Iwona Tomaszkiewicz

Thermochemistry of octasulfur-bis-hexafluoroarsenate S8(AsF6)2 containing the lattice-stabilized S82+

Abstract The specific energy of combustion of S 8 (AsF 6 ) 2 in fluorine according to the reaction: S 8 (AsF 6 ) 2 (cr) + 23F 2 (g) = 8SF 6 (g) + 2AsF 2 (g) was measured calorimetrically to be − (14327±9) J · g −1 at T = 298.15 K and p o = 101.325 kPa, where the uncertainty is the standard deviation of the mean. From this result was calculated the standard molar enthalpy of formation Δ f H m o {S e (AsF 6 ) 2 , cr, 298.15 K} = −(3121.5 ± 11.7) kJ · mol −1 , where the uncertainty is twice the standard deviation of the mean. The significance of this value with respect to bonding in the title and related compounds is discussed. Thus, the lattice energy of S 8 (AsF 6 ) 2 was estimated to be (1517 ± 36) kJ · mol −1 , and it was shown that S 8 2+ in the gas phase was unstable with respect to dissociation into various S x + (g) cations (2 ⩽ x ⩽ 7), while S 8 2+ in the solid state was lattice stabilized in S 8 (AsF 6 ) 2 .