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Metallosupramolecular chemistry is a diverse and complex field of research. The complicated inter- and intramolecular interactions afford metallosupramolecular assemblies with different properties or functionalities. The targeting of topology in these architectures is possible, the inducement of desirable properties into these materials is of great difficulty. Especially in larger complex systems such as heterometallic cubic cages, the complex cooperative interactions are shown to give rise to complex functionalities. Feedback of intramolecular interactions of metal centres through ligands, as well as intermolecular interactions afforded by contacts between solvent molecules, counterions are major contributors to the emergent properties. In this thesis, the metalloligand [FeL]2+ and two heterometallic [Fe8Pd6L8]28+ and [Fe8Ni6L8(CH3CN)12]28+ cages were designed, synthesised and fully characterised. Conventional and new unconventional structural parameters have been employed to elucidate the structural reconfigurations associated with magnetic behaviour in the metalloligand units of the cages. Firstly, in chapter 2, heterometallic cubic cage [Fe8Pd6L8]28+ was synthesised utilising [FeL]2+ metalloligand. Crystal structures of [FeL]2+ and [Fe8Pd6L8]28+ cage exhibited stabilisation of the HS state. While the [FeL]2+ metalloligand crystallised in the P21/c space group, [Fe8Pd6L8]28+ cage crystallised in higher symmetric space group of Fm-3c with eight cage moieties in the unit cell. Octahedral distortion parameters, as well as two new structural parameters that quantify the angular spread and the twisting of metalloligand arms were investigated. The subtle structural reconformations in metalloligands upon forming the cubic cage architecture leads to compact face to face packing. The tight packing prevents structural reorientations necessary for SCO in the metalloligand units of the [Fe8Pd6L8]28+ cage stabilising the HS state. In chapter 3, using the same metalloligand scaffold, the manipulation of the secondary metal centres from Pd(II) to Ni(II) resulted in drastic changes to the magnetic behaviour. The crystal structure of [Fe8Ni6L8(CH3CN)12]28+ was shown to exhibit complete ST profile, while the magnetic susceptibility experiments of the bulk sample conveyed incomplete ST with five Fe(II) centres stabilising in the HS state at low temperatures. Structural analysis conducted on the single crystals demonstrated the coordination of additional CH3CN ligands on the central Ni(II) metal centres (in the pseudo fourfold symmetry) resulted in offset packing arrangements. Unlike the compact face-to-face packing of the [Fe8Pd6L8]28+ cage, the offset packing manifested by the [Fe8Ni6L8(CH3CN)12]28+ cage in turn allowed enough steric freedom for structural reconfiguration of the metalloligand units to occur at lower temperatures. As a consequence of changes to the solvent composition found in the bulk sample from CH3CN to H2O resulted in changes to the steric environments compared to the single crystals. removal of CH3CN ligands of the Ni(II) metal centres affected the packing arrangement of the bulk sample ultimately stabilising in the HS state.

The engineering of metallosupramolecular materials incorporating multifunctional properties has emerged as a compelling goal to synthetic chemists and materials scientists. These systems can exhibit hugely diverse structural features, and the interplay between the supramolecular structure and constituent chemical units gives rise to a broad spectrum of physical properties. These structurally diverse systems have potential uses in the broadly useful areas of catalysis, drug delivery, and molecular sensing and recognition. This thesis focuses specifically on multifunctional materials like data storage and advanced signalling components by the incorporation of the spin crossover (SCO) property into metallosupramolecular architectures. SCO compounds act as molecular switches, and the multifunctionality afforded by their differentiable and controllable high spin (HS) and low spin (LS) states allows for control over nano-scale processes. Currently, the design of metallosupramolecular architectures exhibiting targeted physical behaviours is unreliable, due not only to the difficulty in predicting the supramolecular topology, but also the complex interplay between structural features and manifest properties. In the endeavour of functional materials design, the metalloligand approach has shown promise, which allows complex architectures to be generated from relatively simple coordination complexes. By incorporating metalloligands of known physical properties into more complex materials, it is feasible to impart the properties of simple individual coordination units into a larger architecture, which further modulates the expressed properties. This project aims to develop a system of analogous dinuclear triple helicate architectures of the form [M2L3]4+ using a new semi-rigid ligand bearing two α-diimine donor groups, and investigate their physical properties – in particular spin crossover of an Fe(II) helicate in this thesis. The designed helicates bear secondary coordination sites, affording them the potential for use as metalloligands. The structural features associated with spin transition (ST), as well as the substitution of various primary metal ions are investigated in detail to assess the suitability of these units for the building of larger supramolecular architectures. To this end, a set of unconventional structural parameters has been developed to assist in the quantification of subtle structural variations in the dinuclear triple helicate archetype. The methodology applied in this project can be readily extended to the analysis of a vast range of coordination complexes, thus assisting in the investigation of microstructural variations, and assisting in the design of metallosupramolecular architectures bearing targeted properties.

a series of complexes of the type MLnX where M=Cu(II), Ni(II), and Cr(III), L=β-diketonate (n=1 for Cu (II) and Ni(II), n=2 for Cr(III)) and X=bridging anion was synthesized in order to study the effect of the bridging group on the magnetic exchange interaction parameter, J.