Abstract
Supramolecular interactions are fundamental to host-guest binding in many chemical and biological processes. Direct visualization of such supramolecular interactions within host-guest systems is extremely challenging, but crucial to understanding their function. We report a comprehensive study that combines neutron scattering, synchrotron X-ray and neutron diffraction, and computational modelling to define the detailed binding at a molecular level of acetylene, ethylene and ethane within the porous host NOTT-300. This study reveals simultaneous and cooperative hydrogen-bonding, π···π stacking interactions and intermolecular dipole interactions in the binding of acetylene and ethylene to give up to 12 individual weak supramolecular interactions aligned within the host to form an optimal geometry for the selective binding of hydrocarbons. We also report the cooperative binding of a mixture of acetylene and ethylene within the porous host, together with the corresponding breakthrough experiments and analysis of adsorption isotherms of gas mixtures.
Highlights
Supramolecular interactions are fundamental to host-guest binding in chemical and biological processes
This study reveals the simultaneous and cooperative hydrogen-bonding, π···π stacking interactions and intermolecular dipole interactions in the binding of acetylene and ethylene to give up to twelve individual weak supramolecular interactions aligned within the host to form an optimal geometry for intelligent, selective binding of hydrocarbons
Host-guest systems involving primarily soft supramolecular interactions usually lead to serious positional disorder of the guest molecules, and hydrogen atoms involved in these binding processes are not readily seen or defined from crystallography studies,13,14 leading to problems in defining the dynamics and motions of such host-guest systems
Summary
Gas adsorption experiment: CH4, C2H2, C2H4, and C2H6 sorption isotherms were recorded at 273-303 K on an IGA-003 system under ultra-high vacuum. Y. et al Metal-organic polyhedral frameworks: high H2 adsorption capacities and neutron powder diffraction studies. X. et al High capacity hydrogen adsorption in Cu(II) tetracarboxylate framework materials: the role of pore size, ligand functionalization, and exposed metal sites. D. et al Hydrocarbon separations in a metal-organic framework with open iron(II) coordination sites. M. Gas adsorption sites in a large-pore metal-organic framework. 17 Xiang, S.-C. et al Rationally tuned micropores within enantiopure metal-organic frameworks for highly selective separation of acetylene and ethylene. B. et al Introduction of π-complexation into porous aromatic framework for highly selective adsorption of ethylene over ethane. Metal-organic frameworks with potential for energy-efficient adsorptive separation of light hydrocarbons. F. et al Diffusion of binary CO2/CH4 mixtures in the MIL-47(V) and MIL-53(Cr) metal−organic framework type solids: a combination of neutron scattering measurements and molecular dynamics simulations.
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