Investigation of Pb-B Bonding in PbB 2 (BO) n - ( n = 0-2): Transformation from Aromatic PbB 2 - to Pb[B 2 (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, PbB 2 - , PbB 3 O - , and PbB 4 O 2 - , which are produced by a laser ablation cluster source and characterized by photoelectron spectroscopy and ab initio calculations. The most stable structures of PbB 2 - , PbB 3 O - , and PbB 4 O 2 - are found to follow the formula, [PbB 2 (BO) n ] - ( n = 0-2), with zero, one, and two boronyl ligands coordinated to a triangular and aromatic PbB 2 core, respectively. The PbB 2 - 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 [PbB 2 (BO) n ] - ( n = 1, 2). The anionic [PbB 2 (BO) 2 ] - and its corresponding neutral closed-shell [PbB 2 (BO) 2 ] contain a BB triple bond. A low-lying Y-shaped isomer is also observed for PbB 4 O 2 - , consisting of a central sp 2 hybridized B atom bonded to two boronyl ligands and a PbB unit.