title: Adsorption of N/S heterocycles in the flexible metal-organic framework MIL-53(Fe(III)) studied by in situ energy dispersive X-ray diffraction.
abstract: The adsorption of N/S-containing heterocyclic organic molecules in the flexible iron(III) terephthalate MIL-53, Fe(III)(OH)(0.6)F(0.4)(O2C-C6H4-CO2)·(H2O), from the liquid phase was studied with in situ energy dispersive X-ray diffraction (EDXRD), in order to follow the adsorption-induced expansion of the structure. For comparison with the diffraction data, liquid phase adsorption isotherms were recorded for uptake of benzothiophene, benzothiazole and indole in isopropanol and in heptane. The solvent not only influences pore opening but is also a competing guest. The in situ EDXRD experiments allow the kinetics of guest uptake and the competition with solvent to be monitored directly. Indole uptake is limited; this adsorbate is barely capable of opening the closed, either hydrated or dehydrated, MIL-53(Fe) structure, or of penetrating the isopropanol-containing material in the concentration range under study. When isopropanol is used as a solvent, the guest molecules benzothiophene and benzothiazole must be present at a certain threshold concentration before substantial adsorption into the metal-organic framework takes place, eventually resulting in full opening of the structure. The fully expanded structures of benzothiophene or benzothiazole loaded MIL-53(Fe) materials have Imcm symmetry and a unit cell volume of ca. 1600 Å(3), and upon uptake of the guest molecules by the closed form (unit cell volume ~1000 Å(3)) no intermediate crystalline phases are seen. Successful uptake by MIL-53(Fe) requires that the adsorbate is primarily a good hydrogen bond acceptor; additionally, based on UV-visible spectroscopy, a charge-transfer interaction between the S atoms of benzothiophene and the aromatic rings in the MOF pore wall is proposed.
authors: Centre for Surface Chemistry and Catalysis, Katholieke Universiteit Leuven, Arenbergpark 23, B-3001 Leuven, Belgium.
authors: Ben
authors: B
authors: Van de Voorde
authors: Alexis S
authors: AS
authors: Munn
authors: Nathalie
authors: N
authors: Guillou
authors: Franck
authors: F
authors: Millange
authors: Dirk E
authors: DE
authors: De Vos
authors: Richard I
authors: RI
authors: Walton
mesh_terms: D000327:Adsorption; D005290:Ferric Compounds / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000737:chemistry*; D013499:Surface Properties; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds; D006571:Heterocyclic Compounds