Transfert couplé d'électron et de proton dans des complexes de métaux de transition modèles et d'intérêts biomimétiques. Etudes mécanistiques par une approche électrochimique.

The biomimetic complexes efficiency involving Proton Coupled electron Transfer could be inherent to the concertation of the both transfers, avoiding the highly energetic intermediates. We have determined the parameters influencing a concerted mechanism thanks to an experimental electrochemical study of an osmium complex ([OsII(bpy)2py(H2O)](PF6)2). We have identified the PCET mechanism for each osmium complex electrochemical couples: the OsII(H2O)/OsIII(OH) follows a stepwise mechanism whereas the OsIII(OH)/OsII=O presents a concerted mechanism. By comparison of these systems, we have been able to determine the parameters promoting a concerted mechanism useful to elaborate an ideal complex: it should present a rigid coordination sphere in order to have a high standard rate constant, a large acidity constant gap, a proximal proton acceptor, a selected environment to avoid an association with an anion instead of the proton acceptor and an adapted ligands in agreement with solubility and stability criteria. Then, a SOD biomimetic manganese complex study has allowed to apply the osmium complex study methodology and to confirm that the proton acceptor concentration increase can cause the prevalence of the concerted mechanism.La performance des complexes biomimétiques utilisés comme catalyseurs pourrait résider dans le fait que, lorsqu'ils impliquent un transfert 1e-,1H+ (PCET) celui-ci ait lieu de manière concertée, évitant ainsi la formation d'intermédiaires coûteux en énergie. Par une approche expérimentale électrochimique, nous avons déterminé les paramètres gouvernant la compétition entre mécanismes séquentiel et concerté pour un PCET grâce à un composé modèle ([OsII(bpy)2py(H2O)](PF6)2). Pour ce faire, les mécanismes propres à chaque PCET présentés par le complexe d'osmium ont été identifiés : le transfert 1e-,1H+ associé au couple rédox OsII(H2O)/OsIII(OH) emprunte un mécanisme séquentiel alors que celui associé au couple rédox OsIII(OH)/OsII=O emprunte un mécanisme concerté. En comparant ces deux systèmes, nous avons pu déterminer les paramètres influençant le mécanisme concerté. Ainsi, un complexe « idéal » présentant un mécanisme concerté possède une sphère de coordination assez rigide afin d'avoir des constantes de vitesse standard élevée, un écart de ses constantes d'acidité important, une base géographiquement proche, doit être dans un environnement ne présentant pas d'anion pouvant s'associer plus fortement avec le complexe que la base et enfin répondre correctement aux critères de solubilité et stabilité chimique dans le milieu ciblé. L'étude d'un complexe de manganèse biomimétique de la superoxyde dismutase a permis d'appliquer la méthodologie mise en place lors de l'étude du complexe d'osmium et de confirmer les conclusions mises à jour par ce dernier: lorsque la concentration en espèce acceptrice de proton est importante, le processus concerté peut devenir prépondérant

Transfert couplé d'électron et de proton dans des complexes de métaux de transition modèles et d'intérêts biomimétiques (études mécanistiques par une approche électrochimique)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Etude du comportement électrochimique des POMs de type Wells-Dawson en solution

International audienc

Electrochemical, Electrocatalytic, and Magnetic Properties of Vanadium-Containing Polyoxometalates

Mono-substituted vanadium-containing Dawson-type polyoxometalates having the general formula α1-[VIVW17X2O62]8− and α2-[VIVW17X2O62]8−, with X = As or P, were synthesised and subject to a comprehensive electrochemical study comprising the pH dependency. These POMs exhibit an electrocatalytic behaviour towards the oxidation of thiols (namely cysteine), rendering them interesting species for mimicking oxidative stress situations, at physiological pH values. The efficiency of the electro-oxidation was assessed with thiols of different nature, and the substrate that responded best was used to compare the electrocatalytic capabilities of the POM series. The magnetic behaviour of these POMs was also evaluated and compared to their analogues, α1- and α2-[VVW17X2O62]7− (X = As or P), at low temperatures and showed, as expected, a paramagnetic behaviour of VIV based compounds

Synthesis and Characterisation of the Europium (III) Dimolybdo-Enneatungsto-Silicate Dimer, [Eu(α-SiW9Mo2O39)2]13−

