A family octanuclear (Fe8)and trinuclear (Fe3) iron-oxo cluster incorporating bridgingpyrazolate ligands has been synthesized and characterized [Inorg. Chem. 2008,47, 645]. Cyclic voltametric studies revealed that the all-ferric Fe8complexes can be reduced in four consecutive one-electron steps, while all-ferricFe3 is reduced by one electron without major structural modifications.This observation prompted us to pursue the chemical reduction on theseclusters. Herein some mixed-valence octanuclear and trinulear clusters derivedfrom the one-, or two-electron chemical reduction of corresponding iron(III)species (formally FeIII 7FeII, FeIII6FeII2and FeIII2FeII) will be presented.Spectroscopic analyses of the reduced clusters reveal remarkable contrast interms of reduction site and charge delocalization behavior between the Fe8and Fe3 species and these properties can be further differentiatedon the basis of terminal ligands (e.g. Cl, Br, NCS, RC6H5O)coordinated to the iron centers. NMR, M�ssbauer, IR, XPS and NIR spectroscopicmethods have been used to probe the reduction site, as well the extent ofelectronic delocalization of those mixed-valence species. X-ray structures havebeen shown for some representative compounds and DFT calculations are also inprogress to understand the electronic structure in some cases.

Mixed-valence tri- and octanuclear iron oxo pyrazolate complexes:
Effect of terminal substitutions on electronic delocalization probed by various
spectroscopic analyses

240th National Meeting (2010)

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Mixed-valence tri- and octanuclear iron oxo pyrazolate complexes: Effect of terminal substitutions on electronic delocalization probed by various spectroscopic analyses