Molecular and electron-spin dynamics in [M(H2O)6][AB6] as studied by solid state NMR

A method using the H-2-NMR spectra was shown to be useful to study the solid state physics in diamagnetic and paramagnetic compounds and in crystals having a modulated structure. The spectra and T-1 of NMR in solids were measured for [M(H2O)(6)] [AB(6)] crystals to investigate the static and dynamic structure of H2O and [M(H2O)(6)](2+) as well as the dynamics of the electron spin in the paramagnetic M2+ ion. The physical properties of [M(H2O)(6)] [AB(6)] were found to be as follows: (1) The spin-lattice relaxations of the electron spin of M2+ in [M(H2O)(6)] [SiF6] (M2+ = Fe2+, Co2+, Ni2+) are dominated by the Orbach process, the Orbach process, and the Raman process, respectively. The spin-lattice relaxation of the electron spin Of Cu2+ in [Cu (H2O)(6)] [PtCl6] is caused by jumping between the Jahn-Teller configurations. (2) In [Cu(H2O)(6)] [PtCl6], H2O and [Cu(H2O)(6)](2+) undergo 180degrees flips and jumping between the different Jahn-Teller configurations, respectively. A weakening of the hydrogen bond O-H...Cl upon deuteration results in a lowering of the transition temperature. (3) In [M(H2O)(6)] [SiF6], H2O and [M(H2O)(6)](2+) undergo 180degrees flips and reorientation about the C-3 axis, respectively. The order-disorder transition is closely related to a freezing of this reorientation. (4) By elongation of [M(H2O)(6)](2)+ along the C-3 axis, the mobility becomes higher. (5) The disorder of [Fe(H2O)(6)](2+) in the high-temperature phase of [Fe(H2O)(6)] [SiF6] is dynamic. Rotational modulation of [Mg(H2O)(6)](2+) along the C-3 axis exists in the incommensurate phase of [Mg(H2O)(6)] [SiF6].