Adiabatic heat capacity and related properties of ammonium hexachlororuthenate, (NH4)2RuCl6, at temperatures from 5 ⩽ T/K ⩽ 325

Abstract The heat capacity of ammonium hexachlororuthenate, (NH 4 ) 2 RuCl 6 , was measured over the temperature range 5 ⩽  T /K ⩽ 325 using adiabatic calorimetry. Our results show that a structural phase transition is not present. However, an anomalous increase in the heat capacity C p ,m occurs in the region 70 ⩽  T /K ⩽ 105 and the heat capacity reaches its maximum at T  = (93.5 ± 0.1) K. The molar entropy change associated with this increase amounts to Δ S m  = (0.465 ± 0.006) R. Standard molar thermodynamic functions are presented at selected temperatures from 5 K to 325 K.