Ab initio calculations of group IVA tetrachloride complexes: IV. Dynamics of the formation of the complex of SiCl<Subscript>4</Subscript> with trimethylamine

Quantum-chemical calculations of the system SiCl₄←N(CH₃)₃ were fulfilled by the RHF/6-31G(d) and B3LYP/6-311G(d) methods with full geometry optimization at varied Si←N distances. The experimental electronic and steric structure of the complex were fit not on full geometry optimization but on the geometry optimization with the Si←N distance fixed at the experimental estimate. The calculations showed that the components polarize each other as come closer together. Furthermore, the electron density is transferred from the H atoms of the donor onto the Cl atoms of the acceptor. The C, N, and Si atoms serve only as electron density conductors. Original Russian Text V.P. Feshin, E.V. Feshina, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77, No. 5, pp. 786–791. For communication XX, see [1].     

Ab initio calculations of complexes of group IVA tetrachlorides: VI. Structure and dynamics of formation of a complex of GeCl<Subscript>4</Subscript> with tetramethylurea

RHF/6-31G(d) calculations of the GeCl₄←OC[N(CH₃)₂]₂ system were done with full geometry optimization and at varied Ge←O distances. The calculated structure of the complex GeCl₄←OC[N(CH₃)₂]₂ and its ³⁵Cl NQR parameters were consistent with the experimental data not at the fully optimized geometry of the system but at the Ge←O distance fixed at 2.0 Å, at which the total energy of the system is higher by 0.264 eV. With a decrease in the Ge←O distance from ∞ to 1.9 Å, the electron density of the Cl atoms increases as a result of the electron density transfer from the H atoms and polarization of the Ge-Cl bonds under the action of the electron-donor fragment. The O, C, and N atoms of this fragment are merely conductors of the electron density from the H atoms of the methyl groups to the Cl atoms of the electron acceptor.     

Ab initio calculations of group IVA tetrachloride complexes: VII. Structure and dynamics of the formation of GeCl<Subscript>4</Subscript> complexes with hexamethylphosphoric triamide

Quantum-chemical calculations by the RHF/6-31G(d) method were performed for the systems GeCl₄←[N(CH₃)₂]₃ and GeCl₄←₂OP[N(CH₃)₂]₃ with full geometry optimization and varied Ge←O distances. The calculations with full geometry optimization gave trigonal-pyramidal and trans-octahedral structures, respectively, which agrees with experimental NQR data. As the components of a system get closer together, mutual polarization followed by electron density transfer from H atoms of the electron donor onto Cl atoms of the electron acceptor take place. The O and Ge atoms act as conductors in this electron density transfer. Nonempirical quantum-chemical calculations do not reproduce adequately the p _σ density of the axial Cl atom in the trigonal-bipyramidal complex.     

Ab initio calculations of complexes of tetrachlorides of Group IVA elements: VIII. Structure of SiCl<Subscript>4</Subscript> complexes with hexamethylphosphoric triamide and dynamics of their formation

Quantum-chemical calculations of the systems SiCl₄←OP[N(CH₃)₂]₃ and SiCl₄←2OP[N(CH₃)₂]₃ with complete optimization of their geometry at various Si←O distances were performed by the RHF/6-31G(d) method. The first system was also calculated by the MP2/6-31G(d) method. The calculations of the systems with the complete geometry optimization resulted in trigonal-bipyramidal and trans-octahedral structures, respectively, having energy minima. When the components of the latter system approach each other, first their mutual polarization occurs, and then it is accompanied by electron density transfer from the H and P atoms of the electron-donor molecules to the Cl atoms of the acceptor. The results of the calculation of the trans-octahedral complex agree with the experimental ³⁵Cl NQR data. The electron density of Cl atoms increases upon complex formation, mainly due to an increase in their p _σ electron density.     

Ab initio calculations of complexes of group IVA element tetrachlorides: II. Dynamics of complex formation of GeCl4 with pyridine

RHF/6-31G(d) calculations of the trans-octahedral complex of GeCl₄ with pyridine were performed with full geometry optimization and at varied coordinate of the complexation reaction. The results obtained do not confirm the hypothesis that the complex is formed owing to interaction of the N atom with unoccupied d orbitals of the Ge atom. The complex formation is initiated by the interaction of the coordination centers (Ge and N), resulting in mutual approach of the system components, their polarization, and, when the distance between the components becomes sufficiently short, transfer of the electron density from the H and C atoms of the electron donor to the Cl atoms of the acceptor. In the process, a multicentered bond involving all the atoms of the Ge coordination polyhedron is formed.     

