Special features of intermolecular bonding A...D(A = Si, Ge and D = nucleophile) in crystal structures.

An investigation of the crystal structures of 3346 silicon- and 718 germanium-containing compounds was carried out with a geometrical-topological analysis. The descriptors of inter- and intramolecular contacts A...D are given. Information on the descriptors of T-A...D (where T = leaving group) interactions in terms of a stereoatomic model of crystal structures was described as being helpful in modelling S(N)2 reactions. It was established that the formation of multiple intermolecular contacts in crystal structures is unfavorable. The dependence of the descriptors of intermolecular contacts T-A...D was studied as a function of the nature of T (leaving group in substitution reactions) and D (nucleophile atom or group of atoms) groups, and the coordination number of an A atom. The constancy of the T-A and A...D bond-order sum in crystal structures was demonstrated.