The chemistry of polyoxometalates (POMs) keeps drawing the attention of researchers, since they constitute a family of discrete molecular entities whose features may be easily modulated. Often considered soluble molecular oxide analogues, POMs possess enormous potential due to a myriad of choices concerning size, shape and chemical composition that may be tailored in order to fine-tune their physico-chemical properties. Thanks to the recent progress in single-crystal X ray diffraction, new POMs exhibiting diverse and unexpected structures have been regularly reported and described. We find it relevant to systematically analyse the different equilibria that govern the formation of POMs, in order to be able to establish reliable synthesis protocols leading to new molecules. In this context, we have been able to synthesise the Eu3+-containing silico-molybdo-tungstic dimer, [Eu(α-SiW9Mo2O39)2]13−. We describe the synthesis and characterisation of this new species by several physico-chemical methods, such as single-crystal X-ray diffraction, 183W NMR and electrochemistry

Electrochemical, Electrocatalytic, and Magnetic Properties of Vanadium-Containing Polyoxometalates

Mono-substituted vanadium-containing Dawson-type polyoxometalates having the general formula α1-[VIVW17X2O62]8− and α2-[VIVW17X2O62]8−, with X = As or P, were synthesised and subject to a comprehensive electrochemical study comprising the pH dependency. These POMs exhibit an electrocatalytic behaviour towards the oxidation of thiols (namely cysteine), rendering them interesting species for mimicking oxidative stress situations, at physiological pH values. The efficiency of the electro-oxidation was assessed with thiols of different nature, and the substrate that responded best was used to compare the electrocatalytic capabilities of the POM series. The magnetic behaviour of these POMs was also evaluated and compared to their analogues, α1- and α2-[VVW17X2O62]7− (X = As or P), at low temperatures and showed, as expected, a paramagnetic behaviour of VIV based compounds

Proton-coupled electron transfers in biomimetic water bound metal complexes. The electrochemical approach.

International audienceWater-bound metal (M) complexes play a central role in the catalytic centers of natural systems such as Photosystem II (PSII), superoxide dismutase, cytochrome c oxidase and others. In these systems, electron transfer reactions involving the metal center are coupled to proton transfers. Besides its fundamental interest, comprehension of these reactions and of possible bio-inspired catalytic devices is an additional motivation for studying the coupling between proton and electron transfer (proton-coupled electron transfers, PCET), starting with an aqua-M(II)/hydroxo-M(III) couple, and going to higher oxidation degrees as in the case of PSII (hydroxo-M(III)/oxo-M(IV) couple). Factors that determine the occurrence of the stepwise and concerted pathways are recalled from the illustrating example of a recently described mononuclear osmium complex, thus opening perspectives for further studies of the biomimicking complex. PCET in a mononuclear aqua/hydroxo manganese couple was then studied using the electrochemical approach

Synthesis, Crystal Structure, Electrochemistry and Electro-Catalytic Properties of the Manganese-Containing Polyoxotungstate, [(Mn(H2O)3)2(H2W12O42)]6−

International audienceWe present the synthesis and structural characterization of the manganese-containing polyoxotungstate, [(Mn(H 2 O) 3) 2 (H 2 W 12 O 42)] 6− (1), obtained by reaction of MnCl 2 with six equivalents of Na 2 WO 4 in the presence of Zn(CH 3 COO) 2 in acetate medium (pH 4.7). This has been assessed by various techniques (FTIR, TGA, UV-Visible, XPS, elemental analysis, single crystal X-ray and electrochemistry). Single-crystal X-ray analyses showed that, in the solid state, 1 forms a 2-D network in which [H 2 W 12 O 42 ] 10− fragments are linked in pairs via Mn 2+ ions, leading to linear chains of the form [(Mn(H 2 O) 3) 2 (H 2 W 12 O 42)] n 6n−. The connection between chains occurs also via Mn 2+ ions which bind [H 2 W 12 O 42 ] 10− fragments belonging to two adjacent chains, forming an infinite 2-D network. A complete electrochemical study was done in aqueous solution where 1 is stable in the pH range 1 to 6. This complex undergoes multiple electron-transfer processes that lead to the electro-generation of manganese high oxidation state species that catalyse water electro-oxidation. 1 is also effective in the electro-catalytic reduction of nitrite and dioxygen

Synthesis, Structure, and Magnetic Electrochemical Properties of a Family of Tungstoarsenates Containing Just Co II Centers or Both Co II and Fe III Centers

International audienc