Cryptands redox-active

Cu(II) is one of the best examples of a redox active guest, but apparently not when it is imprisoned in a cryptand such as 53. In this case, the Cu(II) is silent over a wide potential range during cyclic voltammetry. System 53 is designed as a lumophore-spacer-receptor system such as 28-30 and 33-34 in Section 1 with multiple lumophores. It also shows similar luminescence off-on switching with and even with Cu(II). The possibility of Cu(II) induced production of from moisture appears to have been ruled out. The absence of EET is a mystery which can only be dispelled by further studies on this interesting system. 

Figure 3.53 A CO substrate is sandwiched between a redox-active transition metal and a Lewis acidic alkali metal cation by a cryptand with both hard and soft donor sites.

Hall, C. D., Djedovic, N., The synthesis and complexation of a cobaltocenium-based redox-active cryptand containing the phenanthroline unit. J. Organomet. Chem. 2002, 648, 8-13. 

The electrochemistry associated with these redox-active cryptands is quite intriguing. As pointed out earlier, anodic shifts of the ferrocene redox potential may be used via the Nernst equation to estimate the decrease in binding capacity (Xj/Ki) on coordination with a cation. Beyond this, however, if Kj is determined independently as is the case for 38 (m, n = 2) [63] then Xj may be calculated and correlated with the ratio of cationic radius/charge (Fig. 6-7) — data that reveal that increasing charge density on the cation destabilizes the complex between the oxidised cryptand and the cation, presumably by charge repulsion [68]. Alkali metal cations gave only small (< 20 mV) anodic shifts with this cryptand. 

The dimeric cryptand 19, containing four 2,2 -bipyridine subunits, was synthesized from the ferrocene ft/s-acyl chloride with the corresponding azamacrocycle this redox-active luminescent cryptand was ased to complex cations <97CC2195>. 

A number of other metal-based redox-active centers have been incorporated into supramolecular receptors, representative examples of which are displayed in Fig. 5 (Compounds 24-28). Many of these receptors electro-chemically respond to cations. but species that respond to anions and neutral molecules are also known. A number of the cation binders are organometallic crown ether and metallocrown or metallothiacrown derivatives, for example. Compound 24. Flow-ever, in many cases, the redox processes are not particularly reversible, and relatively small anodic shifts in the metal-centered redox couples are observed. A series of self-assembled [12]metallocrown-3 complexes, two of which are 25 and 26, were found by Severin to bind halide salts of small Group 1 metals strongly in organic solvents, with affinities similar to those of the cryptands. X-ray crystal structures revealed that the metal cation was... 

There are numerous examples of organic redox-active reporter groups that have been incorporated into supra-molecular receptors over the past 20 years. Many of these date to the 1980s and early 1990s. when Gokel and coworkers reported a number of crown ether and cryptand derivatives containing redox-active centeres. Much of this... 

A novel redox-active cryptand, 48, containing two bipyridyl and two ferrocene units incorporated in a macrocycle has been recently described [100, 100a]. 

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