Mass spectrometric determination of the enthalpies of dissociation of gaseous complex fluorides into neutral and charged particles. VI. Enthalpy of formation of zrF 5−

Abstract

The effusion method together with mass spectral analysis has been used to study ion/molecule equilibria involving the negative ions ZrF 5 − and Zr 2F 9 −. The experimental data obtained have made it possible to calculate enthalpies for the reactions ZrF 4+F − =ZrF 5 − Δ H 298 0=−98.1±3.4 kcal mol −1(−410.5 ±14.2 kJ mol −1) ZrF 4+ZrF 5 − =Zr 2F 9 − Δ H 298 0=−51.2±1.0 kcal mol −1(−214.3 ±4.2kJ mol −1) and the following enthalpies of formation:Δ H r.298 0 (ZrF 5 −) gas=−559.2±3.4 kcal mol −1 (−2339.7±14.2 kJ mol −1. Δ H r.298 0(Zr 2F 9 − gas=−1010.4±3.6 kcal mol −1(−4227.5±15.1 kJ mol −1). Based on an analysis of published data. enthalpies of formation and molecular constants have been selected for the complex molecules MZrF 5(M=alkali metal). and their thermodynamic functions and enthalpies of dissociation into ions calculated.