Abstract
A new, air-stable, permanently porous uranium(iv) metal-organic framework U(bdc)2 (1, bdc2- = 1,4-benzenedicarboxylate) was synthesized and its H2 and CH4 adsorption properties were investigated. Low temperature adsorption isotherms confirm strong adsorption of both gases in the framework at low pressures. In situ gas-dosed neutron diffraction experiments with different D2 loadings revealed a rare example of cooperative framework contraction (ΔV = -7.8%), triggered by D2 adsorption at low pressures. This deformation creates two optimized binding pockets for hydrogen (Q st = -8.6 kJ mol-1) per pore, in agreement with H2 adsorption data. Analogous experiments with CD4 (Q st = -24.8 kJ mol-1) and N,N-dimethylformamide as guests revealed that the binding pockets in 1 adjust by selective framework contractions that are unique for each adsorbent, augmenting individual host-guest interactions. Our results suggest that the strategic combination of binding pockets and structural flexibility in metal-organic frameworks holds great potential for the development of new adsorbents with an enhanced substrate affinity.
Highlights
Metal–organic frameworks are a class of chemically-robust, porous, and o en rigid materials, composed of metal ions or clusters connected by bridging organic linkers.[1,2,3,4]
The physical and chemical properties of these materials are highly tunable based on choice of metal and linker, and metal–organic frameworks have been proposed for a wealth of applications,[5,6,7,8,9] including catalysis,[10,11,12,13,14,15] sensing,[16,17,18] carbon capture,[19,20,21,22,23] gas separations,[24,25,26] and gas storage.[27,28,29,30,31]
Structural characterization of Cu2(btc)[3] dosed with low pressures of CD4 con rmed that methane preferably adsorbs at the binding pockets inside small octahedral cages of the framework, rather than through direct interactions at the copper(II) open metal sites
Summary
Metal–organic frameworks are a class of chemically-robust, porous, and o en rigid materials, composed of metal ions or clusters connected by bridging organic linkers.[1,2,3,4] The physical and chemical properties of these materials are highly tunable based on choice of metal and linker, and metal–organic frameworks have been proposed for a wealth of applications,[5,6,7,8,9] including catalysis,[10,11,12,13,14,15] sensing,[16,17,18] carbon capture,[19,20,21,22,23] gas separations,[24,25,26] and gas storage.[27,28,29,30,31] Metal–organic frameworks have attracted particular interest as candidate gas storageTwo main strategies have been developed to achieve strong binding of H2 and CH4 in metal–organic frameworks. Structural characterization of Cu2(btc)[3] dosed with low pressures of CD4 con rmed that methane preferably adsorbs at the binding pockets inside small octahedral cages of the framework, rather than through direct interactions at the copper(II) open metal sites.
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