MOLECULAR AND ELECTRONIC-STRUCTURE OF SOME BOWL-SHAPED UNSATURATED HYDROCARBON MOLECULAR-SYSTEMS, POSSIBLE PRECURSORS OF C-60 FULLERENE

The AM1 calculations of hydrocarbon molecules C20H10 (1) and C30H10 (2 ) and anions C20H15- (3) and C30H15- (4) have been performed with the full energy optimization of the geometric parameters. The chosen topol ogy of the carbon framework of the studied compounds is identical to t he topology of the corresponding carbon fragments of C-60 fullerene. A nalysis of the structure of the frontier orbitals of systems 1-4 demon strated that the tendency of the C20H10 molecule to form sandwich x-co mplexes of the eta(5)-type with transition metal atoms is small; howev er, this tendency is significantly larger than that of C30H10. Moreove r, the exclusion of the five-membered cycle of bowl-shaped unsaturated hydrocarbon molecules and anions from the conjugated system (as a res ult of the conversion of five framing C atoms to saturated carbon cent ers) favors the stabilization of their eta(5)-type a-complexes with M( C5H5) species. The stability of these complexes must approach the stab ility of classical sandwich complexes of the ferrocene type. The resul ts obtained have been extrapolated to polyhedral C-60 and C-70 carbon clusters.