Non-symmetric substituted ureas locked in an (E,Z) conformation: an unusual anion binding via supramolecular assembly

Abstract

Two new asymmetric ureidic receptors L¹ (1-(1H-indol-7-yl)-3-(quinolin-2-yl)urea) and L² (1-(quinolin-2-yl)-3-(quinolin-8-yl)urea) have been synthesised and their affinity towards different anions tested in DMSO-d₆. L¹ adopts both in solution and in the solid state an (E,Z) conformation. A moderate affinity for acetate has been observed for L¹ while no interaction has been observed for L². The different behaviour has been ascribed to the presence/absence of the indole group. In the case of L¹ the indole group causes the formation of a peculiar supramolecular architecture with two molecules of the receptor binding the anions in the (E,Z) conformation via H-bonds. L² also adopts an (E,Z) conformation in the solid state. However, the absence of the indole group in L² hampers the formation of the supramolecular assembly with the participation of anionic species.