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 topology of the carbon framework of the studied compounds is identical to the topology of the corresponding carbon fragments of C-60 fullerene. Analysis of the structure of the frontier orbitals of systems 1-4 demonstrated that the tendency of the C20H10 molecule to form sandwich x-complexes of the eta(5)-type with transition metal atoms is small; however, this tendency is significantly larger than that of C30H10. Moreover, the exclusion of the five-membered cycle of bowl-shaped unsaturated hydrocarbon molecules and anions from the conjugated system (as a result of the conversion of five framing C atoms to saturated carbon centers) favors the stabilization of their eta(5)-type a-complexes with M(C5H5) species. The stability of these complexes must approach the stability of classical sandwich complexes of the ferrocene type. The results obtained have been extrapolated to polyhedral C-60 and C-70 carbon clusters.