Phase transitions and molecular motions in [Ni(ND 3) 6](ClO 4) 2

Abstract

[Ni(ND 3) 6](ClO 4) 2 has three solid phases between 100 and 300 K. The phase transitions temperatures at heating ( T C1 h=164.1 K and T C2 h=145.1 K) are shifted, as compared to the non-deuterated compound, towards the lower temperature of ca. 8 and 5 K, respectively. The ClO 4 − anions perform fast, picosecond, isotropic reorientation with the activation energy of 6.6 kJ mol −1, which abruptly slow down at T C1 c phase transition, during sample cooling. The ND 3 ligands perform fast uniaxial reorientation around the Ni–N bond in all three detected phases, with the effective activation energy of 2.9 kJ mol −1. The reorientational motion of ND 3 is only slightly distorted at the T C1 phase transition due to the dynamical orientational order–disorder process of anions. The low value of the activation energy for the ND 3 reorientation suggests that this reorientation undergoes the translation–rotation coupling, which makes the barrier to the rotation of the ammonia ligands not constant but fluctuating. The phase polymorphism and the dynamics of the molecular reorientations of the title compound are similar but not quite identical with these of the [Ni(NH 3) 6](ClO 4) 2.