FisMat2017 - Submission - View

Abstract's title: Insertion of Mn(II) and Nb(IV) atoms in the cornerstone of MOF-5: XANES and EXAFS studies
Submitting author: Luca Braglia
Affiliation: University of Turin
Affiliation Address: Via Pietro Giuria 7, 10125 Torino
Country: Italy
Oral presentation/Poster (Author's request): Oral presentation
Other authors and affiliations: Elisa Borfecchia (Department of Chemistry, NIS and INSTM Reference Centers, University of Turin, Turin, Italy), Kirill A Lomachenko (European Synchrotron Radiation Facility, 71 avenue des Martyrs, CS 40220, 38043 Grenoble Cedex 9, France), Amanda W. Stubbs (Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States), Maciej Korzyński (Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States), Mircea Dincă (Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States), Carlo Lamberti (International research center “Smart Materials”, Southern Federal University, 5 Zorge street, Rostov-on-Don, 344090, Russia and Department of Chemistry, NIS and eDepartment of Chemistry, CrisDi Interdepartmental Centre and INSRM reference University of Turin, via Pietro Giuria 7, 10125 Turin, Italy)
Abstract

MOF-5 is a metal organic framework composed by Zn4O(BDC)3 (BDC = 1,4 - benzenedicarboxylate) with a cubic three dimensional extended porous structure. It was discovered by Omar Yaghi in 1999 and now is probably one of the most studied MOFs [1]. Since Yaghi's discovery procedures for its synthesis and handling were developed to improve its gas absorption capacities. The studied samples presents metal substitution by postsynthetic ion metathesis (PSIM) of Zn cornerstone's atom by Mn and Nb. The idea was to use the MOF-5 as a platform to explore cation exchange and the isolation of reactive intermediates. Hence, Mn-atom has been placed in the all oxygen ligand field of MOF-5 and explored its reactivity with a variety of oxidants. The insertion of MnII in the MOF-5 inorganic cornerstone, isomorphically substituting ZnII, and the consequent cornerstone distortion was demonstrated by Mn K-edge EXAFS. We also found that oxidation of Mn is possible with t-BuSO2PhIO and that as a result of reaction with adventitious hydrogen, have isolated a Mn(III)-OH, which was confirmed through XANES, DRUV-vis, and EPR studies. Conversely, the XANES and EXAFS studies on Nb-MOF-5 revealed the presence of NbIV not in the cornerstone, replacing the a Zn site, but in extra-framework positions at (3.28 ±0.03) Åfrom the Zn closest atom. EXAFS analysis has been very informative to understand the different possibilities for extra-metal location in the synthesis of the MOF-5 with Nb and Mn sites.

 

[1] Hailian Li, Mohamed Eddaoudi, Michael O'Keeffe, and Omar M. Yaghi, “Design and synthesis of an exceptionally stable and highly porous metal-organic framework," Nature 402 (1999).