The cone-tetranitrocalix[4]arene tetraradical tetraanion as an electrochemically generated ligand for heavier alkali metal cations.

Four-electron electrochemical reduction of the cone-tetranitrocalix[4]arene in DMF results in the stable tetraradical tetraanion. The positive shift of the reduction potential of the title compound with an increasing concentration of alkali metal ions is caused by complex formation. The tetranitrocalix[4]arene thus represents an electrochemically generated ligand - a promising receptor/sensor - for alkali metal ions. Observed stoichiometries and corresponding stability constants for individual complexes of potassium, rubidium and caesium were determined. The immobilization and reduction of nitrocalixarenes on the electrode surface offers new applications in electroseparation of alkali metal ions in analytical chemistry.