Crystal structure and phase transition in perovskite C(NH2)3SnCl3

X-ray single-crystal diffraction, high-temperature powder diffraction and differential thermal analysis at ambient and high pressure have been employed to study the crystal structure and phase transitions of guanidinium trichlorostannate, C(NH2)(3)SnCl3. At 295 K the crystal structure is orthorhombic, space group Pbca, Z = 8, a = 7.7506(2) angstrom, b = 12.0958(4) angstrom and e = 17.8049(6) angstrom, solved from single-crystal data.

It is perovskite-like with distorted corner-linked SnCl6 octahedra and with ordered guanidinium cations in the distorted cuboctahedral voids. At 400 K the structure shows a first-order order-disorder phase transition. The space group is changed to Pnma with Z = 4, a = 12.1552(2) angstrom, b = 8.8590(2) angstrom and c = 8.0175(1) angstrom, solved from powder diffraction data and showing disordering of the guanidinium cations.

At 419 K, the structure shows yet another first-order order disorder transformation with disordering of the SnCl3- part. The space group symmetry is maintained as Pnma, with a = 12.1786(2) angstrom, b = 8.8642(2) angstrom and c = 8.0821(2) angstrom. The thermodynamic parameters of these transitions and the p-T phase diagram have been determined and described.