Thermodynamic properties of microporous crystals for two hydrated aluminoborates, K2[Al(B5O10)] · 4H2O and (NH4)2 [Al(B5O10)] · 4H2O

Two pure hydrated aluminoborates with microporous structure, K2[Al(B5O10)] · 4H2O and (NH4)2[Al(B5O10)] · 4H2O, have been synthesized and characterized by XRD, FT-IR, DTA-TG techniques and chemical analysis. The molar enthalpies of solution of K2[Al(B5O10)] · 4H2O (s) and (NH4)2[Al(B5O10)] · 4H2O (s) in 1 mol · dm−3 HCl (aq) were measured to be −(88.65 ± 0.25) kJ · mol−1 and −(93.37 ± 0.25) kJ · mol−1, respectively. The molar enthalpies of solution of AlCl3·6H2O (s) in (HCl + H3BO3 + KCl) (aq) and in (HCl + H3BO3 + NH4Cl) (aq) were 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 use of the standard molar enthalpies of formation for AlCl3·6H2O (s), KCl (s)/NH4Cl (s), H3BO3 (s), HCl (aq), and H2O (l), the standard molar enthalpy of formation of −(6029.8 ± 4.1) kJ · mol−1 for K2[Al(B5O10)] · 4H2O (s) and −(5775.0 ± 4.1) kJ · mol−1 for (NH4)2[Al(B5O10)] · 4H2O (s) at T = 298.15 K were obtained on the basis of the appropriate thermochemical cycles. Moreover, ΔfHmo([Al(B5O10)]2−) of −4355.3 kJ · mol−1 has also been estimated by a group contribution method, which can be used to predict the standard molar enthalpies of formation of other aluminoborates containing [Al(B5O10)]2− anionic framework.

► M2[Al(B5O10)] · 4H2O (MIK+, NH4+) have been synthesized and characterized.
► The enthalpies of solution of title two compounds were measured.
► The enthalpies of solution of AlCl3·6H2O (s) were measured.
► ΔfHmo for title two compounds were obtained by a thermochemical cycle.