New linear high-valent tetranuclear manganese-oxo cluster relevant to the oxygen-evolving complex of photosystem II with oxo, hydroxo, and aqua coordinated to a single Mn(IV)

Hongyu Chen, Marie Noëlle Collomb, Carole Duboc, Geneviève Blondin, Eric Rivière, J. W. Faller, Robert H. Crabtree, Gary W. Brudvig

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An unprecedented atom connectivity, Mn IV(μ-O)Mn IV(μ-O) 2Mn IV(μ-O)Mn IV, is found in the complex [Mn IV 4O 4(EtO-terpy) 4(OH) 2(OH 2) 2](ClO 4) 6·8H 2O (EtO-terpy = 4′-ethoxyl-2,2′: 6′,2″-terpyridine), which has been characterized by X-ray crystallography, X-ray powder diffraction, EPR spectroscopy, and magnetic studies. This complex is the first example of a compound where a Mn IV ion is coordinated by all three types of water-derived ligands: oxo, hydroxo, and aqua. Bond distances and angles for this complex are consistent with a Mn IV 4 oxidation state assignment. The di-μ-oxo- and mono-μ-oxo-bridged Mn-Mn distances are 2.80 and 3.51 Å, respectively. The variable-temperature magnetic susceptibility data for this complex, in the range of 10-300 K, are consistent with an S = 0 ground state and were fit using the spin Hamiltonian Ĥ HDvV = - J 1Ŝ 2Ŝ 1 - J 2Ŝ 1S 1A - J 1Ŝ 1AŜ 2A (S 1 = S 1A = S 2 = S 2A = 3/2) with J 1 = -432 cm -1 and J 2 = -164 cm -1 (where J 1 and J 2 are exchange constants through the mono-μ-oxo and the di-μ-oxo bridges, respectively). The first excited spin state of this tetramer is a spin triplet state at 279 cm -1 above the diamagnetic ground state. The next spin states are the S = 1 and S = 2 levels at about 700 and 820 cm -1 above the S = 0 ground state, respectively. These large energy gaps are consistent with the absence of an EPR signal for this complex, even at high temperature.

Original languageEnglish
Pages (from-to)9567-9573
Number of pages7
JournalInorganic Chemistry
Issue number25
Publication statusPublished - Dec 12 2005


ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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