Bis(monoazacrown ethers) with an electron-donating substituent at the hinge: A pronounced participation of hydroxyl group in formation of sodium ion sandwich complexes

Abstract

Sodium ion complex formation has been investigated potentiometrically in four homologous bis(crown) series I-IV differing by the nature of substituent placed at the linking trimethylene chain (X = OH, OCH3, OCH2C6H5 and H respectively). A marked enhancement of the complex stability has been observed in the bis(crown) series I and attributed to participation of the lateral hydroxyl group in the sandwich complex formation. Evidence in support of the sandwich structure has been provided (i) by analysis of the potentiometric data indicating a 1:1 complex stoichiometry and (ii) by a comparison of the complex stability data from the bis(crown) series I with the corresponding values from related monocyclic ligand series V, VI and VII revealing a pronounced cooperation of both macrorings in the sodium ion-bis(crown) I complex formation.