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Molecular Magnets, Conducting Metal-Organic Solids and Spin-Crossover Compounds

The study of molecule-based, metal containing materials with conducting, optical, and/or magnetic properties is an area that presents considerable synthetic challenges. Of particular interest are "hybrid" solids that combine two or more properties not traditionally found in the same material. One of our approaches is to combine paramagnetic metal centers and conducting organic sub-lattices. In this vein, we are designing molecules as well as, 1-D, 2-D and 3-D materials with transition or lanthanide metal ions connected by organic radicals. Materials that exhibit high conductivity, magnetic ordering as well as "single molecule magnetism" have been discovered. In another project we are exploring cyanide chemistry of 3d, 4d and 5d transition metals by a step-wise building block approach to prepare families of molecules with predictable geometries whose magnetic properties are modulated by deliberate changes in the molecule. We have synthesized magnetic molecular squares, cubes, trigonal bipyramids and other architectures that display single-molecule magnetism, charge-transfer induced spin transitions, spin-crossover at high temperatures, and photoinduced magnetic behavior. A remarkable finding is that heterobimetallic clusters as small as five metal atoms mimic the properties previously observed only for 3-D "Prussian-Blue" type magnetic materials.

Metals in Medicine

We have developed a program to address several issues in the area of metals in medicinal applications. The main synthetic targets are dirhodium compounds that are known to exhibit carcinostatic activity and ruthenium agents. Among our goals are to
(1) to elucidate sites of binding to biological molecules including DNA and characterize adducts by NMR and X-ray techniques,
(2) to develop redox-active compounds that exhibit low cytotoxity in the dark but which cleave DNA and cause cellular death under irradiation and
(3) to design new generations of compounds with ligands that stabilize the dinuclear core and cause a red-shift in the electronic transition responsible for the photocytotoxity. The ultimate goal of the research is to develop photodynamic therapy drugs.

Anion - π Interactions

Anion-π interactions are gaining significant recognition, and their pivotal role in many key chemical and biological processes is being increasingly appreciated. Research in this emerging area of supramolecular chemistry began in our group years ago with the synthesis and X-ray structures of cationic metal assemblies with encapsulated anions. Computational studies being conducted in our laboratories have confirmed the presence of anion-heterocyclic ring contacts for electropositive ring systems

Overview

Research within the Dunbar Research Group spans a number of topics in synthetic and structural inorganic chemistry with a focus on problems at the interface of materials and biological chemistry. The combined use of many physical techniques (electronic epr, infrared spectroscopies), X-ray crystallography, ac and dc magnetic magnetometry, scanning and transmission electron microscopy, mass spectrometry and electrochemistry to name a subset) reflect the breadth of problems under investigation. Our aim is to define important synthetic challenges and tackle their solution with an arsenal of physical, chemical and spectroscopic data. We are devoted to the use of coordination chemistry as a tool to make new compounds as well as to probe new structure and bonding relationships.

Department of Chemistry | Texas A&M University | State of Texas