Two pure hydrated lead borates, Pb(BO2)(2)center dot H2O and PbB4O7 center dot 4H(2)O, have been characterized by XRD, FT-IR, DTA-TG techniques and chemical analysis. The molar enthalpies of solution of Pb(BO2)(2)center dot H2O and PbB4O2 center dot 4H(2)O in 1 mol dm(-3) HNO3(aq) were measured to be (-35.00 +/- 0.18) kJ mol(-1) and (35.37 +/- 0.14) kJ mol(-1), respectively. The molar enthalpy of solution of H3BO3(s) in 1 mol dm(-3) HNO3(aq) was measured to be (21.19 +/- 0.18) kJ mol(-1). The molar enthalpy of solution of PbO(s) in (HNO3 + H3BO3)(aq) was measured to be -(61.84 +/- 0.10) kJ mol(-1). From these data and with incorporation of the enthalpies of formation of PbO(s), H3BO3(s) and H2O(1), the standard molar enthalpies of formation of -(1820.5 +/- 1.8) kJ mol(-1) for Pb(BO2)(2)center dot H2O and -(4038.1 +/- 3.4) kJ mol(-1) for PbB4O7 center dot 4H(2)O were obtained on the basis of the appropriate thermochemical cycles. (C) 2010 Elsevier B.V. All rights reserved.