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.

The nature of closed-shell Au I ···Au I attraction is still a conundrum in theoretical chemistry. However, for Au 2 F 2 with a zigzag conformation, the d 10 -d 10 closed-shell interaction between the AuF monomers is demonstrated as a coordinate covalent bond. Chemical bonding analysis reveals that the strong Au I ···Au I 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 dsp 2 orbitals, where each Au atom is both an electron donor (Lewis base) and acceptor (Lewis Acid) in dimerization. Actually, the closed-shell Au I ···Au I interaction in the zigzag conformation of Au 2 X 2 (X = F, Cl, Br, I, or NH 2 ) is covalent. Our results provide a rather simple but clear-cut example, where mysterious Au I ···Au I attractions can be possibly explained by the covalent bond theory.