Multi-frequency (S, X, Q and W-band) EPR and ENDOR Study of Vanadium(IV) Incorporation in the Aluminium Metal-Organic Framework MIL-53

Irena Nevjestić; Hannes Depauw; Karen Leus; Vidmantas Kalendra; Ignacio Caretti; Gunnar Jeschke; Sabine Van Doorslaer; Freddy Callens; Pascal Van Der Voort; Henk Vrielinck

doi:10.1002/cphc.201500522

Multi-frequency (S, X, Q and W-band) EPR and ENDOR Study of Vanadium(IV) Incorporation in the Aluminium Metal-Organic Framework MIL-53

Chemphyschem. 2015 Oct 5;16(14):2968-73. doi: 10.1002/cphc.201500522. Epub 2015 Aug 20.

Authors

Affiliations

¹ Department of Solid State Sciences, Ghent University, Krijgslaan 281-S1, B-9000 Gent (Belgium).
² Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281-S3, B-9000 Gent (Belgium).
³ Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 2, CH-8093 Zürich (Switzerland).
⁴ Faculty of Physics, Vilnius University, Sauletekio av. 9, LT-10222 Vilnius (Lithuania).
⁵ Department of Physics, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp (Belgium).
⁶ Department of Solid State Sciences, Ghent University, Krijgslaan 281-S1, B-9000 Gent (Belgium). Henk.Vrielinck@UGent.be.

PMID: 26305910
DOI: 10.1002/cphc.201500522

Abstract

Doping the well-known metal-organic framework MIL-53(Al) with vanadium(IV) ions leads to significant changes in the breathing behaviour and might have repercussions on the catalytic behaviour as well. To understand the properties of such a doped framework, it is necessary to determine where dopant ions are actually incorporated. Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) are applied to reveal the nearest environment of the paramagnetic vanadium(IV) dopant ions. EPR spectra of as-synthesised vanadium-doped MIL-53 are recorded at S-, X-, Q- and W-band microwave frequencies. The EPR spectra suggest that at low dopant concentrations (1.0-2.6 mol %) the vanadium(IV) ions are well dispersed in the matrix. Varying the vanadium dopant concentration within this range or the dopant salt leads to the same dominant EPR component. In the ENDOR spectra, hyperfine (HF) interactions with (1) H, (27) Al and (51) V nuclei are observed. The HF parameters extracted from simulations strongly suggest that the vanadium(IV) ions substitute Al in the framework.

Keywords: ENDOR spectroscopy; EPR spectroscopy; doping; metal-organic frameworks; vanadium.