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 H. 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 (Σ) anion to the neutral BiBH, including the ground state (Π) and two excited states (Σ and Π). Strong vibronic coupling is observed between the Π and Σ 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.