Synthesis and crystal structure of a copper(II) complex of deprotonated N,N′-bis(2-pyridinecarboxamide)-2,2′-biphenyl: Comparative redox study of CuN4 pyridine amide complexes

A new distorted square planar (two CuN2 planes making an angle of ∼43°) copper(II) complex [Cu(L4)] · 0.5EtOH · 0.5MeOH (1) of a deprotonated tetradentate pyridine amide ligand [H2L4 = N,N′-bis(2-pyridinecarboxamide)-2,2′-biphenyl] has been synthesized and structurally characterized. Absorption and EPR spectroscopic properties have also been studied. The E1/2 values (CuII/CuI redox process) of the title complex along with a selected group of structurally characterized CuN4 pyridine amide complexes with systematically varied structural, electronic/steric, and chelate-ring size effects, imposed by the coordinating ligands, have been determined and the observed trend has been rationalized.

Graphical abstractThe tetradentate ligand with biphenyl backbone imposes distorted square planar geometry around copper(II) (two CuN2 planes making an angle of ∼43°). The structural, electronic/steric, and chelate-ring size effects, imposed by the coordinating ligands on E1/2 values (CuII/CuI redox process) have been identified and rationalized.Figure optionsDownload full-size imageDownload as PowerPoint slide