V. V. Sliznev

Ab Initio Structure Investigation of the Enol Forms of β-Diketones RCOCH2COR (R = H, CH3, CF3)

The geometrical parameters, force field parameters, and vibrational frequencies of the enol forms of β-diketones RCOCH2COR (R = H, CH3, CF3) were calculated using the ab initio MO LCAO SCF method involving broad bases of Cartesian Gaussian functions. For acetylacetone (R = CH3), the potential surface of rotation of the two methyl groups was investigated in detail, and the minimal energy route of the transfer of the hydroxyl proton inside the chelate ring was calculated. For hexafluoroacetylacetone (R = CF3) and malonic dialdehyde (R = H), calculations were carried out only for stationary points on the potential energy surface. For all the geometrical configurations under study, the relative energies were refined with inclusion of electron correlation in terms of second-, third-, and fourth-order Möller–Plesset perturbation theory; for molecules with R = H, CH3, the configuration interaction procedure taking account of all single and double excitations was additionally employed. The experimental and theoretical data are compared with those available in the literature. The substituent effect on the geometrical and electronic structure of the chelate ring is studied.

Ab initio study of the ground and lower-lying excited electronic states of CoF2, CoCl2, CoBr2 and CoI2

The ground and lower-lying excited electronic states of CoX2 (X = F, Cl, Br, I) were investigated systematically by ab initio methods. The complete active space self-consistent field (CASSCF) and multiconfigurational quasi-degenerate second-order perturbation (MCQDPT2) levels of theory were employed. It was concluded that the dynamic electron correlation has to be taken into account in the prediction of the properties for such molecules. According to the results of the MCQDPT2 calculations, all investigated molecules have the linear equilibrium configuration and the 4Δg ground state. The equilibrium bond lengths r e(Co−X), force constants and harmonic vibrational frequencies were calculated for the ground and lower-lying excited electronic states. The Renner effect of bending vibrations was estimated to be very small.

Ab initio Study of the Geometrical and Electronic Structures of Sc(MDA)2 and Sc(MDA)3 Molecules

The geometrical parameters, force fields, and vibrational spectra of various geometrical configurations of Sc(MDA)2 and Sc(MDA)3 molecules were calculated using the restricted Hartree—Fock method taking into account electron correlation by second–order Möller–Plesset perturbation theory. The calculations were performed using effective pseudopotentials for describing atomic cores and valence double zeta basis sets supplemented by polarization functions. It was shown that the configurations of D3 [Sc(MDA)3] and D2h [Sc(MDA)2] symmetry correspond to the minimum on the potential energy surface of the ground electronic state. The configurations of D3h symmetry for Sc(MDA)3 and D2d for Sc(MDA)2 correspond to first–order saddle points. The ground electronic states of Sc(MDA)2 and Sc(MDA)3 molecules are the states of 2Ag and 1A1 symmetries, respectively. For both configurations (D2h and D2d of the Sc(MDA)2 molecule, the energies of vertical electron transitions were calculated using the CASSCF method. The formation of chemical bonding in the compounds considered was analyzed. It was shown that the Sc–O bond is predominantly ionic and the π conjugation is characteristic only of the oxygen–carbon skeleton of the chelate fragment. The results obtained are compared with literature experimental and theoretical data for related compounds.

Ab initio Study of the Structure of the Molecular Forms of C3H4O2

The geometrical parameters, force fields, and vibration frequencies were calculated by the ab initio SCF MO LCAO technique using extensive basis sets of Cartesian Gaussian functions for a number of structural isomers of the C3H4O2 molecule. The relative energies of all the isomers were refined in terms of second-order Möller–Plesset (MP2) perturbation theory including electron correlation. For the most energetically favorable forms of the C3H4O2 molecule, geometry optimization was fulfilled in the MP2 approximation. For the main conformer, β-hydroxypropenal, possessing a chelate OCCCO fragment, the data are compared with the experimental and theoretical data available in the literature. The MP2 calculated internuclear distances and bond angles are in good agreement with the experimental values. For each form of the C3H4O2 molecule, the geometrical and electronic structure is analyzed. It is shown that the presence of an intramolecular hydrogen bond is the characteristic feature of the structure of the isomers and an additional stabilizing factor.