Heat capacities and thermodynamics of formation of ε-Keggin MAl 12 Selenates (M=Al(III), Ga(III), or Ge(IV))

•Calorimetry was used to measure ΔdsH for a germanium – substituted Al13 selenate.•The enthalpies, ΔfH° and Δf,oxH, were determined for this GeAl12 selenate.•Heat capacities were measured on the MAl12 selenates, M=Al(III), Ga(III) or Ge(IV).•Standard entropies and free energies were determined for these MAl12 selenates.•Energetics of AlAl12 and GaAl12 were similar; GeAl12 was found to be less stable.