Crystal structure and optical properties of a two-dimensional lead(II) chloride porous metal halide semiconductor.

Abstract

A new member of the recently developed family of porous metal halide semiconductors (PMHS) is reported. Crystals of bis(4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane) tetradecachloridopentaplumbate(II), {(C₁₈H₃₈N₂O₆)₂[Pb₅Cl₁₄]}_n or (DHS)₂Pb₅Cl₁₄ (DHS is the double-protonated [2.2.2]cryptand) were obtained via solution chemistry protocols, with concentrated HCl as the reaction solvent. Single-crystal X-ray diffraction (XRD) revealed a two-dimensional inorganic framework, crystallizing in the hexagonal space group P6₃/m with Z' = 1/6, separated and charge-balanced by double-protonated DHS organic cations. The corresponding material is isostructural with the previously reported water-stable (DHS)₂Pb₅Br₁₄ and both feature broad light emission at room temperature. The lead chloride layer is disordered and was modeled as two components with partial occupancies of 0.585 and 0.415. (DHS)₂Pb₅Cl₁₄ decomposes when placed in water, giving rise to PbCl₂ as a degradation product. We attribute the sharp difference in water stability between the bromide and chloride analogs to differences in hydration energy and halide ionic radius, which affect their affinity for water molecules through hydrogen bonding.