Nanoporous Carbohydrate Metal–Organic Frameworks

Forgan, Ross S.,Smaldone, Ronald A.,Gassensmith, Jeremiah J.,Furukawa, Hiroyasu,Cordes, David B.,Li, Qiaowei,Wilmer, Christopher E.,Botros, Youssry Y.,Snurr, Randall Q.,Slawin, Alexandra M. Z.,Stoddar American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.1

<P>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 γ-cyclodextrin (γ-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 (γ-CD)<SUB>6</SUB> 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 m<SUP>2</SUP> g<SUP>–1</SUP>, and (iii) capable of storing gases and small molecules within their pores. The fact that the −OCCO– moieties of γ-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<SUP>+</SUP>, Cs<SUP>+</SUP>, and Sr<SUP>2+</SUP>. This lack of preorganization is expressed emphatically in the case of Cs<SUP>+</SUP>, 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 γ-CD tori are perfectly stacked in one dimension in a manner reminiscent of the structures of some γ-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.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-1/ja208224f/production/images/medium/ja-2011-08224f_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja208224f'>ACS Electronic Supporting Info</A></P>

Mechanostereochemistry and the mechanical bond

Barin, Gokhan,Forgan, Ross S.,Stoddart, J. Fraser The Royal Society 2012 Proceedings, Mathematical, physical, and engineeri Vol.468 No.2146

<P> The chemistry of mechanically interlocked molecules (MIMs), in which two or more covalently linked components are held together by <I>mechanical bonds</I> , has led to the coining of the term <I>mechanostereochemistry</I> to describe a new field of chemistry that embraces many aspects of MIMs, including their syntheses, properties, topologies where relevant and functions where operative. During the rapid development and emergence of the field, the synthesis of MIMs has witnessed the forsaking of the early and grossly inefficient statistical approaches for template-directed protocols, aided and abetted by molecular recognition processes and the tenets of self-assembly. The resounding success of these synthetic protocols, based on templation, has facilitated the design and construction of artificial molecular switches and machines, resulting more and more in the creation of integrated functional systems. This review highlights (i) the range of template-directed synthetic methods being used currently in the preparation of MIMs; (ii) the syntheses of topologically complex knots and links in the form of stable molecular compounds; and (iii) the incorporation of bistable MIMs into many different device settings associated with surfaces, nanoparticles and solid-state materials in response to the needs of particular applications that are perceived to be fair game for mechanostereochemistry. </P>

Donor–acceptor molecular figures-of-eight

Boyle, Megan M.,Forgan, Ross S.,Friedman, Douglas C.,Gassensmith, Jeremiah J.,Smaldone, Ronald A.,Stoddart, J. Fraser,Sauvage, Jean-Pierre Royal Society of Chemistry 2011 Chemical communications Vol.47 No.43

<P>The intermolecular template-directed synthesis, separation and characterisation of two constitutional isomers that are self-complexing donor–acceptor [1]rotaxanes has been achieved by click chemistry, starting from a π-electron deficient tetracationic cyclophane containing two azide functions and a π-electron rich 1,5-dioxynaphthalene-containing polyether chain terminated by propargyl groups.</P> <P>Graphic Abstract</P><P>The intermolecular template-directed synthesis, separation and characterisation of two constitutional isomers that are self-complexing donor–acceptor [1]rotaxanes has been achieved by click chemistry. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1cc15333a'> </P>

Finite gap behaviour in the superconductivity of the ‘infinite layer’ n-doped high-<i>T</i>_c superconductor Sr_0.9La_0.1CuO₂

White, J S,Forgan, E M,Laver, M,Hä,fliger, P S,Khasanov, R,Cubitt, R,Dewhurst, C D,Park, M-S,Jang, D-J,Lee, H-G,Lee, S-I IOP Pub 2008 Journal of physics, an Institute of Physics journa Vol.20 No.10

<P>We report on the first small-angle neutron scattering measurements from the flux line lattice (FLL) in the high-<I>T</I><SUB>c</SUB> cuprate superconductor Sr<SUB>0.9</SUB>La<SUB>0.1</SUB>CuO<SUB>2</SUB>. Using a polycrystalline sample, the scattered intensity decreases monotonically with scattering angle away from the undiffracted beam, independently of the azimuthal angle around the beam. The absence of clear peaks in the intensity suggests the establishment of a highly disordered FLL within the grains. We find that the intensity distribution may be represented by the form factor for a single flux line in the London approximation, with some contribution from crystal anisotropy. Most interestingly however, we find that, over the observed field range, the temperature dependence of the diffracted intensity is best represented by s-wave pairing, with lower limits of the gap values being very similar to the Bardeen–Cooper–Schrieffer value of Δ(0) = 1.76<I> k</I><SUB>B</SUB><I>T</I><SUB>c</SUB>. However, a qualitative consideration of corrections to the observed intensity suggests that these gap values are likely to be higher, implying strong-coupling behaviour.</P>

Polyporous Metal-Coordination Frameworks

Gassensmith, Jeremiah J.,Smaldone, Ronald A.,Forgan, Ross S.,Wilmer, Christopher E.,Cordes, David B.,Botros, Youssry Y.,Slawin, Alexandra M. Z.,Snurr, Randall Q.,Stoddart, J. Fraser American Chemical Society 2012 ORGANIC LETTERS Vol.14 No.6

<P>Starting from a chiral building block?α-cyclodextrin?and rubidium salts, the crystallization of a complex of chiral helices, which constitute a “green” porous coordination polymer, has been realized. Cyclodextrin molecules coordinated by rubidium ions form porous, infinitely long left-handed helical channels, interdigitated with each other. A theoretical examination of the potential of this new material to act as a medium for chiral separation is presented.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/orlef7/2012/orlef7.2012.14.issue-6/ol300199a/production/images/medium/ol-2012-00199a_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ol300199a'>ACS Electronic Supporting Info</A></P>

Strong and Reversible Binding of Carbon Dioxide in a Green Metal–Organic Framework

Gassensmith, Jeremiah J.,Furukawa, Hiroyasu,Smaldone, Ronald A.,Forgan, Ross S.,Botros, Youssry Y.,Yaghi, Omar M.,Stoddart, J. Fraser American Chemical Society 2011 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.133 No.39

<P>The efficient capture and storage of gaseous CO<SUB>2</SUB> is a pressing environmental problem. Although porous metal–organic frameworks (MOFs) have been shown to be very effective at adsorbing CO<SUB>2</SUB> 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<SUB>2</SUB> 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 <SUP>13</SUP>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.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2011/jacsat.2011.133.issue-39/ja206525x/production/images/medium/ja-2011-06525x_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja206525x'>ACS Electronic Supporting Info</A></P>