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Molecular Recognition in dibenzo-24 crown-8 Ethers

One of the most important areas of supramolecular chemistry is the metal-ion and host-guest chemistry of macrocyclic ligands, which have the utility in different fields and now also considerable biological relevance as model substances of naturally occuring ionophores for the study of ion-transport processes in cell membranes and investigation of receptor-enzyme interactions. Hence the molecular recognition in macrocyclic ethers and their structural studies have captured the interest of many chemists and cystallographers. The chemistry of metal-ion macrocyclic complexes and their crystal structures are influenced by a variety of factors, which include the size and ionic character of the metal ion and the flexibility and cavity size of the macrocycle. All these factors must be taken into account when tailoring ligands to recognize particular metal ions. Much effort has centred on understanding the effects of altering the nature of the metal or ligand on the stoichiometry and structure of the complexes formed. The conformation of the coordinated macrocycle is often different to that observed for the free ligand ring. The conformation of 24-crown-8 macrocyclic ring have been investigated by our X-ray structures and also by searching the Cambridge Structural Database (CSD) and compairing their conformational energies calculated by the means of molecular mechanics, in order to examine the influence of size and ionic character of the metal ion on the structure adopted by their complexes.

macrocyclic ligands; structural studies; 24-crown-8 macrocyclic ring

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