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Light-induced multistep oxidation of dinuclear manganese complexes for artificial photosynthesis

Huang, Ping LU ; Högblom, Joakim LU ; Anderlund, Magnus F; Sun, Licheng; Magnuson, Ann LU and Styring, Stenbjörn LU (2004) In Journal of Inorganic Biochemistry 98(5). p.733-745
Abstract
Two dinuclear manganese complexes, [Mn2BPMP(@m-OAc)2].ClO4 (1, where BPMP is the anion of 2,6-bis{[N,N-di(2-pyridinemethyl)amino]methyl}-4-methylphenol) and [Mn2L(@m-OAc)2].ClO4 (2, where L is the trianion of 2,6-bis{[N-(2-hydroxy-3,5-di-tert-butylbenzyl)-N-(2-pyridinemethyl)amino]met hyl}-4-methylphenol), undergo several oxidations by laser flash photolysis, using rutheniumII-tris-bipyridine (tris(2,2-bipyridyl)dichloro-ruthenium(II) hexahydrate) as photo-sensitizer and penta-amminechlorocobalt(III) chloride as external electron acceptor. In both complexes stepwise electron transfer was observed. In 1, four Mn-valence states from the initial Mn2II,II to the Mn2III,IV state are available. In 2, three oxidation steps are possible from the... (More)
Two dinuclear manganese complexes, [Mn2BPMP(@m-OAc)2].ClO4 (1, where BPMP is the anion of 2,6-bis{[N,N-di(2-pyridinemethyl)amino]methyl}-4-methylphenol) and [Mn2L(@m-OAc)2].ClO4 (2, where L is the trianion of 2,6-bis{[N-(2-hydroxy-3,5-di-tert-butylbenzyl)-N-(2-pyridinemethyl)amino]met hyl}-4-methylphenol), undergo several oxidations by laser flash photolysis, using rutheniumII-tris-bipyridine (tris(2,2-bipyridyl)dichloro-ruthenium(II) hexahydrate) as photo-sensitizer and penta-amminechlorocobalt(III) chloride as external electron acceptor. In both complexes stepwise electron transfer was observed. In 1, four Mn-valence states from the initial Mn2II,II to the Mn2III,IV state are available. In 2, three oxidation steps are possible from the initial Mn2III,IIIstate. The last step is accomplished in the Mn2IV,IV state, which results in a phenolate radical.For the first time we provide firm spectral evidence for formation of the first intermediate state, Mn2II,III, in 1 during the stepwise light-induced oxidation. Observation of Mn2II,III is dependent on conditions that sustain the @m-acetato bridges in the complex, i.e., by forming Mn2II,III in dry acetonitrile, or by addition of high concentrations of acetate in aqueous solutions. We maintain that the presence of water is necessary for the transition to higher oxidation states, e.g., Mn2III,III and Mn2III,IV in 1, due to a bridging ligand exchange reaction which takes place in the Mn2II,III state in water solution. Water is also found to be necessary for reaching the Mn2IV,IV state in 2, which explains why this state was not reached by electrolysis in our earlier work (Eur. J. Inorg. Chem (2002) 2965).In 2, the extra coordinating oxygen atoms facilitate the stabilization of higher Mn valence states than in 1, resulting in formation of a stable Mn2IV,IV without disintegration of 2. In addition, further oxidation of 2, led to the formation of a phenolate radical (g=2.0046) due to ligand oxidation. Its spectral width (8 mT) and very fast relaxation at 15 K indicates that this radical is magnetically coupled to the Mn2IV,IV center. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Manganese, Photosynthesis, Ruthenium, Electron paramagnetic resonance
in
Journal of Inorganic Biochemistry
volume
98
issue
5
pages
733 - 745
publisher
Elsevier
external identifiers
  • pmid:15134919
  • wos:000221678300010
  • scopus:2342492837
ISSN
1873-3344
DOI
10.1016/j.jinorgbio.2003.12.009
language
English
LU publication?
yes
id
e813c17f-4763-43b0-8bc5-3ff4535ff228 (old id 126090)
date added to LUP
2007-07-05 14:28:46
date last changed
2017-12-10 04:35:48
@article{e813c17f-4763-43b0-8bc5-3ff4535ff228,
  abstract     = {Two dinuclear manganese complexes, [Mn2BPMP(@m-OAc)2].ClO4 (1, where BPMP is the anion of 2,6-bis{[N,N-di(2-pyridinemethyl)amino]methyl}-4-methylphenol) and [Mn2L(@m-OAc)2].ClO4 (2, where L is the trianion of 2,6-bis{[N-(2-hydroxy-3,5-di-tert-butylbenzyl)-N-(2-pyridinemethyl)amino]met hyl}-4-methylphenol), undergo several oxidations by laser flash photolysis, using rutheniumII-tris-bipyridine (tris(2,2-bipyridyl)dichloro-ruthenium(II) hexahydrate) as photo-sensitizer and penta-amminechlorocobalt(III) chloride as external electron acceptor. In both complexes stepwise electron transfer was observed. In 1, four Mn-valence states from the initial Mn2II,II to the Mn2III,IV state are available. In 2, three oxidation steps are possible from the initial Mn2III,IIIstate. The last step is accomplished in the Mn2IV,IV state, which results in a phenolate radical.For the first time we provide firm spectral evidence for formation of the first intermediate state, Mn2II,III, in 1 during the stepwise light-induced oxidation. Observation of Mn2II,III is dependent on conditions that sustain the @m-acetato bridges in the complex, i.e., by forming Mn2II,III in dry acetonitrile, or by addition of high concentrations of acetate in aqueous solutions. We maintain that the presence of water is necessary for the transition to higher oxidation states, e.g., Mn2III,III and Mn2III,IV in 1, due to a bridging ligand exchange reaction which takes place in the Mn2II,III state in water solution. Water is also found to be necessary for reaching the Mn2IV,IV state in 2, which explains why this state was not reached by electrolysis in our earlier work (Eur. J. Inorg. Chem (2002) 2965).In 2, the extra coordinating oxygen atoms facilitate the stabilization of higher Mn valence states than in 1, resulting in formation of a stable Mn2IV,IV without disintegration of 2. In addition, further oxidation of 2, led to the formation of a phenolate radical (g=2.0046) due to ligand oxidation. Its spectral width (8 mT) and very fast relaxation at 15 K indicates that this radical is magnetically coupled to the Mn2IV,IV center.},
  author       = {Huang, Ping and Högblom, Joakim and Anderlund, Magnus F and Sun, Licheng and Magnuson, Ann and Styring, Stenbjörn},
  issn         = {1873-3344},
  keyword      = {Manganese,Photosynthesis,Ruthenium,Electron paramagnetic resonance},
  language     = {eng},
  number       = {5},
  pages        = {733--745},
  publisher    = {Elsevier},
  series       = {Journal of Inorganic Biochemistry},
  title        = {Light-induced multistep oxidation of dinuclear manganese complexes for artificial photosynthesis},
  url          = {http://dx.doi.org/10.1016/j.jinorgbio.2003.12.009},
  volume       = {98},
  year         = {2004},
}