Motional freedom of dimethylammonium ions in a cyanoelpasolite, [(CH3)2NH2]2KCo(CN)6, which exhibits phase transition associated with a distinct change in dielectric property.

Abstract

The temperature dependence of the 1H nuclear magnetic resonance spin-lattice relaxation time T1 of [(CH3)2NH2]2KCo(CN)6 and the partially deuterated analogue [(CD3)2NH2]2KCo(CN)6 has been reported. A change in the molecular motion of organic cations through the first-order phase transition at Tc = 246 K has been discussed. Although this first-order transition has been reported as an isosymmetric transition, in which the space group of the crystal does not change, the number of the 14N nuclear quadrupole resonance line changed from three in the high-temperature phase to twelve in the low-temperature phase indicating the lowering of crystal symmetry.