Binding property and redox behaviour of nickel(II) macrocyclic complex containing crown ether toward alkaline earth metal ions

The binding constants of [Ni(L1)]2+ toward alkaline earth metal ions are relatively small compared with those of free 18-crown-6 and those of [Ni(L1)]2+ toward the alkali metal ions. The reduction potential of the [Ni(L1)](ClO4)2 in the presence of alkaline earth metal ions shifts to the positive direction in the order Mg2+ < Ca2+ < Sr2+ and Kred/Kox value of this redox process is increased in the order Li+ < Na+ < K+ < Mg2+ < Ca2+ < Sr2+.