Selective pore opening and gating of the pillared layer metal-organic framework DUT-8(Ni) upon liquid phase multi-component adsorption

The switchable metal-organic framework Ni-2(ndc)(2)dabco (ndc - 2,6-naphthalenedicarboxylate, dabco - 1,4-diazabicyclo[2.2.2]octane), known as DUT-8(Ni) (DUT - Dresden University of Technology) is demonstrated to selectively respond with a crystal structure transformation and subsequent pore opening after exposure specifically to polar aprotic solvents, while a series of representative alcohols does not induce pore opening. A variety of more than 20 representative solvents was investigated with respect to liquid phase adsorption. The host-guest interaction is crucial for the transformation process directing the behaviour of the framework in response to the solvents with specific polarity and chemical constitution. The concentration dependence shown exemplarily for N,N-dimethylformamide/ethanol mixtures was monitored by UV-Vis, GC-MS and powder X-ray diffraction. In these binary mixtures, the adsorption proceeds along a prototypical gate opening isotherm, showing a pronounced step-like switching at a characteristic threshold concentration. Vapour adsorption isotherms confirm the highly selective recognition process and characteristic gating pressures observed depending on the guest-host interaction.