The xenon-fluorine system

Article abstract of DOI:10.1021/ic50046a026

Equilibrium constants have been obtained in the Xe-F₂ system in the temperature range 250-500°. The data show that only three binary fluorides, XeF₂, XeF₄, and XeF₆, are present. There is no evidence for the existence of XeF₈ at 250° and up to 500 atm of F₂. A preparation of pure XeF₆ is described. A molecular weight determination, some infrared measurements, and vapor pressure data obtained with this sample are reported. Values for the thermodynamic properties of formation of XeF₂, XeF₄, and XeF₆ are derived from the equilibrium constant data. The average value of the two missing vibrational modes of XeF₄ is evaluated to be 246 ± 10 cm^-1 from an analysis of the equilibrium constant and molecular data. Thermodynamic properties of XeF₂ and XeF₄ are calculated from molecular data. The value of S° for XeF₄ at 25° is 75.6 cal mole^-1 deg^-1, in agreement with a value of 75.3 cal mole^-1 deg^-1 calculated from calorimetric data and the heat of sublimation. A number of molecular models for XeF₆ are examined in terms of their consistency with the equilibrium constant data. A definite choice among the various models is not possible, but the analysis favors a low symmetry for XeF₆. Values of S° for XeF₆ at 25° are derived for each model and may be useful to help determine the symmetry of XeF₆ when calorimetric data become available. The average bond energy of XeF₂ is 31.0 kcal and that of XeF₄ is 30.9 kcal. For XeF₆ the average bond energy is 29.7 kcal, so that the average energy for forming the last two bonds in XeF₆ is 27.3 kcal.