Energy decomposition analysis of the metal-oxime bond in [M{RC(NOH)C(NO)R}2] (M = Ni(II), Pd(II), Pt(II), R = CH3, H, F, Cl, Br, Ph, CF3)

Quantum chemical calculations using gradient-corrected DFT at the BP86/TZ2P+ level were carried out for the metal-dioxime complexes [M{RC(NOH)C(NO)R}₂]with M = Ni, Pd, Pt, R = CH₃, H, F, Cl, Br, Ph, CF₃. The nature of the metal-ligand bond was investigated with an energy decomposition analysis (EDA). The complexes with electron donating substituents R = H, CH₃ have the strongest metal-ligand interaction energies ΔE_int, as well as the largest bond dissociation energies. The analysis of the bonding situation revealed that the metal ← ligand σ donation is much stronger than the metal → ligand π backdonation. The breakdown of the orbital interactions into the contributions of orbitals with different symmetry indicates that the donation from the in-plane lone-pair donor-orbitals of nitrogen into the d_xy AO of the metal provides about one half of the stabilization which comes from ΔE_orb. Inspection of the EDA data indicates that the electrostatic term ΔE_elstat is more important for the trend of the metal-oxime interactions in [M{RC(NOH)C(NO)R}₂] than the orbital term ΔE_orb.     

Thermodynamics of proton dissociations from aqueous threonine and isoleucine at temperatures from (278.15 to 393.15) K,molalities from (0.01 to 1.0) mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of zwitterionic,protonated cationic,and deprotonated anionic forms

We have measured the densities of aqueous solutions of isoleucine, threonine, and equimolal solutions of these two amino acids with HCl and with NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, at molalities 0.01 ⩽ m/mol · kg⁻¹ ⩽ 1.0, and at the pressure 0.35 MPa using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a twin fixed-cell differential temperature-scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values from the literature for V_ϕ(T, m) and C_p,ϕ(T, m) for HCl(aq), NaOH(aq), and NaCl(aq) and the molar heat capacity change Δ_rC_p,m(T, m) for ionization of water to calculate parameters for Δ_rC_p,m(T, m) for the two proton dissociations from each of the protonated aqueous cationic amino acids. We used Young’s Rule and integrated these results iteratively to account for the effects of equilibrium speciation and chemical relaxation on V_ϕ(T, m) and C_p,ϕ(T, m). This procedure gave parameters for V_ϕ(T, m) and C_p,ϕ(T, m) for threoninium and isoleucinium chloride and for sodium threoninate and isoleucinate which modeled our observed results within experimental uncertainties. We report values for Δ_rC_p,m, Δ_rH_m, pQ_a, Δ_rS_m, and Δ_rV_m for the first and second proton dissociations from protonated aqueous threonine and isoleucine as functions of T and m.     

Thermodynamics of proton dissociations from aqueous alanine at temperatures from (278.15 to 393.15) K,molalities from (0.0075 to 1.0) mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of alanine,alaninium chloride,and sodium alaninate

We have measured the densities of aqueous solutions of alanine, alanine plus equimolal HCl, and alanine plus equimolal NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, at molalities 0.0075 ⩽ m/mol · kg⁻¹ ⩽ 1.0, and at the pressure p = 0.35 MPa using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a twin fixed-cell differential temperature-scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values from the literature for V_ϕ(T, m) and C_p,ϕ(T, m) for HCl(aq), NaOH(aq), and NaCl(aq) and the molar heat capacity change Δ_rC_p,m(T, m) for ionization of water to calculate parameters for Δ_rC_p,m(T, m) for the two proton dissociations from protonated aqueous cationic alanine. We integrated these results in an iterative algorithm using Young’s Rule to account for the effects of speciation and chemical relaxation on V_ϕ(T, m) and C_p,ϕ(T, m). This procedure yielded parameters for V_ϕ(T, m) and C_p,ϕ(T, m) for alaninium chloride {H₂Ala⁺Cl⁻(aq)} and for sodium alaninate {Na⁺Ala⁻(aq)} which successfully modeled our observed results. Values are given for Δ_rC_p,m, Δ_rH_m, pQ_a, Δ_rS_m, and Δ_rV_m for the first and second proton dissociations from protonated aqueous alanine as functions of T and m.     

