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 (ΔHE) of gaseous tungsten hexafluoride and molybdenum hexafluoride have thence been estimated as ΔHE[WF6(g)]=–490 ± 5 and ΔHE[MoF6(g)]=–517 ± 6 kJ mol–1, at 298 K. For the reactions MF5(c)+ F–(g)→ MF6–(g) the fluoride ion affinities (ΔHF) of tungsten pentafluoride and molybdenum pentafluoride are estimated to be –491 ± 5 and –412 ± 6 kJ mol–1 respectively.