Complexes H2 CO:PXH2 and HCO2 H : PXH2 for X=NC, F, Cl, CN, OH, CCH, CH3 , and H: Pnicogen Bonds and Hydrogen Bonds.

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate H2 CO : PXH2 pnicogen-bonded complexes and HCO2 H : PXH2 complexes that are stabilized by pnicogen bonds and hydrogen bonds, with X=NC, F, Cl, CN, OH, CCH, CH3 , 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 HCO2 H : PXH2 complexes are stabilized by both a pnicogen bond and a hydrogen bond, resulting in greater binding energies for the HCO2 H : PXH2 complexes compared to H2 CO : PXH2 . 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 CH3 or H. The pnicogen bond is the more important stabilizing interaction in the HCO2 H : PXH2 complexes except when the substituent X is a more electropositive group. EOM-CCSD spin-spin coupling constants 1p J(O-P) across pnicogen bonds in H2 CO:PXH2 and HCO2 H : PXH2 complexes increase as the O-P distance decreases, and exhibit a second order dependence on that distance. There is no correlation between 2h J(O-P) and the O-P distance across the hydrogen bond in the HCO2 H : PXH2 complexes. 2h J(O-P) coupling constants for complexes with X=CH3 and H have much greater absolute values than anticipated from their O-P distances.