Our research emphasizes the detailed application of a wide variety of spectroscopic methods combined with molecular orbital calculations to probe the electronic structure of a transition metal complex and its relation to physical properties and reactivity. Three areas of physical-inorganic and bioinorganic chemistry are of general interest.

The first is chemical and spectroscopic studies of metalloprotein active sites. The general philosophy of these studies is to treat the metalloprotein as a metal complex with an ultimate ligand and to extend the concepts of coordination chemistry, spectroscopy, and electronic structure to this system. Studies in Bioinorganic Chemistry thus far have focused on structure-function correlations over copper cluster containing proteins, detailed spectral and theoretical studies of the unusual electronic structures of the Blue Copper, CopperA and iron sulfur active sites and their contribution to electron transfer reactions, and active sites in mononuclear and binuclear non-heme iron enzymes involved in O 2 binding and activation.

The second research area is detailed spectroscopic and electronic structure studies of high symmetry transition metal complexes. This research involves the application of polarized single crystal electronic absorption, variable temperature-variable field magnetic circular dichroism, electron paramagnetic resonance, superconducting magnetic susceptibility, resonance Raman, photoelectron and x-ray absorption spectroscopies to important problems in transition metal chemistry. Topics of interest include excited state contributions to inorganic photochemistry, inorganic potential energy surfaces and the Jahn-Teller effect, excited state origin of ground state properties including antiferromagnetic exchange coupling and spin Hamiltonian parameters, electronic structures required for dioxygen binding, activation, multielectron reduction to water and O-O bond formation, and experimental evaluations of covalency. We are also very interested in the development of new spectroscopic methods in bioinorganic chemistry.

A third research emphasis is the development of synchroton spectroscopies (at SSRL) to solve important problems in inorganic chemistry. Projects include: 1) variable energy photoelectron spectroscopy (PES) to probe small molecule bonding interactions with metal oxide surfaces related to heterogeneous, homogeneous and biological catalysis; 2) PES studies of electronic structure and electronic relaxation contributions to electron transfer processes in transition metal complexes; 3) use of ligand K-edges in determining covalency of ligand-metal bonds; 4) development of metal L-edge X-ray absorption spectroscopy to probe metal sites in highly covalent ligand environments (e.g. heme vs. non-heme iron).

1) "O2 and N2O Activation by Binuclear, Trinuclear and Tetranuclear Cu Clusters in Biology," E.I. Solomon, R. Sarangi, J.S. Woertink, A.J. Augustine, J. Yoon, and S. Ghosh, Accounts of Chemical Research, 40, 581, (2007).

2) "Fe L-Edge X-ray Absorption Spectroscopy of Low-Spin Heme Relative to Non-heme Fe Complexes: Delocalization of Fe d-Electrons into the Porphyrin Ligand," R.K. Hocking, E.C. Wasinger, Y-L. Yan, F.M.F. DeGroot, F.A. Walker, K.O. Hodgson, B. Hedman, and E.I. Solomon, J. Am. Chem. Soc., 129, 113, (2007).

3) "Spectroscopic and Electronic Structure Study of the Enzyme-Substrate Complex of Intradiol Dioxygenases: Substrate Activation by a High Spin Ferric Non-Heme Iron Site," M.Y.M. Pau, M.I. Davis, A.M. Orville, J.D. Lipscomb and E.I. Solomon, J. Am. Chem. Soc., 129, 1944, (2007).