Synthesis, characterization and thermodynamic properties of NaCs[B4O5(OH)4]·4H2O

The crystalline form of a new tetraborate, NaCs[B4O5(OH)4]·4H2O was synthesized and characterized. The enthalpies of solution of NaCs[B4O5(OH)4]·4H2O in approximately 1 mol dm−3 HCl(aq) and of CsCl in aqueous (HCl + H3BO3 + NaCl) were determined. From these results and the enthalpy of solution of H3BO3 in approximately 1 mol dm−3 HCl(aq), the enthalpy of solution of NaCl(s) in aqueous (HCl + H3BO3) and the standard molar enthalpies of formation of NaCl(s), CsCl(s), H3BO3(s) and H2O(l), the standard molar enthalpy of formation for NaCs[B4O5(OH)4]·4H2O as being −(5140.55 ± 1.94) kJ mol−1. The standard molar entropy of formation of NaCs[B4O5(OH)4]·4H2O was calculated from the thermodynamic relation with the standard molar Gibbs free energy of formation of NaCs[B4O5(OH)4]·4H2O computed from a group contribution method.