Bridging the Gap Between Solution & Solid State, Low & High Nuclearity Studies in the Self Assembly of Nanoscale Polyoxometalate Clusters

Lead Research Organisation: University of Glasgow
Department Name: School of Chemistry


Aim: To propose an approach to understanding the self assembly of nanoscale polyoxometalate clusters using a combination of cryospray mass spectrometry, ligand design, and crystallographic analysis, bridging the gap between solution and solid state studies for the first time. By using the cryospray mass spectrometry to 'scan' our reaction systems we will be able to 'discover' new clusters in solution that range from low to high nuclearity clusters, understand the complex equilibria present, 'trap' and stabilize highly reactive clusters, and assemble fundamentally new types of cluster. Ultimately the aim is to establish and control a library of real building blocks that can be used in the assembly of pre-designed nanoscale polyoxometalate clusters. This will allow us to move from discovery with the grand aim of pre-determining cluster formation as reliably as the synthesis of organic molecules. The realisation of this goal would open up a plethora of scientific, industrial and technological applications of polyoxometalates from new materials to catalysts and nano-electronic components.


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Description As a result of the research funded by this proposal we have been able to develop a new, combined approach for the study of polyoxometalate self-assembly and formation on moving from solution to the solid state. These nanoscale metal-oxide clusters can be thought of as assembling from a complex mixture of solution-based 'building blocks' and, by identifying these transient species and the factors that control their assembly, we have gained fundamental new insights into the initial steps of how polyoxometalate clusters can form. Significantly, this same approach has also allowed us to follow the complete formation of intact polyoxometalate clusters, from their initial precursors in solution through to final products prior to isolation in the solid state, thus allowing for a more complete mechanistic understanding of the factors which influence the self-assembly of the transient solution-based building blocks into the final cluster architecture. Moreover, we have also demonstrated how mass spectrometry may be used as a powerful discovery tool in the synthetic chemists arsenal, allowing for the in situ screening of reaction mixtures in order to identify and subsequently 'trap' new cluster species by careful cation control, such as previously unknown unconventional {XW18} Dawson-type species. Finally, the mass spectrometry based strategy we have employed has also been shown to successfully identify very large supramolecular aggregates of polyoxometalate clusters based on carefully mediated, ligand-controlled interactions and study their behaviour in the gas phase.
Exploitation Route Whilst polyoxometalate clusters have been studied for many years and a vast library of solid state structures is now known, it remains exceptionally difficult to predict the outcome of a given synthesis due to the complex interplay of factors which govern the self-assembly of these species in solution. This is problematic since it effectively precludes any attempt at the rational design of new cluster species (in a manner analogous to the targeted synthesis of complex organic molecules, for instance), which would enable the synthesis of designer, nano-structured cluster materials for a wide-range of industrial and technological applications (such as catalysis, molecular electronics etc.) This proposal has been successful in developing a new strategy for the study of polyoxometalate self-assembly, using a combination of mass spectrometry, computational modelling, cation/ligand design and crystallography to bridge the gap between our understanding of these clusters in the solution and solid states. This powerful concept will allow all chemists interested in the molecular self-assembly of complex clusters in solution to probe, understand and thus, ultimately, control the formation of such species with targeted functions and applications in mind. Moreover, we have shown how mass spectrometry can be used to 'screen' reactions in situ, allowing researchers to identify and then select-for entirely new cluster types prior to their eventual (and often time-consuming) isolation in the solid state. It is hoped that this strategy, and the fundamental insights it may provide, will move polyoxometalate and cluster chemistry one step closer to the ultimate goal of targeted and rational synthesis of new functional species.
Sectors Chemicals,Electronics,Energy

Description Whilst the findings arising as a result of the work undertaken as part of this proposal have been of a primarily fundamental nature, they have directly inspired or preceded further work of more significant wider impact. In particular, the discovery of unconventional polyoxometalate structures containing redox-active heteroatoms (aided significantly by the cryospray mass spectrometry screening approach developed by this proposal) has led to exciting interdisciplinary work on polyoxometalate-based nanoelectronics. This spans the fields of chemical synthesis, theoretical modelling and electronic engineering and has significant technological and commercial potential for new devices and device architectures.9, 10 More broadly, the approach outlined by the work conducted as a result of this proposal has seen significant uptake by the wider research community as a powerful analytical tool, whereby mass spectrometric analysis (coupled with structural data/modelling) is able to both identify, and probe the formation of, complex supramolecular structures which are not necessarily represented in the solid state.