Standard molar enthalpy of formation of Ca2[B4O7(OH)2]

A pure calcium borate Ca2[B4O7(OH)2] has been synthesized under hydrothermal condition and characterized by XRD, FT-IR and TG as well as by chemical analysis. The molar enthalpy of solution of Ca2[B4O7(OH)2] in HCl·54.549H2O was determined. From a combination of this result with measured enthalpies of solution of H3BO3 in HCl·54.517H2O and of CaO in (HCl + H3BO3) solution, together with the standard molar enthalpies of formation of CaO(s), H3BO3(s), and H2O(l), the standard molar enthalpy of formation of -(4398.9 ± 3.8) kJ mol−1 for Ca2[B4O7(OH)2] was obtained.