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

Two pure microporous copper borates (NaCuB 7 O 12   ·   H 2 O and KCuB 7 O 12   ·   H 2 O) have been synthesised and characterized by XRD, FT-IR, TG techniques and chemical analysis. The molar enthalpies of solution of NaCuB 7 O 12   ·   H 2 O (s) and KCuB 7 O 12   ·   H 2 O (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 H 3 BO 3 were measured, respectively. The molar enthalpies of solution of 2.09   mg of CuCl 2   ·   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 H 3 BO 3 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 H 3 BO 3 (s) in 1   mol   ·   dm −3 HCl (aq), together with the standard molar enthalpies of formation for CuCl 2   ·   2H 2 O (s), NaCl (s)/KCl (s), H 3 BO 3 (s), HCl (aq) and H 2 O (l), the standard molar enthalpies of formation of – (5373.3   ±   5.6)   kJ   ·   mol −1 for NaCuB 7 O 12   ·   H 2 O (s) and – (5375.0   ±   5.6)   kJ   ·   mol −1 for KCuB 7 O 12   ·   H 2 O (s) at T   =   298.15   K were obtained on the basis of the appropriate thermochemical cycles. It is obvious that KCuB 7 O 12   ·   H 2 O (s) is more thermal stable than that of NaCuB 7 O 12   ·   H 2 O (s).