A neutral triple-helical trinuclear oxo-centered mixed-valent iron complex: Mossbauer spectroscopic and magnetic susceptibility studies

V. Coropceanu, V. Schünemann, C. Ober, M. Gerdan, A. X. Trautwein, J. Köhler, R. W. Saalfrank

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7 Scopus citations


The electronic properties of the trimeric oxo-centred [Fe3OL3] complex (L is a doubly negatively charged pentadentate ligand, providing five nitrogens for iron coordination) have been investigated by Mossbauer spectroscopy, magnetic susceptibility and a theoretical treatment including the phenomena of double-exchange interaction. Two quadrupole doublets I and II with the ratio ~ 2:1 are observed at 4.2 K. By comparing the isomer shifts of these doublets (δ(I) = 0.52 mm s-1 and δ(II) = 0.99 mm s-1) with those of other mixed metal complexes with comparable iron-ligand coordination it is concluded in this study that [Fe3OL3] exhibits a partially delocalised ground state: Fe2.9+-Fe2.9+-Fe2.2+. At elevated temperatures the Mossbauer spectra of [Fe3OL3] exhibit two additional doublets III and IV (δ(III) = 0.60 mm s-1 and δ(IV) = 0.80 mm s-1 at 20 K), which are ascribed to an additional partially delocalised state, i.e. Fe2.75+-Fe2.75+-Fe2.5+. By admitting the coexistence of two types of clusters with different delocalised valence states, it is possible to consistently fit the Mossbauer spectra over the whole temperature range (4.2-332 K) being investigated. Temperature-dependent magnetic susceptibility data of [Fe3OL3] from 2 to 295 K can be analysed by the Heisenberg-Dirac-Van Vleck model with only two exchange parameters J = -140 cm-1 and J1 = -49 cm-1, describing the Fe(III)-Fe(III) and Fe(III)-Fe(II) exchange interactions and yielding a net antiferromagnetic coupling of the three paramagnetic sites with a spin-triplet ground state. In order to explain the seemingly contradictory situation that the Mossbauer spectra of [Fe3OL3] exhibit partial valence delocalisation while it is possible to analyse the magnetic data with valence-trapped ground state and exited states a theoretical treatment is presented, which includes antiferromagnetic exchange, double exchange and vibronic interactions. (C) 2000 Elsevier Science S.A.

Original languageEnglish (US)
Pages (from-to)875-881
Number of pages7
JournalInorganica Chimica Acta
StatePublished - Apr 30 2000
Externally publishedYes


  • Magnetic susceptibility studies
  • Mossbauer spectroscopy
  • Oxo-centered mixed-valent
  • Theoretical treatment
  • Trinuclear iron complexes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry


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