Complexes H2CO:PXH2 and HCO2H : PXH2 for X=NC, F, Cl, CN, OH, CCH, CH3, and H: Pnicogen Bonds and Hydrogen Bonds

Abstract

Ab initio MP2/aug’-cc-pVTZ calculations have been carried out to investigate HCO : PXH pnicogen-bonded complexes and HCOH : PXH complexes that are stabilized by pnicogen bonds and hydrogen bonds, with X=NC, F, Cl, CN, OH, CCH, CH, and H. The binding energies of these complexes exhibit a second-order dependence on the O−P distance. DFT-SAPT binding energies correlate linearly with MP2 binding energies. The HCOH : PXH complexes are stabilized by both a pnicogen bond and a hydrogen bond, resulting in greater binding energies for the HCOH : PXH complexes compared to HCO : PXH. Neither the O−P distance across the pnicogen bond nor the O−P distance across the hydrogen bond correlates with the binding energies of these complexes. The nonlinearity of the hydrogen bonds suggests that they are relatively weak bonds, except for complexes in which the substituent X is either CH or H. The pnicogen bond is the more important stabilizing interaction in the HCOH : PXH complexes except when the substituent X is a more electropositive group. EOM-CCSD spin-spin coupling constants J(O−P) across pnicogen bonds in HCO:PXH and HCOH : PXH complexes increase as the O−P distance decreases, and exhibit a second order dependence on that distance. There is no correlation between J(O−P) and the O−P distance across the hydrogen bond in the HCOH : PXH complexes. J(O−P) coupling constants for complexes with X=CH and H have much greater absolute values than anticipated from their O−P distances.