Lead Oxychloride Borates Obtained under Extreme Conditions

[Pb₁₀O₄]­Pb₂(B₂O₅)­Cl₁₂ (1) and [Pb₁₈O12]­Pb­(BO₂OH)₂Cl₁₀ (2) were obtained via high-temperature high-pressure experiments. [O₁₂Pb₁₈]¹²⁺ and [O₄Pb₁₀]¹²⁺ oxocentered structural units of different dimensionality are excised from the ideal [OPb] layer in tetragonal α-PbO. 2 is formed with an excess of lead oxide component, and 1 is formed with an excess of borate and halide reagents. The structure of 2 can be visualized as the incorporation of {Pb(10)­Cl₄(BO₂OH)₂} clusters into alternating PbO and chloride layers, with the existence of square vacancies in both. However, the structure of 1 is described as the intrusion of [O₄Pb₁₀]¹²⁺ tetramers linked by disordered Pb­(B₂O₅) groups into a halogen three-dimensional matrix. The structure of 2 contains 10 symmetrically independent Pb positions. The 6s² lone electron pair is stereochemically active on Pb(1)–Pb(9) atoms, whereas it is inert on Pb(10). All of the Pb coordinations in the structure of 2, in accordance with ECC_v (volume eccentricity) parameters and the density of states (DOS), can be subdivided into three groups. The current study is the first attempt to analyze this unusual behavior in structurally complex oxyhalide material with the rare case of Pb²⁺ cations, demonstrating both stereochemically active and inactive behavior of the lone pair via charge and first-principle calculations.