Aluminium atoms at high connectivity sites in polyhedral polyborane analogous clusters: From aluminaboranes to carbaalanes

Cluster chemistry in the third main group has long been restricted to compo unds of the lightest element boron. However, about 30 years ago the first c ompounds were synthesized and characterized in which single aluminium atoms adopted positions of high connectivity in polyhedral borane or carbaborane clusters. The next successful step in these efforts to establish a chemist ry analogous to that of the polyboranes with the heavier elements of the th ird main-group was the synthesis of closo-dodecaaluminate [Al(12)iBu(12)](2 -) at the beginning of the nineties, which was the first homonuclear alumin ium analogue of a polyborate anion and had a core exclusively formed by alu minium atoms. Another class of interesting new aluminium compounds was form ed by the carbaalanes, which were synthesized and characterized for the fir st time only recently. They have clusters of aluminium and carbon atoms, an d are similar to the carbaborane analogues in that their structures seem to be determined by the number of electron pairs in their molecular centers i n accordance with the Wade rules.