A theoretical investigation on Cu/Ag/Au bonding in XHP⋯MY(X = H, CH, F, CN, NO; M = Cu, Ag, Au; Y = F, Cl, Br, I) complexes.

Intermolecular interaction of XHP···MY (X = H, CH, F, CN, NO; M = Cu, Ag, Au; Y = F, Cl, Br, I) complexes was investigated by means of an method. The molecular interaction energies are in the order Ag < Cu < Au and increased with the decrease of R. Interaction energies are strengthened when electron-donating substituents X connected to XHP, while electron-withdrawing substituents produce the opposite effect. The strongest P···M bond was found in CHHP···AuF with -70.95 kcal/mol, while the weakest one was found in NOHP···AgI with -20.45 kcal/mol. The three-center/four-electron (3c/4e) resonance-type of P:-M-:Y hyperbond was recognized by the natural resonance theory and the natural bond orbital analysis. The competition of P:M-Y ↔ P-M:Y resonance structures mainly arises from hyperconjugation interactions; the bond order of b and b is in line with the conservation of the idealized relationship b + b ≈ 1. In all MF-containing complexes, P-M:F resonance accounted for a larger proportion which leads to the covalent characters for partial ionicity of MF. The interaction energies of these Cu/Ag/Au complexes are basically above the characteristic values of the halogen-bond complexes and close to the observed strong hydrogen bonds in ionic hydrogen-bonded species.