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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.
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Supramolecular and cluster chemistry:
high nuclearity complexes
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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.
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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:
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(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.
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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.
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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.
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Crystal structure of PS II
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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.
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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.
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We are currently working on a 3rd generation of
structural models, based on the very recent knowledge of the protein's
Mn4 structure.
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3rd generation models for WOC
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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).
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The first dimer of exchange-coupled SMMs
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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.
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All these complexes are characterized by different
techniques, i.e.: magnetic studies, electrochemistry, Paramagnetic
NMR, etc...
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Magnetic Studies
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Electrochemitry
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Paramagnetic NMR
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