Potentiometric discrimination between planar and octahedral anionic metal cyano complexes by liquid membrane electrodes based on lipophilic macrocyclic dioxopolyamines

Abstract

AbstractA novel type of poly(vinyl chloride) matrix liquid membrane electrodes that are capable of discriminating between planar and octahedral anionic metal cyano complexes has been developed by exploiting as the sensory elements lipophilic derivatives of macrocyclic dioxopolyamines (13‐hexadecyl‐1,4,8,11‐tetraaza‐12,14‐dioxocyclotetradecane, 15‐hexadecyl‐1,4,7,10,13‐pentaaza‐14,16‐dioxocyclohexadecane). Potentiometric response behaviors of these electrodes for a series of anionic metal cyano complexes were compared with those of the electrodes based on the corresponding nondioxo macrocyclic pentaamine (15‐hexadecyl‐1,4,7,10,13‐pentaazacyclohexadecane) as well as a conventional anion exchanger (Capriquat®). The electrodes based on the dioxopolyamines displayed strong potentiometric responses at pH 4.0 to the metal cyano complexes having a planar structure ([Ni(CN)4]2−, [Pt(CN)4]2−). In contrast, the responses to the metal cyano complexes having an octahedral structure ([Fe(CN)6]3−, [Fe(CN)6]4−) were only negligible. On the other hand, for all of the guests tested, the electrodes based on the nondioxo macrocyclic pentaamine or the anion exchanger showed strong linear responses to both planar and octahedral complexes. These results represent a new mode of potentiometric discrimination displayed by dioxo‐type macrocyclic polyamines having both amine and amide moieties.