Magnetic and spectroscopic properties of some heterotrinuclear basic acetates of chromium(III), iron(III), and divalent metal ions

  • Blake A
  • Yavari A
  • Hatfield W
 et al. 
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Reaction of Fe, M, and acetate ions in aqueous solution gives [FeMO(MeCO)(HO)][middle
dot]3HO (M = Mg, Mn, Co, Ni, or Zn), which on crystallisation from
pyridine (py) is converted into [FeMO(MeCO)(py)]. Reaction of chromium()
acetate with metal() acetate in pyridine in the presence of air gives
[CrMO(MeCO)(py)](M = Mg, Co, or Ni), and with [FeMO-(MeCO)(py)] in
pyridine inthe absence of air gives [CrFeMnO(MeCO)(py)](M = Mn or
Fe) and [CrFeO(MeCO)(py)]. The compounds with co-ordinated pyridine
have been examined crystallographically and magnetically. The CrMg,
CrNi, FeNi, and CrFeNi compounds crystallise in the monoclinic system,
space group or 2/, = 4, but the other seven compounds are rhombohedral
and isomorphous with [MO(MeCO)(py)][middle dot]py (M = Mn or Fe),
indicating that the three metal atoms are crystallographically equivalent
as a result of disorder in the molecular orientation. Powder magnetic
susceptibilities for the CrCo and CrNi compounds(4.2-60 K), for the
FeMn and FeNi compounds (4.2-295 K), and for the FeNi(aquo) and FeMg
compounds (80-295 K) have been fitted by use of an exchange Hamiltonian
to yield values of the exchange parameters for the Cr-Cr, Fe-Fe,
Cr-Ni, Fe-Ni, and Fe-Mn interactions, which are discussed in terms
of superexchange mechanisms. The values of in the FeMg, FeMn, and
FeNi compounds and of in the CrCo and CrNi compounds are approximately
twice their values in the cations [MO(MeCO)(HO)](M = Cr or Fe), indicating
that the [small micro]-O atom provides the main super-exchange pathway.
Diffuse-reflectance and solution spectra (6 000-40 000 cm) of the
compounds have been recorded at room temperature and are discussed
in terms of the ligand-field model; a band in the spectra of the
FeFe and CrFeFe compounds at . 7 000 cm is assigned to intervalence
transfer. The room-temperature spectra of [MO(MeCO)L]Cl (M= Cr, CrFe,
CrFe or Fe; L = HO or py) have also been obtained, and intense absorption
bands at . 19 000 and 26 000 cm are tentatively assigned to simultaneous
(Cr, Fe) double excitations.

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  • Antony B. Blake

  • Ahmad Yavari

  • William E. Hatfield

  • C. N. Sethulekshmi

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