Research

Prof. George Christou’s Research Group in the Department of Chemistry at the University of Florida is a synthetic and physical inorganic group with strong interests in synthesis and characterization of multinuclear transition metal complexes. We characterize our samples using IR, paramagnetic NMR, electrochemistry, magnetism studies, mass spectroscopy and X-ray crystallography.

There are several projects being investigated, and below are given brief descriptions of the three primary research areas:

• Supramolecular and cluster chemistry: high nuclearity complexes
• Bioinorganic chemistry: models for metalloenzymes
• Materials and nanoscale magnets

Supramolecular and cluster chemistry: high nuclearity complexes

	We have a general interest in the synthesis of high nuclearity clusters for numerous applications. We have developed many synthetic routes to obtain a variety of high nuclearity clusters of the 3d metals V to Cu, with the largest till date being a Mn84 cluster.The use of poly-pyridine and poly-ß-diketonate ligands with mononuclear metal centers has been the foundation of the growing area of Supramolecular Chemistry. We are combining the use of such ligands with our experience of cluster chemistry, and are investigating to what extent such ligands can:(i) join together polynuclear metal clusters (rather than single metal ions) into supramolecular structures, (ii) cause the formation of new polynuclear clusters not attainable with simpler ligands, (iii) encourage formation of extremely large molecular clusters (nanoscale size) by hydrolysis and alcoholysis, and (iv) facilitate formation of mixed-metal, transition metal-lanthanide clusters.
All of these approaches have already been successful in this project, leading to a variety of new Co8, Fe8, Mn25, Mn84, Mn8Ce and other products.
Co8	Mn84	Fe8

Bioinorganic chemistry: models for metalloenzymes

An important source of information about the structure and mechanism of action of metallobiomolecules is the study of synthetic species that mimic the structure and properties of the corresponding native site.

Crystal structure of PS II One of these biological systems is Photosystem II (PS II), the enzyme that catalyzes H2O oxidation to O2 in green plants and cyanobacteria. The species responsible for this reaction, called the water oxidizing complex (WOC), is a tetranuclear Mn cluster, with oxide and carboxylate ligation.		We have synthesized a number of tetranuclear, oxide bridged, Mn carboxylate complexes involving high oxidation state metal ions to function as synthetic models for the WOC. The 2nd generation models ([Mn4O3X(RCO2)3(dbm)3]) exhibit many of the reactions of the biological system.
We are currently working on a 3rd generation of structural models, based on the very recent knowledge of the protein’s Mn4 structure.
	3rd generation models for WOC

Materials and nanoscale magnets

During the last few years there have been explosive new thrusts into all areas of nanoscience. One of these, is the search for nanoscale magnetic materials for advanced applications such as high density information storage and quantum computing. This has provided an alternative, molecular approach to nanomagnets. Many of these, particularly those of Mn, such as [Mn12O12(O2CR)16(H2O)4] and [Mn4O3Cl4(O2CEt)3(py)3]2 have been found to be the first examples of nanoscale magnets and are referred to as single-molecule magnets (SMMs).

The first dimer of exchange-coupled SMMs

The Mn12 and Mn4 clusters have been found to exhibit hysteresis (as any magnet should) and also to show quantum tunneling effects, showing that they bridge the classical/quantum interface, a fact of great current interest in both the Chemistry and the Physics communities.

All these complexes are characterized by different techniques, i.e.: magnetic studies, electrochemistry, Paramagnetic NMR, etc…

Magnetic Studies
Electrochemistry	Paramagnetic NMR