1H and 13C NMR and Electrical Conductivity Studies on New Ionic Plastic Crystals of Tetraalkylammonium Tetraethylborate

Abstract

Abstract Eight plastic crystals of the types NEt x Me(4 − x)BEt4 and NEt y Pr(4 − y)BEt4 (x=0–4, y=1–3) were found in a new region of ionic plastic crystals. In this area, globular cations and anions are assembled by weak interactions. Based on the results of solid-state 1H and 13C nuclear magnetic resonance (NMR) measurements, it was revealed that the ions performed isotropic reorientations in the NEt x Me(4–x)BEt4 crystals (x=0–4). Additionally, X-ray diffraction (XRD) of these compounds was able to identify the CsCl-type cubic structure. In contrast, the XRD reflections of NEt y Pr(4−y)BEt4 (y=1–3) could be successfully fitted by distorted cubic lattices (trigonal symmetry). The NMR line shapes observed in these compounds were explained by overall molecular motions with large amplitudes (pseudo-isotropic reorientations). Differential scanning calorimetry (DSC) spectra of NEt y Pr(4 − y)BEt4 (y=1–3) showed a low entropy change (ΔS mp) of 6–8 J K−1 mol−1 at the melting point. Ionic diffusion was identified by electrical conductivity measurements of NEt x Me(4 − x)BEt4 and NEt y Pr(4–y)BEt4 (x=0–4, y=1–3). In the case of NPr4BEt4 crystals, ionic diffusion was also detected, although complex powder patterns and large ΔS mp values were observed by XRD and DSC measurements, respectively.