Research Areas
 
We are generally interested in novel inorganic systems, with foci on pyrrolic macrocycles, the chemistry of rhenium carbonyl complexes, and borate-based materials .
 
 
Porphyrin Analogs and Isomers
 
            The chemistry of metalloporphyrins has been extensively studied over the past century, and has been extremely useful for understanding the behavior of heme enzymes and for developing new catalysts and advanced materials.  However, the analogs and isomers of porphyrins are not nearly as well understood.  We are exploring the fundamental chemistry and metal binding of planar, aromatic, polypyrrolic macrocycles, in part to understand why porphyrin is the tetrapyrrole of choice in biological systems.
            We have started our work on N-confused porphyrin (NCP) an isomer of porphyrin with a carbon at the pore and a nitrogen on the exterior.  We have found that the electronic structure of this macrocycle differs significantly from that of normal porphyrin, and that its metal binding characteristics deviate from typical macrocycle binding. This can be seen in the manganese complexes of NCP, where the interior C-H bond remains intact despite the presence of the metal, and where the exterior nitrogen can participate in coordination to form dimer complexes.  More recently, we have continued this work with carbon modified hemiporphyrazines, antiaromatic phthalocyanine analogs.  The metal complexes of dicarbahemiporphyrazine (dchp) and benziphthalocyanine (bzpc) exhibit many of the same features as seen in N-confused porphyrns. 


Tricarbonyl Rhenium(I) Complexes and Other Aqueous Organometallics

    We have also recently begun to investigate the fundamental aqueous chemistry of the Re(CO)₃⁺ fragment.  This unit is isoelectronic to Tc(CO)₃⁺, which is currently being probed as a next generation source of technetium for imaging radiopharmaceuticals.  Yet, in spite of its relevance to medicinal chemistry, the fundamental chemistry of Re(CO)₃⁺ remains surprisingly unexplored. 
    In collaborative work with Richard Herrick at the College of the Holy Cross, we are synthesizing Re(CO)₃⁺complexes bound by tripodal ligands.  These compounds can be readily generated from aerobic, aqueous solutions and are remarkably stable and non-toxic.  In addition, this work has sparked our interest in the aqueous chemistry of organometallic complexes in general.  We carried out the first X-ray crystallographic study of the Re(H₂O)₃(CO)₃⁺ cation, and are continuing this work with other metal ions including manganese and osmium.  

Coordination Polymers using Borates
 
            Many naturally occurring or synthetic minerals have open topologies.  Access to the interior of these solids can occur either through porosity, as in zeolites, or through interlayer spacings, as seen in clays or transition metal dichalcogenides.  As a result, many porous and layered compounds exhibit topology-dependent reactivity, such as guest absorption or selective ion exchange.
            In our work, we are replicating such structures by constructing crystalline arrays from discrete molecular building blocks.  We are using the coordination polymer approach, where we link together metal cations with organic bridging units to form network solids.  Our organic linkers of choice are borates, such as cyanoborates and azolylborates.  These anions are multidimensional, coordinating, easy to synthesize, and very robust.  We have already shown success at developing new materials based on borate building blocks, and are exploring our new materials for advanced applications.  For example, our material Pb[B(Im)₄](NO₃)·1.35 H₂O forms a layered structure, and exhibits both the intercalation of neutral guests and the ability to selectively sequester soft anions, such as iodide.