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|Title: ||Selective Binding of O(2) over N(2) in a Redox-Active Metal-Organic Framework with Open Iron(II) Coordination Sites|
|Authors: ||Bloch, ED|
|Issue Date: ||21-Sep-2011|
|Publisher: ||American Chemical Society|
|Citation: ||Bloch, E.D., Murray, L.J., Queen, W.L., Chavan, S., Maximoff, S.N., Bigi, J.P., Krishna, R., Peterson, V.K., Grandjean, F., Long, G.J., Smit, B., Bordiga, S., Brown, C.M., Long, J.R. (2011). Selective Binding of O(2) over N(2) in a Redox-Active Metal-Organic Framework with Open Iron(II) Coordination Sites, Journal of the American Chemical Society, 133(37), 14814-14822.|
|Abstract: ||The air-free reaction between FeCl2 and H4dobdc (dobdc4â€“ = 2,5-dioxido-1,4-benzenedicarboxylate) in a mixture of N,N-dimethylformamide (DMF) and methanol affords Fe2(dobdc)Â·4DMF, a metalâ€“organic framework adopting the MOF-74 (or CPO-27) structure type. The desolvated form of this material displays a Brunauerâ€“Emmettâ€“Teller (BET) surface area of 1360 m2/g and features a hexagonal array of one-dimensional channels lined with coordinatively unsaturated FeII centers. Gas adsorption isotherms at 298 K indicate that Fe2(dobdc) binds O2 preferentially over N2, with an irreversible capacity of 9.3 wt %, corresponding to the adsorption of one O2 molecule per two iron centers. Remarkably, at 211 K, O2 uptake is fully reversible and the capacity increases to 18.2 wt %, corresponding to the adsorption of one O2 molecule per iron center. MoÌˆssbauer and infrared spectra are consistent with partial charge transfer from iron(II) to O2 at low temperature and complete charge transfer to form iron(III) and O22â€“ at room temperature. The results of Rietveld analyses of powder neutron diffraction data (4 K) confirm this interpretation, revealing O2 bound to iron in a symmetric side-on mode with dOâ€“O = 1.25(1) Ã… at low temperature and in a slipped side-on mode with dOâ€“O = 1.6(1) Ã… when oxidized at room temperature. Application of ideal adsorbed solution theory in simulating breakthrough curves shows Fe2(dobdc) to be a promising material for the separation of O2 from air at temperatures well above those currently employed in industrial settings. © 2011, American Chemical Society|
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