35Cl NQR Spin-Lattice Relaxation Mechanism in Ni(H2O)6SnCl6 and Mg(H2O)6SnCl6 Crystals

Abstract

Abstract The 35Cl NQR spin-lattice relaxation mechanism in isomorphous Ni(H2O)6SnCl6 and Mg(H2O)6SnCl6 crystals is reported. The spin-lattice relaxation time T1Q in the Ni compound is determined mainly by a paramagnetic relaxation. However, above ca. 400 K T1Q decreased rapidly and a log vs. T1 curve was almost linear. This steep decrease of T1Q was explained by reorientational motions of the anions with an activation energy of 73 kJ mol-1. In addition, a double minimum in T1Q, which can be interpreted as arising from the fluctuation o f the electric field gradient (EFG) at the chlorine site caused by cationic thermal motions, was observed around room temper ature. The temperature dependence of the 35Cl NQR T1Q in the Mg salt is re-analysed in the light of the EFG -modulation effect caused by a 180° flip motion of the H2O molecules and an overall reorientational motion of the [Mg(H2O)6]2+ octahedral cations as a whole.