Occurence of Charge-Assisted Hydrogen Bonding in Bis-amidine Complexes Generating Macrocycles

Abstract

Bis-amidine and bis-carboxylate derivatives have been studied in this work to extend the knowledge of charge-assisted hydrogen bonding (CAHB) which counts among the strongest noncovalent bonding observed so far and arises from the combination of two well-identified types of interactions, namely, electrostatic attraction and hydrogen bonding. The formation of such bridges and the associated formation of macrocycles were screened for substituted (1) and nonsubstituted (2) bis-benzamidines through the use of isomeric proton acceptors aromatic bis-carboxylic (3–6) and bis-sulfonic acids (7–8). A library made from the combination of amidines and carboxylic/sulfonic acids was assessed both in solution and in the solid state. The formation of the CAHB motif was found to be highly dependent on the E,Z isomerization of the amidine moiety. Interesting double dipolar motifs were identified in the solid state.