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 2 . 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 - ( 1 Σ + ) anion to the neutral BiBH, including the ground state ( 2 Π 3/2 ) and two excited states ( 2 Σ + and 2 Π 1/2 ). Strong vibronic coupling is observed between the 2 Π 3/2 and 2 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.