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Final Report Summary - STU POSTERMAC (Studies of Polynuclear Clusters for Biomass Conversion)

The objectives of this project are to study a new class of compounds developed in the Betley group at Harvard University, USA. Specifically, they are termed polynuclear cluster compounds, and they are named so because they make use of the incorporation of several transition metals into a single well-defined molecule. Traditionally, chemists employ only one transition metal in well-defined molecules (and are, as such, mononuclear organometallic compounds), and the research performed in the Betley group is therefore of ground-breaking nature.
Initially, the objectives were to study the chemical behaviour of the clusters in order to map out the possibilities with respect to biomass conversion. However, it turned out that even though the clusters hold great potential as future biomass conversion catalysts, it is today too soon to strive for any applications in that direction (see Main results in this report for more details). Instead, the objectives were re-directed to focus on exploiting the gained knowledge on the chemical behaviour of the clusters, that I have collected, in other directions. In particular, this involved creating network assemblies based on these clusters as nodes. The objectives were to connect the clusters in such a way that all the dimension networks (1D, 2D, and 3D) could be obtained.

I conducted a deep, thorough, and meticulous investigation on the chemical behaviour of the clusters. Based on my work, some interesting features of the clusters have been revealed. The results can be divided in to a couple of major topics.
First of all, I have shown that they can take part in chemistry typical for traditional mononuclear organometallic compounds albeit in an extended manner. In other words, one can do more chemistry on one molecule of a polynuclear cluster compound, than is feasible to do on one molecule of a mononuclear organometallic compound. In technical terms, I have demonstrated that the polynuclear cluster (H L)2Fe6 is capable of undergoing three oxidative addition reactions, whereas traditional organometallic complexes can do merely one of these reactions at the time.
In addition, my work shows that when performing chemistry on the (H L)2Fe6 cluster, molecular attachment to a cluster happens in a spatially controlled manner. Importantly, this control is inherently governed by the electronic setup of the cluster. This is important because of a number of reasons. For example, it opens up for a new way of controlling spatial complexity in structures. Secondly, the very fact that this control exists is intriguing from a fundamental research point-of-view. Moreover, it is the first time this type of an electron based directionality is shown.
Based on these results I have devised procedures for achieving network assemblies centred on the clusters as nodes. Because of the spatial control of how molecules attach to the clusters, it is possible to direct whether 1D, 2D, or 3D dimension network assemblies are built. Hence, I have demonstrated that each of the dimension network assemblies can be selectively achieved.
Unfortunately, I have so far been unable to perform any biomass conversion reactions using the clusters as reagent. At the current stage of development, it turns out that the clusters are either too unstable to react with some biomass without breaking apart or too stable to react with other biomass to react at all.

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