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

Two new asymmetric ureidic ligands 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 (two different polymorphs) an (E,Z) conformation. A moderate affinity for acetate has been observed with L1 while no interaction has been observed with 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 (E,Z) conformation via H-bonds. L2 also adopts an (E,Z) conformation in the solid state. However, the absence of the indole in L2 hampers the formation of the supramolecular assembly with the partecipation of anionic species.