Research in the group explores problems in coordination chemistry and organic synthesis using the relatively new field of supramolecular chemistry as a tool. Research projects include developing specific metal chelators for a variety of toxic and environmentally hazardous metals; investigating the synthesis and applications of inorganic cluster compounds; and using multiple weak interactions within small molecule receptors to target environmentally and biologically relevant substrates. The research in the group spans a diverse range of disciplines: organic synthesis of ligands and receptors; inorganic chemistry of supramolecular coordination complexes and inorganic clusters; computer modeling and ligand design; analytical chemistry of metal ion extraction; solution thermodynamics and physical organic chemistry of host-guest and metal-ligand complexes; and materials science of supramolecular assemblies and thin film semiconductors. The characterization of these nanoscale molecules requires investigation by X-ray crystallography, calorimetry, multidimensional NMR techniques, and other spectroscopic methods.

I. Supramolecular Main Group Chemistry and Specific Metal Chelation
We are elaborating a design strategy for forming coordination capsules comprised of toxic metal ions or main group elements (such as arsenic, antimony, or mercury). We have recently shown that ligand H₂L binds arsenic(III) within a very stable As₂L₃ cage. Surprisingly, two As₂L₂Cl₂ macrocycles were also isolated as intermediates in the reaction. Applications in metal remediation, both environmental and medical, are envisioned by designing the ligands to target a specific toxic or hazardous metal ion. Furthermore, incorporating these nanoscale coordination capsules into extended solid-state structures leads to applications in materials science, and the novel cavity environments in these capsules will lead to unusual host-guest properties.

II. Inorganic Nanoclusters
Developing predictive design strategies to prepare inorganic cluster compounds has attracted much research interest, due in part to the potential applications of these novel materials. We have developed an unusual new synthetic strategy for preparing discrete inorganic clusters, and we have used this strategy to prepare the first crystalline example of an inorganic tridecameric Ga hydroxide cluster (Ga₁₃, see figure). A slightly altered facile synthetic methodology also yields the analogous tridecameric aluminum complex and a series of mixed Ga/In tridecameric clusters in preparative scales within one to two weeks. We are currently exploring the use of these inorganic aggregates as synthons for the generation of a wider range of particles and assemblies via exchange of the peripheral water ligands with appropriate organic ligands.  In a collaboration with Prof. Douglas A. Keszler at Oregon State University, we are exploring the use of these clusters as solution precursors to prepare thin film transistor devices (Angew. Chem. Int. Ed. 2008, 9484-9486).

III. Interactions between Anions and Aromatic Rings
A recent area of study in the lab seeks to understand the how anions interact with electron-deficient aromatic rings. The related “cation-π” interaction is well-documented, but only recently has the more counter-intuitive interaction between anions and aromatic rings become appreciated. We have shown in a model system that the presence of an electron-deficient pentafluorophenyl ring enhances halide binding in solution. We have also highlighted in the solid state and in silico our observations that anions can form as many as four different attractive interactions with electron-deficient aromatic rings (J. Am. Chem. Soc. 2007, 48-58). Recently, we have used this knowledge to develop a design strategy for synthesizing tripodal anion receptors that utilize only electron-deficient aromatic rings to bind anions in solution. We seek to understand this interaction in greater detail by improving receptor design and developing new electron-deficient arenes to bind anions. Will this emerging interaction motif provide new anion binding selectivities in solution? Can new sensors and remediation materials be prepared that use these interactions to target anionic contaminants in the environment?  We also have begun a new collaboration with Prof. Michael M. Haley’s lab at UO investigating the design and synthesis of modular receptors for anions based off of inherently fluorescent arylethynyl cores.