The redox-switching behavior of complex between calix[4]arenediquinone (CDQ) and Ca(2+) were investigated in acetonitrile(AN) and N,N-dimethylformamide(DMF) media. The spectroscopic and electrochemical results in AN suggest the formation of Ca(2+)-CDQ complex with a 1:1 stoichiometry, which exhibits a typical redox-switching behavior. The addition of Ca(2+) to CDQ in DMF, however, leads to no change in spectroscopic measurements. Even though the cyclic voltammogram of CDQ in DMF exhibits similar redox waves as in AN, in the presence of Ca(2+), an irreversible single reduction wave appears at a more positive potential than that of the original free ligand wave and consecutive negative scans produces a new redox couple at more positive potential than the irreversible reduction wave. The nature of the new redox couple induced both by Ca(2+) and the reduced form of quinone moiety is investigated by electrochemical and spectroscopic methods. (C) 2009 Elsevier B.V. All rights reserved.