Thermodynamic properties of two mixed alkali metal borates with NLO behaviour: Li6Rb5B11O22 and Li4Cs3B7O14

Two pure mixed alkali metal borates with Non-Linear Optical (NLO) properties, Li 6 Rb 5 B 11 O 22 and Li 4 Cs 3 B 7 O 14 , have been synthesized by a high-temperature solid state reaction, and characterized by XRD, FT-IR, DTA-TG techniques and chemical analysis. The molar enthalpies of solution of Li 6 Rb 5 B 11 O 22 and Li 4 Cs 3 B 7 O 14 in 1   mol   ·   dm −3 HCl (aq), and of LiCl·H 2 O(s) in (1   mol   ·   dm −3 HCl   +   H 3 BO 3   +   RbCl/CsCl) (aq) have been determined by microcalorimeter at T   =   298.15   K, respectively. From these data and with the incorporation of the previously determined enthalpy of solution of H 3 BO 3 (s) in 1   mol   ·   dm −3 HCl (aq), together with the use of the standard molar enthalpies of formation for LiCl·H 2 O(s), RbCl(s)/CsCl(s), H 3 BO 3 (s), HCl(aq) and H 2 O(l), the standard molar enthalpies of formation of −(11173.1   ±   9.5)   kJ   ·   mol −1 for Li 6 Rb 5 B 11 O 22 and −(7145.1   ±   5.9)   kJ   ·   mol −1 for Li 4 Cs 3 B 7 O 14 were obtained on the basis of the appropriate thermochemical cycles.