Chemical Science International Journal

In order to investigate new ionic plastic crystals, differential-scanning-calorimetry (DSC), nuclear-magnetic-resonance (NMR), and electrical conductivity measurements were carried out in NR₄BBu₄ (R = Me, Et, Pr, Bu, Pen) salts. DSC measurements showed a low entropy change of 29.1 J K^-1 mol^-1 at a melting point and large values of 35.7 and 17.8J K^-1 mol^-1 at phase transitions in NEt₄BBu₄ crystals. In contrast, the other compounds of NR₄BBu₄ (R = Me, Pr, Bu, Pen) showed large entropy changes at each melting point. On the basis of solid-state ¹H and ¹³C NMR spectra results, tumbling motions were detected in the NMe₄BBu₄ and NEt₄BBu₄ crystals. Isotropic reorientation motions of partial ions were observed in the NPr₄BBu₄ crystals. Although NR₄BBu₄ (R = Me, Et, Pr) have no plastic phases, low activation energies of ion transfer were recorded in these salts. These results suggest that the tumbling motions can perform the resemble effect as isotropic reorientation in plastic crystals.