Abstract
Pincer ligands occupy three coplanar sites at metal centers and often support both stability and reactivity. The five-coordinate [FeIIICl2(tia-BAI)] complex (tia-BAI− = 1,3-bis(2’-thiazolylimino)isoindolinate(−)) was considered as a potential pre-catalyst for water oxidation providing the active form via the exchange of chloride ligands to water molecules. The tia-BAI− pincer ligand renders water-insolubility to the Fe–(tia-BAI) assembly, but it tolerates the presence of water in acetone and produces electrocatalytic current in cyclic voltammetry associated with molecular water oxidation catalysis. Upon addition of water to [FeIIICl2(tia-BAI)] in acetone the changes in the Fe3+/2+ redox transition and the UV-visible spectra could be associated with solvent-dependent equilibria between the aqua and chloride complex forms. Immobilization of the complex from methanol on indium-tin-oxide (ITO) electrode by means of drop-casting resulted in water oxidation catalysis in borate buffer. The O2 detected by gas chromatography upon electrolysis at pH 8.3 indicates >80% Faraday efficiency by a TON > 193. The investigation of the complex/ITO assembly by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) before and after electrolysis, and re-dissolution tests suggest that an immobilized molecular catalyst is responsible for catalysis and de-activation occurs by depletion of the metal.
Highlights
Artificial photosynthesis, on the analogy of the natural process, is an exciting strategy that may meaningfully contribute to our sustainable-energy future
A heterocyclic pincer ligand was utilized in a FeIII dichloride complex (Figure 1), which served as precursor for the electrocatalyst aqua-form in water oxidation
In this study we discussed the electrochemical properties of the [FeIII Cl2] complex in homogeneous water/acetone mixture to reveal the signatures of Cl− to H2 O ligand exchange and proposed a molecular mechanism for the catalytic cycle
Summary
Artificial photosynthesis, on the analogy of the natural process, is an exciting strategy that may meaningfully contribute to our sustainable-energy future. The water oxidation reaction (Equation (1)) still stands as a great challenge in artificial systems, because it is an energetically uphill process, and due to its kinetics making catalysis indispensable [1], as happens at the. Mn4 CaO5 active site of the oxygen-evolving enzyme of photosystem II [2]. Reactions 2020, 1, 16–36; doi:10.3390/reactions1010003 pH F (1). 2020, 13, x FOR PEER REVIEW Reactions. Molecular water oxidation catalysts (WOCs) promote this field by providing mechanistic. Molecular oxidation (WOCs) this A field by providing mechanistic insight into thewater complex processcatalysts of the O=O bondpromote formation
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