Thermodynamics of Ammonium Halopallidates II. Heat Capacity and Thermodynamic Properties of (ND4)2PdCl6 at Temperatures from 5 K to 325 K

The heat capacity of deuterated ammonium hexachloropallidate (ND4)2pDCl6 was measured from 5 K to 325 K by adiabatic calorimetry. One λ‐shaped phase transition, absent in the protonated salt, was found in the curve for heat capacity against temperature. This transition reaches its maximum Cp.m ≃ 150 · R at (30.2 ± 0.1) K with ΔtrsSm0 = (2.005 ± 0.009) · R (R = 8.31451 J · K−1 · mol−1) and marks the change from the high temperature cubic structure to the low temperature tetragonal structure. The Debye temperature at 0 K equals (96.5 ± 2.4) K and below 10 K, only lattice vibrations make significant contributions to the heat capacity. Smoothed values of the standard thermodynamic quantities for pure (ND4)2PdCl6 are tabulated up to 320 K and the Sm0(273.15 K) = (49.80 ± 0.05) · R.