THERMODYNAMICS OF AMMONIUM HALOPALLIDATES .2. 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 lambda-shaped phase transition, absent in the protonated salt, was found in the curve for heat capacity against temperature. This transition reaches its maximum C(p,m) congruent-to 150 . R at (30.2 +/- 0.1) K with DELTA(trs)S(M)o = (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 S(m)o(273.15 K) = (49.80 +/- 0.05) . R.