Motional freedom of dimethylammonium ions in a cyanoelpasolite, [(CH)NH]KCo(CN), which exhibits phase transition associated with a distinct change in dielectric property

The temperature dependence of the 1 H nuclear magnetic resonance spin-lattice relaxation time T 1 of [(CH 3 ) 2 NH 2 ] 2 KCo(CN) 6 and the partially deuterated analogue [(CD 3 ) 2 NH 2 ] 2 KCo(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 14 N 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. Although the phase transition of (DMA) 2 KCo(CN) 6 has been reported as an isosymmetric transition, 14 N NQR spectra showed a lowering of crystal symmetry.