Low-temperature X-ray diffraction studies of [(CH3)2NH2]5Cd3Cl11 crystals

Abstract

[(CH{sub 3}){sub 2}NH{sub 2}]{sub 5}Cd{sub 3}Cl{sub 11} crystals are grown by the method of isothermal evaporation from saturated aqueous solutions containing dimethylamine and cadmium chlorides, [(CH{sub 3})2NH{sub 2}]Cl and CdCl{sub 2.5}H{sub 2}O. The crystal grown are studied by the X-ray diffraction method. It is established that the crystals are orthorhombic with the unit-cell parameters at room temperature a = 18.115 {+-} 0.004 A, b = 11.432 {+-} 0.002 A, and c = 15.821 {+-} 0.003 A. The unit-cell parameters a, b, and c of the [(CH{sub 3}){sub 2}NH{sub 2}]{sub 5}Cd{sub 3}Cl{sub 11} crystals are measured as functions of temperature in the temperature range 100-320 K. The data obtained were used to determine the thermal expansion coefficients along the main crystallographic axes. The temperature curves of the unit-cell parameters and thermal expansion coefficients showed pronounced anomalies in the vicinity of the temperatures T{sub 1} = 120, T{sub 2} = 150, and T{sub 3} = 180 K corresponding to the phase transitions in the [(CH{sub 3}){sub 2}NH{sub 2}]{sub 5}Cd{sub 3}Cl{sub 11} crystals. The crystals are also characterized by a pronounced anisotropy of thermal expansion.