POMzites: polyoxometalate based frameworks
Polyoxometalates (POMs) or, molecular metal oxides, are discrete
molecular structures composed of metal ions bridged by oxide
anions.[5] POMs are primarily constituted of
early-transition-metal (d-block ) elements in their highest
oxidation states, a great majority of these structures are anionic and
consequently salts with charge balancing cations. They are composed of
between 6 to 368 metal ions in a single molecule and are commonly
assembled under ‘one-pot’ reaction conditions. POMs, especially tungsto-
and molybdophospates and silicates, are widely used in industry for
catalysis.[6] Theoretical estimates for new
polyoxometalate (POM) materials and their properties lead to a deeper
understanding faster, and more efficiently than with test and
experimentation alone. First principles multiscale modelling has allowed
a deep understanding of materials by enabling accurate prediction of
electronic properties of materials at a low computational cost, for
instance, band gaps that are crucial for memory device
applications.[7] Computer simulations have
represented a breakthrough in materials science and engineering since
simulations offer help in directing experimental efforts. POMs are also
called molecular metal oxides due to their molecular composition and
their position between monomeric entities and bulk oxides. Despite being
well known in the literature for over a hundred years, their
self-assembly mechanisms remain semi-opaque and controlling the desired
output in a reaction is not always possible. This is because POMs are
prepared and isolated from both aqueous and non-aqueous solutions
whereby−the polymerisation of acidified solutions of
MoVI or WVI yields to a chaotic
mixture of materials.[8] Preliminary
work,[9] shows that we can obtain information of
the building blocks formed in the synthetic mixtures, hence we are
closer to the design of new metal-oxide materials with the targeted
properties. As happens with zeolites, the preparation of metal oxides
can seem like a black art and predicting function and synthesis is
notoriously difficult.