Two pure zinc borates, Zn2B6O11 center dot 7H(2)O and Zn3B10O18 center dot 14H(2)O have been synthesized and characterized by XRD, FT-IT, DTA-TG techniques and chemical analysis. The molar enthalpies of Solution of Zn2B6O11 center dot 7H(2)O(s) and Zn3B10O18 center dot 14H(2)O(s) in 1 mol dm(-3) HCl(aq) were measured to be 15.42 +/- 0.03 kJ mol(-1) and 57.78 +/- 0.11 kJ mol(-1), respectively. The molar enthalpy of solution of ZnO(s) in (HCl + H3BO3)(aq) was determined to be -80.01 +/- 0.15 kJ mol(-1). With incorporation of the previously determined enthalpy of solution of H3BO3(s) in 1 mol dm(-3) HCl(aq), and the standard molar enthalpies of formation for ZnO(s), H3BO3(s), and H2O(1), the standard molar enthalpies of formation of -6738.1 +/-4.8 kJ mol(-1) for Zn2B6O11 center dot 7H(2)O and -11,786.4 +/- 8.0 kJ mol(-1) for Zn3B10O18 center dot 14H(2)O were obtained. (C) 2008 Elsevier B.V. All rights reserved.