E. G. Gal'pern

Fullerene C{sub 60} as a {eta}{sup 5-} and {eta}{sup 6}-ligand in sandwitch-type {pi}-complexes with transition metals

The molecular and electronic structures of some hypothetical sandwich-type π-complexes of transition metals with fullerene C60 were modeled. The M-C60 bonds in η5-C60MCp+ complexes (M = Fe, Ru, Os) are less strong than the M-Cp bonds in ferrocene, ruthenocene, and osmocene, respectively. The η6-C60MC6H6 complexes (M = Cr, Mo, W) should be less stable than their classical analogs (C6H6)M(C6H6). The coordination of a metal atom with the fullerene at its pentagonal face is more energetically favorable than at a hexagonal face.

Molecular and electronic structure of several heterofullerene BNC58 and B2N2C56 oligomers and [B2N2C56]n macromolecule

Molecular and electronic structure of heterofullerene BNC58 (Cs) and B2N2C56 (C2h) monomers, B2N2C116 and B4N4C112 dimers, and B6N6C168 trimer (the last three molecules withC2h symmetry) was simulated by the MNDO method. Clusters BNC58 and B2N2C56 are formed by replacement of carbon atoms participating in one or two of the most distant oppositely lying (6,6)-type C−C bonds in fullerene C60 by B and N atoms. In one of the two studied isomers of the B2N2C116 dimer, the monomers are linked by the four-membered carbon cycle, while the heteroatoms form the most distant oppositely lying bonds of the dimer. In the other isomer of the B2N2C116 dimer, as well as in the B4N4C112 dimer and B6N6C168 trimer, the monomers are linked by four-membered B2N2 cycles with alternation of the atoms. For all the systems studied, the optimum geometric parameters, heats of formation, ionization potentials, and atomic charges were calculated. Dimerization energies of heterofullerenes BNC58 and B2N2C56 lie in the range from 33 to 49 kcal mol−1. It was found that the B2N2C116 dimer, in which the monomers are linked by the four-mernbered carbon cycle, is the most stable system. In the case of B2N2C56 trimerization, the energy gain (compared to the triple monomer energy) is about twice as large as the dimerization energy. Molecular structure of the quasi-linear [B2N2C56)n macromolecule was simulated, and extended Hückel calculations of its energy band structure by the crystal orbital method were performed. It was found that the electron energy spectrum is of semiconducting type (the band gap is equal to 1.27 eV.

Molecular and electronic structures of some trimers of polyhedral carbon clusters

Geometries and electronic structures of four crimped linear carbon clusters were modeled by the MNDO/PM3 method. Three of these clusters (C180 clusters) are trimers ofIh-C60 fullene, which differ from each other by the mode of linkage of the monomers. The fourth cluster (C172 pseudo-trimer) consists of two C58 fragments of C60 fullerene linked to each other through the C56 cluster. The optimum geometric parameters, hieats of formation, and ionization potentials were calculated for the above-mentioned systems as well as for the corresponding C120 and C116 dimers. The possibility of extrapolation of the data on dimers and trimers to linear oligomers of the C60 and C56 clusters with a larger number of repeating fragments is discussed. The character of linkages of monomers was analyzed for the two trimers under consideriation, which have the most complex mode of binding of the C60 fullerene molecule and its fragments, using the C60H20 and C72H24 molecules (whose carbon skeletons model the structures of these linkages) as examples.

Simulation of molecular and electronic structure of polyhydrogenated (n,0)-tubulenes and their analogs intercalated with lithium

Molecular and electronic structure of four polyhydrogenated (n,0)-tubulenes, namely, [−C24H4−]m (1), two isomers of composition [−C28H4−]m (2 and3), and [−C32H4−]m (4) withn benzene rings in the cross section (n=6, 7, 7, and 8, respectively), was simulated atm>1 (m is the number of repeating fragemnts). It was assumed that hydrogen atoms are attached to all carbon atoms lying on the two most distant elements of the cylinders of the corresponding tubulenes. The energy band structures of macromolecules1–4 and their Li-intercalated analogs [−C24H4Li−]m (5) [−C28H4Li−]m (two isomers,6 and7), and [−C32H4Li−]m (8), containing one Li atom per repeating unit at each center, were obtained in the EHT approximation by the crystal orbital method. Geometric parameters of repeating units of structures1–8 were found after MNDO/PM3 optimization of the energies of hydrocarbon molecules C72H24, C84H26 (two geometric isomers), and C96H28, containing three repeating units of corresponding tubulenes1–4 each. The conductivity types of polyhydrogenated tubulenes1–4 are the same as those of their precursors, (6,0)-, (7,0)-, and (8,0)-tubulenes. Dispersion curves of systems5–8 are much the same as those of macromolecules1–4; however, electron energy spectra of5–8 possess metallic conductivity type and the positions of Fermi levels for these systems are higher than for compounds1–4.

Simulation of the structure of some silicon carbide clusters by the MNDO method

Simulations of the geometric and electronic structure of C44, C45, Si45, C40Si5, and C44Si clusters were performed by the MNDO method. The geometries of the filled clusters, calculated by the MM2 method, were used as initial approximations. It was found that the filled clusters C45 and C44Si are transformed into endohedral clusters X@C44 (X-C or Si, respectively) after energy optimization. The highest occupied energy level of the HOMO of the filled tetrahedral cluster Si45 ofT symmetry is triply degenerate and is only occupied by four electrons. The structure of Si452− dianion ofT symmetry was calculated. Two filled structures for the C40Si5 cluster were found. The coordination numbers of the central Si atom in these structures are 4 and 3, respectively.

ESR spectra and electronic structure of the C120·+ radical cation and the paramagnetic C120O2+ dication and C120O2− dianion

Electronic structure of the C120·+ radical cation and the paramagnetic C120O2+ dication and C120O2− dianion in the triplet state was calculated by the MNDO/PM3 method in the valence approximation. The density distributions of the unpaired electrons in these systems were found and the ESR spectra of the above species were interpreted.