Thermochemistry of alkali metal hexafluoromolybdates(V) and hexafluorotungstates(V)

Abstract

From measurements of the respective heats of alkaline hypochlorite hydrolysis at 298 K, the standard enthalpies of formation of KWF₆, RbWF₆, CsWF₆, KMoF₆, RbMoF₆, and CsMoF₆ have been derived. They are –2224 ± 6, –2236 ± 9, –2258 ± 6, –2075 ± 9, –2099 ± 8, and –2117 ± 7 kJ mol^–1 respectively. Values for the electron affinities (ΔH_E) of gaseous tungsten hexafluoride and molybdenum hexafluoride have thence been estimated as ΔH_E[WF_6(g)]=–490 ± 5 and ΔH_E[MoF_6(g)]=–517 ± 6 kJ mol^–1, at 298 K. For the reactions MF_5(c)+ F^–_(g)→ MF₆^–_(g) the fluoride ion affinities (ΔH_F) of tungsten pentafluoride and molybdenum pentafluoride are estimated to be –491 ± 5 and –412 ± 6 kJ mol^–1 respectively.