Determination of formal redox potentials in aqueous solution of copper(II) complexes with ligands having nitrogen and oxygen donor atoms and comparison with their EPR and UV–Vis spectral features

•Formal redox potentials in aqueous solution have been determined for copper(II) complexes with N and O donor atoms.•Spin Hamiltonian parameters and UV–Vis absorption data have been obtained for all the simple and mixed copper(II) complexes.•The copper(II) complexes under investigation have well known stereochemistries so that a rough correlation could be done among formal redox potentials and spectral (EPR and UV–Vis) data.•When considering distorted coordination geometries of copper(II) complexes some ambiguity can arise in the interpretation of their spectral (EPR and UV–Vis) data.•It is suggested that the measurement of the formal redox potential could be of a great help in solving ambiguities in the interpretation of spectra data.

Formal redox potentials in aqueous solution were determined for copper(II) complexes with ligands having oxygen and nitrogen as donor atoms. All the chosen copper(II) complexes have well-known stereochemistries (pseudo-octahedral, square planar, square-based pyramidal, trigonal bipyramidal or tetrahedral) as witnessed by their reported spectroscopic, EPR and UV–visible (UV–Vis) features, so that a rough correlation between the measured redox potential and the typical geometrical arrangement of the copper(II) complex could be established. Negative values have been obtained for copper(II) complexes in tetragonally elongated pseudo-octahedral geometries, when measured against Ag/AgCl reference electrode. Copper(II) complexes in tetrahedral environments (or flattened tetrahedral geometries) show positive redox potential values. There is a region, always in the field of negative redox potentials which groups the copper(II) complexes exhibiting square-based pyramidal arrangements. Therefore, it is suggested that a measurement of the formal redox potential could be of great help, when some ambiguities might appear in the interpretation of spectroscopic (EPR and UV–Vis) data. Unfortunately, when the comparison is made between copper(II) complexes in square-based pyramidal geometries and those in square planar environments (or a pseudo-octahedral) a little perturbed by an equatorial tetrahedral distortion, their redox potentials could fall in the same intermediate region. In this case spectroscopic data have to be handled with great care in order to have an answer about a copper complex geometrical characteristics.

Graphical abstractRedox potentials in aqueous solution were measured for a series of copper(II) complexes having different stereochemistries and a correlation between the measured redox potential and the typical geometrical arrangement of the copper(II) complex has been established.Figure optionsDownload full-size imageDownload as PowerPoint slide