An x-ray and nuclear magnetic resonance study of structure and ion motions in (C(NH2)3)3AlF6

Authors:

• M. Grottel,
• Asja Kozak,
• H. Maluszyriska,
• Zdzisław Pająk

Abstract

Guanidinium hexafluoroaluminate (C(NH₂)₃) ₃AlF₆ crystallizes in a cubic system in the space group P2₁/a3,a=13.953(2) AA, Z=8. The guanidinium cation does not exhibit any symmetry; the hexafluoroaluminate anion has 3 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.