¹¹B NMR chemical shifts, calculated at the II//MP2/6-31G^* level, are also in accord with experiment. The formation of1a and1b by association of B₄H₈ and CO is computed to be exothermic by 22.8 and 22.2 kcal/mol, respectively, at the MP2(Full)/6-31G^*//MP2(Full)/6-31G^* + ZPE(6-31G^*) level of theory. The Lewis acid strength of B₄H₈ toward CO is comparable to that of BH₃.     

Molecular structures of acetylene derivatives of tin

The geometry and force fields of the bis(trimethylstannyl)acetylene molecule (a conformer withD _3d symmetry corresponding to a minimum of the total energy of the molecule) were calculated by the RHF and MP2(fc) methods. The effective core potential in SBK form with the optimized 31G^* valence basis set was employed in the case of Sn atoms. The 6–31G^** and 6–311G^** basis sets were used for carbon and hydrogen atoms. Vibrational spectra of the light and perdeuterated isotopomers of bis(trimethylstannyl)acetylene were interpreted using the procedure of scaling the quantum-chemical force fields. For Part 5, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 616–626, April, 2000.     

Ab initio study of molecular structure and internal rotation in methyldicyanophosphine and methyldiisocyanophosphine. The Raman spectrum of methyldicyanophosphine and its interpretation with the use of scaling ofab initio force fields

The equilibrium geometric parameters and structures of transition states of internal rotation for the molecules of methyldicyanophospine MeP(CN)₂ and its isocyano analog MeP(NC)₂ were calculated by the RHF and MP2 methods with the 6–31G^* and 6–31G^** basis sets. At the MP2 level, the total energy of cyanide is −35 kcal mol⁻¹ lower than that of isocyanide and the barriers to internal rotation of methyl group for MeP(CN)₂ and MeP(NC)₂ are 2.2 and 2.7 kcal mol⁻¹, respectively. For both molecules, the one-dimensionalab initio potential functions of internal rotation approximated by a truncated Fourier series were used to determine the frequencies of torsional transitions by solving direct vibrational problems for a non-rigid model. The Raman spectrum of crystalline MeP(CN)₂ was recorded in the range 3500–50 cm⁻¹. The vibrational spectra of this compound were interpreted by scalingab initio force fields calculated by the RHF and MP2 method. The vibrational spectrum of methyldiisocyanophosphine was predicted with the use of the obtained scale factors. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1703–1714, September, 1998.     

Hydration and protonation ofO-vinylacetoxime in the gas phase: anab initio study

Ab initio HF/6–31G^* calculations ofO-vinylacetoxime monohydrates and cations were performed. Each conformer forms two stable H-complexes with participation of N and O atoms. The former have planar heavy-atom skeletons, whereas the water molecule in the latter is located above the plane of the proton-acceptor complex. The complexes stabilized by N...HO and O...HO bonds have different dipole moments and frequencies of the OH stretching vibrations. The most energetically favorable cation is formed by adding a proton to the C_β atom of the vinyl group ofO-vinylacetoxime. Theap,ap-conformer (ap is antiperiplanar) of this cation is 6.5 and 34.9 kcal mol⁻¹ more stable than the onium cations with the NH⁺ and OH⁺ fragments, respectively, and is characterized by polarization and appreciable lengthening of the N−O and C=C bonds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 597–600, April, 2000.     

Synthesis and characterization of spinel-type CuAl<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocrystalline by modified sol–gel method

Nanocrystalline Copper aluminate (CuAl₂O₄) was prepared by sol–gel technique using aluminum nitrate, copper nitrate, diethylene glycol monoethyl ether and citric acid were used as precursor materials. This method starts from of the precursor complex, and involves formation of homogeneous solid intermediates, reducing atomic diffusion processes during thermal treatment. The formation of pure crystallized CuAl₂O₄ nanocrystals occurred when the precursor was heat-treated at 600 °C in air for 2 h. The stages of the formation of CuAl₂O₄, as well as the characterization of the resulting compounds were done using thermo–gravimetric analysis, X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The products were analyzed by transmission electron microscopy and ultraviolet–visible (UV–Vis) spectroscopy to be round, about 17–26 nm in size and E _g = 2.10 eV.     

