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The Covalent AuI-AuI Bond in (AuF)n (n = 2∼4): A Perspective to Understand the Closed-Shell AuI···AuI Interaction.

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.