Ab initio calculations of complexes of group IVA element tetrachlorides: II. Dynamics of complex formation of GeCl4 with trimethylamine

RHF/6-31G(d) calculations of the system GeCl₄←N(CH₃)₃ were performed with full geometry optimization and at varied Ge←N distance. Mutual approach of the system components is accompanied by their mutual polarization followed by electron density transfer from the H atoms of the donor to the Cl atoms of the acceptor. The C, N, and Ge atoms act merely as conductors of this electron density. The total energy of the system decreases until the Ge←N distance of 3.412 Å is attained; at this distance, however, the complex is not yet formed. The complex formation involves an increase in the energy by 0.213 eV. The applicability of the RHF/6-31G(d) method to studying the trigonal-bipyramidal complex was assessed.     

Ab initio calculations of group IVA tetrachloride complexes: IX. Special features of the energy characteristics of the complexes

Quantum-chemical calculations of systems Cl₄M L and Cl₄M 2L (M = Si, Ge) with full geometry optimization and with a fixed M L distance, as well as calculations of the individual components of the complexes are performed by the RHF/6-31G(d) and B3LYP/6-311+G(2d,p) methods. It is shown that in the crystal state the molecular form may differ from that most favored by energy. The total energy of trans-octahedral complexes of GeCl₄ with organic ligands is lower than the sum of the energies of their constituent components, while that of analogous SiCl₄ complexes may be either lower or higher than the sum of the energies of their constituent components. Even though trigonal-bipyramidal complexes of MCl₄ with organic ligands are commonly energetically unfavorable, they still can form. The formation of MCl₄ complexes is affected substantially by intermolecular interactions in crystal.     

ab initio calculations of complexes of group IVA tetrachlorides: I. Dynamics of complex formation of SiCl4 with pyridine

Quantum-chemical calculations of a trans-octahedral complex of SiCl₄ with pyridine involving complete optimization of its geometry and variation of the coordinate of the complex-formation reaction were fulfilled by the RHF/6-31G(d) method. The calculated electron distributions of chlorine atoms in the complex were confirmed by experimental ³⁵Cl NQR data. As the components of the system SiCl₄←2NC₅H₅ come closer together, the electron density on N atoms increases and on the Si atom decreases as a result of polarization of these components. On further mutual approach of the components, the electron density is transferred from the ligand to chlorine atoms (mainly on their p orbitals).     

Molecular structure of C(SiCl<Subscript>3</Subscript>)<Subscript>4</Subscript> tetrakis-(trichlorosilyl)methane

Methods of quantum chemistry and gas phase electron diffraction (at a temperature of 303±5 K) are applied to determine parameters of the geometric configuration of C(SiCl₃)₄ tetrakis(trichlorosilyl)methane. Frequencies of the vibrational spectrum are calculated. The value of the internal rotation barrier of SiCl₃ groups relative to the Si-C bond is 148.7 kJ/mol.     

Formation and structure specifics of the SnCl<Subscript>4</Subscript> complex with pyridine-3-carboxylic acid chloride by ab initio calculations

Feasible structures of the SnCl₄ complex with pyridine-3-carboxylic acid chloride were calculated by the MP2/LANL2DZ method. The results of calculations were compared to experimental ³⁵Сl nuclear quadrupole resonance (NQR) data. The coordination site of the ligand was found to be the nitrogen atom and not the carbonyl oxygen atom. The partial negative charge of the electron-donating center and the positive charge of the electron-drawing center increase appreciably upon complex formation.     

Silicon nitride nanofibers produced by the pyrolysis of SiCl<Subscript>4</Subscript> in H<Subscript>2</Subscript> and N<Subscript>2</Subscript> media

The synthesis of fibrous Si₃N₄ nanostructures by gas-phase chemical deposition during the pyrolysis of silicon tetrachloride in a hydrogen and nitrogen atmosphere was investigated. It was shown that the products contained both amorphous Si₃N₄ nanofibers and their α and β phases both with and without a silicon coating. In addition to the Si₃N₄ nanofibers the products also contained nanoribbons. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 81–84, March–April, 2007.     

Phase formation in the Ag<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-MgMoO<Subscript>4</Subscript>-Al<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> system

The subsolidus region of the Ag₂MoO₄-MgMoO₄-Al₂(MoO₄)₃ ternary salt system has been studied by X-ray phase analysis. The formation of new compounds Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.4) and AgMg₃Al(MoO₄)₅ has been determined. The Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ variable-composition phase is related to the NASICON type structure (space group R \(\bar 3\) c). AgMg₃Al(MoO₄)₅ is isostructural to sodium magnesium indium molybdate of the same formula unit and crystallizes in triclinic system (space group P \(\bar 1\), Z = 2) with the following unit cell parameters: a = 9.295(7) Å, b = 17.619(2) Å, c = 6.8570(7) Å, α = 87.420(9)°, β = 101.109(9)°, γ = 91.847(9)°. The compounds Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ and AgMg₃Al(MoO₄)₅ are thermally stable up to 790 and 820°C, respectively.     

