Research in the Dunbar group spans topics in synthetic, structural and physical inorganic and bioinorganic chemistry. The use of a range of tools including spectroscopy, X-ray crystallography, magnetometry, electron microscopy, mass spectrometry and electrochemistry reflect the breadth of problems under investigation.
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-pi 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.
Schottel, B.L.; Chifotides, H.T.; Dunbar, K.R. Anion-π Interactions: A Tutorial Review. Chem. Soc. Rev. 2008, 37, 68-83
Nazario, L.; Zhao, H.; Prosvirin, A.V.; Chouai, A.; Shatruk, M.; Dunbar, K.R. Conversion of a Porous Material Based on a Mn(II)-TCNQF4 Honeycomb Net to a Molecular Magnet Upon Desolvation. Chem. Commun. 2007, 44, 4611-4613.
Schelter, E.J.; Karadas, F.; Avendano, C.; Prosvirin, A.V.; Dunbar, K.R. A Family of Mixed Metal Cyanide Cubes with Alternating Octahedral and Tetrahedral Corners Exhibiting a Variety of Magnetic Behaviors Including Single Molecule Magnetism. J. Am. Chem. Soc. 2007, 129, 8139-8149.
Shatruk, M.; Gragulescu-Andrasi, A.; Chambers, K.; Stoian, S.A.; Bominaar, E.L.; Achim, C.; Dunbar, K.R. Properties of Prussian Blue Materials Manifested in Molecular Complexes: Observation of Cyanide Linkage Isomerism and Spin-Crossover Behavior in Pentanuclear Clusters. J. Am. Chem. Soc., 2007, 129, 6104-6116.
Chifotides, H.T.; Dunbar, K.R. Interactions of MetalMetal-Bonded Antitumor Active Complexes with DNA Fragments and DNA. Acc. Chem. Res. 2005, 38, 146-156.