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.