Reviving Chirality in Microporous Materials

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Science  14 May 2004:
Vol. 304, Issue 5673, pp. 929
DOI: 10.1126/science.304.5673.929d

Two routes are being pursued for creating chiral microporous materials from metal-organic frameworks for isomer-selective separations or catalysis. One is to use ligands that are already chiral. The other is to use less expensive achiral ligands and to induce chirality, typically as helicity within the structure, with chiral templates that can be desorbed and reused. However, the latter approach is often hampered by “collapse” of the material into a nonporous material after template removal.

Bradshaw et al. show that some “collapsed” structures can be revived by making a small change in the framework ligands. Frameworks based on Ni2+ complexes with btc (1,3,5-benzenetricarboxylate) and pyridine ligands formed interpenetrating networks of chiral helices under the direction of chiral propan-1,2-diol guests, but an amorphous nonporous material resulted after template removal. Nevertheless, reaction of this material with 3-methylpyridine created a thermally stable chiral microporous material; the same material could also be made directly by substituting 3-methylpyridine for pyridine in the original synthesis. Structural studies indicate that the change imparted by the methyl group led to small but significant stabilizing interactions; notably, the use of 4-methylpyridine did not stabilize the network. — PDS

J. Am. Chem. Soc. 10.1021/ja316420 (2004).

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