Background 5448 3.2. Transition Metal Helicate Templation 5449 3.3. "All-in-One" Approaches to Molecular Solomon Links 5450 4. Borromean Rings 5452 4.1. Background 5452 4.2. The "Ring-in-Ring" Approach to Molecular Borromean Rings 5453 4.3. "All-in-One" Approaches to Molecular Borromean Rings 5455 5. More Complex Entities 5457 6. Conclusions 5458 Author Information 5459 Biographies 5459 Acknowledgment 5459 References 5459

Metal-organic frameworks (MOFs) represent [1] an extensive class of porous crystals in which organic struts link metalcontaining clusters. The success in controlling the functionality and structure of MOFs has led to numerous applications, [2] most notably gas adsorption, [3] storage of clean gas fuels, [4] catalysis, [5] separations, [6] and drug delivery. [7] However, the vast majority of MOFs described to date are composed of organic struts derived from non-renewable petrochemical feedstocks and transition metals. The challenge in preparing MOFs from natural products lies in the inherent asymmetry of the building units, which are not amenable to crystallization in the form of highly porous frameworks. Herein, we report a strategy to overcome this problem using g-cyclodextrin (g-CD), a symmetrical cyclic oligosaccharide that is mass-produced enzymatically from starch [8] and comprised of eight asymmetric a-1,4-linked dglucopyranosyl residues. These g-CD building units are then linked by potassium ions, in aqueous media at ambient temperature and pressure, to form a body-centered cubic structure, termed CD-MOF-1, which has the empirical formula [(C 48 H 80 O 40 )(KOH) 2 ] n . CD-MOFs can be prepared entirely from edible ingredients: combining food-grade g-CD with salt substitute (KCl) or potassium benzoate (food additive E212) in bottled water and Everclear grain spirit (EtOH) yields porous frameworks which constitute edible MOFs.While there have been a few reports of MOFs assembled from amino acids, [9] nucleobases, [7a, 10] peptides, [11] magnesium formates, [12] and metal glutarates, [13] examples of these materials are not common despite the rapidly growing desire to fabricate MOFs from naturally available building blocks. We suspect that the key to our success in assembling CD-MOFs lies in the symmetric arrangement (C 8 ) within the g-CD torus of eight asymmetric (C 1 ) a-1,4-linked d-glucopyranosyl residues and the ready availability of g-CD as a chiral molecular building block (Figure 1). CD-MOF-1 was prepared by combining 1.0 equiv of g-CD with 8.0 equiv of KOH in aqueous solution, followed by vapor diffusion of MeOH into the solution during 2-7 days, resulting in colorless, cubic, single crystals, suitable for X-ray crystallography, in approximately 70 % yield. Other CD-MOFs were readily obtained using salts of Na + , Rb + , and Cs + , giving rise to an extensive new family of porous materials. A complete list of metal salts employed to form CD-MOFs and the full synthesis of CDMOFs are provided in Section S2 of the Supporting Information.The X-ray crystal structure of CD-MOF-1 [14] reveals that eight-coordinate K + ions not only assist in the assembly of (g-CD) 6 cubes (Figure 2 a,b), wherein six g-CD units occupy the faces of a cube, but they also serve to link these cubes together in a three-dimensional array which extends throughout the crystal (Figure 2 c). The (g-CD) 6 repeating motifs adopt a body-centered cubic packing arrangement wherein each symmetrically equivalent K + ion links two co...

Alkanediamines serve as neutral guests for the recently discovered host pillar[5]arene. The proposed [2]pseudorotaxane nature of the superstructure of the 1:1 host-guest complexes is supported by the template-directed synthesis of a related [2]rotaxane. A synthetic route to monofunctional pillar[5]arenes has also been developed, allowing for the creation of a fluorescent sensor for alkylamine binding. The precursors to this host could act as starting points for a large library of monofunctional pillar[5]arene macrocycles.

The efficient capture and storage of gaseous CO(2) is a pressing environmental problem. Although porous metal-organic frameworks (MOFs) have been shown to be very effective at adsorbing CO(2) selectively by dint of dipole-quadruple interactions and/or ligation to open metal sites, the gas is not usually trapped covalently. Furthermore, the vast majority of these MOFs are fabricated from nonrenewable materials, often in the presence of harmful solvents, most of which are derived from petrochemical sources. Herein we report the highly selective adsorption of CO(2) by CD-MOF-2, a recently described green MOF consisting of the renewable cyclic oligosaccharide γ-cyclodextrin and RbOH, by what is believed to be reversible carbon fixation involving carbonate formation and decomposition at room temperature. The process was monitored by solid-state (13)C NMR spectroscopy as well as colorimetrically after a pH indicator was incorporated into CD-MOF-2 to signal the formation of carbonic acid functions within the nanoporous extended framework.

Metal-organic frameworks (MOFs) have received particular attention over the last 20 years as a result of their attractive properties offering potential applications in a number of areas. Typically, these characteristics are tuned by functionalisation of the bulk of the MOF material itself. This Feature Article focuses instead on modification of MOF particles at their surfaces only, which can also offer control over the bulk properties of the material. The differing surface modification techniques available to the synthetic chemist will be discussed, with a focus on the effect of surface modification of MOFs on their fundamental properties and application in adsorption, catalysis, drug delivery and other areas.