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Our primary research area is the determination of the molecular structures and electronic charge distributions of transition metal complexes, hydrogen-bonded complexes and small molecules using microwave spectroscopy. Complete, accurate, 3-D structures are very helpful in understanding reaction mechanisms and in understanding the bonding and electronic structures of molecules. There are many important examples in chemistry and biochemistry where a detailed knowledge of molecular structures provided the key to understand reaction mechanisms. The most accurate structures for small molecules in the gas phase have been obtained from microwave rotational spectra, and these gas-phase structures can be directly compared with quantum theory results.
 

Transition metals and transition metal complexes function as catalysts in a wide variety of chemical reactions which are important in biology and the chemical industry. To better understand how the bonding and reactivity of compounds are modified by forming complexes with metal atoms, it is important to determine the structures and electronic properties of the complexes, or related model compounds. Comparisons of the measured and calculated structures and electronic properties is very usefulin testing and improved the theoretical models so they can be used with more confidence in prdicting properties of larger and mor complex molecules. Much of our recent work has involved transition metal hydrides, which are quite difficult to characterize using diffraction methods, yet are very important in organometallic chemistry. We can accurately locate hydrogen atoms in complexes using microwave spectroscopy. Most of the published microwave studies of transition metal complexes were done by our research group during the past five years. Some examples of transition metal hydrides and dihydrides are shown below:

A few structures for other complexes are shown here: 

These studies were carried out with a pulsed-beam, Fourier transform microwave spectrometer which was constructed at the University of Arizona. This system provides excellent resolution and extremely high sensitivity for studies on complexes and molecules. We are doing further development work on computer controlled microwave spectrometers, in addition to the spectroscopic studies of the complexes. We hope to extend our work to dinuclear complexes, organometallic radicals and weakly-bound complexes involving organometallics.

Hydrogen bonding interactions are important in replication, transcriptions and translation of genetic information and in determining the folding and three dimensional structure of proteins and other large molecules. Detailed information about hydrogen bonding can be obtained from microwave work on wealkly-bound complexes and pulsed-beam, Fourier transform microwave spectroscopy is one of the key methods for studies of hydrogen-bonded complexes. 

Selected Publications:

"Molecular Structure of Tetracarbonyldihydroiron: Microwave Measurements and Density Functional Theory Calculations," B.J. Drouin and S.G. Kukolich, J. Am. Chem. Soc. 120, 6774-6780 (1998).

"Measurements of Structural and Quadrupole Coupling Parameters for Bromoferrocene Using Microwave Spectroscopy," B.J. Drouin, T.G. Lavaty, P.A. Cassak and S.G. Kukolich, J. Chem. Phys. 107, 6541-6548 (1997).

"Microwave Measurements of the Gas-Phase Molecular Structure of Cobalt Tetracarbonyl Hydride, S.G. Kukolich and S.M. Sickafoose, J. Chem. Phys. 105, 3466 (1996).

"Microwave Molecular Structure Measurements for Tetracarbonyl Dihydro Osmium, A Classical Dihydride," S.G. Kukolich, S.M. Sickafoose and S.M. Breckenridge, J. Am. Chem. Soc. 118, 205 (1996).

"Alternating C-C Bond Lengths in Gas-Phase Benzene Chromium Tricarbonyl," S.G. Kukolich, J. Amer. Chem. Soc. 117, 5512 (1995).

"Measurements of the Microwave Spectrum, Re-H Bond Length and Re Quadrupole Coupling for HRe(CO)₅," S.G. Kukolich and S.M. Sickafoose, J. Chem. Phys. 99, 6465 (1993).

"Microwave Measurements of the Rotational Spectrum and Structure of Butadiene Iron Tricarbonyl," S.G. Kukolich, M.A. Roehrig, D.W. Wallace and G.L. Henderson, J. Am. Chem. Soc. 115, 2021 (1993).
 

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