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.