Attractive PH•••HP interactions revealed by state-of-the-art ab initio calculations

We report in this work a combined structural and state-of-the-art computational study of homopolar P-H center dot center dot center dot H-P intermolecular contacts. Database surveys have shown the abundance of such surprisingly unexplored contacts, which are usually accompanied by other weak interactions in the solid state. By means of a detailed theoretical study utilizing SAPT(DFT), MP2, SCS-MP2, MP2C and CCSD(T) methods and both aug-cc-pVXZ and aug-cc-pCVXZ (X = D, T, Q, 5) basis sets as well as extrapolation to the CBS limit, we have shown that P-H center dot center dot center dot H-P contacts are indeed attractive and considerably strong. SAPT(DFT) calculations have revealed the dispersive nature of the P-H center dot center dot center dot H-P interaction with only minor contribution of the inductive term, whereas the first-order electrostatic term is clearly overbalanced by the first-order exchange energy. In general the computed interaction energies follow the trend: E-int(MP2C) approximate to E-int(SCS-MP2) < E-int(SAPT(DFT)) < E-int(MP2) . Our results have also shown that the aug-cc-pVDZ (or aug-cc-pCVDZ) basis set is not yet well balanced and that the second-order dispersion energy term is the slowest converging among all SAPT(DFT) energy components. Compared to aug-cc-pVXZ basis sets, their core-correlation counterparts have a modest influence on all supermolecular interaction energies and a negligible influence on both the SAPT(DFT) interaction energy and its components.