New mesophases in ionic crystals: piperidinium perchlorate and nitrate studied by 1H, 2H, 14N and 35Cl NMR

Measurements of 1H, 2H, 14N and 35Cl NMR, differential thermal analysis, differential scanning calorimetry and powder X-ray diffraction were carried out in solid piperidinium perchlorate and nitrate above room temperature. Two and one solid-solid phase transitions were observed for the perchlorate and nitrate, respectively. The crystal structure in the highest-temperature phase of the perchlorate is CsCl-type cubic (a = 6.02(6) Å and Z = 1) while that of the nitrate is NaCl-type cubic (a = 9.35(5) Å and Z = 4). In this phase of the perchlorate self-diffusion of the cation and isotropic rotation of both cation and anion were revealed. In the highest-temperature phase of the nitrate, the isotropic rotation of both ions was detected. These phases are highly disordered and especially the phase of the perchlorate can be assigned to an anionic plastic phase.