Exploring the (H2C═PH2)(+):N-Base Potential Surfaces: Complexes Stabilized by Pnicogen, Hydrogen, and Tetrel Bonds.

Abstract

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to determine the structures, binding energies, and bonding properties of complexes involving the cation (H2C═PH2)(+) and a set of sp-hybridized nitrogen bases including NCCH3, NP, NCCl, NCH, NCF, NCCN, and N2. On each (H2C═PH2)(+):N-base surface, four types of unique equilibrium structures exist: a complex with a P···N pnicogen bond formed through the π system of (H2C═PH2)(+) (ZB-π); a complex with a P···N pnicogen bond formed through the σ system of (H2C═PH2)(+) (ZB-σ); a hydrogen-bonded complex with a P-H···N hydrogen bond (HB); and a tetrel-bonded complex with a C···N bond (TB). Binding energies of complexes stabilized by the same type of intermolecular interaction decrease in the order NCCH3 > NP > NCCl > NCH > NCF > NCCN > N2. For a given base, binding energies decrease in the order ZB-π > HB > ZB-σ > TB, except for a reversal of HB and ZB-σ with the weakest base N2. Binding energies of ZB-π, HB, and ZB-σ complexes increase exponentially as the corresponding P-N distance decreases, but the correlation is not as good between the binding energies of TB complexes and the intermolecular C-N distance. Charge-transfer energies stabilize all complexes and also exhibit an exponential dependence on the corresponding intermolecular distances. EOM-CCSD spin-spin coupling constants (1p)J(P-N) for ZB-π and ZB-σ complexes, and (2h)J(P-N) for HB complexes increase quadratically as the corresponding P-N distance decreases. Values of (1t)J(C-N) for TB are small and show little dependence on the C-N distance. (1)J(P-H) values for the hydrogen-bonded P-H bond in HB complexes correlate with the corresponding P-H distance, whereas values of (1)J(P-H) for the non-hydrogen-bonded P-H correlate with the P-N distance.