As found in biological systems, proper combinations of stereo-controlled ligands and functional metal centers are demonstrated to generate sophisticated functions in several non-asymmetric processes. This review highlights stereochemical approaches to the synthetic ligands effective for efficient cation recognition and selective luminescence anion sensing processes.
A new series of Ag
+ ion-specific ligands was designed, in which three pyridine donors selectively bound the Ag
+ ion in a tridentate fashion. In addition to such unique coordination geometry, the stereo-controlled substitution on the podand-type ligand significantly enhanced Ag
+ ion selectivity in binding, extraction, and membrane transport processes.
Chiral versions of tripode ligands were also synthesized in a stereo-controlled fashion. They formed stable complexes with several lanthanide cations in which three sidearm donors and tertiary nitrogen atom were cooperatively involved. Their Eu
3+ and Tb
3+ complexes gave characteristic luminescence upon ligand chromophore excitation, and the observed luminescence intensity sensitively depended on the natures of external guest anions. In these lanthanide luminescence sensory processes, the use of stereo-controlled ligands remarkably increased the anion-responsibility.
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