Volumetric,acoustic, and viscometric studies of molecular interactions in binary mixtures of diethylene glycol monomethyl ether with 1-alkanols at temperatures from (293.15 to 308.15) K

In this work, densities ρ, speeds of sound u, and viscosities η, have been measured over the whole composition range for the binary mixtures of diethylene glycol monomethyl ether (DEGMME), CH₃(OCH₂CH₂)₂OH with 1-hexanol, CH₃(CH₂)₅OH, 1-octanol, CH₃(CH₂)₇OH, and 1-decanol, CH₃(CH₂)₉OH at T = (293.15, 298.15, 303.15, and 308.15) K along with the properties of the pure components. By using the experimental values of ρ, u, and η, excess molar volume, $V_m^E$, deviations in viscosity, Δη, isentropic compressibility κ_S, deviations in isentropic compressibility Δκ_S, deviations of the speed of sound Δu, have been calculated. The viscosity results have also been analysed in terms of some semi-empirical equations.     

Energy analysis of metal-metal bonding in [RM-MR] (M = Zn, Cd, Hg; R = CH3, SiH3, GeH3, C5H5, C5Me5)

The metal-metal bonds of the title compounds have been investigated with the help of energy decomposition analysis at the DFT/TZ2P level. In good agreement with experiment, computations yield Hg-Hg bond distance in [H₃SiHg-HgSiH₃] of 2.706 Å and Zn-Zn bond distance in [(η⁵-C₅Me₅)Zn-Zn(η⁵-C₅Me₅)] of 2.281 Å. The Cd-Cd bond distances are longer than the Hg-Hg bond distances. Bond dissociation energies (-BDE) for Zn-Zn bonds in zincocene −70.6 kcal/mol in [(η⁵-C₅H₅)₂Zn₂] and −70.3 kcal/mol in [(η⁵-C₅Me₅)₂Zn₂] are greater amongst the compounds under study. In addition, [(η⁵-C₅H₅)₂M₂] is found to have a binding energy slightly larger than those in [(η⁵-C₅Me₅)₂M₂]. The trend of the M-M bond dissociation energy for the substituents R shows for metals the order GeH₃ < SiH₃ < CH₃ < C₅Me₅ < C₅H₅. Electrostatic forces between the metals are always attractive and they are strong (−75.8 to −110.5 kcal/mol). The results demonstrate clearly that the atomic partial charges cannot be taken as a measure of the electrostatic interactions between the atoms. The orbital interaction (covalent bonding) ΔE_orb is always smaller than the electrostatic attraction ΔE_elstat. The M-M bonding in [RM-M-R] (R = CH₃, SiH₃, GeH₃, C₅H₅, C₅Me₅; M = Zn, Cd, Hg) has more than half ionic character (56-64%). The values of Pauli repulsions, ΔE_Pauli, electrostatic interactions, ΔE_elstat, and orbital interactions, ΔE_elstat are larger for mercury compounds as compared to zinc and cadmium.     

Ligands of low electronegativity in the vsepr model: electron-rich hydrides MH3E2, MH4E,MH5E,and MH6E

Hydrides FH₃, ClH₃, and OH^?₃ of type MH₃E₂ are calculated to adopt D_3h structures: NH₃^2?, PH₃^2?, and SH₃^? each have two energy minima, one at D_3h and the other at a T-shaped geometry, of which the D_3his the more stable for SH₃^? but the less stable for NH₃^2? and PH₃^2?. Hydrides NH₄^2?, OH₄, and ClH₄⁺ of type MH₄E have a single energy minimum at T_d: CH₄^2?, SiH₄^2?, PH₄^?, and SH₄ each have two minima, one at T_d (more stable for SH₄ only) and one at an SF₄-like C_2v geometry, which is the more stable for CH₄^2?, SiH₄^2? and PH₄^?. D_3h and C_4V structures are very close in energy for all hydrides of type MH₅E, with no activation barrier between the two configurations: D_3h is the more stable configuration for OH₅^?, FH₅, SH₅, and ClH₅, but C_4V is the more stable for NH₅^2?, SiH₅^3?, and PH₅^?. The T_1u bending force constant in hydrides MH₆E becomes negative, for C_3V distortion, in PH₆^3? and SiH₆^4?. Both the equilibrium geometries and the force constants strongly support an interpretation, in terms of the second-order Jahn-Teller effect, of the observed stereochemical inactivity of non-bonding electrons in the presence of ligands of low electronegativity. Molecular energies, equilibrium geometries, orbital energies and electron populations are reported for all species considered in this study. Three molecular states of ClH₄^?, of type MH₄E₂, were also briefly investigated.     

