Low-Dimensional Tin(II) Iodide Perovskite Structures Templated by an Aromatic Heterocyclic Cation

Single-crystal X-ray diffraction demonstrates that the sterically demanding 5,6-dicarboxybenzimidazolium cation is able to template and support a two-dimensional perovskite structure based on [SnI4](n)(2n-) layers (1). The latter are formed by corner-sharing SnI6 octahedra. Keys for the templating effect are the N-H center dot center dot center dot I-terminal hydrogen bonds and the match of the cation into the footprint provided by the inorganic tin(II) iodide sheets in much the same way as is the case for plain benzimidazolium or its 5,6-difluoro-substituted derivative. The 5,6-dicarboxybenzimidazolium cation also permits the formation of [SnI5](n)(3n-) chains composed of corner-sharing SnI6 octahedra, leading to the crystallization of a stable one-dimensional (1D) perovskite compound (2); such types of 1D perovskites have rarely been reported. Alongside the inorganic [SnI5](n)(3n-) chains, rings of eight carboxyl groups of four 5,6-dicarboxybenzimidazolium cations aggregate to form tubular hydrophilic pockets. Linearly extended ribbon-like assemblies of hydrated I- anions balance the overall charge of the compound. Single-crystal resistivity measurements of the stable 1D tin iodide perovskite reveal semiconducting behavior with a fairly high room temperature electrical conductivity of around 0.5 S cm(-1). DFT calculations reveal a low band gap (similar to 1 eV) for 1 and also support the experimental observation of the high electrical conductivity for 2.