Synthesis, Calorimetric and X ray diffraction studies of the solid Solution [Rb0.92(NH4)0.08]2TeCl4Br2

The structure of [Rb-0.92(NH4)(0.08)](2)TeCl4Br2 has been determined from conventional X-ray powder diffraction data, by Rietveld method, in P4/mnc tetragonal space group (a = 7.315 (2) angstrom, c = 10.354(4) angstrom, Z = 2). The refinement of the structure led to final factor chi(2) = 4.20%. The structure is considered as isolated octahedred TeCl4Br22-. These anions show a 4 rotation around the fourfold axis against the cubic arrangement of the K2PtCl6 type structure. The monovalent cations (Rb+/NH4+) are located between the octahedra ensuring the stability of the structure by ionic and hydrogen bonding contacts: Rb center dot center dot center dot center dot Cl/Br and N-H center dot center dot center dot Cl/Br. At low temperature a second order transition phase was detected at 213K by DSC.