S. G. Shevchenko

Quantum-chemical analysis of silicon atom pentacoordination

Abstract The energy characteristics and dynamics of charge redistribution in the X ax (H 3 ) eq Si…Y group in changing the Si ← Y coordination bond length and rehybridization of the silicon atom valence shell have been calculated in MNDO approximation. The calculations are carried out with a complete optimization of molecular geometry of C 3y symmetry. The formation of complex anions X = H, F, Cl; Y = H − (I) and molecular complex F ax (H 3 ) eq Si ← OCHOH (II) is discussed. The main difference between pentacoordinate structures I and II is a weaker perturbation of the FSiH 3 molecule caused by the OCHOH ligand as compared to that of H − . When tetrahedral silicon is involved in the formation of an additional donor-acceptor Si ← Y bond, this atom acquires a higher positive charge as compared with the tetracoordinate state of its valence shell. In this case, the electronic density is transferred to the axial and equatorial atoms attached to silicon, affecting predominantly the substituent X ax charge. The complexing energies calculated are as follows, kJ/mol: −253.9 (X = H), −273.2 (X = F), −398.7 (X = Cl) for I and 72.4 for II.

The influence of intermolecular interactions on the SiH bond vibration in silatrane and its c-substituents

Abstract Spectra of the silatrane HSi(OCHRCH2)3N and its 3,7,10-trimethyl- and -trifluoromethyl derivatives have been studied. The dependences of frequency and integral intensity of the SiH vibration on solvent polarity and temperature have been established. It has been shown that interaction of silatrane molecules with the solvent is universal in character. The phenomenon of the changing SiH vibration is explained by the possible formation of a three-centered orbital bending the atoms of hydrogen, silicon and nitrogen. In contrast to triethoxysilane, a dependence between v(SiH) and Σσ∗ values of substituents in the cycle has been observed for silatranes.

Quantum-Chemical Study of Interactions between the Hydroxonium Cation and the Monomethyl Mercury Cation in Aqueous Media

AbstractThe potential surface of the reaction between the polyhydrated monomethyl mercury cation and the hydroxonium cation is considered. An

X-ray spectral study of the electronic structure of organic four- and five-coordinated silicon derivatives

S_{N^2 }

Quantum-Chemical Study of Hydration Effects for Monomethylmercury, -Cadmium, and -Zinc Cations

type reaction, resulting in solvate-separated products (mercury dication and methane molecule), was found to be thermodynamically probable. The thermal balance of the reaction is 132.3 kJ/mole. The activation energy of the limiting stage of the process is 56.7 kJ/mole.

Mechanism of mercury monomethyl cation detoxication in the interaction with 1-chloro-2,2-propane dithiol

In the MNDO approximation with full or partial optimization of geometry, we have calculated the energy characteristics and charge redistribution in the model systems Xax(H3)eqSi...Y with variation in the length of the coordination bond Si ← Y and rehybridization of the AOs of the valence shell of the silicon atom. We have considered the formation of the complex anions X=H, F, Cl; Y=H− (I) and the complex X=F, Y=O=CH-OH (II). Upon formation of the intramolecular coordination bond Si ← Y, transfer of electron density occurs to the axial and equatorial atoms surrounding the silicon. We have calculated the complexation energy (kJ/ mole): −253.9 (X=H, Y=H−), −273.2 (X=F, Y=H−), −298.7 (X=Cl, Y=H−) and 72.4 for X=F, Y=O=CH-OH.

Quantum chemical study of complexation effects of monomethyl mercury cation with inorganic ligands (Cl, Br, I, HO, HS, HSe) in aqueous medium

The chemical shifts of the SiK~ and CIK~ lines have been determined. They have been used to obtain the Pauling charges on the silicon and chlorine atoms in silatrane molecules of the type XSi(0CHRCH2)3-n(0CH2CH2)n N (R = H, CH3, n = 0-3), the corresponding Si-substituted derivatives of triethoxysilane XSi(0CH2CH3)3 (X = H, CI, CH3, CICH2), and the heterocyclic compounds (CH3)2Si(0CH2CH2)2Y, where Y = O, CH3N, and (CH3)2Si(0CH2CH3)~. It has been shown that increase in the coordination number of the silicon atom leads to an increase in its positive charge, and that this increase may be reduced by N + Si interaction.

Quantum chemical study of the effects of interaction of polyhydrated Hg(II) with methylcobalamin — A derivative of vitamin B12

The dipole moments of the trialkyl(phenoxy) derivatives of the Group IVB elements in the ground and first singlet excited states show that in the excited state the electron-acceptor properties of the MR3 groups relative to the unshared pair of the oxygen atom increase in the following order of change in M (Si < Ge < Sn), which is the reverse of the change in the ground state.