title: Water oxidation catalysis upon evolution of molecular Co(III) cubanes in aqueous media.
abstract: The increasing global energy demand has stimulated great recent efforts in investigating new solutions for artificial photosynthesis, a potential source of clean and renewable solar fuel. In particular, according to the generally accepted modular approach aimed at optimising separately the different compartments of the entire process, many studies have focused on the development of catalytic systems for water oxidation to oxygen. While in recent years there have been many reports on new catalytic systems, the mechanism and the active intermediates operating the catalysis have been less investigated. Well-defined, molecular catalysts, constituted by transition metals stabilised by a suitable ligand pool, could help in solving this aspect. However, in some cases molecular species have been shown to evolve to active metal oxides that constitute the other side of this catalysis dichotomy. In this paper, we address the evolution of tetracobalt(III) cubanes, stabilised by a pyridine/acetate ligand pool, to active species that perform water oxidation to oxygen. Primary evolution of the cubane in aqueous solution is likely initiated by removal of an acetate bridge, opening the coordination sphere of the cobalt centres. This cobalt derivative, where the pristine ligands still impact on the reactivity, shows enhanced electron transfer rates to Ru(bpy)3(3+) (hole scavenging) within a photocatalytic cycle with Ru(bpy)3(2+) as the photosensitiser and S2O8(2-) as the electron sink. A more accentuated evolution occurs under continuous irradiation, where Electron Paramagnetic Resonance (EPR) spectroscopy reveals the formation of Co(ii) intermediates, likely contributing to the catalytic process that evolves oxygen. All together, these results confirm the relevant effect of molecular species, in particular in fostering the rate of the electron transfer processes involved in light activated cycles, pivotal in the design of a photoactive device.
authors.affiliation: Department of Chemical Sciences, University of Padova and ITM-CNR, via Marzolo 1, 35131 Padova, Italy. andrea.sartorel@unipd.it.
authors.forename: Andrea
authors.initials: A
authors.lastname: Genoni
authors.affiliation: Dipartimento di Scienze Chimiche, Università di Messina and Centro Interuniversitario per la Conversione Chimica dell'Energia Solare, sezione di Messina, Via Sperone 31, 98166 Messina, Italy.
authors.forename: Giuseppina
authors.initials: G
authors.lastname: La Ganga
authors.affiliation: Department of Chemical Sciences, University of Padova and ITM-CNR, via Marzolo 1, 35131 Padova, Italy. andrea.sartorel@unipd.it.
authors.forename: Andrea
authors.initials: A
authors.lastname: Volpe
authors.affiliation: Dipartimento di Scienze Chimiche, Università di Messina and Centro Interuniversitario per la Conversione Chimica dell'Energia Solare, sezione di Messina, Via Sperone 31, 98166 Messina, Italy.
authors.forename: Fausto
authors.initials: F
authors.lastname: Puntoriero
authors.affiliation: Department of Chemical Sciences, University of Padova and ITM-CNR, via Marzolo 1, 35131 Padova, Italy. andrea.sartorel@unipd.it.
authors.forename: Marilena
authors.initials: M
authors.lastname: Di Valentin
authors.affiliation: Department of Chemical Sciences, University of Padova and ITM-CNR, via Marzolo 1, 35131 Padova, Italy. andrea.sartorel@unipd.it.
authors.forename: Marcella
authors.initials: M
authors.lastname: Bonchio
authors.affiliation: Dipartimento di Scienze Chimiche e Farmaceutiche, Università di Ferrara and Centro Interuniversitario per la Conversione Chimica dell'Energia Solare, sezione di Ferrara, Via Fossato di Mortara 17-19, 44121 Ferrara, Italy. mirco.natali@unife.it.
authors.forename: Mirco
authors.initials: M
authors.lastname: Natali
authors.affiliation: Department of Chemical Sciences, University of Padova and ITM-CNR, via Marzolo 1, 35131 Padova, Italy. andrea.sartorel@unipd.it.
authors.forename: Andrea
authors.initials: A
authors.lastname: Sartorel