Cage-Type Receptors Containing Metal Ions

2 Cage-Type Receptors Containing Metal Ions 

The controlled self-assembly of appropriate ligands and metal ions to yield large hollow coordination cages has become a popular approach in the programmed synthesis of nano-sized objects, some of which possess interesting inclusion properties [14]. Important contributions in this context came from the groups of Albrecht [15], Dalcanale [16], Fujita [17], Nitschke [18], Raymond [19], Saalfrank 

The anion-binding carcerand 11 was described by the Amouri group [31]. This complex contains a tetrafluoroborate anion coordinated to two cobalt(II) ions. Each cobalt ion adopts a square-pyramidal geometry. Four benzimidazole arms of the bridging ligands fill the equatorial positions, and solvent molecules (acetonitrile) coordinate to the outside axial positions. Inside the complex the included tetrafluoroborate anions interacts with the cobalt ions whose inside axial positions are otherwise coordinatively unsaturated. No exchange of the anion was observed even at 60 °C. A detailed study of the anion-binding properties in the crystal state of similar metalla-macrotricyclic cryptands has been performed by Adarsh et al. [32], 

Pioneering work in this area was carried out by the groups of Lehn and Martell [34, 35]. One example of a metal containing cryptand is dicopper(II) complex 14 which was shown to interact with various anions such as N3 , OCX. SCN. SO)2. HCOCT, CH3COO, HC03-, and 03 [36]. Complex formation can easily be detected by the color change of an aqueous solution of the receptor from blue in the absence of suitable anionic substrates to green in their presence. 

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