Potentiometric studies of complexation properties of tetrafunctionalized resorcinarene-based cavitands

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 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 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.