Thermochemical properties of microporous materials for two borogermanates, β-K2[B2Ge3O10] and NH4[BGe3O8]

•Two microporous materials for borogermanates have been synthesized and characterized.•Enthalpies of solution of two borogermanates were measured by microcalorimeter.•A series of enthalpies of solution of other solutes were also measured by microcalorimeter.•ΔfHmθ for both borogermanates were obtained by thermochemical cycles.

Two pure dehydrated borogermanates with microporous structure, β-K2[B2Ge3O10] and NH4[BGe3O8], have been synthesized and characterized by XRD, FT-IR, TG techniques. The molar enthalpies of solution of 2.51 mg of GeO2 (s)/0.99 mg of H3BO3 (s)/1.98 mg of H3BO3 (s) in 2.00 cm3 of 1 mol · dm−3 NaOH (aq) were measured, respectively. The molar enthalpies of solution of 2.44 mg of K2B4O7 · 4H2O (s) and 2.18 mg of NH4B5O8 · 4H2O (s) in the mixture solvent of 2.00 cm3 of 1 mol · dm−3 NaOH (aq) which contains 2.51 mg of GeO2 (s) were measured, respectively. The molar enthalpies of solution of 3.82 mg of β-K2[B2Ge3O10] (s) in the mixture solvent of 2.00 cm3 of 1 mol · dm−3 NaOH (aq) which contains 0.99 mg of H3BO3 (s), and 3.00 mg of NH4[BGe3O8] (s) in the mixture solvent of 2.00 cm3 of 1 mol · dm−3 NaOH (aq) which contains 1.98 mg of H3BO3) (s) were also measured, respectively. With the use of standard molar enthalpies of formation for NH4B5O8 · 4H2O (s), K2B4O7 · 4H2O (s), GeO2 (s), H3BO3 (s) and H2O (l), the standard molar enthalpies of formation of – (3937.1 ± 4.7) kJ · mol−1 for β-K2[B2Ge3O10] and – (2713.7 ± 6.0) kJ · mol−1 for NH4[BGe3O8] at T = 298.15 K were obtained on the basis of the appropriate thermochemical cycles, respectively.