Macrobicyclic cage, structure

The remarkable physical properties exhibited by the divalent macrobicyclic cage complex [Co(sep)]2+ (29) are unparalleled in Co chemistry.219 The complex, characterized structurally, is inert to ligand substitution in its optically pure form and resists racemization in stark contrast to its [Co(en)3]2+ parent. The encapsulating nature of the sep ligand ensures outer sphere electron transfer in all redox reactions. For example, unlike most divalent Co amines, the aerial oxidation of (29) does not involve a peroxo-bound intermediate. 

Severin and coworkers reported (146) the reaction of tris(2-aminoethyl)amine and 4-formylphenylboronic acid with penta-erythritol to give, via multicomponent assembly, the boronic acid based macrobicyclic cage 35 (Fig. 25). The cage has the form of an ellipsoid with a diameter of 20.5 A and binds two Cud) ions in a fashion similar to the smaller tren-based cryptands. The reversible formation of boronic esters has also been employed to build other hollow structures such as nanotubes (147) and porous covalent organic frameworks (148,149). 

The medium may have a marked effect on the shape of receptor molecules itself. Shape modifications could strongly influence their substrate binding properties, for instance in the case of amphiphilic cyclophane receptors subjected to hydrophobic-hydrophilic factors in aqueous solution. Such medium effects in action are visualized by the solid state structures of two different forms of the water-soluble hexasodium salt of the macrobicyclic cyclophane 66, which could be crystallized in two very different shapes an inflated cage structure 71 building up cylinders disposed in a hexagonal array and a flattened structure 72 stacked in molecular layers separated by aqueous layers in a lamellar arrangement [4.73]. These two... 

When immobilized on polymer surfaces, cage complexes may be utilized for modifications of electrodes. The increase in the electron-transfer rate on such surfaces is governed by two factors a high rate of electron transfer in cobalt clathrochelates and the regular disposition of these complexes on the surface. The properties of immobilized macrobicyclic complexes have been considered in Refs. 94, 410, and 411. Cyclic voltammetry has been used to characterize the incorporation of a range of structurally different d-metal sarcophaginates and sepulchrates into Nafion polymer [412]. 

Cryptands are ligands, mainly represented by macrobicyclic or macrotricyclic structure, capable of ion encapsulation due to their cage-Uke structures (see Fig. 8). The inclusion compound formed by a metal ion encapsulated within a... 

Similar dicopper cascade complexes of the caging ligand 14 with encapsulated fiij-cyanamide and dicyanamide bridging anions (Scheme 2.67) have been isolated and structurally characterized in [78]. Para-phenylene analog 7 of this macrobicyclic ligand is reported in [79] to form a H302 -bridged dicopper covalent capsule shown Scheme 2.68. 

Protonated form of a macrobicyclic receptor 110 has been used in [100] for encapsulation of linear triatomic azide anion, forming 1 1 cage complex by Scheme 2.88. The single-crystal X-ray diffraction structures of 1 1 cage complexes of H 6 110 with fluoride, chloride, bromide, and azide anions have been determined in [100]. The small fluoride ion is tetracoordinated by this macrobicyclic ligand, while chloride and bromide... 

The protonated forms of octaamine macrobicyclic ligands 138, 144, and 146 are reported in [108] to encapsulate chloride and bromide anions by (Scheme 2.96), thus giving 1 1 cage complexes, which were structurally characterized by single-crystal X-ray diffraction data. The cova-... 

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