Can HN=NH, FN=NH, or HN=CHOH bridge the σ-hole and the lone pair at P in binary complexes with H2XP, for X = F, Cl, NC, OH, CN, CCH, CH3, and H?

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate the properties of complexes formed between H2XP, for X = F, Cl, NC, OH, CN, CCH, CH3, and H, and the possible bridging molecules HN=NH, FN=NH, and HN=CHOH. H2XP: HNNH and H2XP: FNNH complexes are stabilized by P center dot center dot center dot N pnicogen bonds, except for H-2(CH3)P:FNNH and H3P:FNNH which are stabilized by N-H center dot center dot center dot P hydrogen bonds. H2XP:HNCHOH complexes are stabilized by P center dot center dot center dot N pnicogen bonds and nonlinear O-H center dot center dot center dot P hydrogen bonds. For a fixed H2XP molecule, binding energies decrease in the order HNCHOH > HNNH > FNNH, except for the binding energies of H-2(CH3)P and H3P with HNNH and FNNH. Binding energies of complexes with HNCHOH and HNNH increase as the P-N-1 distance decreases, but binding energies of complexes with FNNH show little dependence on this distance. The large binding energies of H2XP:HNCHOH complexes arise from a cooperative effect involving electron-pair acceptance by P to form a pnicogen bond, and electron-pair donation by P to form a hydrogen bond. The dominant charge-transfer interaction in these complexes involves electron-pair donation by N across the pnicogen bond, except for complexes in which X is one of the more electropositive substituents, CCH, CH3, and H. For these, lone-pair donation by P across the hydrogen bond dominates. AIM and NBO data for these complexes are consistent with their bonding characteristics, showing molecular graphs with bond critical points and charge-transfer interactions associated with hydrogen and pnicogen bonds. EOM-CCSD spin-spin coupling constants (1p)J(P-N) across the pnicogen bond for each series of complexes correlate with the P-N distance. In contrast, (2h)J(O-P) values for complexes H2XP:HNCHOH do not correlate with the O-P distance, a consequence of the nonlinearity of these hydrogen bonds.