Excess molar volumes of (cyclohexanone+trichloromethane,or 1,2-dichloroethane,or trichloroethene,or 1,1,1-trichloroethane,or cyclohexane) at T=308.15 K,and of (cyclohexanone+dichloromethane) at T=303.15 K

Excess molar volumes V_m^E have been measured using a dilatometric technique for mixtures of cyclohexanone (C₆H₁₀O) with trichloromethane (CHCl₃), 1,2-dichloroethane (CH₂ClCH₂Cl), trichloroethene (CHClCCl₂), 1,1,1-trichloroethane (CCl₃CH₃), and cyclohexane (c-C₆H₁₂) at T=308.15 K, and for cyclohexanone+dichloromethane (CH₂Cl₂) at T=303.15 K. Throughout the entire range of the mole fraction χ of C₆H₁₀O, V_m^E has been found to be positive for χ C₆H₁₀O+(1−χ)c-C₆H₁₂, and negative for χ C₆H₁₀O+(1−χ)CH₂Cl₂, χ C₆H₁₀O+(1−χ)CHClCCl₂, χ C₆H₁₀O+(1−χ)CHCl₃, and χ C₆H₁₀O+(1−χ) CCl₃CH₃. For χ C₆H₁₀O+(1−χ)CH₂ClCH₂Cl, V_m^E has been found to be positive at lower values of χ and negative at high values of χ, with inversion of sign from positive to negative values of V_m^E for this system occurring at χ∼0.78. Values of V_m^E for the various systems have been fitted by the method of least squares with smoothing equation, and have been discussed from the viewpoint of the existence specific interactions between the components.     

Thermodynamics of proton dissociations from aqueous glycine at temperatures from 278.15 to 393.15 K,molalities from 0 to 1.0 mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of glycine,glycinium chloride,and sodium glycinate

We have measured the densities of aqueous solutions of glycine, glycine plus equimolal HCl, and glycine plus equimolal NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, molalities 0.01 ⩽ m/mol · kg⁻¹ ⩽ 1.0, and at p = 0.35 MPa, using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a fixed-cell differential scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values of V_ϕ(T, m) and C_p,ϕ(T, m) for HCl(aq), NaOH(aq), NaCl(aq) from the literature to calculate parameters for Δ_rC_p,m(T, m) for the first and second proton dissociations from protonated aqueous cationic glycine. We then integrated this value of Δ_rC_p,m(T, m) in an iterative algorithm, using Young’s Rule to account for the effects of speciation and chemical relaxation on the observed V_ϕ and C_p,ϕ of the solutions. This procedure yielded parameters for V_ϕ(T, m) and C_p,ϕ(T, m) for glycinium chloride {H₂Gly⁺Cl⁻(aq)} and sodium glycinate {Na⁺Gly⁻(aq)} which successfully modeled our observed results. We have then calculated values of Δ_rC_p,m, Δ_rH_m, Δ_rV_m, and pQ_a for the first and second proton dissociations from protonated aqueous glycine as functions of T and m.     

Thermodynamic and optical studies of some ethylene glycol ethers in aqueous solutions at T = 298.15 K

Experimental results of density (ρ), speed of sound (u), and refractive index (n_D) have been obtained for aqueous solutions of ethylene glycol monomethyl ether (EGMME), ethylene glycol monoethyl ether (EGMEE), diethylene glycol monomethyl ether (DEGMME), and diethylene glycol monoethyl ether (DEGMEE) over the entire concentration range at T = 298.15 K. From these measurements, the derived parameters, apparent molar volume of solute (?_V), excess molar volume (V^E), isentropic compressibility of solution (β_S), apparent molar isentropic compressibility of solute (?_KS), deviation in isentropic compressibility (Δβ_S), molar refraction [R]_1,2 and deviation in refractive index of solution (Δn_D) have been calculated. The Redlich–Kister equation has been fitted to the calculated values of V^E, Δβ_S and Δn_D for the solution. The results obtained are interpreted in terms of hydrogen bonding and various interactions among solute and solvent molecules.     

