Sara Helvoigt

Graduate Student
Inorganic Chemistry

B.S. Chemistry, 1992
Ithaca College

My research focuses on the chemistry of the multielectron excited states of quadruply bonded metal-metal bimetallic complexes, M2Cl4P4, where each of the metals has a square pyramidal configuration. We have found that excitation of the metal to metal charge transfer transitions (MMCT) of these complexes gives rise to localized two electron excited states, or Zwitterionic states. We have proven the existence of the Zwitterionic state through the use of two-photon spectroscopy. The MMCT results in the transfer of an electron from one metal center to another, resulting in an effective lone pair on one metal center. The excited state intermediate is believed to be an edge-sharing bioctahedral structure (ESBO), in which each metal center has an octahedral configuration. To obtain this ESBO type structure, the Cl atoms from one metal fold to a bridging position between both metals. The fold-over of the Cl atoms serves to increase the electron density on the oxidized metal and decrease electron density on the reduced metal. This distortion in the excited state breaks up the symmetry of the molecule and increases the lifetime of the excited state, enabling it to do photochemistry. "The lone pair" on the reduced metal center is perfectly set up for two electron reactions, for example, oxidative addition and atom transfer.

We have been able to use the molecules for oxidative addition with small substrates such as MeI and PhSSPh with visible light excitation. In the process of trying to expand the multielectron chemistry of these molecules, we have learned more about the higher energy excited states also. If the quadruply bonded metal-metal bimetallic complexes are excited in a metal to ligand charge transfer (MLCT) transition, the two electron chemistry is circumvented by a one electron reduction of halogenated solvents, producing radicals. This one electron chemistry is not observed in aromatic solvents, such as benzene, due to the increased strength of a C-H bond as compared to a C-Cl bond. The overall reaction is summarized in Scheme 1.

In progress, is work on sulfur and oxygen atom transfer. We have found that this is possible using a sulfur or an oxygen atom donor and that the reaction can be driven with light as low in energy as 495nm.

I received my BS in chemistry in the spring of 1992 from Ithaca College and started working in Dan’s group at Michigan State University in June. I am currently in my fourth year and I specialize in Inorganic synthesis and photochemistry. I plan to graduate with a Ph.D. in the summer of 1997. I hope to obtain employment in an industrial job as synthetic chemist.


Send Mail To Sara Helvoigt at

helvoigt@cemvax.cem.msu.edu