(C5H6N)Pb2X5 (X = Cl, Br): Hybrid Lead Halides Based on Seven-Coordinate Pb(II)

Hybrid lead halides are a diverse family of compounds, of interest for their optoelectronic properties, thatvary in the dimensionality and connectivity of their inorganicsubstructures. The great majority of these compounds are based onlead-centered octahedra, with few examples featuring inorganicarchitectures containing higher coordination numbers. Here, wereport the synthesis and characterization of a pyridinium leadbromide phase that is based on seven-coordinate Pb(II) centers.Through edge- and face-sharing, the polyhedra form a corrugated,two-dimensional inorganic substructure. Electronic structurecalculations were used to examine the band structure and therole of the stereoactive lone pair in the inherently asymmetric,seven-coordinate Pb(II) geometry. For reference, we havevisualized the role of the lone pair in the binary halide PbBr2, which also has a seven-coordinate inner ligand sphere. A comparisonof the new structure with the limited number of existing hybrid lead halides with similar inorganic architectures highlights thetemplating role of the organic cation for these compounds. We also contribute characterization and discussion of isomorphicpyridinium lead chloride, which had been deposited in the Cambridge Structural Database but never, to our knowledge, addressed inthe literature. The compounds were synthesized using solution conditions and structures determined with single-crystal X-raydiffraction. The materials were also characterized via powder X-ray diffraction, combustion elemental analysis, and diffuse reflectanceUV-vis spectroscopy. While the structures reported here are centrosymmetric, the seven-coordinate, capped trigonal prismaticgeometry that we have identified is a source of local asymmetry that could be used as a component in designing globally noncentrosymmetric structures