Spectroscopic characterization of a Be2-benzene complex featuring BeBe quasi-triple bond.

In this study, we successfully synthesized and characterized three Be-Benzene species (marked A, B, C) and two Be2-Benzene species (marked D, E) in solid neon. These compounds have been identified by infrared spectroscopy with D, 13C isotopic substitutions benzene reagents as well as quantum chemical calculations. The Be2-Benzene complex (D) exhibits a unique half sandwich structure with an unusually short BeBe distance (1.913 Å). Bonding analysis reveals that two beryllium atoms are bonded together by a classical two-center two-electron BeBe σ bond and two non-classical eight-center two-electron bonds, thereby indicating the formation of a non-classical BeBe quasi-triple bond. Two beryllium atoms in species E possess a longer interatomic distance of 1.997 Å, which is characterized by electronic structure analysis as a classical BeBe single bond. The observation of species with a BeBe quasi-triple bond extends our understanding on the chemical bonding involving beryllium atoms.