posted on 2022-02-17, 20:45authored byNabanita Chatterjee, Clive L. Oliver
Four two-dimensional (2D), fluorinated
metal–organic frameworks
(MOFs), [Cu(hfipbb)(DMF)]n·0.5(DMF)n (1), [Cu(hfipbb)(DEF)]n (2), [Cu3(hfipbb)3(DMA)3]n·6(DMA)n·2(H2O)n (3), and [Cu2(hfipbb)2(DEA)2]n·2(DEA)n·2(H2O)n (4), have been synthesized where hfipbb = 4,4′-(hexafluoroisopropylidene)bis(benzoate),
DMF = N,N′-dimethylformamide,
DEF = N,N′-diethylformamide,
DMA = N,N′-dimethylacetamide,
and DEA = N,N′-diethylacetamide.
The choice of either a formamide or acetamide solvent ligand leads
to a 2D, doubly interpenetrated (1 and 2) or noninterpenetrated (3 and 4) MOF structure.
Despite their lower potential void spaces, the doubly interpenetrated
structures have superior carbon dioxide and hydrogen sorption properties.
Their 195 K CO2 sorption isotherms display inflection points,
followed by ∼3-fold increases in their sorption capacities
and very large extents of hysteretic behavior. This shows that small
changes in the identity of the ligated solvent ligand can affect whether
the resulting MOF is interpenetrated or noninterpenetrated and so
drastically affect the sorption properties. In addition, the activated
phase of a fifth MOF, synthesized through DMF ligand exchange with
water in 1 (1W), does not display an inflection
point and subsequent increased CO2 sorption at 195 K, despite
having the same degree of interpenetration, showing that even more
subtle differences in the desolvated phases can lead to marked differences
in their sorption behavior.