Secondary Structures in Inorganic Helicates of an Octadentate Phenanthroline-Type Schiff Base Ligand

To analyze the contribution of supramolecular interactions to helical architectures and to investigate whether ligand folding can be induced by only protons in a similar fashion in the absence of metal ions, a new 1,10‐phenanthroline (phen)‐based extended ligand, C12H6N2[CHNC6H4NH(C10H6N)]2 (L1), its copper(I) complexes, [Cu2(C12H6N2{CHNC6H4NH(C10H6N)}2)2] [PF6]2 (1), [Cu2(C12H6N2{CHNC6H4NH(C10H6N)}2)2][BF4]2 (2), [Cu2(C12H6N2{CHNC6H4NH(C10H6N)}2)2][CuCl2]2·CH2Cl2 (3), and [Cu4(C12H6N2{CHNC6H4NH(C10H6N)}2)2][Cu2I4] (4), were prepared and structurally characterized. Ligand L1 wraps copper(I) ions in two intriguingly different fashions depending on the nature of the anions. Although dicopper helicates 1–3 and tetracopper helicate 4 show significant intermolecular interactions that show considerable structural relationships with DNA, helicate 4 more closely resembles the structural features of DNA that even phen‐based stacking interactions are present between the two helical strands. In complex 4, the dinuclear [Cu2I4]2– dianion is involved in intermolecular interactions, which joins two cationic units in a linear fashion, whereas the monoanions in complexes 1–3 (i.e., PF6–, BF4–, and CuCl2–) are only involved in intramolecular interactions or connect the cations laterally. The anion‐dependent topology serves as a reminder that the helical topology of a cation can be altered by changing the nature of the anion. A 1,10‐phenanthroline (phen)‐based ligand wraps CuI ions in two ways depending on the nature of the anion. The ligand can also fold through H‐bonding interactions in the absence of Cu ions. Although both dicopper helicate 1 and tetracopper(I,II) helicate 4 show significant intermolecular interactions, 4 more closely resembles a DNA structure and phen‐based stacking interactions are observed.