Two pure microporous copper borates (NaCuB7O12 center dot H2O and KCuB7O12 center dot H2O) have been synthesised and characterized by XRD, FT-IR, TG techniques and chemical analysis. The molar enthalpies of solution of NaCuB7O12 center dot H2O (s) and KCuB7O12 center dot H2O (s) in 1 mol . dm(-3) HCl (aq) were determined to be -(24.12 +/- 0.12) kJ . mol(-1) and -(35.07 +/- 0.08) kJ . mol(-1), respectively. The molar enthalpies of solution of 0.72 mg of NaCl (s) and 0.91 mg of KCl in the mixture solvent of 2.00 cm(3) of 1 mol . dm(-3) HCl (aq) which contains 5.3 mg of H3BO3 were measured, respectively. The molar enthalpies of solution of 2.09 mg of CuCl2 center dot 2H(2)O (s) in the mixture solvent of 2.00 cm(3) of 1 mol . dm(-3) HCl (aq) which contains 5.3 mg of H3BO3 and 0.72 mg of NaCl/0.91 mg of KCl were also measured, respectively. With the incorporation of the previously determined enthalpy of solution of H3BO3 (s) in 1 mol . dm(-3) HCl (aq), together with the standard molar enthalpies of formation for CuCl2 center dot 2H(2)O (s), NaCl (s)/KCl (s), H3BO3 (s), HCl (aq) and H2O (l), the standard molar enthalpies of formation of -(5373.3 +/- 5.6) kJ.mol(-1) for NaCuB7O12 center dot H2O (s) and -(5375.0 +/- 5.6) kJ.mol(-1) for KCuB7O12 center dot H2O (s) at T = 298.15 K were obtained on the basis of the appropriate thermochemical cycles. It is obvious that KCuB7O12 center dot H2O (s) is more thermal stable than that of NaCuB7O12 center dot H2O (s). (C) 2015 Elsevier Ltd. All rights reserved.