Structure and phase transition in (C2H5NH3)3Sb2Cl9•(C2H5NH3)SbCl4;: X-ray, DSC and dielectric studies

The structure of (C2H5NH3)(3)Sb2Cl9 . (C2H5NH3)SbCl4 at 295 K has been determined. The crystals are orthorhombic, space group Pna2(1) (a = 16.925(3), b = 24.703(5), c = 7.956(2) Angstrom, V = 3326.4(12) Angstrom(3), Z = 4, d(c) = 2.018, d(m) = 2.01(1) Mg m(-3)). They consist of an anionic sublattice composed of two different polymeric zig-zag chains. One is built of Sb2Cl93- units (corner sharing octahedra) and the other one is made of corner sharing SbCl52- square pyramids. In the cavites between the polyanionic chains four non-equivalent ethylammonium cations are located. Three of them are disordered. The cations are connected to the anions by weak N-H...Cl hydrogen bonds. A first order phase transition of the order-disorder type was found at 274 K. It was studied by DSC, dielectric and X-ray diffraction methods. The mechanism of the phase transition is attributed to the ordering of at least one of the ethylammonium cations.