Ab initio parametrized polarizable force field for rutile-type SnO<Subscript>2</Subscript>

We report a new, polarizable classical force field for the rutile-type phase of SnO₂, casserite. This force field has been parametrized using results from ab initio (density functional theory) calculations as a basis for fitting. The force field was found to provide structural, dynamical and thermodynamic properties of tin oxide that compare well with both ab initio and experimental results at ambient and high pressures.     

Phase formation in the InPO<Subscript>4</Subscript>-Na<Subscript>3</Subscript>PO<Subscript>4</Subscript>-Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> ternary system

The 950°C isothermal section of the InPO₄-Na₃PO₄-Li₃PO₄ ternary system was studied and constructed; one-, two, and three-phase fields are outlined. Five solid-solution regions exist in the system: solid solutions based on the complex phosphate LiNa₅(PO₄)₂ (olympite structure), the indium ion stabilized high-temperature Na₃PO₄ phase (Na_{3(1 − x)}In _x (PO₄); space group Fm [`3]\bar 3 m), the complex phosphate Na₃In₂(PO₄)₃, and the α and β phases of the compound Li₃In₂(PO₄)₃. A narrow region of melt was found in the vicinity of eutectic equilibria. All the phases detected in the system are derivatives of phases existing in the binary subsystems. Isovalent substitution of lithium for sodium in Na₃In₂(PO₄)₃ leads to a significant increase in the region of a NASICON-like solid solution.     

Triple-decker complexes with a central borole ligand C<Subscript>4</Subscript>H<Subscript>4</Subscript>BR

The review summarizes the results of the recent author’s research on the synthesis of triple-decker complexes with bridging borole ligand. Electrophilic stacking of sandwich compounds with [(ring)M] ⁿ⁺ (n = 1, (ring)M = (C₅R₅)Ru, (C₄Me₄)Co; n = 2, (ring)M = Cp*Co, Cp*Rh, etc.) cationic fragments were used as a general method of synthesis of the complexes. The influence of the substituent at the boron atom on the course of stacking reactions is discussed. The spectral, structural, and electrochemical properties of the complexes synthesized are also considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 1–7, January, 2008.     

A study of phase formation in the subsolidus region of the system Na<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-MnMoO<Subscript>4</Subscript>-Cr<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Phase relationships in the subsolidus region of the system Na₂MoO₄-MnMoO₄-Cr₂(MoO₄)₃ were studied by means of X-ray diffraction and differential-thermal analyses. The possibility of obtaining a variablecomposition phase Na_1?x Mn_1?x Cr_1+x (MoO₄)₃ (0 ≤ x ≤ 0.5) and ternary molybdate NaMn₃Cr(MoO₄)₅ was examined. The temperature dependence of the conductivity of the phase Na_1?x Mn_1?x Cr_1+x (MoO₄)₃ was analyzed.     

Ab initio investigation of the lower-energy candidate structures for (H<Subscript>2</Subscript>O)<Subscript>10</Subscript><Superscript>+</Superscript> water cluster

Low-lying structures of water cationic clusters and the compounds with the OH radical have become a hot topic in recent years. We here investigate the cluster \( {\left({\mathrm{H}}_2\mathrm{O}\right)}_{10}^{+} \) and calculate its ideal structures by the quantum chemical calculation together with the particle swarm optimization method. We analyzed the properties of the obtained lower-energy isomers of \( {\left({\mathrm{H}}_2\mathrm{O}\right)}_{10}^{+} \). Their energies are further re-optimized and demonstrated at three different methods with two basis sets. Based on our numerical calculations, a new cage-like structure of \( {\left({\mathrm{H}}_2\mathrm{O}\right)}_{10}^{+} \) with the lowest energy is obtained at MP2/aug-cc-pVDZ level. Our results showed the comparison of energy order at different conditions and demonstrated the influence of temperature on the relative Gibbs energy and IR spectra. Moreover, we also contained the molecule orbitals to discuss the stability of these representative isomers.     

Phase formation of complex phosphate K<Subscript>4</Subscript>Ti<Subscript>3</Subscript>Ni(PO)<Subscript>4</Subscript> in K<Subscript>2</Subscript>O-P<Subscript>2</Subscript>O<Subscript>5</Subscript>-TiO<Subscript>2</Subscript>-NiO melt solutions

The principles of complex phosphate crystallization in K₂O-P₂O₅-TiO₂-NiO solution melts are studied for the ratios K/P = 0.7?1.4, Ti/P = 0.15, and Ni/Ti = 0.1?2.0. The phase-formation field and parameters are determined for a new complex phosphate K₄Ti₃Ni(PO₄)₆, which is isostructural to langbeinite. A single-crystal X-ray diffraction experiments is carried out for this phosphate (space group P2₁3, a = 9.8247(10) Å).