Nanoporous Carbohydrate Metal鈥揙rganic Frameworks

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• 作者：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 M. Z. Slawin ; J. Fraser Stoddart
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：January 11, 2012
• 年：2012
• 卷：134
• 期：1
• 页码：406-417
• 全文大小：826K
• 年卷期：v.134,no.1(January 11, 2012)
• ISSN：1520-5126

文摘

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鈥揼uest supramolecular chemistry in the 1970s and 1980s. The arrangement of 鈭扥CCO鈥?and 鈭扥CCN鈥?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 鈭扥CCO鈥?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 纬-cyclodextrin (纬-CD) is linked by coordination to Group IA and IIA metal cations to form metal鈥搊rganic 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 (纬-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 1200 m² g^鈥?, and (iii) capable of storing gases and small molecules within their pores. The fact that the 鈭扥CCO鈥?moieties of 纬-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 纬-CD tori are perfectly stacked in one dimension in a manner reminiscent of the structures of some 纬-CD solvates, but with added crystal stability imparted by metal鈥搃on 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.