Tuning the Mix

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Science  18 May 2012:
Vol. 336, Issue 6083, pp. 782
DOI: 10.1126/science.336.6083.782-b

Metal organic framework materials hook together metal ions or clusters, using organic linkers to make crystalline compounds with two- or three-dimensional porosity. The zeolitic imidazolate framework (ZIF) subset of this class of materials has imidazole molecules as linkers and forms structures analogous to the aluminosilicate lattices of zeolites. In addition to molecular sieving properties, ZIFs can manifest a gating phenomenon whereby interaction with adsorbates leads to an increase in guest uptake. This gating is caused by a rotation of the linker molecules. Thompson et al. explored the effects of making ZIFs with a mixture of linking molecules, based on ZIF-8, ZIF-90, and ZIF-7 parent materials, which use 2-methylimidazole, carboxaldehyde-2-imidazole, and benzimidazole linkers, respectively. In particular, ZIF-8 can selectively remove carbon dioxide from a complex mixture of gases, so finding ways to enhance its properties without reducing its stability is of practical importance. Changes in the gate-opening phenomenon emerged for varying specific compositions. Overall, the results indicate that it may be possible to tune the fine structure of a ZIF framework at the synthesis stage, rather than through complicated postsynthetic modifications.

Chem. Mater. 24, 10.1021/cm3006953 (2012).

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