Nickel and copper complexes of pyrrolecarboxamide ligands -stabilization of M³⁺ species and isolation of Ni³⁺ complexes

We report Ni^II and Cu^II complexes of a few pyrrolecarboxamide ligands containing -H, -Cl, and -CH₃ substituents on the phenylene ring. Solid-state X-ray diffraction and solution- based spectral studies substantiated a square-planar geometry around the metal ions in all six of the M^II complexes. Electrochemical studies showed that the electronic substituents considerably influence the M^3+/2+ redox potentials. All of the complexes exhibit considerably low M^3+/2+ redox potentials owing to their tetraanionic coordination environments. Chemical and,or electrochemical oxidation has resulted in the isolation of Ni³⁺ complexes and the generation of Cu³⁺ species. The spectroscopic studies revealed squareplanar geometries around the metal ions in the resultant Ni³⁺ and Cu³⁺ complexes.