  Variations in the band structures of the two-dimensional C60-polymers are
studied, when pi-conjugation conditions are changed. We investigate the
rectangular and triangular polymers, in order to discuss metal-insulator
transitions, using a semiempirical model with the Su-Schrieffer-Heeger type
electron-phonon interactions. We find that electronic structures change among
direct-gap insulators and the metal, depending on the degree of pi-conjugations
in the rectangular polymer. The triangular polymer changes from the indirect
gap insulator to the metal as the pi-conjugations increase. High pressure
experiments could observe such pressure-induced metal-insulator transitions.
