title: Multi-frequency (S, X, Q and W-band) EPR and ENDOR Study of Vanadium(IV) Incorporation in the Aluminium Metal-Organic Framework MIL-53.
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.
authors: Department of Solid State Sciences, Ghent University, Krijgslaan 281-S1, B-9000 Gent (Belgium).
authors: Irena
authors: I
authors: Nevjestić
authors: Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281-S3, B-9000 Gent (Belgium).
authors: Hannes
authors: H
authors: Depauw
authors: Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281-S3, B-9000 Gent (Belgium).
authors: Karen
authors: K
authors: Leus
authors: Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 2, CH-8093 Zürich (Switzerland).|Faculty of Physics, Vilnius University, Sauletekio av. 9, LT-10222 Vilnius (Lithuania).
authors: Vidmantas
authors: V
authors: Kalendra
authors: Department of Physics, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp (Belgium).
authors: Ignacio
authors: I
authors: Caretti
authors: Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 2, CH-8093 Zürich (Switzerland).
authors: Gunnar
authors: G
authors: Jeschke
authors: Department of Physics, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp (Belgium).
authors: Sabine
authors: S
authors: Van Doorslaer
authors: Department of Solid State Sciences, Ghent University, Krijgslaan 281-S1, B-9000 Gent (Belgium).
authors: Freddy
authors: F
authors: Callens
authors: Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281-S3, B-9000 Gent (Belgium).
authors: Pascal
authors: P
authors: Van Der Voort
authors: Department of Solid State Sciences, Ghent University, Krijgslaan 281-S1, B-9000 Gent (Belgium). Henk.Vrielinck@UGent.be.
authors: Henk
authors: H
authors: Vrielinck
keywords: ENDOR spectroscopy; EPR spectroscopy; doping; metal-organic frameworks; vanadium