ALTERNANT BORON-NITRIDE CAGES - A THEORETICAL-STUDY

Heteroatomic cages (BN/2NN/2) with borons and nitrogens fully replacin g alternant sets of carbons in cages are built graph-theoretically and investigated via the semiempirical MNDO Hamiltonian. The comparison w ith their parent carbon cages C-N is made in terms both of electronic and of geometric changes. Infinite classes first of octahedral symmetr y and second of hexagonal-bipyramidal symmetry fullerenoid cages are c onsidered in detail. The difference in the electronegativities for bor on and nitrogen implies the opening of HOMO-LUMO gaps for alternant BN clusters. In general, the borons prefer planar geometry (sp(2) hybrid ization) while the nitrogens prefer pyramidalization (sp(3) hybridizat ion). (C) 1997 John Wiley & Sons, Inc.