Investigation of Pb–B Bonding in PbB2(BO)n− (n = 0–2): Transformation from Aromatic PbB2− to Pb[B2(BO)2]−/0 Complexes with BB Triple Bonds

Boron has been found to be able to form multiple bonds with lead. To probe Pb-B bonding, here we report an investigation of three Pb-doped boron clusters, PbB₂^-, PbB₃O^-, and PbB₄O₂^-, which are produced by a laser ablation cluster source and characterized by photoelectron spectroscopy and ab initio calculations. The most stable structures of PbB₂^-, PbB₃O^-, and PbB₄O₂^- are found to follow the formula, [PbB₂(BO)_n]^- (n = 0-2), with zero, one, and two boronyl ligands coordinated to a triangular and aromatic PbB₂ core, respectively. The PbB₂^- cluster contains a BB double bond and two Pb-B single bonds. The coordination of BO is observed to weaken Pb-B bonding but strengthen the BB bond in [PbB₂(BO)_n]^- (n = 1, 2). The anionic [PbB₂(BO)₂]^- and its corresponding neutral closed-shell [PbB₂(BO)₂] contain a BB triple bond. A low-lying Y-shaped isomer is also observed for PbB₄O₂^-, consisting of a central sp² hybridized B atom bonded to two boronyl ligands and a PbB unit.