Thermodynamics of proton dissociations from aqueous l-methionine at temperatures from (278.15 to 393.15) K,molalities from (0.0125 to 1.0) mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of l-methionine,methioninium chloride,and sodium methioninate

We have measured the densities of aqueous solutions of l-methionine, l-methionine plus equimolal HCl, and l-methionine plus equimolal NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, at molalities 0.0125 ⩽ m/mol · kg⁻¹ ⩽ 1.0 as solubilities allowed, and at p = 0.35 MPa using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a twin fixed-cell differential temperature-scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values from the literature for V_ϕ(T, m) and C_p,ϕ(T, m) for HCl(aq), NaOH(aq), and NaCl(aq) and the molar heat capacity change Δ_rC_p,m(T, m) for ionization of water to calculate parameters for Δ_rC_p,m(T, m) for the two proton dissociations from protonated aqueous cationic l-methionine. We integrated these results in an iterative algorithm using Young’s Rule to account for the effects of speciation and chemical relaxation on V_ϕ(T, m) and C_p,ϕ(T, m). This procedure yielded parameters for V_ϕ(T, m) and C_p,ϕ(T, m) for methioninium chloride {H₂Met⁺Cl⁻(aq)} and for sodium methioninate {Na⁺Met⁻(aq)} which successfully modeled our observed results. Values are given for Δ_rC_p,m, Δ_rH_m, pQ_a, Δ_rS_m, and Δ_rV_m for the first and second proton dissociations from protonated aqueous l-methionine as functions of T and m.     

Jahn–Teller coupling and the influence of strain in Tg and Eg ground and excited states – A ligand field and DFT study on halide MIIIX6 model complexes [M = TiIII–CuIII; X = F−, Cl−]

In contrast to well established experimental results of vibronic coupling effects in octahedral dⁿ complexes with E_g ground states (Cu²⁺, Ag²⁺; Cr²⁺, Mn³⁺ etc.), not much useful material is available for the Jahn–Teller (JT) effect in orbital triplet ground states. The present study is concerned with this deficiency, providing data for octahedral halide model complexes with 3dⁿ cations – in particular for Ti^III, V^III and high-spin Co^III, Ni^III with T_2g and T_1g ground states, which involve, to first-order, solely splitting of the π-antibonding t_2g MOs. Besides experimental results – structural and spectroscopic, mainly from d–d spectra – data from computations are needed for a quantitative treatment of the T_g ? (?_g + τ_2g) vibronic interaction as well as in the E_g ? ?_g coupling case (Mn^III, low-spin Ni^III); DFT was the method of choice, if only critically selected outcomes are utilised. The theoretical bases of the treatment are the dⁿ ligand field matrices in O_h, extended by the inclusion of lower-symmetry distortion parameters, and the conventional theory of vibronic coupling. Caution is needed when classifying the effects of interelectronic repulsion; DFT does not reproduce the magnitudes of the Racah parameters B, C, as deduced from the d–d spectra, properly – the presumed reasons are analysed. DFT even allows one to deduce reliable vibronic coupling constants via the analysis of orbitally degenerate excited states (Cr^III, ⁴A_2g ground state). The group-theoretical analysis of the interaction with the JT-active ?_g and τ_2g modes yields D_4h, D_3d and D_2h as the possible distortion symmetries in the case of a T_g ground state. The DFT-calculations give clear evidence, that the D_4h stationary points represent the absolute minima in the T_g ? (?_g + τ_2g) potential surface – in agreement with experiment, where available. For the first time, vibronic coupling constants, characterising JT splitting of ground and excited T_g states, can be presented for trivalent 3dⁿ cations in octahedral halide ligand fields. They turn out to be smaller by a factor of almost 3 in comparison to those, which determine the coupling in σ-antibonding e_g MOs.The tetragonal splitting of T_g states is typically only small, around 0.1 eV, and suggests that strain influences from a specific ligand arrangement and/or the presence of different ligands may modify the potential surface considerably. We have studied such effects via compounds A^IM^IIIF₄, where an elastic strain induced by the host structure, and a binding strain, due to the simultaneous existence of (largely) terminal and of bridging ligands, are active. A novel strain model, in its interplay with JT coupling, is proposed and applied – using energies from the d–d spectra, structural results and data from DFT.Chloride complexes are only known for Ti^III to Fe^III; the rather small electronegativity already of Co^III suggests a reducing ligand-to-metal (3dⁿ) electron transfer for n ≥ 6. Similarly, the low-lying ligand-to-metal charge transfer bands in the d–d spectra of the Cu^IIIF₆^3? complex and the reduced T_g ? ?_g coupling strength suggest a pronounced covalency of the Cu^III–F, and, even more distinctly, of the Cu^III–O bond, which is of interest for superconductivity. The Ni^IIIF₆^3? polyhedron possesses a low-spin configuration in the elpasolite structure. The spectroscopic evidence and the DFT data indicate, that the minimum positions of the alternative _a²A_1g(_a²E_g) and _a⁴A_2g (_a⁴T_1g) potential curves are only ≤0.02 eV apart, giving rise to interesting high-spin/low-spin phenomena. It is the strong E_g ? ?_g as compared to the T_1g ? ?_g coupling, which finally stabilises a spin-doublet ground state in D_4h.We think, that the selected class of solids is unique particularly for the study of Jahn–Teller coupling in T ground states, with model character for other systems. In our overview a procedure is sketched, which uses reliable computational results (here from DFT) for supplementing incomplete experimental data, and presents – on a semiquantitative scale – convincing statements, consistent with chemical intuition. It is also a pleading for ligand field theory, which rationalises d-d spectra in terms of chemical bonding; though the latter spectra provide frequently only rather coarse information, their assistance in the energy analysis is crucial.     

