PYRAMIDAL STRUCTURES WITH A B3H6 RING - POSSIBILITY OF TERMINAL HYDROGENS OPPOSITE THE CAPPING GROUP

Ab initio molecular orbital studies on a series of pyramidal B3H6X str uctures (X = NH+, N, CH, BH-, P, PH+, SiH, NO, PO, Co(CO)3) indicate t hat, for structures where X = NH+, N, and NO, the terminal hydrogens ( H(t)) of the basal B3H6 ring are toward the direction of the capping g roup. In contrast, the H(t)'s are found to be away from the capping gr oup for X = CH, BH-, P, PH+, SiH, PO, and Co(CO)3. All structures exce pt that of B4H7- are calculated to be minima. The six pi interstitial electron rule for three-dimensional delocalization and the compatibili ty of orbitals in overlap are used to explain the structural and bondi ng preferences in these pyramidal molecules.