Thermochemical properties of two mixed alkali-alkaline earth metal borates as non-linear optical materials: NaSrBO3 and KSr4B3O9

Two mixed alkali-alkaline earth metal borates of NaSrBO 3 and KSr 4 B 3 O 9 have been synthesized by high-temperature solid state reaction, which were further characterized by XRD, FT-IR, DTA-TG techniques and chemical analysis. The molar enthalpies of solution of NaSrBO 3 (s) and KSr 4 B 3 O 9 (s) in 2.00   cm 3 of 1   mol   ·   dm −3 HCl(aq), at T   =   298.15   K were measured to be −(206.84   ±   0.43)   kJ   ·   mol −1 and −(494.59   ±   0.53)   kJ   ·   mol −1 , respectively. The molar enthalpy of solution of NaCl(s) in 2.00   cm 3 of {1   mol   ·   dm −3 HCl   +   H 3 BO 3   +   Sr(OH) 2   ·   8H 2 O}(aq) mixed solvent at T   =   298.15   K was measured to be (5.17   ±   0.02)   kJ   ·   mol −1 . From these data and with the incorporation of the previously determined enthalpies of solution of H 3 BO 3 (s) in HCl(aq) of Sr(OH) 2   ·   8H 2 O(s) in (HCl   +   H 3 BO 3 )(aq), and of KCl(s) in {HCl   +   H 3 BO 3   +   Sr(OH) 2   ·   8H 2 O}(aq), together with the use of the molar enthalpies of formation for NaCl(s)/KCl(s), Sr(OH) 2   ·   8H 2 O(s), H 3 BO 3 (s), HCl(aq) and H 2 O(l), the standard molar enthalpies of formation of NaSrBO 3 (s) and KSr 4 B 3 O 9 were calculated to be −(1653.1   ±   1.4)   kJ   ·   mol −1 and −(5071.1   ±   3.4)   kJ   ·   mol −1 on the basis of the designed thermochemical cycles, respectively.