This award, in the Inorganic, Bioinorganic and Organometallic Chemistry Program, will support studies on very rapid intra- molecular rearrangements of organometallic molecules using the technique of microwave dielectric relaxation. The systems chosen for study are primarily those that have previously resisted characterization by dynamic, NMR techniques because their rates of rearrangement. Systems to be studied include tetrahedral - square planar interconversions in four coordinate nickel(II) complexes, Berry pseudorotation processes in trigonal bipyramidal compounds of P, Sb, Ru and Os, and eight coordinate beta-diketonate complexes of Zr, Ce, Th, and U. Measurements will be made as a function of temperature so that activation energies can be extracted from the data. %%% It has been recognized for some time that many molecules undergo a variety of types of intramolecular motions. In the case of many organometallic compounds these motions may result in the interconversion of stereoisomers and can have important consequences for chemical reactivity. In other cases, such as those to be examined here, the rearrangements are degenerate and result in no apparent change in the structure of the molecule. Understanding the nature of the energy barriers to such rearrangements is fundamental to understanding the process itself. Degenerate rearrangements frequently occur at such high rates that there are very few experimental techniques that can be utilized. Microwave dielectric relaxation is one technique that can be applied to certain compounds. Although Professor DiCarlo is located at a primarily undergraduate institution, his laboratory is one of the few in the world that is equipped to make these measurements and to provide some badly needed quantitative information concerning the barriers to rearrangement in some important classes of compounds.
