Functionalization in Flexible Porous Solids: Effects on the Pore Opening and the Host−Guest Interactions

Abstract

The synthesis on the gram scale and characterization of a series of flexible functionalized iron terephthalate MIL-53(Fe) type solids are reported. Chemical groups of various polarities, hydrophilicities, and acidities (-Cl, -Br, -CF(3), -CH(3), -NH(2), -OH, -CO(2)H) were introduced through the aromatic linker, to systematically modify the pore surface. X-ray powder diffraction (XRPD), molecular simulations, thermogravimetric analyses, and in situ IR and (57)Fe Mössbauer spectrometries indicate some similarities with the pristine MIL-53(Fe) solid, with the adoption of the narrow pore form for all solids in both the hydrated and dry forms. Combined XRPD and computational structure determinations allow concluding that the geometry of the pore opening is predominantly correlated with the intraframework interactions rather than the steric hindrance of the substituent. Only (MIL-53(Fe)-(CF(3))(2)) exhibits a nitrogen accessible porosity (S(BET) approximately 100 m(2) g(-1)). The adsorption of some liquids leads to pore openings showing some very specific behaviors depending on the guest-MIL-53(Fe) framework interactions, which can be related to the energy difference between the narrow and large pore forms evaluated by molecular simulation.

Synthesis and Structural Flexibility of a Series of Copper(II) Azolate‐Based Metal–Organic Frameworks

“…While the exact mechanism giving rise to the solvent substitution is currently unknown, one origin for the different behavior may lie in the strength of the binding of the bridging solvent molecules as a result of electronic effects and steric demands imposed by the various bridging ligands. Similar effects have been reported recently by Férey and co-workers for derivatives of the MIL-53(Fe) structure type, [14] which exhibited linker-dependent flexibility upon immersion in a variety of organic solvents. Ongoing studies will be directed towards gaining a more detailed understanding of the mechanism of solvent substitution and effects on the resulting gas sorption properties.…”

Rationally tuned micropores within enantiopure metal-organic frameworks for highly selective separation of acetylene and ethylene

“…The pores within porous MOFs, particularly those within isoreticular MOFs whose structures are pre-determined by the coordination geometries of the secondary building blocks, can be systematically modified by changing the organic bridging linkers and controlling the framework interpenetration [2][3][4][5] . Furthermore, the pore surfaces of porous MOFs can be functionalized by the immobilization of different recognition sites, such as open metal sites, Lewis basic/acidic sites and chiral pockets, to direct the recognition of small molecules [6][7][8][9][10][11][12][13][14] . Systematically tuning micropores can achieve size-specific encapsulation of small gas molecules, and immobilization of functional sites enables varying substrate interactions: microporous MOF materials have emerged as promising microporous media for the recognition and separation of small molecules [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] .…”

Effect of Diamine in Amine-Functionalized MIL-101 for Knoevenagel Condensation

“…These properties have led to a number of application potential in catalysis, gas storage, drug delivery and adsorptive separation. [7][8][9][10] One important challenge has to realize is funtionalization via incorporation of binding site or reactive centers for catalysis. The functionalization methods of metal organic frameworks (MOFs) in a wide range of applications are two possible approaches including pre-and postmodification with functional groups.…”