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Polymetallic Cages as Molecular Magnets and Catalysts

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The number of reports of the synthesis, characterisation and study of polynuclear cages has increased markedly in the last few years. However much work remains before the chemistry and physics of these species are understood. The programme "Polymetallic Cages as Molecular Magnets and Catalysts" will investigate new methods for making such compounds, and their applications as novel magnetic materials and oxidation catalysts.

Our synthetic studies will explore three reactions. The first involves reaction of small metal cages (typically oxo-centred triangles) at high temperature. Initial results indicate that such compounds can eliminate weakly bound solvent molecules or protonable ligands with a concomitant oligomerisation of the metal core. We intend to carry out a systematic investigation of this thermally activated growth process. We will also compare the results with our second synthetic project, where we will heat metal precursors to high temperatures in non-coordinating high boiling solvents. Our previous results have shown this produces a series of new small cages; we wish to see whether this approach only produces tetranuclear cages and smaller entities, or whether conditions can be modified to create new large polynuclear compounds. The third synthetic strand will look at the addition of H-bond donors, chiefly protonated amines, to metal-fluoride-carboxylate reaction matrices, with the intention that N-H...F bonding will direct structure in new directions. This work builds on initial results where a {Cr8} wheel was converted into a {Cr6}2 double-horseshoe.

Structural characterisation of the cages will involve X-ray diffraction. Magnetic properties of the cages will be studied by susceptibility measurements, however more detailed information about magnetic structure will be obtained by resonance spectroscopy. EPR spectroscopy at a range of frequencies (270 GHz to 9.4 GHz) and temperatures, and Mössbauer spectroscopy down to 1.8 K will be performed on suitable samples.

Catalytic studies will examine the propensity of the cages to catalyse peroxide decomposition as an initial screening process. Promising cages will be further studied as catalysts for oxidation of alkenes. We will also look at strategies for attaching cages to inert supports as a method for combining the advantages of homogenous and heterogeneous catalysts within one material.

The magnetic and catalytic studies will have full support from quantum chemical calculations. These calculations will involve modelling magnetic susceptibility behaviour in an empirical sense, but also matching observed behaviour with that predicted from the electronic structure of cages.

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University of Manchester
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Oxford Road
M13 9PL Manchester
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Letzte Aktualisierung: 30 Oktober 2002

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Permalink: https://cordis.europa.eu/project/id/INTAS-2000-00172/de

European Union, 2024