From a monomer to a protein-sized, doughnut-shaped coordination oligomer-the influence of side chains of C3-symmetric ligands in supramolecular chemistry

Herein we describe the importance of side chains in C3-symmetric ligands in supramolecular chemistry. The reaction of the new ligand tris(5-bromo-2-methoxybenzylidene)triaminoguanidinium chloride [H3Me3Br3L]Cl (1) with ZnCl2 results in the formation of the monomeric complex (Et3NH)2[(ZnCl2)3Me3Br3L] (2), in which the ligand remains in a conformation less favourable for the coordination of metal centres. The use of the related tris(5-bromo-2-hydroxybenzylidene)triaminoguanidinium chloride, [H6Br3L]Cl, under similar conditions, results in the formation of two different dimeric compounds (NH4)[{[Zn(NH3)]3Br3L}2{mu-(OH)}3]1/4MeOH (3) and [Zn{Zn2(OH2)3(NH3)Br3L}2] (4), depending on the solvent mixture used. The comparable reaction of the ligand tris(5-bromo-2-hydroxy-3-methoxybenzylidene)triaminoguanidinium chloride [H6(OMe)3Br3L]Cl (5), leads to the formation of a doughnut-shaped, protein-sized coordination oligomer (Et3NH)18[{Zn[Zn2Cl{(OMe)3Br3L}]2}6(mu-Cl)6(OH2)6]x CH3CN (6), which comprises six dimeric [Zn5{(OMe)3Br3L}2] units. Whereas 3 and 4 decompose in DMSO solution, 6 is surprisingly stable in the same solvent.