Structural Variations In (001)-Oriented Layered Lead Halide Perovskites, Templated By 1,2,4-Triazolium

A new hybrid lead(ii) halide perovskite, (TzH)(2)PbCl4, ([TzH(+)] = 1,2,4-triazolium), adopts a (001)-oriented layered perovskite structure, which can be considered as derived from the n = 1 Ruddlesden-Popper (RP) type. Variable temperature single crystal X-ray diffraction reveals a structural phase transition in the region 125 K < T < 173 K between a high temperature, high symmetry polymorph, space group Cmcm, and a low temperature, low symmetry chiral polymorph, space group P2(1)2(1)2(1), which has a tripled unit cell volume. UV-Vis spectra suggest a band gap of 3.30 eV for (TzH)(2)PbCl4. A second polymorph of the bromide analogue, (TzH)(2)PbBr4-II, is also reported, and structural relationships between all three variants are discussed.