Redox reactions of a dinuclear manganese complex : the influence of water

• The redox properties of the dinuclear manganese complex [(Mn2L)-L-III,III(mu-OAC)(2)](+) (1) (where L is the trianion of the heptadentate ligand 2,6-bis{[(3,5-di-tert-butyl-2-hydroxybenzyl)(2-pyridylmethyl)amino]methy l)-4-methylphenol) were studied in acetonitrile solutions containing different concentrations of water. Electrochemical reactions as well as reactions with different chemical and photochemical redox reagents were monitored, using a variety of analytical techniques, namely cyclic voltammetry, UV/Vis spectroelectrochemistry, and EPR spectroscopy. We found that even small concentrations of water influence the compound's redox behaviour significantly, especially the oxidation reactions. As a consequence, the presence of water reduces the overall potential span needed to reach the highest oxidation state observed for 1 (M-2(III,IV)) from its most reduced state (Mn-2(II,II)) to about 1.1 V Higher oxidation states of I are stabilized, most likely by water coordination and the formation of mu-oxido bridge(s) between the two manganese atoms. For reducing conditions, an unprecedented 25-line EPR signal was observed, which might originate from reduced 1 in its Mn-2(II,II) or Mn-2(II,II) state after considerable ligand rearrangement. As complexes like I have been designed to act as potential water oxidation catalysts, the complicated redox- and ligand-exchange chemistry found for 1 in the presence of water, its intended substrate, might be exemplary for many of the dinuclear manganese compounds currently under investigation.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

manganese

N

O ligands

biomimetic synthesis

redox chemistry

EPR spectroscopy

Chemistry

Kemi

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