Thermochemical properties for a series of transition metal borates of M[B12O14(OH)10] (MII = Mn, Zn, Fe, Co, Ni)

A pure zinc borate, Zn[B 12 O 14 (OH) 10 ], has been synthesized and characterized by XRD, FT-IR, simultaneous TG-DTA techniques, and chemical analysis. The molar enthalpy of solution of Zn[B 12 O 14 (OH) 10 ] (s) in 1   mol·dm −3 HCl(aq) was measured by microcalorimeter at T   =   298.15   K. The molar enthalpy of solution of ZnO(s) in the mixture solvent of 2.00   cm 3 of 1   mol·dm −3 HCl(aq) and calculated amount of H 3 BO 3 was also measured. With the incorporation of the previously determined enthalpy of solution of H 3 BO 3 (s) in 1   mol·dm −3 HCl(aq), together with the use of the standard molar enthalpies of formation for ZnO(s), H 3 BO 3 (s), and H 2 O(l), the standard molar enthalpy of formation of −(9646.6   ±   9.6)   kJ·mol −1 at T   =   298.15   K was obtained on the basis of an appropriate thermochemical cycle. In addition, the molar enthalpy of formation of −9492.7   kJ·mol −1 for [B 12 O 14 (OH) 10 ] 2− has also been estimated by a group contribution method, which has been used to predict the Δ f H m θ of a series of transition metal borates of M[B 12 O 14 (OH) 10 ] (M II   =   Mn,   Zn,   Fe,   Co,   Ni). These estimated data have been used to further compare the stability of this series of transition metal borates.