AN X-RAY AND NUCLEAR-MAGNETIC-RESONANCE STUDY OF STRUCTURE AND ION MOTIONS IN [C(NH2)3]3ALF6

Guanidinium hexafluoroaluminate [C(NH2)3]3AlF6 crystallizes in a cubic system in the space group P2(1)/a3BAR, a = 13.953(2) angstrom, Z = 8. The guanidinium cation does not exhibit any symmetry; the hexafluoroaluminate anion has 3BAR symmetry and occupies two inequivalent (4a) and (4b) positions. The ions are connected by relatively strong N-H ... F hydrogen bonds. Proton and fluorine spin-lattice relaxation times as well as second moments have been measured over a wide range of temperatures. The analysis of all cross-relaxation effects for the system of four unlike spins has been performed. Activation parameters for the C3 reorientation of the cation and for the NH2 group motion have been derived. Unlike in other guanidinium salts, anion reorientation is hindered by a much higher energy barrier than cation reorientation.