title: Insights into water coordination associated with the Cu(II)/Cu(I) electron transfer at a biomimetic Cu centre.
abstract: The coordination properties of the biomimetic complex [Cu(TMPA)(H2O)](CF3SO3)2 (TMPA = tris(2-pyridylmethyl)amine) have been investigated by electrochemistry combined with UV-Vis and EPR spectroscopy in different non-coordinating media including imidazolium-based room-temperature ionic liquids, for different water contents. The solid-state X-ray diffraction analysis of the complex shows that the cupric centre lies in a N4O coordination environment with a nearly perfect trigonal bipyramidal geometry (TBP), the water ligand being axially coordinated to Cu(II). In solution, the coordination geometry of the complex remains TBP in all media. Neither the triflate ion nor the anions of the ionic liquids were found to coordinate the copper centre. Cyclic voltammetry in all media shows that the decoordination of the water molecule occurs upon monoelectronic reduction of the Cu(II) complex. Back-coordination of the water ligand at the cuprous state can be detected by increasing the water content and/or decreasing the timescale of the experiment. Numerical simulations of the voltammograms allow the determination of kinetics and thermodynamics for the water association-dissociation mechanism. The resulting data suggest that (i) the binding/unbinding of water at the Cu(I) redox state is relatively slow and equilibrated in all media, and (ii) the binding of water at Cu(I) is somewhat faster in the ionic liquids than in the non-coordinating solvents, while the decoordination process is weakly sensitive to the nature of the solvents. These results suggest that ionic liquids favour water exchange without interfering with the coordination sphere of the metal centre. This makes them promising media for studying host-guest reactions with biomimetic complexes.
authors.affiliation: Laboratoire de Chimie, Electrochimie Moléculaires et Chimie Analytique, CNRS, UMR 6521, Université de Brest, 6 av. Le Gorgeu, 29328 Brest cedex, France. nicolas.lepoul@univ-brest.fr.
authors.forename: Ana Gabriela
authors.initials: AG
authors.lastname: Porras Gutiérrez
authors.forename: Joceline
authors.initials: J
authors.lastname: Zeitouny
authors.forename: Antoine
authors.initials: A
authors.lastname: Gomila
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Douziech
authors.forename: Nathalie
authors.initials: N
authors.lastname: Cosquer
authors.forename: Françoise
authors.initials: F
authors.lastname: Conan
authors.forename: Olivia
authors.initials: O
authors.lastname: Reinaud
authors.forename: Philippe
authors.initials: P
authors.lastname: Hapiot
authors.forename: Yves
authors.initials: Y
authors.lastname: Le Mest
authors.forename: Corinne
authors.initials: C
authors.lastname: Lagrost
authors.forename: Nicolas
authors.initials: N
authors.lastname: Le Poul
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry / Q000378:metabolism; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D055664:Electrochemical Techniques; D004579:Electron Transport; D004583:Electrons; D052578:Ionic Liquids / Q000138:chemical synthesis / Q000737:chemistry; D007700:Kinetics; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D001672:Biocompatible Materials; D056831:Coordination Complexes; D052578:Ionic Liquids; D014867:Water; D003300:Copper