Ongoing core research activities in Powell group (INT/Uni)
1. Molecular Magnets.
We are synthesising materials which are described as Single Molecule Magnets or SMMs. These are molecules which show hysteresis in their magnetisation and can be used to store or process information in future applications. We have discovered a molecule with 19 manganese centres which has the largest ground spin state ever seen at S = 83/2 . We have also developed synthetic routes to access mixed 3d/4f systems. We find that 4f ions such as Dy(III) are very useful for introducing anisotropy into these molecules which, along with non-zero spin, is required for the observation of SMM behaviour . In addition, we are looking at pure 4f systems and have several exotic systems including a triangular arrangement of Dy(III) ions which represents the molecular archetype of the noncollinear Ising model and offers real prospects for developing qubit design strategies . Finally, we have also begun to explore using supramolecular effects to enhance magnetic properties .
2. MOFs and SMOFs.
In addition to long-standing research interests in making the coordination networks which have become known as MOFs we have developed design principles to using metal coordination clusters as building units for “Super Metal Organic Frameworks” or SMOFs. In the past we have published structures build up from Al15 , Fe13 and Cu44 units and recently we have synthesised SMOFs made up from building blocks containing large numbers of rare earth ions, such as a Dy36 and Y79 (not yet published). The attractive thing about this approach is that even if a network becomes interpenetrating, the building blocks are so large that there is still plenty of accessible volume for small molecules such as water or hydrogen.
. We are currently looking at two areas, although in the past we have looked at iron clusters as models for loaded ferritin and this is still an area of general interest. Firstly, we have found that using Schiff-base ligands gives access to a system with 4 Mn and 1 Ca ion which is the best model so far for the Oxygen Evolving Centre of Photosystem II . Secondly, we have been looking at calcium carbonate biomineralisation mimics. We find that even using relatively simple polycaboxylates we can produce complicated structures including “microtrumpets” which are formed from the organisation of high-aspect ratio nanocrystals of calcite .
4. Processing of Coordination Compounds.
Coordination compound-based systems can be processed, for example through thermolysis, to give materials with novel structural characteristics. For example, a simple dinuclear iron building block can be organised into supramolecularly connected arrays with various architectures depending on the substitution at the ligand peripheries . Thermolysis of one such array where the space is divided into an inorganic honeycomb structure filled with carbon atoms from phenyl rings leads to hexagonally organised nano-bundles of sodium carbonate and iron oxide . Likewise, heating an array of Mn21 clusters organised into a cubic structure leads to a highly porous manganese oxide material which has potential as a battery anode material as well as showing very good catalytic activity [submitted].
5. Multifucntional Materials.
Many of the systems described above can be seen to have the potential to be developed as multifunctional materials. Such materials allow for miniaturisation of systems and cut-down on the resources required for producing devices. This requires testing materials in a variety of ways to establish which useful functions can be performed. Examples include systems such as porous MOFs which are also magnetically ordered .