Anion receptors ditopic calix arenes

In an effort to impart selectivity and enhance complex stability for this class of anion receptor novel ditopic biscobaltocenium receptor molecules (Fig. 42) have been synthesized and their coordination and electrochemical properties have been studied (Beer et al., 1993f, 1995h). The two positively charged metallocene centres linked by various alkyl, aryl and calix[4]arene spacers... 

In an effort to produce selective anion spectroelectrochemical reagents the Lewis acidic redox-active cobalticinium unit and the redox- and photo-active ruthenium(II) bipyridyl moiety have recently been incorporated into calixarene host structural frameworks to produce novel calix[4]arene anion receptors which are extremely rare. The calix[4]arene ditopic anion receptor (22) containing two cobalticinium moieties was prepared as shown in Scheme 4 and its crystal structure is illustrated in (Fig 7). Proton NMR titration experiments suggested (22) acts as a ditopic anion receptor forming (22) 2X"(X = Cl",Br",N03, HS04") stoichiometric solution complexes. Analogous titration... 

Exotic calix[4]arene monotopic (23) and ditopic (24) anion receptors containing one and two ruthenium(II) bipyridyl moieties have been prepared (Schemes 5 and 6) and shown by NMR and cyclic voltammetry to bind and electrochemically recognise halide, dihydrogen phosphate and hydrogen sulphate anions. 

The stability of the polypyridyl rhenium(I) compounds mentioned above stimulated applications of this coordination chemistry. Thus, new heterotopic bis(calix[4]arene)rhenium(I) bipyridyl receptor molecules have been prepared and shown to bind a variety of anions at the upper rim and alkali metal cations at the lower rim. A cyclodextrin dimer, which was obtained by connecting two permethylated /3-cyclodextrins with a bipy ligand, was used for the preparation of a luminescent rhenium(I) complex. The system is discussed as a model conipound to study the energy transfer between active metal centers and a bound ditopic substrate. The fluorescence behavior of rhenium(I) complexes containing functionalized bipy ligands has been applied for the recognition of glucose. ... 

A ditopic receptor 71, comprising a semitubular calix[4]arene system [91] for cation recognition and urea moieties for anion recognition, was reported very recently. The complexation of sodium or potassium cations into the central ethylene glycol cavity invokes substantial enhancement of the binding strength (more than one order of magnitude) towards selected anions (halides, acetate). 

Beer. P.D. Hesek, D. Kingston. J.E. Smith, D.K. Stokes, S.E. Drew, M.G.B. Anion recognition by redox-responsive ditopic bis-cobaltocenium receptor molecules including a noVel calix[4]arene derivative that binds a dicarboxylate dianion. Organometallics 1995. 14. 3288. 

A ditopic receptor consisting of two calix[4]arene units linked by two ethylene chains at the lower rim for cation recognition and urea-based hydrogen-bonding recognition sites for anions, 40, has been developed by the group of Beer in the United Kingdom." ... 

The synthesis of functionalized calix[4]pyrroles able to accommodate ion pairs within their cavities was first approached by using crown ether-like polyether straps to link two of the four meso-csxhon atoms of the calix[4]pyrrole framework. The first of such ditopic systems, receptor 7, reported by Kim, Sessler, and coworkers, was designed to contain a the calix[4]arene crown-6-moiety for cesium cation recognition, while retaining a calix[4]pyrrole subunit for anion recognition (cf. Fig. 12.6) [22]. In the solid state, the individual ions within the CsF ion pair complex, which are bound to 7, are separated from one another by a single methanol molecule that was presumably captured during crystallization. Proton NMR spectroscopic analyses, carried out in deuterated methanol/chloroform (1 9 vA ),... 

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