S. G. Semenov

Adamant-1,3,5-triyl super dodecahedranes

By quantum chemical DFT M06-2X/6-31G(d,p) method, the equilibrium parameters of rigid and stable hydrocarbon clusters of icosahedral symmetry with a dodecahedron structure whose sites are occupied by 20 adamant-1,3,5-triyl moieties linked with each other either directly or through bridges containing two or four carbon atoms are determined. The radius of the smallest studied quasispherical molecules is 1.05 nm and that of the largest one is 1.76 nm. The radius of the inner cavity in them varies from 0.37 nm (C200H260) to 1.06 nm (C320H260). Perfluorination increases the outer and decreases the inner radius of super dodecahedrane.

A quantum chemical study of silsesquioxanes: H8Si8O12, Me8Si8O12, H@Me8Si8O12, He@Me8Si8O12+, and He@Me8Si8O12

Quantum chemical PBE0 and B3LYP/cc-pVTZ, PBE0, B3LYP, RHF and MP2/6-31G(d,p) methods are employed to calculate the structural parameters of octa(silsesquioxane) H8Si8O12 and octa(methylsilsesquioxane) Me8Si8O12. These molecules and complexes H@Me8Si8O12, He@Me8Si8O12+, and He@Me8Si8O12 have highly symmetric (Oh) equilibrium configurations. With the use of the PBE0 method and a cc-pVTZ multicenter basis set common for the complex and its components coincidence is achieved between the calculated polarizability of a free He atom and the experimental value of 0.21 Å3 and the polarizability depression of 0.17 Å3 was found for He@Me8Si8O12. In order to avoid the false conclusion about molecular symmetry the calculations of the structure of silsesquioxanes must be performed with sufficiently high accuracy (Int = ultrafine and Opt = tight in the use of the GAUSSIAN program).

A quantum chemical study of the Fe@C 60 endocomplex

At the DFT (U)PBE0/cc-pVDZ level the structural parameters of a hypothetical Fe@C60 endocomplex are determined. The (A1//C3v)–Fe@C60 state characterized by the electron spin square of 3.07 au, the free valence of 4.15, the dipole moment of 1.15 D, and the 172 pm Fe nuclear shift relative to the center of inertia of С60 corresponds to the energy minimum. The Stone–Wales rearrangement in the quasi-triplet state increases the endocomplex energy by 1.56 eV and by 0.79 eV in the quasi-quintet state.

A quantum chemical study of tricyclooctane and its congeners

A PBE0/6-311G(3d5f7,p) quantum chemical method is used to determine the structural parameters of the molecules of sin- and anti-tricyclo[4.2.0.02.5]octane, [2.2.2]propellane, tricyclo[3.3.0.02.6]octane, prismanes (CH)2n (n = 1–7), and dicubane C12H8. Bond lengths in anti-tricyclo[4.2.0.02.5]octane amount to 1.572 Å, The tetratomic ring in tricyclo[3.3.0.02.6]octane is a flattened tetrahedron with internuclear distances of 1.551Å and 2.037 Å. The symmetry of C8H8sin-tricyclo[4.2.0.02.5]octa-3,4,7,8-tetrayl moieties in prismanes and metal organic compounds (C8H8RhCl2RhC8H8, C8H8RhCl2RhC7H8, and C8H8PdCl2) is higher than the symmetry of a free sin-tricyclo[4.2.0.02.5]octane molecule.

A Quantum Chemical Study of the Acidity of Acetylene and 1,2-Dihydrobuckminsterfullerene Derivatives

DFT PBE0/cc-pVDZ method and the polarizable continuum model were used to determine pKa values for buckminsterfullerene-acetylene hybrids C60HCCH, C60HCN, tert-butylacetylene, and propyne relative to tert-BuC60H in a vacuum, carbon disulfide, tetrahydrofuran, and dimethyl sulfoxide. The energies of the СH-acid molecule and the carbanion (fulleride- or acetylide anion) were calculated using the same number of Gaussian orbitals. The surfaces of cavities formed by molecules and anions in a solvent are composed of spheres encompassing both atomic nuclei and lone electron pairs. An additional sphere excludes the solvent from the inner cavity of the fullerene.

