How Many Pnicogen Bonds can be Formed to a Central Atom Simultaneously?

[Image: see text] A central ZF(3) molecule (Z = P, As, Sb, Bi) is allowed to interact with a number of nucleophiles exemplified by NCH, NH(3), and NC(–) anion. The Z···N pnicogen bond (ZB) to a single base grows stronger for heavier Z atom: P < A < Sb < Bi and follows the NCH < NH(3) < NC(–) order for the three bases. The maximum number of ZBs depends on both the nature of the base and pnicogen atom. PF(3) and AsF(3) can pnicogen bond with only a single CN(–); SbF(3) and BiF(3) can interact with two anions but only weakly. The weak NCH nucleophile can engage in a maximum of two ZBs, while three ZBs occur for NH(3). The latter NH(3) maximum can be extended to four ZBs but only for BiF(3). The fourth ZB is somewhat longer and weaker than the others, and the entire (H(3)N)(4)···BiF(3) complex relies partially on secondary interactions for its stability.