CONTRASTING STRUCTURES OF PYRAMIDAL CARBOCATIONS AND THEIR SILICON ANALOGS

Caution-is required when drawing analogies between carbon and silicon compounds. This is proven by the calculations presented here, accordin g to which the Si compounds analogous to 1 do not correspond to minima on the potential energy surfaces. The most stable structures are of t ype 3. Reminiscent of nido-B5H9, structures 2 with H bridges also corr espond to local minima, although these are high in energy. X = BH, SiH +, Si.