Mass spectra of monohapto-cyclopentadienyl derivatives of group IVB elements

Dissociative ionisation of organometallic cyclopentadiene derivatives containing one, two or three M(CH₃)₃ groups (M  Si, Ge, Sn) has been studied.Among the monometallated compounds, C₅H₅Si(CH₃)₂Cl, C₅H₅Si(CH₃)₂OCH₃ and (C₅H₅)₄Sb have also been investigated. To verify fragmentation patterns, the spectra of deuterated compounds such as C₅D₅Si(CH₃)₃, C₅D₅Sn(CH₃)₃, C₅D₄Si₂(CH₃)₆ and C₅D₃Si₃)₉ have been measured. Dissociative ionisation of h¹-cyclopentadienyl derivatives has been shown to differ essentially from that of h⁵-compounds.     

Thermodynamics of proton dissociations from aqueous serine at temperatures from (278.15 to 393.15) K,molalities from (0.01 up to 1.0) mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of serine,serinium chloride,and sodium serinate

We have measured the densities of aqueous solutions of serine, serine plus equimolal HCl, and serine plus equimolal NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, molalities 0.01 ⩽ m/mol · kg⁻¹ ⩽ 1.0, and at the pressure p = 0.35 MPa, using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a fixed-cell differential temperature-scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values from the literature for V_ϕ(T,m) and C_p,ϕ(T,m) for HCl(aq), NaOH(aq), and NaCl(aq) and the molar heat capacity change Δ_rC_p,m(T,m) for ionization of water to calculate Δ_rC_p,m(T,m) for proton dissociations from protonated aqueous cationic serine and from the zwitterionic form. We integrated these results in an iterative algorithm using Young’s rule to account for the effects of speciation and chemical relaxation on the observed V_ϕ(T,m) and C_p,ϕ(T,m) of the solutions. This procedure yielded parameters for V_ϕ(T,m) and C_p,ϕ(T,m) for serinium chloride {H₂Ser⁺Cl⁻(aq)} and for sodium serinate {Na⁺Gly⁻(aq)} which successfully modeled our observed results. We have then calculated Δ_rC_p,m, Δ_rH_m, Δ_rV_m and pQ_a for the first and second proton dissociations from protonated aqueous serine as functions of T and m.     

