Thermodynamic properties of microporous materials for two copper borates, MCuB7O12·H2O (M=Na,K)

Two pure microporous copper borates (NaCuB7O12 · H2O and KCuB7O12 · H2O) have been synthesised and characterized by XRD, FT-IR, TG techniques and chemical analysis. The molar enthalpies of solution of NaCuB7O12 · H2O (s) and KCuB7O12 · 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 cm3 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 · 2H2O (s) in the mixture solvent of 2.00 cm3 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 · 2H2O (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 · H2O (s) and – (5375.0 ± 5.6) kJ · mol−1 for KCuB7O12 · H2O (s) at T = 298.15 K were obtained on the basis of the appropriate thermochemical cycles. It is obvious that KCuB7O12 · H2O (s) is more thermal stable than that of NaCuB7O12 · H2O (s).