Exploring the (H2C═PH2)+:N-Base Potential Surfaces: Complexes Stabilized by Pnicogen, Hydrogen, and Tetrel Bonds
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 1pJ(P—N) for ZB-π and ZB-σ complexes, and 2hJ(P—N) for HB complexes increase quadratically as the corresponding P—N distance decreases. Values of 1tJ(C—N) for TB are small and show little dependence on the C—N distance. 1J(P—H) values for the hydrogen-bonded P—H bond in HB complexes correlate with the corresponding P—H distance, whereas values of 1J(P—H) for the non-hydrogen-bonded P—H correlate with the P—N distance.