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Porous metal–organic polyhedra: morphology, porosity, and guest binding

DOI: 10.1021/acs.inorgchem.0c01935 DOI Help

Authors: Stephen P. Argent (University of Nottingham) , Ivan Da Silva (ISIS Facility) , Alex Greenaway (University of Nottingham; Research Complex at Harwell) , Mathew Savage (University of Manchester) , Jack Humby (University of Manchester) , Andrew J. Davies (University of Nottingham) , Harriott Nowell (Diamond Light Source) , William Lewis (University of Nottingham) , Pascal Manuel (ISIS Facility) , Chiu C. Tang (Diamond Light Source) , Alexander J. Blake (University of Nottingham) , Michael W. George (University of Nottingham) , Alexander V. Markevich (University of Nottingham; University of Vienna) , Elena Besley (University of Nottingham) , Sihai Yang (University of Nottingham; University of Manchester) , Neil R. Champness (University of Nottingham) , Martin Schroeder (University of Nottingham; University of Manchester)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Inorganic Chemistry

State: Published (Approved)
Published: October 2020
Diamond Proposal Number(s): 861 , 11622 , 15833 , 9443

Open Access Open Access

Abstract: Designing porous materials which can selectively adsorb CO2 or CH4 is an important environmental and industrial goal which requires an understanding of the host–guest interactions involved at the atomic scale. Metal–organic polyhedra (MOPs) showing permanent porosity upon desolvation are rarely observed. We report a family of MOPs (Cu-1a, Cu-1b, Cu-2), which derive their permanent porosity from cavities between packed cages rather than from within the polyhedra. Thus, for Cu-1a, the void fraction outside the cages totals 56% with only 2% within. The relative stabilities of these MOP structures are rationalized by considering their weak nondirectional packing interactions using Hirshfeld surface analyses. The exceptional stability of Cu-1a enables a detailed structural investigation into the adsorption of CO2 and CH4 using in situ X-ray and neutron diffraction, coupled with DFT calculations. The primary binding sites for adsorbed CO2 and CH4 in Cu-1a are found to be the open metal sites and pockets defined by the faces of phenyl rings. More importantly, the structural analysis of a hydrated sample of Cu-1a reveals a strong hydrogen bond between the adsorbed CO2 molecule and the Cu(II)-bound water molecule, shedding light on previous empirical and theoretical observations that partial hydration of metal−organic framework (MOF) materials containing open metal sites increases their uptake of CO2. The results of the crystallographic study on MOP–gas binding have been rationalized using DFT calculations, yielding individual binding energies for the various pore environments of Cu-1a.

Journal Keywords: Ligands; Crystal structure; Molecules; Physical and chemical processes; Materials

Subject Areas: Materials, Chemistry

Instruments: I11-High Resolution Powder Diffraction , I19-Small Molecule Single Crystal Diffraction

Other Facilities: WISH beamline at ISIS; 11.3.1 at ALS