The calorimetry of some xenon fluoride complexes

Abstract

The enthalpies of solution in water and in 1M alkali of the complexes XeF 2·CrF 4 and XeF 2·VF 5 have been measured, and from the results the enthalpies of formation are estimated to be −1438 and −1673 kJ mol −1 respectively. The values imply that XeF 2·CrF 4 is formed slightly endothermally from XeF 2(c) and CrF 4(c), whereas XeF 2·VF 5 is formed exothermically with respect to XeF 2(c) and VF 5(ℓ); this result is consistent with the existence of XeF 2·VF 5 in the vapour phase. Measurement of the enthalpy of hydrolysis of XeF 2·MnF 4 in 1−M alkali gives a value of Δ(hydr.) of −720 kJ mol −1, from which the enthalpy of formation of the compound is estimated to be −1288 kJ mol −1. XeF 2·MnF 4 is, therefore, formed exothermally from XeF 2(c) and MnF 4(c). The complex XeF 6·CrF 4 hydrolyses violently in water; the stoichiometry of the reaction is nearly in accordance with the equation: 3XeF 6·CrF 4 + 15H 2O → 3CrO 3aq + 3OHFaq + 2Xeaq + XeO 3aq + ▪ From the enthalpy of hydrolysis (−660 kJ mol −1) the enthalpy of formation of the complex is estimated to be about −1620 kJ mol −1, which implies that for the reaction CrF 4(s) + XeF 6(s) → XeF 6·CrF 4, ΔH ≅ O.