title: Photochemical hydrogen production and cobaloximes: the influence of the cobalt axial N-ligand on the system stability.
abstract: We report on the first systematic study of cobaloxime-based hydrogen photoproduction in mixed pH 7 aqueous/acetonitrile solutions and demonstrate that H2 evolution can be tuned through electronic modifications of the axial cobalt ligand or through introduction of TiO2 nanoparticles. The photocatalytic systems consist of various cobaloxime catalysts [Co(dmgH)2(L)Cl] (L = nitrogen-based axial ligands) and a water soluble porphyrin photosensitizer. They were assayed in the presence of triethanolamine as a sacrificial electron donor. Optimal turnover numbers related to the photosensitizer are obtained with electron-rich axial ligands such as imidazole derivatives (1131 TONs with N-methyl imidazole). Lower stabilities are observed with various pyridine axial ligands (443 TONs for para-methylpyridine), especially for those containing electron-acceptor substituents. Interestingly, when L is para-carboxylatopyridine the activity of the system is increased from 40 to 223 TONs in the presence of TiO2 nanoparticles.
authors.affiliation: Laboratory of Bioinorganic Chemistry, Department of Chemistry, University of Crete, Voutes Campus, 70013 Heraklion, Crete, Greece. acoutsol@uoc.gr.
authors.forename: Athanassios
authors.initials: A
authors.lastname: Panagiotopoulos
authors.affiliation: Laboratory of Bioinorganic Chemistry, Department of Chemistry, University of Crete, Voutes Campus, 70013 Heraklion, Crete, Greece. acoutsol@uoc.gr.
authors.forename: Kalliopi
authors.initials: K
authors.lastname: Ladomenou
authors.affiliation: Laboratoire de Chimie et Biologie des Métaux, Université Grenoble Alpes, CNRS, CEA, 17 rue des Martyrs, 38000 Grenoble, France. vincent.artero@cea.fr.
authors.forename: Dongyue
authors.initials: D
authors.lastname: Sun
authors.affiliation: Laboratoire de Chimie et Biologie des Métaux, Université Grenoble Alpes, CNRS, CEA, 17 rue des Martyrs, 38000 Grenoble, France. vincent.artero@cea.fr.
authors.forename: Vincent
authors.initials: V
authors.lastname: Artero
authors.affiliation: Laboratory of Bioinorganic Chemistry, Department of Chemistry, University of Crete, Voutes Campus, 70013 Heraklion, Crete, Greece. acoutsol@uoc.gr.
authors.forename: Athanassios G
authors.initials: AG
authors.lastname: Coutsolelos