X-ray study of [N(CH3)4]2ZnCl4 at low temperatures

The unit cell parameters a, b, and c of [N(CH3)(4)](2)ZnCl4 have been measured by x-ray diffraction in the temperature range 80-293 K. Temperature dependences of the thermal expansion coefficients alpha(a), alpha(b), and alpha(c) along the principal crystallographic axes and of the unit cell thermal expansion coefficient alpha(V) were determined. It is shown that the a = f(T), b = f(T), and c = f(T) curves exhibit anomalies in the form of jumps at phase transition temperatures T-1 = 161 K and T-2 = 181 K and that the phase transition occurring at T-3 = 276 K manifests itself in the a = f(T) and b = f(T) curves as a break. A slight anisotropy in the coefficient of thermal expansion of the crystal was revealed. The phase transitions occurring at T-1 = 161 K and T-2 = 181 K in [N(CH3)(4)](2)ZnCl4 were established to be first-order. (C) 2004 MAIK "Nauka / Interperiodica".