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

Two pure dehydrated borogermanates with microporous structure, β -K 2 [B 2 Ge 3 O 10 ] and NH 4 [BGe 3 O 8 ], have been synthesized and characterized by XRD, FT-IR, TG techniques. The molar enthalpies of solution of 2.51   mg of GeO 2   (s)/0.99   mg of H 3 BO 3   (s)/1.98   mg of H 3 BO 3   (s) in 2.00   cm 3 of 1   mol   ·   dm −3 NaOH   (aq) were measured, respectively. The molar enthalpies of solution of 2.44   mg of K 2 B 4 O 7   ·   4H 2 O   (s) and 2.18   mg of NH 4 B 5 O 8   ·   4H 2 O   (s) in the mixture solvent of 2.00   cm 3 of 1   mol   ·   dm −3 NaOH   (aq) which contains 2.51   mg of GeO 2   (s) were measured, respectively. The molar enthalpies of solution of 3.82   mg of β -K 2 [B 2 Ge 3 O 10 ]   (s) in the mixture solvent of 2.00   cm 3 of 1   mol   ·   dm −3 NaOH   (aq) which contains 0.99   mg of H 3 BO 3   (s), and 3.00   mg of NH 4 [BGe 3 O 8 ]   (s) in the mixture solvent of 2.00   cm 3 of 1   mol   ·   dm −3 NaOH   (aq) which contains 1.98   mg of H 3 BO 3 )   (s) were also measured, respectively. With the use of standard molar enthalpies of formation for NH 4 B 5 O 8   ·   4H 2 O   (s), K 2 B 4 O 7   ·   4H 2 O   (s), GeO 2   (s), H 3 BO 3   (s) and H 2 O (l), the standard molar enthalpies of formation of – (3937.1   ±   4.7)   kJ   ·   mol −1 for β -K 2 [B 2 Ge 3 O 10 ] and – (2713.7   ±   6.0)   kJ   ·   mol −1 for NH 4 [BGe 3 O 8 ] at T   =   298.15   K were obtained on the basis of the appropriate thermochemical cycles, respectively.