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.