Polymorphs and Polymorphic Transformations that Alter Chemical Bonding Alan L. Balch, Chemistry, University of California, One Shields Avenue, Davis, CA 95616 This proposal is designed to examine the structures and inter-conversion between polymorphs of transition metal complexes. The project emphasizes compounds where significant changes in chemical interactions between molecules produce marked spectral differences between the polymorphs. Toward the goal of developing these compounds into sensors we will determine conditions under which the transformations can be made reversible. The photograph shows two of the polymorphs we have grown and structurally characterized for dicarbonyl[2(p-tolylimino)penten-3-olato-4]iridium(I)