Photochemical Generation, Kinetics and Chemistry of Transition Metal Nitrosyl Linkage Isomers

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This award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports research by Dr. Thomas Bitterwolf, Chemistry Department, University of Idaho, to study metal bound nitrosyl ligands and their linkage isomers using both frozen matrix methods and time-resolved infrared (IR) techniques. For many years the NO ligand has been known to bind metals through either the nitrogen or oxygen. Recently its ability bind a metal in a side-on fashion has been demonstrated. In addition, time resolved crystallographic and infrared studies have shown that nitrosyl ligands in organometallic and coordination compounds can undergo photochemical linkage isomerizations. This study will build an understanding of the factors that lead to the formation and stabilization of nitrosyl linkage isomers by examining several classes of compounds representing a range of ligand types and electron counts. These include: [CpMn(CO)2NO] cation; [Fe(CO)3NO] anion; salts of Roussin's red, [Fe2(NO)4(S)2] dianion, and black, [Fe3(NO)7(S )] anion; Co(II)(salen)(NO) and Co(II)(acacen)(NO); Fe(S2CNR2)2(NO); and CpM(NO)2X, where M = Cr, Mo or W and X is a variety of anionic species. Frozen organic matrix methods will be used to identify those classes of compounds for which side bonded linkage isomers are formed upon photolysis and time-resolved IR spectroscopy will be used to study the kinetics of relaxation of the linkage isomers back to the terminal nitrosyl form. From these data, the thermodynamic activation parameters will be derived. The final portion of the project will utilize time-resolved IR and other flash kinetics methods to examine several reactions in which side bonded linkage isomers may be involved. Nitrogen oxide plays a mediating role in intercellular communication, smooth muscle relaxation, and cytotoxic immune response. There is a great interest in identifying compounds that will liberate nitrogen oxide in biological systems. Optimization of these materials requires a more detailed understanding of the mechanism of nitrogen oxide liberation. This study will determine the details of the release of NO groups that are attached to metals. The studies will be carried out in partnership with the Pacific Northwest National Laboratory. This will give an excellent experience for the postdoctoral, graduate, and undergraduate students who work on the project. High school teachers and Native American high school students will be exposed to the project through the PI's participation in the Murdock Foundation Partners in Science Program.