Phase Transition in C 8 H 20 XN·2CH 4 N 2 S (X=I, Br, Cl)

The title compounds were prepared by an addition of thiourea to the tetoracthylammonium iodide, bromide and chloride. C 8 H 20 IN. 2CH 4 N 2 S undergoes a phase transition at 288K. The structure at room temperature belongs to orthorhombic system with the space group Ibca; the low temperature phase is orthorhombic Pccb. Both phase are centric and Z=8. Large differences of the cell dimensions were not found between both phases. The structure consists of the tetraethylammonium cations, iodide anions and thiourea molecules. The main difference between both structures is that the cations show a disordered arrangement at room temperature whereas they are ordered in the low-temperature phase. As the result of structural analysis of tetraedlylammonium bromide salt and tetraethylammonium chloride salt, instead of crystallization that two thiourea was added to, it become clear to be crystallization added 4 thiourea and 5 thiourea to.