Thermochemistry of fluoroantimonates and related compounds

Abstract

From alkaline hydrolysis measurements the enthalpy of formation of SbF 5(ℓ) is estimated to be −1324 ± 12 kJ mol −1, in agreement with the most recent fluorine bomb calorimetry value of −1328 kJ mol −1 [1]. The enthalpy of the process 1 4(SbF 5) 4(g)→SbF 5(g) has been estimated from vapour density measurements to be 18.4 kJ mol −1; by combining this value with the known enthalpy of vapourisation of SbF 5(ℓ), 43.4 kJ mol −1, and the degree of association at the b.p. (n = 3.0) [2,3], the enthalpy of the process SbF 5(ℓ) → SbF 5 (g, monomer), is estimated to be −1301 ± 15 kJ mol −1. From alkaline hydrolysis and aqueous solution measurements the enthalpies of formation of LiSbF 6(s), NaSbF 6(s), KSbF 6(s), CsSbF 6(s), and SbF 6 −aq, are estimated to be −2062 ± 5, −2060 ± 6, −2080 ± 3, −2082 ± 15, −1635 ± 3, and −1789 ± 4 kJ mol −1 respectively. These results, combined with lattice energy calculations on the salts LiSbF 6 and KSbF 6, indicate that the Sb atom in the SbF 6 −(g) ion has a charge of +1.7 (assuming Li and K = +1.0). The fluoride ion affinity of SbF 5(ℓ) is estimated to be −418 kJ mol −1, and that of SbF 5(g) to be −445 kJ mol −1 [4].