STUDIES ON THE NATURE OF CHEMICAL-BONDS I N BORANES .2. THE 4-CENTER BOND IN B3H7 AND THE 3 SEPARATED HYDROGEN BRIDGED 3-CENTER BOND IN B3H9

As a result of 'ab initio' study, using Dunning's basis set, it is sho wn that, in B3H7 (1103),the two three-center bonds have been fused int o a four-center bond, owing to the sigma(-) conjugation effect. The pr operties in bond strength of this four-center bond are: f(B(1)-B(2))=0 .1653, f(B-Hh-B)=0.3416, f(B(2)-B(3))=0.1429, f(4center)=0.7193 hartre e/bohr. No sigma- conjugation effect can take place between the three separated three(-) centerbonds in B3H9, whose properties are: f(B-B)=0 .0558, f(B-Hb-B)=0.3992, f(Hb3cen.)=0.5115 hartree/bohr.