Abstract
The microporous crystal of Na2[CoB3P2O11(OH)]·0.67H2O has been synthesized under hydrothermal conditions and characterized by XRD, FT-IR, DTA-TG techniques and chemical analysis. The molar enthalpies of solution of Na2[CoB3P2O11(OH)]·0.67H2O (s) in 1mol·dm–3 HCl (aq), of NaH2PO4·2H2O (s) in (H3BO3+HCl+H2O) (aq), and of CoCl2·6H2O (s) in (NaH2PO4·2H2O+H3BO3+HCl+H2O) (aq) were measured, respectively. With the incorporation of the previously determined enthalpy of solution of H3BO3 (s) in 1mol·dm–3 HCl (aq), together with the use of the standard molar enthalpies of formation for CoCl2·6H2O (s), NaH2PO4·2H2O (s), H3BO3 (s), HCl (aq) and H2O (l), the standard molar enthalpy of formation of – (5104.7±2.6) kJ·mol–1 for Na2[CoB3P2O11(OH)]·0.67H2O at T=298.15K was obtained on the basis of the appropriate thermochemical cycle. In addition, the molar enthalpy of formation of −4373.9kJ·mol–1 for [B3P2O11(OH)]4– has also estimated by a group contribution method, which has been used to predict the ΔfHmo of the others four kinds of Na2[MIIB3P2O11(OH)]·0.67H2O. These estimated data have been further used to compare the stabilities of this series of compounds.
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