Potentiometric studies of complexation properties of tetrafunctionalized resorcinarene-based cavitands

Abstract

Resorcinarene-based cavitands functionalized with [–NH–C(O)–CH₂–(Ph)₂PO] (I), [–NH–C(O)–CH₂–(EtO)₂PO] (II), [–NH–C(S)–NHC(O)Ph] (III) and [–NH–C(O)–NHC(O)Ph] (IV) moieties have been characterized potentiometrically. Both P-containing cavitands (I and II) form very stable complexes (log β_IL > 18) for most of the examined cations as determined with the segmented sandwich membrane method. The order of the stability constants was found to be: Eu³⁺ > UO₂²⁺ > Pb²⁺, Cd²⁺, Sr²⁺ and Cu²⁺. Much weaker complexation occurs in the case of compounds III and IV (log β_IL < 10.6) and the order of the stability constants was: Eu³⁺ > Pb²⁺ > Cu²⁺ > Ag⁺ > UO₂²⁺ > Na⁺ > K⁺ for III and UO₂²⁺ > Cd²⁺ > Pb²⁺ > Eu³⁺Cu²⁺ > Na⁺ > Ag⁺ > K⁺ for IV. The response to representatives of various cation groups and the selectivity of polymeric membrane electrodes based on these compounds are presented. While cavitands functionalized with phosphine oxide or phosphonate moieties (I or II) exhibited the highest selectivity for UO₂²⁺ and Pb²⁺ and a pronounced discrimination of Ag⁺ ions, thioamide- (III) and amide-functionalized (IV) cavitands showed preferences for Ag⁺ and Pb²⁺ and reduced selectivity toward UO₂²⁺ ions. The correlation between the potentiometric selectivity and the ability of examined cavitands to form metal–ligand complexes is discussed.