Effect of Ligand Topology on the Structure of Lead Coordination Complexes
Project Description
The goal of this project is to develop spectroscopic methods to probe the electronic structure of the heavy main-group metals in complex matrices (i. e., proteins), and to understand how the nature of the ligands affects the stereochemical activity of their lone pair. We are attempting to produce a wide variety of coordination compounds of Pb2+ where the Pb2+ has different coordination numbers, geometries and ligand topologies. The focus has been on polydentate amine ligands. These are good starting points because they form relatively stable complexes with Pb2+ (complexes of Pb2+ with primary and secondary thiolates are unstable in basic solution with respect to PbS), do not bridge metal centers (like thiolate and phenolate), which complicates structural studies, and they are relatively easy to synthesize and manipulate. With these ligands, the resulting complex is charged and this allows us to examine the counter ion's effects on structure.
We work in collaboration with Russ Baughman here at Truman to structurally characterize these compounds by single-crystal X-ray crystallography. Solid state 207Pb NMR (at the University of Iowa) and solution 207Pb NMR here at Truman are used to probe the chemical environment around the Pb. The 207Pb NMR chemical shift has been shown to be a sensitive probe of the metal ion’s environment, but no systematic study to correlate structural changes with changes in the chemical shift has been undertaken. By performing NMR in the solid state, on samples for which we know the structure, we can directly probe how chemical shift depends on structure without solvent effects. Using this study as a basis, we can then probe the changes that occur upon solvation using solution NMR.
This work is being extended to other heavy metals, such as Bi3+, Tl+, Sn2+ and Sb3+.
We work in collaboration with Russ Baughman here at Truman to structurally characterize these compounds by single-crystal X-ray crystallography. Solid state 207Pb NMR (at the University of Iowa) and solution 207Pb NMR here at Truman are used to probe the chemical environment around the Pb. The 207Pb NMR chemical shift has been shown to be a sensitive probe of the metal ion’s environment, but no systematic study to correlate structural changes with changes in the chemical shift has been undertaken. By performing NMR in the solid state, on samples for which we know the structure, we can directly probe how chemical shift depends on structure without solvent effects. Using this study as a basis, we can then probe the changes that occur upon solvation using solution NMR.
This work is being extended to other heavy metals, such as Bi3+, Tl+, Sn2+ and Sb3+.
Background Needed
Project involves a great deal of ligand synthesis, but it also involves some spectroscopy and other physical methods. At least one year of college chemistry, or extensive laboratory experience, is required. Organic chemistry is useful, but not essential. A willingness to learn/carry out good laboratory practices is required because of the toxicity of the metals involved.