ANION SELECTIVITY OF TETRAVALENT TIN-COMPOUNDS IN MEMBRANES STUDIED BY SN-119-NMR, C-13-NMR AND H-1-NMR

The fundamental molecular aspects of trialkyltin compounds of the type R3SnY have been investigated in view of their applicability as ion‐selective components in solvent polymeric membranes. The interaction between these compounds and anions has been studied using 119Sn‐ and 13C‐NMR. Neutral tetracoordinated trialkyltin compounds form a negatively charged pentacoordinated complex upon interaction with Cl‐ions in homogeneous organic phases as well as in membranes in contact with aqueous solutions. Although in a homogeneous phase, the electronegative substituent Y determines the complex‐formation constant, it has no influence on the potentiometric anion selectivity in liquid membranes containing trialkyltin carriers R3SnY with different Y. The observed selectivity pattern is not given by the magnitude of the stability constants in a homogeneous phase but is dictated by the prevailing association‐dissociation process leading to tetracoordinated compounds which change in constitution due to varying sample composition, The results obtained from equilibrium studies of tetravalent mono tin compounds with anions in both homogeneous phase and in two‐phase systems confirm the earlier hypothesis that trialkyltin compounds incorporated in solvent polymeric membranes act as electrically neutral carriers for anions. Copyright © 1990 Verlag GmbH & Co. KGaA, Weinheim