Abilities of different electron donors (D) to engage in a P···D noncovalent interaction

Previous work has documented the ability of the P atom to form a direct attractive noncovalent interaction with a N atom, based in large measure on the charge transfer from the N lone pair into the σ* antibonding orbital of the P-H that is turned away from the N atom. The present work considers whether other atoms, namely, O and S, can also participate as electron donors, and in which bonding environments. Also considered are the π-systems of multiply bonded C atoms. Unlike an earlier observation that the interaction is unaffected by the nature of the electron-acceptor atom, there is strong sensitivity to the donor. The P···D binding energy diminishes in the order D = NH(3) > H(2)CO > H(2)CS > H(2)O > H(2)S, different from the patterns observed in both H and halogen bonds. The P···D interactions are comparable to, and in some cases stronger than, the analogous H-bonds formed by HOH as proton donor. The carbon π systems form surprisingly strong P···D complexes, augmented by the back-donation from the P lone pair to the C-C π* antibond, which surpass the strengths of H-bonds, even some with HF as proton donor.