A Quantum Chemical Study of C60Cl30, C60(OH)30 Molecules and Fe@C60(OH)30 Endocomplex

Abstract(U)PBE0/cc-pVDZ method is used to study the structure of C60Cl30, C60(OH)30 molecules and Fe@C60(OH)30 endocomplex. The triplet state of the endocomplex is shown to be the lowest in energy among its four states corresponding to different spin multiplicities and positions of Fe nucleus within the fullerene cavity. This state is characterized by bonding between the iron atom and one of two benzenoid cycles of the carbon cage, six internuclear Fe–C distances (208 pm), and 1s22s22p63s23p63d7.24s0.14p0.3 electron configuration of iron with spin population of 2.36.

A quantum chemical study of gallium(III) (μ-oxo)bis[phthalocyaninate] and gallium(III) (μ-oxo)bis[perfluorophthalocyaninate] molecules

By the DFT (U)PBE0 method the structural parameters of molecules, cations, dications, and anions of gallium(III) (μ-oxo)bis[phthalocyaninate], gallium(III) (μ-oxo)bis[perfluorophthalocyaninate], and heteroleptic bis-phthalocyaninate FPcGaOGaPc are determined. The ∠GaOGa bond angle and the Ga⋯Ga internuclear distance depend non-monotonically on the charge. The ionization potential of the (PcGa)2O molecule of 5.71 eV, the second electron detachment energy of 7.94 eV, and the electron affinity of 2.14 eV increase to 6.14 eV, 8.37 eV, and 2.72 eV after the perfluorination of one Pc moiety and to 6.60 eV, 8.70 eV, and 3.13 eV respectively after complete fluorination.

A quantum chemical study of the structure of dodecasilsequioxane H12Si12O18

Quantum chemical B3LYP/cc-pVTZ, PBE0/cc-pVTZ, and MP2(full)/6-311G(d,p) methods are used to calculate the structural parameters of dodecasilsequioxane H12Si12O18 and the H12Si12O18+ cation. According to DFT/cc-pVTZ calculations the energy of H12Si12O18 (D6h) is 1.3–1.7 kcal/mol higher than the energy of H12Si12O18 (D2d). A reduction of the basis set results in a greater energy difference of H12Si12O18 isomers. For the cation 2B2u and 2B1 electronic states are obtained, which correspond to symmetric equilibrium structures H12Si12O18+ (D6h) and (D2) respectively. For the He@H12Si12O18 endocomplex the D2d symmetry is obtained; for He2@H12Si12O18 the D2h symmetry; and for H2@H12Si12O18 the D6h symmetry.

A quantum chemical study of [1.1.1.1]pagodane and its related compounds

The PBE0/6-31G** quantum chemical method is used to determine the symmetry and equilibrium structural parameters of the molecules of [1.1.1.1]pagodane (C20H20, D2h), two dienes (C20H20, D2h), two diradicals (C20H20, C2ν), and two dications (C20H202+, D2h and C2ν). The energy of a highly symmetric dication with a rectangular cycle is lower by 36 kcal/mole than that of a low symmetric dication with a trapezoidal cycle. The polarization interaction with liquid methylene chloride causes its decrease by 147 kcal/mole.

Electronic structures of 2, 5,8-trimethyl-10-phenylphenazaborine and 2,8-dibromo-5-methyl-10-(β-aminoethoxy)phenazaborine

SCF MO LCAO has been used in the CNDO/2 approximation to determine the valence states for borine and nitrogen in substituted phenazaborines containing 3-coordinated and 4-coordinated boron atoms. In the first case, the heterocyclic electron structure has donor-acceptor interaction for the heteroatom π orbitals via the π-electron system in the phenylene groups and substantial conjugation of the latter via the heteroatom π orbitals. In the second, those effects are much weaker and the heterocycle has a nonplanar structure. The valence index VB(4) for the 4-coordinated B(4) does not exceed VB(3).