Nitrite formation in aerated aqueous azide solutions: A radiation chemical study

Gamma radiolysis of oxygenated 1–10 mM azide solutions was carried out at various pH values. In oxygenated 10 mM azide solutions, H₂O₂ and NO ₂ ⁻ were observed as radiolytic products while NH3 was not. The concentration of H₂O₂ reached its maximum level at a dose of 1 kGy, whereas NO ₂ ⁻ yield increased non-linearly beyond 2 kGy in this system. Both in aerated and oxygenated systems, G(NO ₂ ⁻ ) and G(H₂O₂) were found to vary with N ₃ ⁻ concentration. The yield of NO ₂ ⁻ was found to be dependent on both dose rate and pH. On pulse radiolysis, NO ₂ ⁻ was found as a radiolytic product in aerated 1 mM azide solution at pH 6.8. In this system the intermediate generated exhibits absorbance around 250 nm. The overall results obtained during the present study reveal that in presence of both reducing radical (mainly e _aq ⁻ ) and oxygen, N ₃ ⁻ produced an intermediate possibly NH₂O ₂ ^• radical, which is the prime source for NO ₂ ⁻ generation.     

Hydrogenation of nitrate in water over bimetallic Pd-Ag/Al2O3 catalysts

Hydrogenation of nitrate (NO₃ ⁻) in water was studied with 0.8 ×10⁻³–3.2 ×10⁻³ mol/dm³ of reactant in the temperature range of 293–313 K over palladium promoted Ag catalysts. Pd-Ag catalysts with a low ratio of Ag/Pd were characterized by high efficiency in the reduction of nitrates. The degradation of nitrates followed approximately first order decay and the estimated apparent activation energy was about 4 kJ/mol.     

Ab initio calculations of atomic interaction in the ClCH2OCH3 molecule

Ab initio calculations of both ClCH₂OCH₃ and ClCH₂CH₃ molecules and various ClCH₂OCH₃ structures with fixed angles of rotation of the methoxy group about the C−O bond were performed by the restricted Hartree-Fock method in the valence-split 6–31 G^* basis set with full optimization of the geometry. The populations of the valent p-orbitals of the chlorine atoms in these molecules have been analyzed. The³⁵Cl NQR frequencies and the asymmetry parameters of the electric field gradient (EFG) at the³⁵Cl nuclei have been calculated. Good agreement with experimental NQR frequencies was obtained for the calculations where only the populations of the less diffuse 3p-components of these orbitals were used. The³⁵Cl NQR frequency in ClCH₂OCH₃ is lower than that in ClCH₂CH₃ due to the higher population of the less diffuse component of the p_σ-orbital of the Cl atom in the former molecule. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 431–434, March, 1997.     

Thermochemistry of europium and dithiocarbamate complex Eu(C5H8NS2)3(C12H8N2)

A solid complex Eu(C₅H₈NS₂)₃(C₁₂H₈N₂) has been obtained from reaction of hydrous europium chloride with ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen⋅H₂O) in absolute ethanol. IR spectrum of the complex indicated that Eu³⁺ in the complex coordinated with sulfur atoms from the APDC and nitrogen atoms from the o-phen. TG-DTG investigation provided the evidence that the title complex was decomposed into EuS. The enthalpy change of the reaction of formation of the complex in ethanol, Δ_r H _m ^θ(l), as –22.214±0.081 kJ mol^–1, and the molar heat capacity of the complex, c _m, as 61.676±0.651 J mol^–1 K^–1, at 298.15 K were determined by an RD-496 III type microcalorimeter. The enthalpy change of the reaction of formation of the complex in solid, Δ_r H _m ^θ(s), was calculated as 54.527±0.314 kJ mol^–1 through a thermochemistry cycle. Based on the thermodynamics and kinetics on the reaction of formation of the complex in ethanol at different temperatures, fundamental parameters, including the activation enthalpy (ΔH _≠ ^θ), the activation entropy (ΔS _≠ ^θ), the activation free energy (ΔG _≠ ^θ), the apparent reaction rate constant (k), the apparent activation energy (E), the pre-exponential constant (A) and the reaction order (n), were obtained. The constant-volume combustion energy of the complex, Δ_c U, was determined as –16937.88±9.79 kJ mol^–1 by an RBC-II type rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δ_c H _m ^θ, and standard enthalpy of formation, Δ_f H _m ^θ, were calculated to be –16953.37±9.79 and –1708.23±10.69 kJ mol^–1, respectively.     

