Inorganic anion regulated phase transition in a supramolecular adduct: 4-Trifluoromethoxyanilinium hexafluorophosphate-18-crown-6

Abstract

A new supramolecular adduct 4-trifluoromethoxyanilinium hexafluorophosphate-1,4,7,10,13,16-hexaoxacyclooctadecane ([C7H7NOF3–(18-crown-6)]+[PF6]−) was synthesized and separated as crystals. DSC measurement detected that this compound undergoes a reversible phase transition at about 158K with a heat hysteresis of 4.8K. The single crystal X-ray diffraction data obtained at 213K and 113K suggest that the phase transition undergoes from a high temperature phase with a space group of Pnma to a low temperature one with a space group of P21/n, the symmetry breaking occurs with an Aizu notation of mmmF2/m. The driving force of the transition may be ascribed to the order–disorder transformation of the inorganic PF6− anion. Broad peak dielectric anomaly observed at 157K further confirms this phase transition.