We will present structural, electrochemical and spectroscopic studies of a family of octanuclear complexes, [Fe8(�4-O)4(�-4-R-pz)12X4] -- R = H, Cl, Br, Me, Et; X = Cl, Br, NCS, N3, OAr -- containing a Fe4O4-cubane core, which can be reversibly reduced in four consecutive steps from an all-ferric, [Fe8], to four mixed-valence ferric/ferrous states, [Fe8]�/2�/3�/4�.  The [Fe8] species are antiferromagnetically coupled with a diamagnetic ground state.  Spectroscopic (electronic, vibrational, M�ssbauer, XPS) analysis of mixed-valent [Fe8]� species indicates partial charge delocalization over the four Fe4O4-cubane Fe-sites.  The magnetic susceptibility data of [Fe8]� complexes have been modeled with the help of magnetization measurements at pulsed magnetic fields of 65 T and 100 T, allowing an estimation of their double-exchange parameters. A twice reduced [Fe8]2� species, containing an iron-oxo core isoelectronic to magnetite, Fe3O4, shows, upon cooling, a transition from a delocalized to localized valence, over a temperature range overlapping with that of the �Verwey transition�. The spectroscopic and magnetic analysis of this species places the 99-year old issue of the Verwey transition of bulk magnetite into a new, molecular level perspective.

Mixed-valent octanuclear iron oxide complexes and a fresh look at the “Verwey transition”

244th National Meeting (2012)

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