Microwave Measurements of Structures and Electronic Properties of Transition Metal Complexes, Hydrogen-Bonded Complexes, and Radicals

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With this award from the Chemical Structure, Dynamics and Mechanisms program, Professor Stephen Kukolich of the University of Arizona will modify and use pulsed-beam, Fourier-transform microwave spectrometers to measure rotational transition frequencies in the 1 to 18 GHz region of the microwave spectrum. The completion of a new 1-10 GHz, spectrometer provides an unusual capability for measuring lower frequency transitions of larger molecules and complexes. A laser-photodissociation beam source will be used for measurements on organometallic radicals and their reaction products. The overall objectives of this work include measurements of the three-dimensional gas-phase structures, quadrupole coupling strengths and magnetic interaction parameters. These measurements are proposed for: a) mononuclear and dinuclear transition metal complexes, b) weakly-bound complexes involving transition metals, c) hydrogen-bonded complexes and d) transition metal radicals. The quadrupole coupling strengths and magnetic interaction parameters directly characterize the electronic charge distributions. Quantum mechanical (DFT or mp2) calculations will be carried out for all of the complexes studied. The coordination of experimental work with the theoretical calculations helps to make the measurements more efficient, improves our understanding of the electronic structure of molecules and provides guidelines and experimental examples for improvements in ab initio, quantum chemistry calculations. Transition metal complexes are very important in the chemical industry, in biological systems and as an area of study in inorganic chemistry. Millions of tons of chemical products are produced each year using reactions which involve transition metal catalysts. The active sites of many enzymes and transport proteins in living systems contain transition metal complexes. A large fraction of the research and study in inorganic chemistry is focused on transition metal complexes, and the proposed work will provide new contributions to the structural database that is used in research, industry and education. The proposed work will often involve smaller, "model" complexes, but will provide results relevant to the larger, more complex systems. The accurate, three-dimensional structures for transition metal complexes, are helpful in understanding reaction mechanisms. Successful modeling of reaction mechanisms in chemistry and biology often depends on the accurate and reliable experimental structural information. Improving calculation methods and basis sets through correlation with new experimental data is useful because the calculations are presently the only source of detailed information on short-lived radicals or high-energy reaction intermediates. Studies of metal dihydrogen complexes may provide information which will be useful for improving hydrogen storage technology. Graduate and undergraduate research students will learn fundamentals of chemistry, quantum mechanics and methods and techniques involved in computer work, microwave electronics and making physical measurements through direct involvement in the proposed projects. Participation in the research by underrepresented minorities and secondary school teachers, or non-Ph.D. college students will be actively sought for the proposed projects.