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, K-2[Al(B5O10)] center dot 4H(2)O and (NH4)(2)[Al(B5O10)] center dot 4H(2)O, have been synthesized and characterized by XRD, FT-IR, DTA-TG techniques and chemical analysis. The molar enthalpies of solution of K-2[Al(B5O10)] center dot 4H(2)O (s) and (NH4)(2)[Al(B5O10)] center dot 4H(2)O (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 center dot 6H(2)O (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 center dot 6H(2)O (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 K-2[Al(B5O10)] center dot 4H(2)O (s) and -(5775.0 +/- 4.1) kJ . mol(-1) for (NH4)(2)[Al(B5O10)] center dot 4H(2)O (s) at T = 298.15 K were obtained on the basis of the appropriate thermochemical cycles. Moreover, Delta H-f(m)o([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. (C) 2012 Elsevier Ltd. All rights reserved.