Isomerically pure α1- and
α2-[Fe(OH2)P2W17O61]7-
and
α2[Fe(OH2)P2Mo2W15O61]7-
were synthesized as aqueous-soluble potassium salts. The iron-substituted complexes as well as
their immediate lacunary precursors have
been characterized by IR, UV−visible, and 31P NMR
spectroscopies. The acid−base equilibria were studied
for
the iron-substituted complexes. The hydroxo compound
α2-[Fe(OH)P2W17O61]8-
has also been synthesized, and
its elemental analysis is correct. Its further characterization
and study will be published elsewere. For a given
pH value, the comparisons of the cyclic voltammograms reveal the
influence of the location of the iron-filled site
in the framework. This influence is strong in the α1
isomer and makes its electrochemistry clearly different
from
that of the α2 isomer. This observation is ascribed
mainly to the large framework distortion induced by the
vacancy in the α1 site, to subtle variations in the
detailed protonation events which ensue, and to the nature of
the
iron substituent, which can be considered not to fill “completely”
the vacancy. The distortion effect is found to
favor the coalescence of waves, as also do lower and lower pH media.
The combination of these parameters
appears to be beneficial for the observation of multiple electronation
processes on the first wave of heteropolyanions
under very mild conditions.
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