The pnictogen bond forming ability of bonded bismuth atoms in molecular entities in the crystalline phase: a perspective

Thousands of crystal structures containing bismuth have been deposited in various crystal structure databases since late last century; in many, a covalently or coordinately bonded bismuth atom in molecular entities features a positive region(s) on its electrostatic surface. We have shown that this positive region attracts a variety of Lewis bases, including, for example, O, N, F, P, Cl, Br, I, S, Se, Te, and Bi atoms, as well as those with regions of pi-density in C-pi (arene) and (C = C)(pi) moieties present in the same or different molecular entities, resulting in the formation of bismuth-centered pnictogen bonds (or simply, bismuth bonds). The characteristics of these bismuth bonds, including geometric features such as inter-and intramolecular distances, were evaluated using several techniques, which were also used to verify the less than the sum of van der Waals radii concept, and the use of interaction angles, a measure of the directionality of the interaction. The results of molecular electrostatic surface potential, quantum theory of atoms in molecules, and charge density based on the independent gradient model are discussed for some selected systems wherever necessary.