Journal of Structural Chemistry

Novikov, A. N.; Bacherikov, V. A.; Shapiro, Yu. E.; Gren, A. I.

doi: 10.1007/s10947-006-0419-0pmid: N/A

The cone conformation of C4 symmetry is shown by the Hartree-Fock method (3-21G basis) to be the predominant conformer of calix[4]arene; the compressed cone of C2 symmetry is the major conformer of calix[6]arene. Using quantum chemical methods we calculated hydrogen bond cleavage energies for calix[4]-(ab initio and density functional methods) and calix[6]arene (ab initio), and also for the complex of calix[4]arene with carbon disulfide. These energies along with structural data point to the cooperative effect of hydrogen bonds. The results of these studies provided an explanation to the greater conformational lability of calix[6]arene compared with calix[4]arene molecules. It is also predicted that the nucleophilic substitution reaction involving calix[6]arene in the presence of weak bases and in aprotic solvents, as well as in the gas phase, will occur via diastereomeric transition states.

Mileev, M.; Kuzmin, S.; Parfenyuk, V.

doi: 10.1007/s10947-006-0420-7pmid: N/A

Clusters of boron nitride BxNx (x = 1–4, 12, 15, 30) were investigated by the Hartree-Fock and density functional methods using the 6-31G* basis. It was found that linear, cyclic, and shell structures are stable against minor deformations of the BxNx cluster. Inclusion of electron correlation in calculation markedly changes the electron density distribution and the structure of the clusters.

Sizova, O.; Sizov, V.

doi: 10.1007/s10947-006-0421-6pmid: N/A

A procedure that allows for solvation effects is suggested; it is designed for quantum chemical calculations of the electronic spectra of complex compounds. Based on Monte Carlo (MC) simulation of the solvation shell one can calculate the electrostatic potential created by the solvation shell at the sites of all atoms of the complex; appropriate corrections are added to the diagonal elements of the Fock matrix and to the matrix elements of the Hamiltonian in the configuration interaction method. The method suggested has been implemented based on the semiempirical (CINDO) version of the CI (configuration interaction) technique and tested on the following compounds: [Ru(NH3)5(py)]2+, [Ru(NH3)5(pyz)]2+, [Ru(bpy)(CN)4]2−, [Ru(NO)(py)4-NC-Ru(py)4(CN)]3+.

Prokuda, O.; Belosludov, V.; Igumenov, I.; Stabnikov, P.

doi: 10.1007/s10947-006-0422-5pmid: N/A

Experimental data have been analyzed and interpreted for four volatile acetylacetonates of trivalent metals Al, Cr, Fe, and Ir. The crystal lattice energies were calculated by the atom-atom potential method. The lattice energies obtained by using the Buckingham potential are in better agreement with the sublimation heats of these metal complexes than those calculated from the Lennard-Jones potential. The experimental dependences of vapor pressure for the complexes are in satisfactory agreement with the values obtained from the calculated lattice energies and entropies of crystal-gas transitions.

Shagun, V.; Smirnov, V.; Shagun, L.

doi: 10.1007/s10947-006-0423-4pmid: N/A

The detoxication properties of 2-mercapto-2-methyltetrahydro-1,4-thiazino[2,3,3,4-i,j]quinolinium chloride (II) with respect to the methylmercury cation (I) in the presence of six water molecules have been studied using the density functional theory (DFT) method. Interaction between I and II leads to generation of the hydroxonium cation, which catalyzes the demethylation process. The elementary stages of two reaction routes have been localized, and their thermodynamic and kinetic characteristics have been determined.

Talipov, M.; Ryzhkov, A.; Hursan, S.; Safiullin, R.

doi: 10.1007/s10947-006-0424-3pmid: N/A

Density functional theory methods correctly describe some properties of nitrosooxides. Electronic spectral data have been calculated for seven para-substituted aromatic nitrosooxides in different solvents using the UB3LYP/6-311+G(d,p) approximation. The calculated positions of maxima in UV spectra correlate with experimental data with high coefficient. Equations are suggested for predicting the positions of absorption maxima for the para-R-C6H4-NOO under study.

Alekseev, N.; Chernyshev, E.

doi: 10.1007/s10947-006-0425-2pmid: N/A

The density functional theory (DFT) method (GAUSSIAN-98 software, B3LYP functional, 6-311G(d,p) basis set) was used to calculate the spatial and electronic structures of a series of trichlorogermanes with the general formula Cl3GeCH2YC(O). AIM calculations gave the topological characteristics of the Ge-O dative bonds of these molecules. Analysis of the results showed that Ge and O atoms interact as closed-shell atoms and that the major contribution to Ge-O bonding is from Coulomb interaction between the germanium and oxygen atoms charged in the opposite sense.

Chipanina, N.; Aksamentova, T.; Voronkov, M.; Turchaninov, V.

doi: 10.1007/s10947-006-0426-1pmid: N/A

According to the data of quantum chemical calculations (HF, DFT), the isolated sp,sp conformer of (acetoxymethyl)trifluorosilane — pentacoordinated silicon compound — forms dimers with two intermolecular bonds Si-F→Si. The =O→Si intramolecular coordination bonds become stronger, which leads to the general stabilizing effect. In polar media, dimer formation is energetically unfavorable relative to monomer formation.

Girichev, G.; Tverdova, N.; Shlykov, S.; Rybkin, V.; Kuzmina, N.; Rogachev, A.

doi: 10.1007/s10947-006-0427-0pmid: N/A

In a mass spectrometric study, it was found that the saturated vapor over gadolinium tris-hexafluoroacetylacetonate Gd(C5O2HF6)3 contains molecular forms with a mass exceeding the mass of the dimer. The vapor overheated to 250–300°C contains only the monomer form. Simultaneous electron diffraction and mass spectrometric experiment aimed at investigating the structure of the Gd(hfa)3 monomer molecule was carried out at 284(5)°C. The Gd(hfa)3 molecule was found to have the symmetry of the equilibrium D 3 configuration. The basic structural parameters are r h1(Gd-O) = 2.291(10) Å, r h1(O-C) = 1.257(10) Å, r h1(C-Cr) = 1.404(6) Å, r h1(CF-F)av = 1.341(3) Å, ∠OGdO = 72.8(0.4)°. The GdO6 coordination polyhedron has the structure of a distorted antiprism. The rotation angle of the O-O-O trigonal faces relative to their position in a regular prism is 18.7(0.9)°. Quantum chemical calculations (HF/SBK, 6-31G*) generally reproduce the experimental structure, but the Gd-O internuclear distance is exaggerated by 0.04 Å.

Upadhyay, S.; Kumar, P.; Arora, V.

doi: 10.1007/s10947-006-0428-zpmid: N/A

The interaction of quinolone drugs Norfloxacin (NR) and Ciprofloxacin (CP) with magnesium, calcium and barium perchlorates was investigated. Solid complexes, obtained as products of this interaction, were isolated and characterized by elemental and thermal analysis, FT-IR spectral and electrical conductivity measurements. The spectral studies of the isolated complexes suggest that NR and CP act as bidentate ligands that bind through one carboxylic oxygen atom and the exocyclic carbonyl oxygen atom. The obtained results indicate the formation of the complexes of the following formulas: [M(CP)2](ClO4)2·xH2O and [M(NR)2](ClO4)2·xH2O, where M = Mg(II), Ca(II), and Ba(II).