A Structural Study of [N(CH3)4]2CdBr4in Connection with Its Phase Transition

Abstract

The crystal structure of [N(CH 3 ) 4 ] 2 CdBr 4 was studied at 21°C in the room temperature phase and at -3, -8, -35, -80 and -115°C in the low temperature phase by single crystal diffractometry. In the room temperature phase, CdBr 4 ion and two kinds of N(CH 3 ) 4 ions were determined to be in disorder from Fourier synthesis and the significance test. In the low temperature phase, the occupation probabilities of ions as well as positional and thermal parameters were determined. The structure is characterized by two kinds of chains composed of CdBr 4 and N(CH 3 ) 4 ; one is along [001] and the other is along [100]. The deviation Δβ of monoclinic angle β from 90° shows the characteristic temperature dependence as reported in [N(CH 3 ) 4 ] 2 ZnBr 4 and [N(CH 3 ) 4 ] 2 CoBr 4 ; Δβ increases rapidly just below the transition temperature then decreases almost linearly as temperature decreases and changes its sign at about -72°C.