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Molecular Magnetism and EPR Spectroscopy

Research into the magnetic properties of polymetallic compounds involves David Collison, Eric McInnes and Richard Winpenny. The major achievement of this research has been the design of synthetic routes to decametallic and larger clusters for V(III), Cr(III), Mn(II/III/IV), Fe(III), Co(II/III) and Ni(II), via “conventional” coordination chemistry, solid state thermolysis, solvothermal and hydrolysis routes. The group, especially Eric McInnes and David Collison, has developed the use of EPR spectroscopy as applied to molecular magnets.

Recent key results include:
(i) many very high spin ground state clusters, including the highest spin ground states known for Fe (S =25), Cr (S = 15), Ni (S = 12) and mixed 3d-4f clusters (S = 34).
(ii) the highest nuclearity cages known for V(III), Fe(III), Cr(III), Co(II) and Ni(II)
(iii) many new single molecule magnets, i.e. cages that show slow relaxation of magnetisation
(iv) new phenomena for molecular magnets including very high magnetocaloric effects for high spin clusters, single molecule phonon traps, linked cages for quantum computing, quantum fluctuations of total spin.
 
This world-leading research is supported by a major £1.1M EPSRC strategic grant to support the synthetic efforts in this area over the next 5 years and to exploit the “critical mass” of expertise. The work is also supported by the European Commission and The Leverhulme Trust.

 

 

 

The group has pioneered the synthesis of polymetallic compounds via solvathermal methods. The route produces high symmetry cages which show unusual properties, e.g. very high spin clusters with strong magnetocaloric effects and the first single molecule spin glasses

The group has exploited several new ligands in synthesis of polymetallic cages. Previously these have included N-heterocycles such as pyridones and pyrazolinones. At present the main focus is on phosphonates and related ligands. Several very high spin cages and new single molecule magnets have been made.

The group published the first controlled synthesis of heterometallic rings in 2003. The beauty of the structures and the synthetic control we can achieve is wonderful. Better yet the compounds are exceptionally suited to studying novel quantum phenomena such as the fluctuation of spin at avoided crossings, and show immense promise as Qubits to be used in quantum information processing.

The group uses EPR spectroscopy to characterise magnetic clusters, but also more generally as Eric McInnes and David Collison run the EPSRC funded EPR service for the UK. EPR studies of very high spin cages, using unconventional techniques such as parallel mode spectroscopy, have been performed allowing derivation of spin Hamiltonian parameters. EPR studies of rings are leading to a new method for modelling EPR spectroscopy as the “strong exchange” limit breaks down.