Département de chimie moléculaire

The redox properties and electronic structures of phenoxo- and hydroxo-bridged dicopper(II) complexes were explored. Complexes (1a-c)2+ are based on sym. ligands with bis(2-methylpyridyl)aminomethyl as complexing arms bearing different substituting R groups (CH3, OCH3, or CF3) in the para position of the phenol moiety. Complex 2a2+ is based on a sym. ligand with bis(2-ethylpyridyl)aminomethyl arms and R = CH3, while complex 3a2+ involves an unsym. ligand with two different complexing arms (bis(2-ethylpyridyl)aminomethyl and bis(2-methylpyridyl)aminomethyl). Studies were done by electrochem. and spectroelectrochem. means and correlated to theor. calcns. as this series of complexes offers a unique opportunity of an in-depth comparative anal. The voltammetric studies showed that the redox behavior of the dicopper complexes is not influenced by the nature of the solvent. However, the increase of the spacer chain length and the unsym. design induce significant modifications of the voltammetric responses for both oxidn. and redn. processes. DFT calcns. of the redox potentials using a computational ref. redox couple calcd. at the same level of theory to reduce systematic errors confirm these results. Ligand contributions to the electronic structure of the different species were analyzed. The good agreement between exptl. and theor. results has validated the developed calcn. method, which would be used in the following to design new dinuclear Cu complexes. Subtle modification of the ligand topol. can significantly affect the redox and spectroscopic properties. In particular, the unsym. design gave a transient mixed-valent Cu(II)-Cu(III) phenoxo complex detected upon spectroelectrochem. expts. at room temp., which evolves toward a dicopper (II,II) phenoxyl complex. The latter displays an intense $π$ → $π$* transition band at 393 nm in the UV-visible spectrum compared to the less intense ligand to metal charge transfer band at 518 nm obsd. for the mixed-valent Cu(II)-Cu(III) phenoxo complex. [on SciFinder(R)]