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Redox Reactions of a Dinuclear Manganese Complex – the Influence of Water
Author(s) -
Kurz Philipp,
Anderlund Magnus F.,
Shaikh Nizamuddin,
Styring Stenbjörn,
Huang Ping
Publication year - 2008
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200700888
Subject(s) - chemistry , redox , manganese , ligand (biochemistry) , electron paramagnetic resonance , oxidation state , non innocent ligand , acetonitrile , reagent , cyclic voltammetry , electrochemistry , inorganic chemistry , photochemistry , catalysis , organic chemistry , electrode , biochemistry , physics , receptor , nuclear magnetic resonance
The redox properties of the dinuclear manganese complex [Mn III,III 2 L(μ‐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]methyl}‐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 (Mn III,IV 2 ) from its most reduced state (Mn II,II 2 ) to about 1.1 V. Higher oxidation states of 1 are stabilized, most likely by water coordination and the formation of μ‐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 II,II 2 or Mn II,III 2 state after considerable ligand rearrangement. As complexes like 1 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)