Two-phase reactions of tin(IV)–tetraphenylporphine complexes as carrier of anion selective electrodes

Abstract

Two-phase reactions of [Sn(OH) 2(tpp)] with lipophilic anions and inorganic acids were studied and compared with those of [Zr(OH) 2(tpp)] having the same oxidation state of the central metal ion but different structural characteristics. The reaction with tetrakis[3,5-bis(trifluoromethyl)phenyl]borate formed a 2:1 cationic dimer and 1:1 and 1:2 ion-pairs, while the reaction with dodecyl sulfate formed 1:1 and 1:2 ion-pairs. The 1:1 and 1:2 species formed concomitantly in the reaction with HCl and CH 3COOH having higher coordination abilities, while forming in stepwise manner in the reaction with HClO 4 and HNO 3 having lower coordination abilities. The 2:1 cationic dimer of Sn(IV) had significantly lower stability than that of Zr(IV). The affinity of Sn(IV) for Cl − relative to OH − was much higher, compared with Zr(IV). Except in extremely acidic media, [SnCl 2(tpp)] working as a carrier in PVC membranes hydrolyzed to give [Sn(OH)Cl(tpp)] or [Sn(OH) 2(tpp)], which showed stronger but less-selective potential responses at lower pH and weaker but more-selective responses to salicylate at higher pH. The affinities and responses of Sn(IV) complexes to oxygen-containing anions were weaker than those of Zr(IV) complexes.