Solvent-switchable continuous-breathing behaviour in a diamondoid metal-organic framework and its influence on CO2 vs CH4 selectivity

Carrington, Elliot J. and McAnally, Craig A. and Fletcher, Ashleigh J. and Thompson, Stephen P. and Warren, Mark and Brammer, Lee (2017) Solvent-switchable continuous-breathing behaviour in a diamondoid metal-organic framework and its influence on CO2 vs CH4 selectivity. Nature Chemistry, 9 (9). pp. 882-889. ISSN 1755-4330 (https://doi.org/10.1038/nchem.2747)

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Abstract

Flexible metal-organic frameworks (MOFs) are class of porous crystalline materials that show a structural change upon external stimulus. Understanding this behaviour underpins the design of new responsive porous materials that can target specific applications such as gas separation, molecular sensing, catalysis and drug delivery. Most flexible MOFs undergo well-defined crystallographic transitions between open and closed-pore forms known as “breathing”. By contrast, continuous flexible behaviour is rare and detailed characterisation is very limited. Here we report a continuous breathing mechanism that can be followed by single-crystal diffraction in a MOF with a diamondoid network, (Me2NH2)[In(ABDC)2] (ABDC = 2-aminobenzene-1,4-dicarboxylate) (1). The mechanism is highly solvent-dependent and desolvation from different pore-solvent content enables access to two polymorphic desolvated forms with very different pore openings. These two forms exhibit markedly different gas adsorption capacities and different CO2 vs CH4 selectivity. Partial desolvation introduces a gating pressure associated with CO2 adsorption, absent in the desolvated forms, leading to a combination of stepped and continuous breathing of the framework.

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