Quantum chemical study of the structure of tetrasilacyclobutadiene,its dication,and dianion

MINDO/3 calculations have indicated the instability of the D _2h planar geometrical configuration of tetrasilacyclobutadiene relative both to pyramidalization of the silicon atoms with the formation of a nonplanar C _2h structure and acoplanarization of the silicon skeleton leading to a C _s nonplanar bicyclic structure. Such distortions are also characteristic for the D _4h structure of the tetrasilabicyclobutadiene dianion. The dication of tetrasilabicyclobutadiene has D _2d nonplanar symmetry, similar to that for the dication of cyclobutadiene.Physical and Organic Chemistry Research Institute, Rostov State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 6, pp. 23–32, November–December, 1989.