The Covalent Au^I–Au^I Bond in (AuF)_n (n = 2∼4): A Perspective to Understand the Closed-Shell Au^I···Au^I Interaction

Abstract

The nature of closed-shell AuI···AuI attraction is still a conundrum in theoretical chemistry. However, for Au2F2 with a zigzag conformation, the d10–d10 closed-shell interaction between the AuF monomers is demonstrated as a coordinate covalent bond. Chemical bonding analysis reveals that the strong AuI···AuI attraction is caused by the participation of the extraordinary active 5d orbital of Au. Based on our study, one of the 5d orbitals of the Au atom is activated to hybridize with its 6s and 6p orbitals to form hybridized dsp2 orbitals, where each Au atom is both an electron donor (Lewis base) and acceptor (Lewis Acid) in dimerization. Actually, the closed-shell AuI···AuI interaction in the zigzag conformation of Au2X2 (X = F, Cl, Br, I, or NH2) is covalent. Our results provide a rather simple but clear-cut example, where mysterious AuI···AuI attractions can be possibly explained by the covalent bond theory.

Signature of Au as a Halogen

“…Thus, the chemistries of two Au atoms in Figure a are different from each other. The Au–Au bond length (2.57 Å in neutral Au 2 F 2 ) is much shorter than the nearest-neighbor distance (2.89 Å in closely packed gold metal) . The geometry of AuF 3 in Figure b is similar to that of Au 2 F 2 in which the Au atom in the latter takes the place of the F atom in the former.…”

“…Thus, the chemistries of two Au atoms in Figure 3a closely packed gold metal). 32 The geometry of AuF 3 in Figure 3b is similar to that of Au 2 F 2 in which the Au atom in the latter takes the place of the F atom in the former. Both Au atoms in neutral Au 2 F 2 carry positive charges; the one bonded to two F atoms carries a charge of 0.77e, while the one bonded to the Au carries a charge of 0.47e.…”

“…As Au + is a closed-shell species with a 5d 10 electronic configuration, there has been significant interest in understanding the interaction between Au and Au in gold chemistry. − Due to the strong relativistic effects and dispersion type electron correlations, aurophilic interactions arise, which are intermediate between van der Waals forces and covalent bonding. This dominates the structural chemistry of the system containing Au atoms. − A detailed analysis of the bonding interaction between Au and Au and between Au and F in Au 2 F 2 is presented by Yu et al Our NPA charge analysis, Au–Au and Au–F bond lengths, Mayer bond order analysis, and electron localization function (Figure a) are consistent with the analysis done by Yu et al A similar conclusion can be drawn by analyzing the nature of the NPA charges and the ELF (Figure b) for the Au–Au bond in AuF 2 .…”

“…This implies that the interaction between two Au atoms in Au 2 F 2 is large. Indeed, in a recent theoretical study, Yu et al 32 categorized the Au−Au bond in Au 2 F 2 as "covalent coordinate". In addition, the computed EA of Au 2 F 2 , is 3.51 eV, which agrees well with our measured value of 3.30 eV.…”

“…This dominates the structural chemistry of the system containing Au atoms. 39−41 A detailed analysis of the bonding interaction between Au and Au and between Au and F in Au 2 F 2 is presented by Yu et al 32 Our NPA charge analysis, Au−Au and Au−F bond lengths, Mayer bond order analysis, and electron localization function (Figure 7a) are consistent with the analysis done by Yu et al A similar conclusion can be drawn by analyzing the nature of the NPA charges and the ELF (Figure 7b) for the Au−Au bond in AuF 2 . Gold, due to relativistic effects, exhibits properties very different from those of other coinage metal atoms, Cu and Ag.…”