Magnets are ubiquitous in modern society, employed in an enormous range of applications from biomedical imaging and cancer therapy to information technology, national and international defence and security, and outer-space research. One of the main goals of modern research, in both the industrial and academic sectors, is the miniaturisation of such technologies. This is entirely reliant upon fundamental scientific research, and the investigation and understanding of the intrinsic relationship between structure and magnetic behaviour. This requires chemists to design and build families of molecules and molecule-based materials, and through extensive collaboration with a network of condensed matter physicists, theoreticians and materials scientists, understand and ultimately exploit their underlying physical properties. This was demonstrated beautifully with the recent construction of single-molecule spin valves and transistors by Wernsdorfer and co-workers, and through IBMs report of information storage in surface arrays of Fe atoms. The academic field of molecular magnetism represents an atom-by-atom, molecule-by-molecule approach to building new magnetic materials. The molecular or "bottom-up" approach has many potential advantages over the "top-down" approach: molecules are soluble, monodisperse in size and shape, amenable to change through simple synthetic chemistry generating materials with tuneable, designer, physical properties. This proposal first concerns the synthesis, structural and magnetic characterisation of a library of mononuclear complexes based on highly anisotropic 4/5d ions. These complexes are then used as metalloligands towards 3d metal ions or complexes, promising a rational route toward the construction of pre-designed metal cages with predictable structures and tuneable magnetic behaviour. It also involves the attachment of anisotropic metalloligands to well-known and well characterised, pre-made molecular magnets, such as Co4, Mn6, Ni12, Fe17, in order to examine the effect on magnetisation relaxation dynamics and to derive detailed magneto-structural correlations.