(81e) Structure, Dynamics, and Reactivity for Alkane Oxidation of Fe(II) Sites Situated in the Nodes of a Metal-Organic Framework
Matthew C. Simonsa, Jenny G. Vitillob, Melike Babuccic, Adam Hoffmand, Michelle Beauvaise, Zhihengyu Chene, Christopher J. Cramerb, Karena Chapmane, Simon Bared, Bruce C. Gatesc, Connie Lub, Laura Gagliardib, Aditya Bhan*a
aDepartment of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States
bDepartment of Chemistry, Chemical Theory Center, and Supercomputing Institute, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States
cDepartment of Chemical Engineering, University of California, Davis, California 95616, United States
dSSRL, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
eDepartment of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York 11794, United States
We demonstrate the ability of mononuclear, high spin (S=2), Fe(II) sites, situated in the nodes of MIL-100(Fe) to convert propane via dehydrogenation, hydroxylation, and overoxidation pathways utilizing an atomic oxidant. Pair distribution function (PDF) analysis, N2 isotherms, X-ray diffraction, and infra-red (IR) and Raman spectroscopy confirm the single-phase crystallinity and stability of MIL-100(Fe) over reaction conditions (523K in vacuo, 378-408 K C3H8+N2O). Density Functional Theory (DFT) calculations suggest that the reaction occurs via a radical rebound mechanism involving the oxidation of Fe(II) species to Fe(III) via a high spin, Fe(IV)=O intermediate, which is supported by X-ray adsorption and Mössbauer spectroscopy. The identity of the Fe(II) active site is confirmed and quantified using in-situ chemical titrations. N2 and C3H6 production rates were calculated to both be first order in N2O pressure and zero order in C3H8 pressure, concurring with DFT cluster calculations that predict the reaction of Fe(II) with N2O to be rate-limiting.