The relationship between reorientational molecular motions and phase transitions in [Mg(H2O)6](BF4)2, studied with the use of (1)H and (19)F NMR and FT-MIR.

A (1)H and (19)F nuclear magnetic resonance study of [Mg(H2O)6](BF4)2 has confirmed the existence of two phase transitions at Tc1 ≈ 257 K and Tc2 ≈ 142 K, detected earlier by the DSC method. These transitions were reflected by changes in the temperature dependences of both proton and fluorine of second moments M2 (H) and M2 (F) and of spin-lattice relaxation times T1 (H) and T1 (F). The study revealed anisotropic reorientations of whole [Mg(H2O)6](2+) cations, reorientations by 180° jumps of H2O ligands, and aniso- and isotropic reorientations of BF4 (-) anions.