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We report the use of nitrone C–H groups as hydrogen bond donors for binding anions. Acyclic anion receptors with two nitrone moieties were synthesized by condensation reactions between aryl-aldehydes and m-phenylenedihydroxylamines. The solid-state structure of dinitrones revealed C–H⋯O hydrogen bonds. Anion binding properties were investigated using NMR titration with halide and phosphate salts. [ABSTRACT FROM AUTHOR]

Programming the synthesis and self-assembly of molecules is a compelling strategy for the bottom-up fabrication of ordered materials. To this end, shape-persistent macrocycles were designed with alternating carbazoles and triazoles to program a one-pot synthesis and to bind large anions. The macrocycles bind anions that were once considered too weak to be coordinated, such as PF6−, with surprisingly high affinities ( β2=1011 M−2 in 80:20 chloroform/methanol) and positive cooperativity, α=(4 K2/ K1)=1200. We also discovered that the macrocycles assemble into ultrathin films of hierarchically ordered tubes on graphite surfaces. The remarkable surface-templated self-assembly properties, as was observed by using scanning tunneling microscopy, are attributed to the complementary pairing of alternating triazoles and carbazoles inscribed into both the co-facial and edge-sharing seams that exist between shape-persistent macrocycles. The multilayer assembly is also consistent with the high degree of molecular self-association observed in solution, with self-association constants of K=300 000 M−1 (chloroform/methanol 80:20). Scanning tunneling microscopy data also showed that surface assemblies readily sequester iodide anions from solution, modulating their assembly. This multifunctional macrocycle provides a foundation for materials composed of hierarchically organized and nanotubular self-assemblies. [ABSTRACT FROM AUTHOR]

Anions stabilize stacking of C5-symmetric macrocycles, called cyanostars, into dimers in solution and herein we demonstrate this stacking in solid-state crystals. We further show that this guest binding can be applied as a route to bilayer growth at the solution--graphite interface. [ABSTRACT FROM AUTHOR]

Since the discovery of crown ethers, macrocycles have been recognized as powerful platforms for supramolecular chemistry. Although their numbers and variations are now legion, macrocycles that are simple to make using high-yielding reactions in one pot and on the multigram scale are rare. Here we present such a discovery obtained during the creation of a C5-symmetric cyanostilbene 'campestarene' macrocycle, cyanostar, that employs Knoevenagel condensations in the preparation of its cyanostilbene repeat unit. In the solid state, cyanostars form π-stacked dimers constituted of chiral P and M enantiomers. The electropositive central cavity stabilizes anions with CH hydrogen-bonding units that are activated by electron-withdrawing cyano groups. In solution, the cyanostar shows high-affinity binding as 2:1 sandwich complexes, log β2 ≈ 12 and ΔG ≈ −70 kJ mol−1, of large anions (BF4−, ClO4− and PF6−) usually considered weakly coordinating. The cyanostar's size preference allowed formation of an unprecedented [3]rotaxane templated around a dialkylphosphate. [ABSTRACT FROM AUTHOR]

Photoresponsive receptors allow users to modulate when and where molecular hosts can bind and release their targets. This capability was pioneered in biochemistry, trained on cations, and is only now emerging in the recognition chemistry of anions. This mini review outlines the five instances where anion receptors have been manipulated by light. Cylindrical, acyclic, and helical receptors have been integrated with azobenzenes, stiff-stilbenes, and dithienylethenes to generate modest-to-moderate changes in the binding affinities for various halides and polyatomic anions. The central design requirement involves choosing the appropriate photoswitch such that the two photostates can define two different organizations of the receptor, thus, enabling one state to bind better than the other. This challenge underscores the importance of analyzing the possible conformations, complexes, and stoichiometries that may be accessible by host and guest as a means to identify structures that will successfully elicit a switching response. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]