Structures of alatetraborane(10) and gallatetraalane(10) isomers

Tetraborane(10) is well known and 2-gallatetraborane(10) has been synthesized. Other isomers of both systems along with gallaborane(10), digallatetraborane(10) and tri-gallatetrabo rane(10) have been studied using ab initio quantum chemical methods. This study extends this theoretical work to tetraborane(10) with aluminium substitution of boron and tetraalane(10) with gallium substitution of aluminium. The structures of the aluminium substituted tetraborane(10) structures are very similar to the gallium substituted tetraborane(10) structures. The heavier aluminium atom prefers the 'wing-tip' position in the arachno structures. However, the stabilization of the aluminium substituted bis(diboranyl) structures when the aluminium is in the central position is less marked than for the gallium substituted bis(diboranyl) structures. In the gallium substituted tetraalanes, somewhat surprisingly the heavier gallium atom prefers the central positions in both the arachno and the bis(diboranyl) structures. � 2005 Taylor & Francis Group Ltd.