Investigation of New Ionic Plastic Crystals in NR4BBu4 (R = Me, Et, Pr, Bu, Pen)

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.