Ab initio MO calculations at the MP2/6-31G level indicate a nonplanar
structure (1) to be the favored arrangement for B-3(mu-H)(3)X(3)(+) (
X = H, F, and Li). In contrast, B-3(mu-Li)(3)H-3(+) (2) is calculated
to be a minimum in the planar arrangement. The structural preferences
of 1 and 2 are explained from their molecular orbital pattern and char
ge distributions.