¹H, ²H, ¹⁹F, ³¹P, and ³⁵Cl NMR studies on molecular motions in ionic plastic phases of pyrrolidinium perchlorate and hexafluorophosphate

Measurements of ¹H, ²H, ¹⁹F, ³¹P, and ³⁵Cl NMR, differential scanning calorimetry (DSC), and X-ray powder diffraction were carried out in solid pyrrolidinium perchlorate ([C₄H₈NH₂]ClO₄) and hexafluorophosphate ([C₄H₈NH₂]PF₆). Five and three solid phases were obtained in perchlorate and hexafluorophosphate, respectively, by DSC measurement above 150 K. X-Ray powder patterns showed the highest-temperature solid phase of both salts to be CsCl-type cubic, indicating that both cations and anions take isotropically disordered orientations. The measurements of the NMR linewidth and its second moment revealed that the C₄H₈NH₂⁺ and PF₆^- ions perform self-diffusion as well as isotropic rotation in this phase. From the dynamical behaviour of ions, the highest-temperature phase can be assigned to be an ionic plastic phase; this is the first example of an ionic plastic phase containing pyrrolidinium cations.