U.S.-Greece Dissertation Enhancement: Mössbauer Spectroscopic Studies of Redox-Active Fe4O4-Cubanes

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NSF-0827841U.S.-Greece Dissertation Enhancement: Mössbauer Spectroscopic Studies of Redox-Active Fe4O4 Cubanes ABSTRACTThis project will send Dalice M. Piñero, a student from the University of Puerto Rico at Río Piedras, to the Institute of Materials Science, NCSR ?Demokritos?, Athens, Greece, for two one-month periods to conduct 57Fe Mössbauer Spectroscopy experiments as part of her doctoral dissertation work on oligonuclear iron pyrazolato complexes. Mrs. Piñero will work with Dr. Yiannis Sanakis, an active collaborator of Dr. Raphael Raptis, the PI on this award and Mrs. Piñero?s Thesis advisor at the University of Puerto Rico. The project proposes the use Mössbauer spectroscopy to study the redox-active Fe4O4-cubane contained within the core of [Fe8O4(4-R-pz)12X4]0/n- (R = H, Cl, Br, Me, Ph; X= Cl-, Br-, SCN-, N3-) over a range of redox-modified oxidation states; five oxidation states are electrochemically accessible in these systems, from [FeIII8] to [FeIII4FeII4]. Mössbauer spectroscopy allows the differentiation between the two structurally distinct Fe-sites present in these octanuclear complexes, as well as the differentiation between oxidation states. The possible existence of Fe4O4 cubanes at the electron transfer sites of proteins has been suggested resently. Results obtained in this project will (1) contribute to the creation of a spectroscopic ?fingerprint? data bank to be used for recognition of these motifs in Nature, (2) will serve to study their electronic states with regard to localized/delocalized nature of mixed valence states, and (3) by the application of external magnetic fields, will probe the magnetic states at each oxidation state, accessed by redox modification of the all-ferric compounds. The Intellectual Merit of the project consists of the systematic study of a rare, stepwise redox-modified multi-iron cluster. The international experience to be gained by an under-represented minority student during this project and the training in techniques not available locally constitute the Broader Impacts of this project.