Elongation of Planar Boron Clusters by Hydrogenation: Boron Analogues of Polyenes

摘要

Dihydrogenated boron clusters, H_2B_n~- (n = 7—12), were produced and characterized using photo-electron spectroscopy and computational chemistry to have ladderlike structures terminated by a hydrogen atom on each end. The two rows of boron atoms in the dihydrides are bonded by delocalized three-, four-, or five-center σ and n bonds. The n bonding patterns in these boron nanoladders bear similarities to those in conjugated alkenes: H_2B_7~-, H_2B_8, and H_2B_9~-, each with two n bonds, are similar to butadiene, while H_2B_(10)~(2-), H_2B_(11)~-, and H_2B_(12), each with three n bonds, are analogous to 1,3,5-hexatriene. The boron cluster dihydrides can thus be considered as polyene analogues, or "polyboroenes". Long polyboroenes with conjugated π bonds (analogous to polyacetylenes), which may form a new class of molecular wires, should exist.