MACROCYCLIC EFFECT ON ANION BINDING - A POTENTIOMETRIC AND ELECTROCHEMICAL STUDY OF THE INTERACTION OF 21-MEMBERED AND 24-MEMBERED POLYAZAALKANES WITH [FE(CN)6]4- AND [CO(CN)6]3-

The interactions of the cyclic polyazaalkanes 1,4,7,10,13,16,19-heptaazacyclohenicosane, 1,4,7,10,13,16,19,22-octaazacyclotetracosane and of the open-chain counterparts 1,17-bis(methylamino)-3,6,9,12,15-pentaazaheptadecane and 1,20-bis(methylamino)-3,6,9,12,15,18-hexaazaicosane with the complex anions hexacyanoferrate(II) and hexacyanocobaltate(III) have been studied at 298.15 K in 0.15 mol dm-3 NaClO4 by using potentiometric and electrochemical techniques. Both types of polyamines, cyclic and linear, form stable complexes with 1:1 anion: receptor stoichiometry. This result has been obtained either by treatment of electromotive force data with the computer program SUPERQUAD or by analysing the variations of [Fe(CN)5]3- -[Fe(CN)6]4- voltammograms with the ratio [Fe(CN)6]4 :polyamine. A macrocyclic effect for anion binding is observed, namely the stability of the 'super-complexes' of the cyclic ligands is higher than those formed by their open-chain counterparts. Both types of ligands interact more strongly with [Fe(CN)6]4 than with [Co(CN)6]3-. From the electrochemical measurements it has been estimated that the affinity of [Fe(CN)6]3 for these polyammonium receptors is similar to that presented by the equally charged complex anion [Co(CN)6]3-.