Observation of an electron-precise metal boryne complex: [BiBH].

Metal-boron triple bonds are rare due to the electron deficiency of boron. This study uncovers a simple electron-precise metal boryne complex, [BiBH]-, which is produced within an ion trap through chemical reactions of the open-shell BiB- anion with H2. Photoelectron imaging is used to investigate the electronic structure and chemical bonding of the BiBH- complex. The B atom in the linear closed-shell BiBH- is found to undergo sp hybridization, forming a B-H single bond and a BiB triple bond. Photoelectron imaging reveals three detachment transitions from the BiBH- (1Σ+) anion to the neutral BiBH, including the ground state (2Π3/2) and two excited states (2Σ+ and 2Π1/2). Strong vibronic coupling is observed between the 2Π3/2 and 2Σ+ states, evidenced by the appearance of bending vibrations and their unique photoelectron angular distributions. The BiBH- complex not only stands as the simplest metal boryne complex, but also serves as an ideal molecular system to investigate both spin-orbit and vibronic couplings.