Crystal structure and dynamic behavior of CaSnCl 66H 2O

Abstract

In order to investigate the origin of the anomalous temperature dependence of Cl NQR frequency in CaSnCl 66H 2O, we carried out the determination of crystal structure by X-ray diffraction and NQR Zeeman effect measurements. The crystal is trigonal with a space group of R3̄, a=10.750, c=11.474 A and Z=3 at room temperature. The complex ions, Ca(H 2O) 2+ 6 and SnCl 2− 6 , form a rhombohedrally distorted CsCl type structure through hydrogen bonds. The asymmetry parameter is 0.035 and the x and y axes of EFG tensor direct to the hydrogen bonding between the chlorine atom and the water molecule. The precise measurement of the temperature variation of NQR frequency showed one minimum (at 230 K) and one maximum (at 370 K) values in the temperature range of 77 to 390 K, and the signal faded out at 390 K. The temperature dependence of proton NMR and Mn 2+ -doped ESR spectral line shapes indicates that the anomaly in the NQR data is due to the thermal motion associated with the hydrogen bond among the complex ions in crystal. Several successive phase transitions were also found by X-ray diffraction, DTA and ESR measurements. The transition temperatures are 360, 401, and 413 K.