Theoretical study of the structure and stability of the dimers of heme analogues (MC34H32N4O4)2 and their ions (MC34H32N4O4) 2+ with 3 d -metal atoms M

The electronic and geometric structures and the energetic characteristics of a series of monomeric MC₃₄H₃₂N₄O ₄ ^0,+ and dimeric (MC₃₄H₃₂N₄O₄) ₂ ^0,+ molecules, heme analogues and their positively charged ions with 3d-metal atoms M = Ti, V, Cr, and Mn, have been calculated by the density functional theory B3LYP method with the Gen−1 = 6−31G^*(Fe) + 6−31G(C, H, N, O) and Gen−2 = 6−311+G^*(Fe) + 6−31G^*(C, H, N, O) basis sets. The computation results are compared with the analogous calculated data on the heme dimers (heme) ₂ ^0,+ . Computations show that for the (MC₃₄H₃₂N₄O₄) ₂ ^0,+ dimers, high-spin states are preferable. In these dimers, the rings are linked with each other by a pair of M-carbonyl bridges M⋯O_b=C(OH) and a pair of hydrogen bridges OH_b⋯N. The calculated energies of dissociation D of the dimers into monomers point to a rather high stability of the dimers at the beginning of the 3d series (D ∼ 2.3–3.6 eV for M = Ti, V), which decreases rapidly as the atomic number of M increases (D ∼ 0.5 eV for M = Cr and ∼0.4 eV for (heme)₂). The positive ions (MC₃₄H₃₂N₄O₄) ₂ ⁺ are ∼0.8–1.0 eV are more stable to dissociation than their neutral congeners (MC₃₄H₃₂N₄O₄)₂. The trends in the behavior of the energetic and structural characteristics of the dimers (distances R(M—N), displacements of M atoms from the porphyrin ring plane, parameters of the carbonyl and hydrogen bridges, character of ring distortions, etc.), as well as in the spin density distribution between the metal atoms and the rings in the monomers MC₃₄H₃₂N₄O₄ and dimers (MC₃₄H₃₂N₄O₄)₂ caused by their ionization and going along the 3d series, are examined. In the mixed dimer (FeC₃₄H₃₂N₄O₄)(VC₃₄H₃₂N₄O₄), the rings are linked by only one strong carbonyl bridge V⋯O_b=C(OH), with some contribution made by the neighboring hydrogen bridge. The dissociation energy of this mixed dimer into monomers is close to a half of the dissociation energy of the “symmetric” dimer (VC₃₄H₃₂N₄O₄)₂. Original Russian Text ? O.P. Charkin, N.M. Klimenko, D.O. Charkin, S.H. Lin, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 8, pp. 1332–1346.     

Multiple bond migration with participation of a protophilic agent

Ab initio study of the pathways of migration of the double bond in the 3-methylthioprop-1-ene (1) and 3-methoxyprop-1-ene (2) molecules with participation of hydroxide ion was carried out by the RHF/6-31+G^* and MP2/6-31+G//RHF/6-31+G^* methods. Conformational isomerism of the initial molecules and reaction products was considered. The distinctions are discussed in the spatial and electronic structure of intermediate carbanions stabilized (for1) due to the negative hyperconjugation. Stationary points corresponding to complexes between the molecules under study and the hydroxide ion and between the corresponding carbanion and water molecule were localized on the potential energy surfaces of the proton transfer reactions. For2, the single-stage mechanism of prototropic rearrangement involving the H atom of the hydroxide ions was found to be more energetically preferable than the two-stage mechanism, whereas both mechanisms are expected to be equiprobable for1. For Parts 1–3, see Refs. 1–3. Translated fromIzvestiya Akademii Nauk. Seriya Kimicheskaya, No. 3, pp. 407–413, March, 2000.     

Facile preparation and electrochemical properties of large-scale Li<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript> nanobelts

Large-scale Li_1+x V₃O₈ nanobelts were successfully fabricated using filter paper as deposition substrate through a simple surface sol–gel method. The nanobelts were as long as tens of micrometers with widths of 0.4–1.0 μm and thickness of 50–100 nm. The nanobelts were characterized by X-ray diffration (XRD), Fourier infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM). The formation mechanism of the nanobelts was investigated, showing that the morphology of the nanobelts is mainly determined by the calcination temperature. Electrochemical properties of the Li_1+x V₃O₈ nanobelts were characterized by charge–discharge experiments, and the results demonstrate that the Li_1+x V₃O₈ nanobelts exhibit a high discharge capacity (278 mAh g⁻¹) and excellent cycling stability.     

