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 T_c = 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.