Resonance Character of Copper/Silver/Gold Bonding in Small Molecule⋅⋅⋅MX (X=F, Cl, Br, CH 3 , CF 3 ) Complexes

The resonance character of Cu/Ag/Au bonding is investigated in B⋅⋅⋅MX (M=Cu, Ag, Au; X=F, Cl, Br, CH 3 , CF 3 ; B=CO, H 2 O, H 2 S, C 2 H 2 , C 2 H 4 ) complexes. The natural bond orbital/natural resonance theory results strongly support the general resonance‐type three‐center/four‐electron (3c/4e) picture of Cu/Ag/Au bonding, B:MX↔B + M:X − , which mainly arises from hyperconjugation interactions. On the basis of such resonance‐type bonding mechanisms, the ligand effects in the more strongly bound OC⋅⋅⋅MX series are analyzed, and distinct competition between CO and the axial ligand X is observed. This competitive bonding picture directly explains why CO in OC⋅⋅⋅AuCF 3 can be readily replaced by a number of other ligands. Additionally, conservation of the bond order indicates that the idealized relationship b B⋅⋅⋅M + b MX =1 should be suitably generalized for intermolecular bonding, especially if there is additional partial multiple bonding at one end of the 3c/4e hyperbonded triad.