Abstract:
: Due to the wide range of applications of band-gap
engineering in optoelectronics and photocatalysis, the rational
design of polyoxometalate (POM) frameworks is highly desired.
Here, we have successfully synthesized a series of mixed addenda
(Mo and W) sandwich POMs by systematically varying pH,
concentrations of salts, and counterions in Weakley-type sandwich
POMs by incorporating Mo into the framework of tetrasubstituted
sandwich POMs. Crystallographic analysis reveals the centrosymmetric structure; with variation in the Mo to W ratio, Mo
preferentially binds to μ2 oxygen connected to transition metals in
the sandwich position. UV−visible spectroscopy, electrochemical,
and theoretical modeling rationalize the band-gap modulations.
Theoretical studies and cyclic voltammograms indicate that during
the reduction, the incoming electrons preferentially go to substituted transition metals followed by Mo. Flat band potential
calculated from the Mott−Schottky enables tuning of the electronic properties of composites based on these sandwich POMs.
Moreover, the dioxygen binding and activation studies of these polyoxometalates have been highlighted.
