Supramolecular compounds crown-type

C. J. Pedersen, J. Am. Chem. Soc. 1967, 89, 2495 G. Gokel, Crown Ethers and Cryptands in Monographs in Supramolecular Chemistry (Ed. J. F. Stoddart), Black Bear Press, Cambridge, 1991, p, 64 E. Weber, F. Vdgtle, Crown-Type Compounds—An Introductory Overview, Top. Curr. Chem. 1981, p. 1. 

Ionic supramolecular self-assembly will be discussed in Chapter 6, but some supramolecular systems based upon ionic interactions will be discussed earlier, e.g. the organocyclosiloxanolates, which form sandwich compounds by intercalating transition metal ions between two macrocyclic rings (held together by ionic interactions) and acting as endo receptors which concurrently have crown-ether-type complexing properties (as exo receptors) (see Section 2.1.2). 

The role of photochemistry and photophysics in most applications of supramolecular chemistry is all important also with organic compounds. As an example, the system composed of a crown ether containing re-electron donating naphthalene units and a 2,7-diazapyrenium re-electron acceptor (see formulae below) associates with a large equilibrium constant in organic solution and yields a pseudorotaxane-type complex. 

Recently, macrocyclic chiral compounds of crown ether or cyclamen type have been attracting wide interest. These compounds contain numerous heteroatoms in their molecules (mainly oxygen, sulfur, and nitrogen) and can find practical applications, for example, as chiral selectors [69,70] and chiral NMR discriminating agents [71]. Asymmetric substitution of two carbon atoms in the ring of crown ether or cyclamen can lead to many different optically active compounds useful in various branches of supramolecular chemistry. Such substitution can be accomplished with appropriate starting compounds that are optically active, for example, amino acids and polyhydroxy alcohols. 

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