Spectroscopic characterization of a Be(2)-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 Be-Benzene species (marked D, E) in solid neon. These compounds have been identified by infrared spectroscopy with D, C isotopic substitutions benzene reagents as well as quantum chemical calculations. The Be-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.