A thermophysical and thermochemical investigation of K-2[(UO2)(W2O8)] was undertaken. K-2[(UO2) (W2O8)] was synthesized by solid-state reaction of KNO3, WO3 and gamma-UO3 and characterized by X-ray powder diffraction and X-ray fluorescence methods. Its low-temperature heat capacity was measured using adiabatic calorimetry from T = (9 to 329) K. Based on these data, the third law entropy, S degrees, at T = 298.15 K is (423 +/- 1) J.K-1.mol(-1). The enthalpy of formation of K2[(UO2)(W2O8)] was determined using HF solution calorimetry giving Delta H-f degrees(298 K, K-2[(UO2)(W2O8)], cr) = -(3897 +/- 10) kJ.mol(-1). From the thermophysical and thermochemical results Delta(f)G degrees (298 K, K-2[(UO2)(W2O8)], cr) = -(3645 +/- 10) kJ.mol(-1) is calculated. Smoothed C-p degrees (T) values between T = (0 and 320) K are presented along with values for S degrees and the functions [H degrees(T) - H degrees(0)] and [G degrees(T) - H degrees(0)]. (C) 2012 Elsevier Ltd. All rights reserved.