Supramolecular [Na(15-crown-5)]⁺cations anchored to face-sharing octahedral lead bromide chains featuring a rotor-like one-dimensional perovskite with a reversible isostructural phase transition near room temperature

Crystal engineering aims at a better understanding of the correlation between the components and crystal structures, so that the desired crystal structure and functionality will be acquired. In this study, a lead bromide perovskite, {[Na(15-crown-5)]PbBr3}∞ (1, 15-crown-5 = 1,4,7,10,13-pentaoxacyclopentadecane), has been obtained by assembly of equal molar quantities of PbBr2, NaBr and 15-crown-5 in DMF, and 1 has been further characterized by microanalysis, IR spectroscopy, TG analysis, and single crystal and powder X-ray diffraction techniques. DSC measurement revealed that 1 experiences a reversible phase transition at ∼299/∼297 K on heating/cooling, which is an isostructural phase transition confirmed by single crystal structure analysis. 1 crystallizes in the orthorhombic space group Pnma in both low- and high-temperature phases, containing face-sharing coordination octahedral [PbBr3]∞ chains and supramolecular [Na(15-crown-5)]+ cations, which are bound to the [PbBr3]∞ chains via Na-Br coordination bonds to form rotor-like neutral chains. Variable-temperature crystal structure analysis revealed that the isostructural phase transition is driven by PbBr6 coordination sphere distortion, which is related to the steric hindrance effect between the inorganic chain and 15-crown-5 molecules. Dielectric relaxation has been observed above 273 K, resulting from the distortion of PbBr6 coordination octahedra and the change in polar Na-Br bonds under an AC electrical field.