Synthesis and magnetic properties of Fe-based homo- and heterometallic clusters

Abstract

Historically, polynuclear FeIII-O clusters have been at the heart of the study of molecular magnetism. From the study of [FeIII2-(μ-O)] dimers detailed magneto structural correlations were developed that can be applied to larger clusters. Larger antiferromagnetic wheels revealed interesting magnetic properties manifesting in stepped magnetisation. The second known single molecule magnet (SMM) was the [Fe8] cluster synthesised by the hydrolysis of the FeCl3(tacn) (tacn = triazacyclononane) monomer.

One particularly interesting aspect of FeIII clusters is their potential to grant access to large ground state spins. Molecules with such properties include the [Fe17/19] twin clusters and the [Fe17] “molecular mineral” species’ which show a huge ground state spin of 35/2.

The discovery of such clusters using relatively simple organic ligands has prompted us to speculate that new FeIII-O clusters may be synthesised that can display larger spin ground states and that new geometries may provide a pathway to interesting magnetic frustration effects. This thesis reports the synthesis and magnetic properties of new homo- and heterometallic FeIII based clusters each chapter aims to form these clusters using different methodologies and ligands.

Chapter 2 discusses work which expands the “molecular mineral” family of clusters reporting 3 new clusters [Fe34], [Fe30] and [Fe8] prepared from reactions involving monodentate pyridine-type ligands. The synthesis of these clusters in described alongside their magnetic properties, all 3 compounds exhibit antiferromagnetic interactions leading to non-zero ground state spins.

Chapter 3 reports new structures built using FeIII ions and the alkoxide ligand triethanolamine. Both homo and heterometallic species are reported. The homometallic [Fe15] describes a centred tetrakishexahedron a topology previously unseen in FeIII cluster chemistry. The heterometallic ring compounds [Fe11Zn4] and [Fe12Zn4] represent some of the largest FeIII ring-type compounds to date with [Fe11Zn4] being the only odd numbered FeIII ring type cluster reported. The magnetic data of all three clusters is reported all show strong antiferromagnetic interactions, with the [Fe15] and [Fe11Zn4] clusters also exhibiting frustration effects at low temperature.

Chapter 4 reports a series of heterometallic Anderson-type wheel clusters built with FeIII, another transition metal (NiII, CoII and ZnII) and the 2-pyridinemethanol ligand. Characterisation of their structures shows that the metal ions are disordered over multiple sites. Magnetic measurements elucidate competing interactions between with the FeIII ions showing antiferromagnetic behaviour.