The structure and phase transition of tris(n-propylammonium) enneachlorodiantimonate (III), (n-C3H7NH3)(3)Sb2Cl9

The crystal structure of (n-C3H7NH3)(3)Sb(2)Cly at 298 K has been determined (monoclinic, space group Cc, a = 19.464(2) Angstrom, b = 17.736(2) Angstrom, c = 8.116(2) Angstrom, beta = 92.81(1)degrees, Z = 4). The structure consists of one-dimensional polyanionic (Sb2Cl93-)(n) chains extended along the c-axis, and n-propylammonium cations located in elongated cavities formed by polyanions. The cations are connected to chlorine atoms by N-H ... Cl hydrogen bonds. Differential scanning calorimetry, the temperature dependence of the lattice parameters and static electric permittivity studies revealed a first-order phase transition at T-c = 232 K of an 'order-disorder' type. It is related to the ordering of n-propylammonium cations that occurs on decreasing the temperature. Debye-like dispersion of the electric permittivity between 30 MHz and 900 MHz is observed over a wide temperature range above T-c. The activation energy of the reorientation of the n-propylammonium cations is found to be 0.29 eV.