Appearance of Phosphate-Selectivity by Hydrolytic Trimerization of Simple Dialkyltin(IV) Compounds Used as Carrier

The complexation equilibria of dimethyltin(IV) and trimethyltin(IV) ions with several anions in aqueous solutions were potentiometrically studied as a model of the interaction of lipophilic dialkyltin(IV) and trialkyltin(IV) compounds, the carriers of ion-selective electrodes, with anions in the membrane phase. Phosphate and arsenate reacted with dimethyltin(IV) ion to yield partially hydrolyzed trimeric species, [(SnMe2)3(OH)2(HPO4)2] and [(SnMe2)3(OH)2(HAsO4)2]. Such oligomerization, which ensures the interaction of phosphates or arsenate with two Sn centers, is also possible for lipophilic dialkyltin(IV) compounds. Moreover, shielding these anions from the solvent by lipophilic alkyl groups projected from Sn atoms may enhance the distribution of the carrier-anion associates into the membrane phase. These cooperate to give lipophilic dialkyltin(IV) compounds with high selectivities to these ions. The presence of such electroactive species in the membrane phase was discussed with reference to the previous studies.