This award provides support for a continuing cooperative research project on solid-state dynamics, between Professor David N Hendrickson, Department of Chemistry, University of California, San Diego, and Professor Michio Sorai, Chemical Thermodynamics Laboratory, Osaka University, Japan. The onset of dynamics associated with ligands, counterions and even solvate molecules in crystals can dramatically affect several phenomena involving transition metal complexes in solid state. Intramolecular electron transfer in mixed- valence complexes, spin-state interconversion in spin- crossover-complexes, and thermochroism in copper and nickel complexes are current phenomena being studied. In all these phenomena, intermolecular interactions in the solid state are important in controlling the events. A study of the onset of the dynamics involved in these phase transitions will help considerably to elucidate the factors controlling these phenomena. Heat capacity measurements and a variety of spectroscopic techniques are being employed to delineate the macroscopic and microscopic details involved in the above phenomena. Thermodynamic studies serve as a powerful tool to elucidate energetic and entropic aspects of a phenomenon, from which one can gain better evidence as to whether a phase transition exists or not. Moreover based on the transition entropy, it is possible to discover the microscopic processes involved in a phase transition that spectroscopic and structural studies fail to detect. On the other hand, spectroscopies and X-ray diffraction provide us with very detailed microscopic information at the atomic or electronic level. The aim of this proposal is to bring together these techniques in order to study the mechanisms of those phase transitions in which electrons play, either directly or indirectly, important roles. The skills of the two research groups involved in this project are both comprehensive and complementary; the Japanese group having considerable expertise in macroscopic calorimetric studies and the US group having similar expertise in microscopic spectroscopies and structural studies. Because of their very different backgrounds Professors Hendrickson and Sorai will bring quite different perspectives to developing a model for a given order-disorder transition. If successful, this project should make a considerable contribution to this complex area.
