Structural variations in (001)-oriented layered lead halide perovskites, templated by 1,2,4-triazolium

Abstract

A new hybrid lead(II) halide perovskite, (TzH)₂PbCl₄, ([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 P2₁2₁2₁, which has a tripled unit cell volume. UV-Vis spectra suggest a band gap of 3.30 eV for (TzH)₂PbCl₄. A second polymorph of the bromide analogue, (TzH)₂PbBr₄-II, is also reported, and structural relationships between all three variants are discussed.