Structural phase transition and molecular motions in [(CH{sub 3}){sub 3}CNH{sub 3}]{sub 2}[ZnCl{sub 4}] studied by {sup 1}H NMR, differential scanning calorimetry, and x-ray diffraction

The crystal structure of bis-t-butylammonium tetrachlorozincate [(CH{sub 3}){sub 3}CNH{sub 3}]{sub 2}[ZnCl{sub 4}] was determined at room temperature to be monoclinic with space group of P2{sub 1}/n by the single-crystal x-ray diffraction method. Differential scanning calorimetry measurements show that the crystal undergoes a first-order structural phase transition at T{sub tr}=404 K. An observed transition entropy of 26.3 J K{sup -1} mol{sup -1} suggests that this transition is of the order-disorder type. {sup 1}H NMR measurements suggest that an isotropic reorientational motion of entire cations does not occur above T{sub tr}. The phase transition is considered to arise from disordering of cations and anions among a number of sites.