Metal ion complexation by acyclic and cyclic multidentate ligands

The importance of cation-ligand complexes due to non-covalent interactions became a focus of attention after the discovery of cyclic polyether ligands (crown ethers) by Charles J. Pedersen. A key feature of crown ethers is that they exhibit a binding selectivity toward certain metal ions. For this discovery, Pedersen along with two other researchers was awarded the 1987 Nobel Prize in Chemistry. Crown ether ligands have found important applications in analytical chemistry and several methods have been developed to study their complexing properties.; This research is an endeavor in the field of metal ion complexation by acyclic and cyclic multidentate ligands. Different factors that dictate the binding ability of multidentate polyether ligands towards alkali metal and some heavy metal cations with special emphasis on crown ether compounds were probed. The studies involved different methodologies of solvent extraction, ion-selective electrodes and fluorometry. Special attention was given to metal ions that of either biological or environmental importance, including Na(I), K(I), Pb(II), and Hg(II).; Systematic studies were conducted to show the influence of structural variation within a crown ether compound upon the selectivity and efficiency of alkali metal cation extraction. The structural variations included replacing cyclohexano with benzo substituents, changing the number of these hydrocarbon substituents which are attached to the periphery of the macrocyclic polyether, and introducing t-butyl groups into these hydrocarbon substituents. The efficiency and selectivity of alkali metal cation extraction by a series of lipophilic crown ethers were also strongly influenced by the identity of the co-extracted anion and by the type of the organic diluent. In several instances, good empirical correlations were obtained showing a dependence of the extraction efficiency and selectivity on the anion hydration energy and some solvent parameters.; Alkali metal cation complexation by a series of dibenzo-16-crown-5, monobenzocrown, and phosphazene-based crown compounds was evaluated in solvent polymeric membrane electrodes. High lipophilicity, adequate mobility, and fast kinetics were found to be the most important requirements for a crown ether to behave as a good neutral carrier in ion-selective electrodes.; The final part of the dissertation is a contribution to the growing field of chemosensors. A new calixarene-based fluorogenic reagent for selective Hg(II) recognition was characterized as a prospective chemosensor.