Interaction between monoaza-, diaza-, or polyazacrown ethers and alkali metal ions in acetonitrile by polarography

The complex formation constants between alkali metal ions and monoaza- or diazacrown ethers (L) in acetonitrile have been obtained by the analytical method of d.c. polarography, in which a positive shift in E-1/2 of the mercury-dissolution wave of L in the presence of a large excess of M+ is utilized. By the conventional method using a negative potential shift of the reduction of MLC in the presence of a large excess of L, similar values of the complex formation constants were given for the 1:1 interaction (ML+ formation) between M+ and L. Concerning the stability of the Li+ and Na+ complexs of 12-crown-4, 15-crown-5, and 18-crown-6, the effects of the NH groups in the crown ethers have been discussed. The interaction between alkaline earth metal ions and L was too strong to obtain the formation constant, except for the BaL2+ species of 1-aza-12-crown-4. The anodic processes of L on DME were clarified: the diaza-12-crown-4 as well as the monoazacrown ethers caused an anodic wave of one-electron for L (i.e., the formation of 1/2[HgL2](2+)), whereas 1,7-diaza-15-crown-5 gave successive two anodic waves. The formation of the monomeric mercurous ion (Hg+) seemed to be stabilized by the diaza-15-crwon-5 in the course of the anodic process into [HgL](2+).