From a Monomer to a Protein‐Sized, Doughnut‐Shaped Coordination Oligomer—The Influence of Side Chains of C 3 ‐Symmetric Ligands in Supramolecular Chemistry

Herein we describe the importance of side chains in C 3 ‐symmetric ligands in supramolecular chemistry. The reaction of the new ligand tris(5‐bromo‐2‐methoxybenzylidene)triaminoguanidinium chloride [H 3 Me 3 Br 3 L ]Cl ( 1 ) with ZnCl 2 results in the formation of the monomeric complex (Et 3 NH) 2 [(ZnCl 2 ) 3 Me 3 Br 3 L ] ( 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, [H 6 Br 3 L ]Cl, under similar conditions, results in the formation of two different dimeric compounds (NH 4 )[{[Zn(NH 3 )] 3 Br 3 L } 2 {μ‐(OH)} 3 ]⋅1/4MeOH ( 3 ) and [Zn{Zn 2 (OH 2 ) 3 (NH 3 ) Br 3 L } 2 ] ( 4 ), depending on the solvent mixture used. The comparable reaction of the ligand tris(5‐bromo‐2‐hydroxy‐3‐methoxybenzylidene)triaminoguanidinium chloride [H 6 (OMe) 3 Br 3 L ]Cl ( 5 ), leads to the formation of a doughnut‐shaped, protein‐sized coordination oligomer (Et 3 NH) 18 [{Zn[Zn 2 Cl{ (OMe) 3 Br 3 L }] 2 } 6 (μ‐Cl) 6 (OH 2 ) 6 ]⋅ x  CH 3 CN ( 6 ), which comprises six dimeric [Zn 5 { (OMe) 3 Br 3 L } 2 ] units. Whereas 3 and 4 decompose in DMSO solution, 6 is surprisingly stable in the same solvent.