The microporous crystal of Na-2[CoB3P2O11(OH)]center dot 0.67H(2)O has been synthesized under hydrothermal conditions and characterized by XRD, FT-IR, DTA-TG techniques and chemical analysis. The molar enthalpies of solution of Na-2[CoB3P2O11(OH)]center dot 0.67H(2)O (s) in 1 mol.dm(-3) HCl (aq), of NaH2PO4 center dot 2H(2)O (s) in (H3BO3 + HCl + H2O) (aq), and of CoCl2 center dot 6H(2)O (s) in (NaH2PO4 center dot 2H(2)O + H3BO3 + HCl + H2O) (aq) were measured, respectively. With the incorporation of the previously determined enthalpy of solution of H3BO3 (s) in 1 mol.dm(-3) HCl (aq), together with the use of the standard molar enthalpies of formation for CoCl2 center dot 6H(2)O (s), NaH2PO4 center dot 2H(2)O (s), H3BO3 (s), HCl (aq) and H2O (l), the standard molar enthalpy of formation of -(5104.7 +/- 2.6) kJ.mol(-1) for Na-2[CoB3P2O11(OH)]center dot 0.67H(2)O at T = 298.15 K was obtained on the basis of the appropriate thermochemical cycle. In addition, the molar enthalpy of formation of -4373.9 kJ.mol(-1) for [B3P2O11(OH)](4-) has also estimated by a group contribution method, which has been used to predict the Delta fH(m)(o) of the others four kinds of Na-2[(MB3P2O11)-B-II(OH)]center dot 0.67H(2)O. These estimated data have been further used to compare the stabilities of this series of compounds. (C) 2012 Elsevier Ltd. All rights reserved.