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