Samples of cesium polymolybdates
Cs2Mo
n
O3n+1 with n = 2, 3, 5, and 7 have been synthesized
by melting and cooling stoichiometric
mixtures of commercially available Cs2MoO4 and
MoO3 powders. The single-phase character of the samples
has been checked by X-ray diffraction. The standard enthalpies of
formation of the Cs2Mo
n
O3n+1 polymolybdates with n = 1, 2, 3, 5, and 7 have been measured by solution calorimetry in
dilute (CsOH·H2O) solvent at 298.15 K under 0.1 MPa.
The values found for the mono and dimolybdates, Δf
H° (Cs2MoO4) = −1513.56
± 1.11 kJ mol–1, Δf
H° (Cs2Mo2O7) = −2301.84
± 2.37 kJ mol–1, are in good agreement with
the already available calorimetric measurements. To our knowledge,
this is the first time that the enthalpies of formation of cesium
tri, penta, and heptamolybdates are measured: Δf
H° (Cs2Mo3O10) = −3077.17
± 3.47 kJ mol–1, Δf
H° (Cs2Mo5O16) = −4601.70
± 5.96 kJ mol–1, and Δf
H° (Cs2Mo7O22) = −6087.16
± 8.79 kJ mol–1, respectively. The convex shape
of the curve constructed from the formation enthalpies of the Cs2Mo
n
O3n+1 polymolybdates referred to the Cs2MoO4 and
MoO3 oxides is consistent with the Cs2MoO4–MoO3 pseudobinary diagram.
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