Hannes Depauw

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

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.

Elucidating the Vibrational Fingerprint of the Flexible Metal–Organic Framework MIL-53(Al) Using a Combined Experimental/Computational Approach

In this work, mid-infrared (mid-IR), far-IR, and Raman spectra are presented for the distinct (meta)stable phases of the flexible metal–organic framework MIL-53(Al). Static density functional theory (DFT) simulations are performed, allowing for the identification of all IR-active modes, which is unprecedented in the low-frequency region. A unique vibrational fingerprint is revealed, resulting from aluminum-oxide backbone stretching modes, which can be used to clearly distinguish the IR spectra of the closed- and large-pore phases. Furthermore, molecular dynamics simulations based on a DFT description of the potential energy surface enable determination of the theoretical Raman spectrum of the closed- and large-pore phases for the first time. An excellent correspondence between theory and experiment is observed. Both the low-frequency IR and Raman spectra show major differences in vibrational modes between the closed- and large-pore phases, indicating changes in lattice dynamics between the two structures. In addition, several collective modes related to the breathing mechanism in MIL-53(Al) are identified. In particular, we rationalize the importance of the trampoline-like motion of the linker for the phase transition.

Discovery of a novel, large pore phase in a bimetallic Al/V metal–organic framework

A new series of bimetallic COMOC-2(V)/DUT-5(Al) frameworks are developed and fully characterized. Electron paramagnetic resonance and transmission electron microscopy confirm the homogeneous dispersion of Al/V in the entire framework. The study of the flexibility by means of CO2 pressure dependent XRPD and high pressure sorption reveals the co-existence of two different large pore phases and a narrow pore phase in the entire pressure regime.

A fluorine-containing hydrophobic covalent triazine framework with excellent selective CO2 capture performance

In this article, a set of fluorine functionalized covalent triazine-based frameworks have been designed and synthesized with 2,2′,3,3′,5,5′,6,6′-octafluoro-4,4′-biphenyldicarbonitrile as the monomer under typical ionothermal conditions. A prominent defluorination process during synthesis etches the networks to release CFn, resulting in a significant loss of fluorine and carbon. Notably, the synergistic effects of polar C–F bonds and rich CO2-philic N sites bestow upon the framework an excellent H2 uptake (1.77 wt%, 77 K and 1 bar) as well as a significantly high CO2 adsorption capacity (5.98 mmol g−1, at 273 K and 1 bar), surpassing all related CTF materials measured under identical conditions that have been reported in the literature to date. Additionally, the material also exhibits a high CO2/N2 selectivity of 31 as predicted by the Henry model. The hydrophobicity of the CTF materials has been significantly enhanced owing to the incorporation of hydrophobic fluorine groups, which was further confirmed by ambient water vapor sorption.