Complexation of macrocyclic ligands with relatively non-solvated metal ions generated in dichloromethane by electrochemical oxidation of amalgam electrodes

Abstract

Oxidation of a dropping amalgam electrode in dichloromethane (0.2 M Bu 4NPF 6) has been used to examine the complexation of essentially non-solvated cadmium(II), lead(II), thallium(I), tin(II) and bismuth(III) cations with the macrocyclic crown ether 1,4,7,10-tetraoxacyclodecane (12-C-4), the azacrown ether 1,4,8,11-tetraazacyclotetradecane (14-N-4 or cyclam) and the thiacrown ether 1,4,6,11-tetrathiacyclotetradecane (14-S-4) ligands. Interestingly, in dichloromethane, stronger complexes are formed with 14-N-4 and 12-C-4 than with 14-S-4 and the ratio of the ligand to metal ion in the complex is generally larger than the 1:1 value commonly found in other media. The unusual nature of the species formed in dichloromethane is attributed to the highly active nature of the relatively non-solvated cations generated at the amalgam electrode surface.