Denitrification in presence of benzene,toluene, and <Emphasis Type="Italic">m</Emphasis>-xylene

Denitrification of the electron donors toluene-C(15–100 mg/L), m-xylene-C (15–70 mg/L), benzene-C (5–25 mg/L), and acetate-C as experimental reference (50–140 mg/L) was carried out in batch culture. An initial concentration of 1.1±0.15 g of volatile suspended solids/L of denitrifying sludge without previous exposure to aromatic compounds was used as inoculum. The results showed toluene and nitrate consumption efficiency (E _T and E _N′ respectively) of 100%. Toluene was completely mineralized (oxidized) to CO₂. In all cases, the N₂ (γ_N2) and HCO ₃ ⁻ yields (γ_HCO3) were 0.97±0.01 and 0.8±0.05, respectively. The consumption efficiency (E _x ) of m-xylene (53±5.7%) was partial. The γ_N2 and γ_HCO3 were 0.96±0.01 and 0.86±0.02, respectively. Benzene was not consumed under denitrifying conditions. The specific consumption rates of toluene (q _T ) and m-xylene (q _X ) were lower than that of acetate (q _A ). The differences in specific consumption rates were probably owing to the negative effect of benzene, toluene, and isomers of xylene on the cell membrane.     

On the Importance of H-Bonding Interactions in Organic Ammonium Tetrathiotungstates

Summary. Four new organic ammonium tetrathiotungstates (N–Me–enH₂)[WS₄] (1), (N,N′-dm-1,3-pnH₂)[WS₄] (2), (1,4-bnH₂)[WS₄] (3), and (mipaH)₂[WS₄] (4), (N–Me–enH₂ = N-methylethylenediammonium, N,N′-dm-1,3-pnH₂ = N,N′-dimethyl-1,3-propanediammonium, 1,4-bnH₂ = 1,4-butanediammonium, and mipaH = monoisopropylammonium) were synthesized by the base promoted cation exchange reaction and characterized by elemental analysis, infrared, Raman, UV-Vis and ¹H NMR spectroscopy as well as single crystal X-ray crystallography. The structures of 1–4 consist of [WS₄]²⁻ tetrahedra which are linked to the organic ammonium cations via N–H⋯S hydrogen bonding. The strength and number of the S⋯H interactions affect the W–S bond lengths as evidenced by distinct short and long W–S bonds. The IR spectra exhibit splitting of the W–S vibrations, which can be attributed to the distortion of the [WS₄]²⁻ tetrahedron. From a comparative study of several known tetrathiotungstates it is observed that a difference of more than 0.033 ? between the longest and shortest W–S bonds in a tetrathiotungstate will result in the splitting of the asymmetric stretching vibration of the W–S bond.     

Alkylation of salts ofN-(β-hydroxyalkyl)-N′-hydroxydiazeneN-oxides with alkyl halides and dimethyl sulfate

Salts ofN-(β-hydroxyalkyl)-N′-hydroxydiazeneN-oxides, RCH(OH)CH₂N(O)=NO⁻ M⁺ (R=Me, Prⁱ, or Bu^t; and M=Li, Na, K, Ag, NH₄, or Me₄N), were prepared. Their alkylation with alkyl halides R′X (X=Cl, Br, or I) and dimethyl sulfate was studied. Generally, alkylation afforded mixtures ofN-(β-hydroxyalkyl)-N′-alkoxydiazeneN-oxides RCH(OH)CH₂N(O)=NOR′ andO-alkyl-N-(β-hydroxyalkyl)-N-nitrosohydroxylamines RCH(OH)CH₂N(NO)OR′. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1996–2001, October, 1998.     

Molar Excess Volumes and Excess Isentropic Compressibilities of Ternary Mixtures Containing <Emphasis Type="Italic">o</Emphasis>-Toluidine

Molar excess volumes, V _ijk ^E, and speeds of sound, U _ijk , of o-toluidine (i) + benzene (j) + cyclohexane or n-hexane or n-heptane (k) ternary mixtures have been measured as a function of composition at 308.15 K. The observed speed of sound data have been utilized to determine the excess isentropic compressibilities, (K _S ^E) _ijk , of the ternary (i+j+k) mixtures. The Moelywn-Huggins concept (Huggins in Polymer 12: 389–399, 1971) of connectivity between the surfaces of the binary mixture constituents has been extended to ternary mixtures (using the concept of a connectivity parameter of third degree of molecules, ³ ξ, which in turn depends on its topology) to obtain an expression that describes well the measured V _ijk ^E and (K _S ^E) _ijk data. The observed data have also been analyzed in terms of Flory’s theory.