Structural study of Ni- or Mg-based complexes incorporated within UiO-66-NH2 framework and their impact on hydrogen sorption properties

• Mg- and Ni-acetylacetonate molecules embedded in the pores of UiO-66-NH2 by PSM.
• Molecules of complexes interact with framework only by van der Waals interactions.
• Type/structure of deposited metal-complex impact hydrogen enthalpy of adsorption.

Nickel and magnesium acetylacetonate molecular complexes were post-synthetically incorporated into microporous zirconium-based MOF (UiO-66-NH2) in order to introduce active open-metal sites for hydrogen sorption. Elemental analysis, nitrogen physisorption and DFT calculations revealed that 5 molecules of Ni(acac)2 or 2 molecules of Mg(acac)2 were incorporated into one unit cell of UiO-66-NH2. 1H–13C CPMAS and 1H MAS NMR spectroscopy showed that, although embedded within the pores, both Ni- and Mg-complexes interacted with the UiO-66-NH2 framework only through weak van der Waals bonds. Inclusion of metal complexes led to the decrease of hydrogen sorption capacities in Ni-modified as well as in Mg-modified samples in comparison with the parent UiO-66-NH2. The isosteric hydrogen adsorption enthalpy slightly increased in the case of Ni-modified material, but not in the case of Mg-modified analogue.

A post-synthesis impregnation of Mg- and Ni-acetylacetonate complexes performed on zirconium-based MOF UiO-66-NH2 does influence the hydrogen sorption performance with respect to the parent matrix. The structural study revealed that Mg- and Ni-acetylacetonate molecules interact with zirconium-terephthalate framework only by weak interactions and they are not covalently bonded to aminoterephthalate ligand. Still, they remain confined into the pores even after hydrogen sorption experiments.Figure optionsDownload as PowerPoint slide