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

Abstract

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 BB double bond and two Pb–B single bonds. The coordination of BO is observed to weaken Pb–B bonding but strengthen the BB bond in [PbB₂(BO)_n]⁻ (n = 1, 2). The anionic [PbB₂(BO)₂]⁻ and its corresponding neutral closed-shell [PbB₂(BO)₂] contain a BB 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.