Water Oxidation by Pentapyridyl Base Metal Complexes? A Case Study.
Manuel BonioloMd Kamal HossainPetko ChernevNina F SuremannPhilipp A HeizmannAmanda S L LyvikPaul BeyerMichael HaumannPing HuangNessima SalhiMun Hon CheahSergii I ShylinMarcus LundbergAnders ThapperJohannes MessingerPublished in: Inorganic chemistry (2022)
The design of molecular water oxidation catalysts (WOCs) requires a rational approach that considers the intermediate steps of the catalytic cycle, including water binding, deprotonation, storage of oxidizing equivalents, O-O bond formation, and O 2 release. We investigated several of these properties for a series of base metal complexes (M = Mn, Fe, Co, Ni) bearing two variants of a pentapyridyl ligand framework, of which some were reported previously to be active WOCs. We found that only [Fe(Py5 OMe )Cl] + (Py5 OMe = pyridine-2,6-diylbis[di-(pyridin-2-yl)methoxymethane]) showed an appreciable catalytic activity with a turnover number (TON) = 130 in light-driven experiments using the [Ru(bpy) 3 ] 2+ /S 2 O 8 2- system at pH 8.0, but that activity is demonstrated to arise from the rapid degradation in the buffered solution leading to the formation of catalytically active amorphous iron oxide/hydroxide (FeOOH), which subsequently lost the catalytic activity by forming more extensive and structured FeOOH species. The detailed analysis of the redox and water-binding properties employing electrochemistry, X-ray absorption spectroscopy (XAS), UV-vis spectroscopy, and density-functional theory (DFT) showed that all complexes were able to undergo the M III /M II oxidation, but none was able to yield a detectable amount of a M IV state in our potential window (up to +2 V vs SHE). This inability was traced to (i) the preference for binding Cl - or acetonitrile instead of water-derived species in the apical position, which excludes redox leveling via proton coupled electron transfer, and (ii) the lack of sigma donor ligands that would stabilize oxidation states beyond M III . On that basis, design features for next-generation molecular WOCs are suggested.
Keyphrases
- electron transfer
- density functional theory
- hydrogen peroxide
- high resolution
- single molecule
- metal organic framework
- computed tomography
- escherichia coli
- nitric oxide
- visible light
- magnetic resonance imaging
- mass spectrometry
- dna binding
- staphylococcus aureus
- solid state
- genome wide
- pseudomonas aeruginosa
- risk assessment
- room temperature
- highly efficient
- aqueous solution
- postmenopausal women
- dna methylation
- bone mineral density
- human health
- atomic force microscopy
- high speed