Nanoporous Carbohydrate Metal-Organic Frameworks

Ross S. Forgan, Ronald A. Smaldone, Jeremiah J. Gassensmith, Hiroyasu Furukawa, David B. Cordes, Qiaowei Li, Christopher E. Wilmer, Youssry Y. Botros, Randall Q. Snurr, Alexandra Martha Zoya Slawin, J. Fraser Stoddart

Research output: Contribution to journalArticlepeer-review

189 Citations (Scopus)

Abstract

The binding of alkali and alkaline earth metal cations by macrocyclic and diazamacrobicyclic polyethers, composed of ordered arrays of hard oxygen (and nitrogen) donor atoms, underpinned the development of host-guest supramolecular chemistry in the 1970s and 1980s. The arrangement of -OCCO- and -OCCN- chelating units in these preorganized receptors, including, but not limited to, crown ethers and cryptands, is responsible for the very high binding constants observed for their complexes with Group IA and IIA cations. The cyclodextrins (CDs), cyclic oligosaccharides derived microbiologically from starch, also display this -OCCO- bidentate motif on both their primary and secondary faces. The self-assembly, in aqueous alcohol, of infinite networks of extended structures, which have been termed CD-MOFs, wherein gamma-cyclodextrin (gamma-CD) is linked by coordination to Group IA and IIA metal cations to form metal-organic frameworks (MOFs), is reported. CD-MOF-1 and CD-MOF-2, prepared on the gram-scale from KOH and RbOH, respectively, form body-centered cubic arrangements of (gamma-CD)(6) cubes linked by eight-coordinate alkali metal cations. These cubic CD-MOFs are (i) stable to the removal of solvents, (ii) permanently porous, with surface areas of similar to 1200 m(2) g(-1), and (iii) capable of storing gases and small molecules within their pores. The fact that the -OCCO- moieties of gamma-CD are not prearranged in a manner conducive to encapsulating single metal cations has led to our isolating other infinite frameworks, with different topologies, from salts of Na+, Cs+, and Sr2+. This lack of preorganization is expressed emphatically in the case of Cs+, where two polymorphs assemble under identical conditions. CD-MOF-3 has the cubic topology observed for CD-MOFs 1 and 2, while CD-MOF-4 displays a channel structure wherein gamma-CD tori are perfectly stacked in one dimension in a manner reminiscent of the structures of some gamma-CD solvates, but with added crystal stability imparted by metal-ion coordination. These new MOFs demonstrate that the CDs can indeed function as ligands for alkali and alkaline earth metal cations in a manner similar to that found with crown ethers. These inexpensive, green, nanoporous materials exhibit absorption properties which make them realistic candidates for commercial development, not least of all because edible derivatives, fit for human consumption, can be prepared entirely from food-grade ingredients.

Original languageEnglish
Pages (from-to)406-417
Number of pages12
JournalJournal of the American Chemical Society
Volume134
Issue number1
DOIs
Publication statusPublished - 11 Jan 2012

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