Halogen-like Behavior of Gold: Can Gold Form Pseudo-Halogen Bonds?

Gold closely resembles halogens in its comparable electronegativity, its closed-shell electronic configuration upon gaining one electron, and its ability to form superhalogen species. This work explores gold's halogen-like bonding behavior, particularly in the formation of halogen bond (XB) analogues, termed pseudo-XB. We conduct density functional theory (DFT) calculations to systematically compare homonuclear dimers X2···X2 (X = F/Cl/Br/I) and M2···M2 (M = Cu/Ag/Au), heteronuclear dimers FX'···X'F (X' = Cl/Br/I) and FAu···AuF, as well as trimers and tetramers of (F-X') and (F-Au). Au2···Au2 and FAu···AuF adopt zigzag configurations analogous to their halogen counterparts. The Lewis structures of these configurations are proposed to explain the bonding mode between monomers, which is further confirmed by the direction of charge transfer upon the formation of dimers. In the studied systems, gold can form pseudo-XBs similar to halogens (especially iodine), and such pseudo-XBs exhibit greater interaction strength than conventional XBs within the investigated systems. Quantum theory of atoms in molecules (QTAIM) and energy decomposition analysis (EDA) reveal that the nature of gold's pseudo-XBs is similar to that of XBs; both are closed-shell interactions and dominated by orbital interactions and electronic correlation energies. These findings support viewing gold as a halogen-like center in the particular families of clusters examined.