Thermodynamic study of (heptane + amine) mixtures. III: Excess and partial molar volumes in mixtures with secondary,tertiary, and cyclic amines at 298.15 K

Excess molar volumes V^E at 298.15 K were determined by means of a vibrating tube densimeter for binary mixtures of {heptane + open chain secondary (diethyl to dibutyl) and tertiary (triethyl to tripentyl) amines} as well as for cyclic imines (C₂, C₃, C₄, C₆, and C₇) and primary cycloalkylamines (C₅, C₆, C₇, and C₁₂). The V^E values were found positive for mixtures involving small size amines, with V^E decreasing as the size increases. Negative V^E’s were found for tributyl- and tripentylamine, heptamethylenimine, and cyclododecylamine. Mixtures of heptane with cycloheptylamine showed an s-shaped curve.Partial molar volumes $V^{°}$ of amines at infinite dilution in heptane were obtained from V^E and compared with $V^{°}$ of hydrocarbons and other classes of organic compounds taken from literature. An additivity scheme, based on the intrinsic volume approach, was applied to estimate group (CH₃, CH₂, CH, C, NH₂, NH, N, OH, O, CO, and COO) contributions to $V^{°}$. These contributions, the effect of cyclization on $V^{°}$, and the limiting slope of the apparent excess molar volumes were discussed in terms of solute–solvent and solute–solute interactions.     

DFT calculations of the defect structures,electronic structures,and EPR parameters for three Rh2+ centers in AgCl

The local structures for various Rh²⁺ centers in AgCl are theoretically studied using density functional theory (DFT) with periodic CP2K program. Through geometry optimizing, the stable ground states with minimal energies and electronic structures are obtained for the tetragonally elongated (T_E), orthorhombically elongated (O_E), and tetragonally compressed (T_C) centers, and the corresponding g and hyperfine coupling tensors are calculated in ORCA level. The calculations reveal obvious Jahn–Teller elongation distortions of about 0.109 and 0.110 Å along [001] axis for T_E and O_E centers without and with 1 next nearest neighbor (nnn) cation vacancy V_Ag in [100] axis, respectively. Whereas T_C center with 1 nnn V_Ag along [001] axis exhibits moderate axial compression of about 0.066 Å due to the Jahn–Teller effect. For O_E and T_C centers with 1 nnn V_Ag, the ligand intervening in the central Rh²⁺ and the V_Ag is found to displace away from the V_Ag by about 0.028 and 0.024 Å, respectively. The present results are discussed and compared with those of the previous calculations based on the perturbation formulas by using the improved ligand field theory.     

Algorithm for variational calculations of molecular symmetry in solving anharmonic vibrational problems

A universal program for variational calculations of molecular symmetry in solving anharmonic vibrational problems, realized by the author, is described. The program uses the group-theoretical method. Symmetrized basis wave functions are constructed with the aid of the generalized KJebsch-Gordan series suggested by the author. The method of constructing symmetrized basis wave functions and the program for adequate calculations of molecular symmetry were verified for many molecules of different symmetry groups: O_h, O, T_d, T_h, T, D_∞h, C_t8v, D_nd, D_nh, D_n, C_nv, C_nh, S_2n, C_n, C_i, C_s, and C₁ where 2 ≤n ≤6. It was confirmed that the program provides correct results and high-speed operation. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 6, pp. 1146–1153, November–December, 1997.     

CH3 + Cl = CH3Cl: RRKM/master equation modeling

Data for the title reaction have been fitted using an RRKM/master equation approach. Energy transfer was modeled using an exponential decay with downward step sizes, ΔE_d, as a fitting parameter. The low temperature (200 < T (K) < 300) combination of CH₃ with Cl atoms in He can be accommodated with ΔE_d (cm^?1) = 400. Higher temperature (1600 < T (K) < 2100) decomposition in Ar required ΔE_d(T) (cm^?1) = 694(T/300)^0.46. Previous analysis of the analogous system CH₄ = CH₃ + H required ΔE_d(T) (cm^?1) = 100(T/300) for He and ΔE_d(T) (cm^?1) = 150(T/300) for Ar. Understanding of the magnitudes and temperature dependence of ΔE_d remains the greatest detriment to quantitative calculation, extrapolation, and prediction of unimolecular rate constants. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 245–254, 2009     

