Standard molar enthalpies of formation for the two mixed alkali/alkaline earth metal borates of LiBaB9O15 and NaBaB9O15

• Two microporous materials MBaB9O15 (MI = Li+, Na+) were synthesized and characterized.
• The enthalpies of solution of title two compounds were measured.
• ΔfHm0 for title two compounds were obtained by a thermochemical cycle.

Two pure mixed alkali/alkaline earth metal borates with three-dimensional framework, LiBaB9O15 and NaBaB9O15, have been synthesized by high-temperature solid state reaction, and characterized by XRD, FT-IR, DTA–TG techniques and chemical analysis. The molar enthalpies of solution of LiBaB9O15 and NaBaB9O15 in 1 mol L−1 HCl(aq), and of LiCl·H2O(s)/NaCl(s) in [1 mol L−1 HCl + H3BO3 + Ba(OH)2·8H2O](aq) have been determined by microcalorimeter at 298.15 K, respectively. From these data and with the incorporation of the previously determined enthalpy of solution of H3BO3(s) in 1 mol L−1 HCl (aq), together with the use of the standard molar enthalpies of formation for Ba(OH)2·8H2O(s), LiCl·H2O(s)/NaCl(s), H3BO3(s), HCl(aq) and H2O(l), the standard molar enthalpies of formation of −(6796.8 ± 7.3) kJ mol−1 for LiBaB9O15 and −(6829.9 ± 7.3) kJ mol−1 for NaBaB9O15 were obtained on the basis of the appropriate thermochemical cycles.