The hypervalent PF4H species dimer: A system with double blue-shifted P–H⋯F hydrogen bonding?

The hypervalent PF4H species dimer has been studied using second-order perturbation theory and coupled-cluster methods with augmented correlation-consistent basis sets up to truncated quadruple-zeta. The dimer involving two P–H⋯F contacts serves a model of weak interaction between PF4H molecules in the crystal. We found dimer structures of C1 and Ci symmetry with interaction energy of the order of −2.5 kcal/mol. SAPT (symmetry-adapted perturbation theory) energy decomposition scheme reveals major electrostatic, polarization and dispersion stabilizing contributions. We are not conclusive as to the presence of improper H-bonding in this complex.