Tetra-hydrides of the third-row transition elements: spin–orbit coupling effects on geometrical deformation in WH4 and OsH4

The dissociation energies of MH₄ (M =  La, Hf–Hg) were computed using full optimized reaction space (FORS) multi-configuration self-consistent field (MCSCF) and second-order multi-reference Møller–Plesset perturbation methods with the SBKJC basis sets augmented by a set of polarization functions (SBKJC(f,p)). It was shown that of the molecules examined, only four tetra-hydrides HfH₄, TaH₄, WH₄, and OsH₄ with T_d symmetry are lower in energy than the corresponding dissociation limits. For WH₄ and OsH₄, the potential energy surfaces from the D_4h to the T_d structure were explored from both theoretical calculations and symmetry arguments based on the pseudo-Jahn- Teller effect. As for WH₄, it is found that the ground state could be ³E_g, ³A_2g, or ³B_2g at the D_4h structure. The present calculations suggest that the ground state is ³E_g, and that this state is stabilized by the e_u deformation into a C_2v structure (³B₁) and then sequentially to the most stable T_d structure (³A₂). If the molecular system is promoted to the lowest ³B_2g state, the D_4h structure can directly deform into the most stable T_d structure along the b_2u vibrational mode. For OsH₄, the ground state (⁵B_1g) at the D_4h structure deforms into a D_2d structure and the resulting ⁵B₂ state strongly interacts with the lowest ³E and ¹A₁ states due to the spin-orbit couplings (SOCs). As a result, it was shown that the relativistic potential energy of the lowest spin-mixed state (ground state) monotonically decreases along the D_2d deformation path from the D_4h to the T_d structure.     

Addition-type polynorbornene with Si(CH3)3 side groups: Detailed study of gas permeation and thermodynamic properties

Polymerization of norbornene bearing Si(CH₃)₃ groups in the five position with the opening of double bonds was performed. By accurate selection of the ratios catalyst/co-catalyst and monomer/catalyst the samples with increased molecular mass (about 400,000) were obtained. Transport parameters of this, addition type poly(trimethylsilyl norbornene) (PTMSN) were measured using the gas chromatographic and mass spectrometric methods for different gases (H₂, He, O₂, N₂, CO₂, CH₄, C₂H₆, C₃H₈ and n-C₄H₁₀). Temperature dependence of the permeability coefficients (P) indicated that low activation energies of permeation (E_P) and diffusion (E_D) are characteristic for PTMSN. In some cases (CO₂, C₂H₆) negative E_P values were observed. Thermodynamics of vapor sorption in this polymer was studied using the inverse gas chromatography method. It was shown that PTMSN is characterized by very large solubility coefficients S similar to those of poly(trimethylsilyl propyne) (PTMSP). The comparison of the P, D, and S values of these highly permeable polymers showed that the greater permeability of PTMSP is determined by the larger D values. Application of different approaches for the determination of the size of microcavities in PTMSN indicated that this polymer is characterized by large size of microcavity (800–1200 ?³).     

Kinetics of biodesulfurization of a high-sulfur coal

The apparent activation and deactivation energies and the corresponding frequency factors of coal desulfurization byThiobacillus ferrooxidans have been determined to be ΔE _a = 60.9 kJ,A _a = 1.45 s^-1 and ΔE_d = 178.3 kJ,A _d = 5.65×10²⁷ s^-1, respectively. The thermo-dynamic values (AG^?, ΔH ^?, and ΔS^?) of the activated complex were calculated. Kinetic parameters of the Monod equation were determined to beV _m = 55.9 mg dm^-3 h^-1 andK = 24.1% pulp density. The maximum rate of desulfurization of coal was found to beV _m = 55.7 mg dm^-3 h^-1 for the particle size. The generalized second order regression equation relating the yield of desulfurization to the leaching parameters was shown to adequately predict coal extraction data and optimum values of process variables. Tank leaching studies using optimum conditions resulted coal desulfurization about 90%. The iron hydrolysis reactions involving the formation of mono- and poly-nuclear, hydroxo- and sulfato complexes of amorphous and crystalline precipitates were discussed.