Macrotetracyclic complexes of nickel(II) containing crown ethers as pendant arms, [Ni(B)](ClO 4 ) 2 and [Ni(C)](ClO 4 ) 2 , were prepared and characterized. The binding constants of the complexes toward alkali metal ions are relatively small compared with those of free 15-crown-5 or 18-crown-6 and the reduction potentials of the [Ni(B)](ClO 4 ) 2 and [Ni(C)](ClO 4 ) 2 in the presence of alkali metal ions shift to the positive direction in the order Li + >Na + >K + and K + >Na + >Li + , respectively.