Selective Binding of O₂ Over N₂ in a Redox-Active Metal-Organic Framework with Open Iron(II) Coordination Sites

Author

Eric D. Bloch
Leslie J. Murray
Wendy L. Queen
Sachin M. Chavan
Sergey N. Maximoff
Julian P. Bigi
Rajamani Krishna
Vanessa K. Peterson
Fernande Grandjean, Missouri University of Science and TechnologyFollow
Gary J. Long, Missouri University of Science and TechnologyFollow
Berend Smit
Silvia Bordiga
Craig M. Brown
Jeffrey R. LongFollow

Abstract

The air-free reaction between FeCl₂ and H₄dobdc (dobdc^4- = 2,5-dioxido-1,4-benzenedicarboxylate) in a mixture of N,N-dimethylformamide (DMF) and methanol affords Fe₂(dobdc) ·4DMF, a metal-organic framework adopting the MOF-74 (or CPO-27) structure type. The desolvated form of this material displays a Brunauer-Emmett-Teller (BET) surface area of 1360 m²/g and features a hexagonal array of one-dimensional channels lined with coordinatively unsaturated Fe^II centers. Gas adsorption isotherms at 298 K indicate that Fe₂(dobdc) binds O₂ preferentially over N ₂, 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. Mössbauer 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 O₂ ^2- 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 d_O-O = 1.25(1) Å at low temperature and in a slipped side-on mode with d_O-O = 1.6(1) Å 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.

Recommended Citation

E. D. Bloch and L. J. Murray and W. L. Queen and S. M. Chavan and S. N. Maximoff and J. P. Bigi and R. Krishna and V. K. Peterson and F. Grandjean and G. J. Long and B. Smit and S. Bordiga and C. M. Brown and J. R. Long, "Selective Binding of O₂ Over N₂ in a Redox-Active Metal-Organic Framework with Open Iron(II) Coordination Sites," Journal of the American Chemical Society, vol. 133, no. 37, pp. 14814 - 14822, American Chemical Society (ACS), Sep 2011.

The definitive version is available at https://doi.org/10.1021/ja205976v

Department(s)

Chemistry

Keywords and Phrases

Break Through Curve; Brunauer-emmett-teller Surface Areas; Capacity Increase; Co-ordinatively Unsaturated; Coordination Sites; Hexagonal Arrays; Ideal Adsorbed Solution Theory; Industrial Settings; Infrared Spectrum; Iron Centers; Irreversible Capacity; Low Temperatures; Metal Organic Framework; Mössbauer; N ,N-Dimethylformamide; One-dimensional Channels; Partial Charge Transfer; Powder Neutron Diffraction Data; Redox-active; Room Temperature; Selective Binding; Structure Type; Charge Transfer; Dimethylformamide; Gas Adsorption; Iron Compounds; Metals; Methanol; Molybdenum; Organic Solvents; Rietveld Analysis; Spectroscopy; Iron; Iron; Metal; Nitrogen; Organic Compound; Oxygen; Air Temperature; Electron Transport; Infrared Spectroscopy; Isotherm; Low Temperature; Neutron; Oxidation Reduction Reaction; Oxygen Consumption; Potassium Transport; Room Temperature; Surface Property

International Standard Serial Number (ISSN)

0002-7863

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2011 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Sep 2011