C2-Symmetric ligands containing hydrogen bond donors: synthesis and properties of Cu(ii) complexes of 2,6-bis[N,N′-(2-carboxamidophenyl)carbamoyl]pyridine

Abstract
The synthesis of the new tridentate ligands 2,6-bis[N,N′-(2-acetamidophenyl)carbamoyl]pyridine (H41Me) and 2,6-bis[N,N′-(2-ferrocenylamidophenyl)carbamoyl]pyridine (H41Fc), and their corresponding CuII complexes is described. In the crystalline phase, H41Fc has a helical structure, which is maintained by a network of intramolecular hydrogen bonds. X-Ray diffraction studies on [CuH21Me(OAc)·Cl]2−, [CuH21Me(Cl)·Cl]2−, and [CuH21Fc(OAc)·Cl]2− reveal that the [H21R]2− ligands bind meridionally. One additional ligand (either OAc or Cl) binds trans to the pyridyl nitrogen to complete coordination in the equatorial plane. The remaining chloride ion (Cl(1)) binds to a second sphere-binding site, which is formed by two convergent hydrogen bonding amide groups. Long Cu⋯Cl(1) bonds distances of >2.75 Å are observed. Electrochemical measurements show a 65 mV cathodic shift in the half-wave potential for [CuH21Fc(OAc)·Cl]2− compared to the free ligand H41Fc.

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