Magnetic and Spectroscopic Properties of Some Heterotrinuclear Basic Acetates of Chromium(III), Iron(III), and Divalent Metal Ions

DOI: 10.1039/DT9850002509

Source and publish data:

Journal of the Chemical Society, Dalton Transactions p. 2509 - 2520 (1985)

Update date:2022-07-30

Topics:

Authors:

Blake, Antony B.

Yavari, Ahmad

Hatfield, William E.

Sethulekshmi, C. N.

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Article abstract of DOI:10.1039/DT9850002509

Reaction of Fe³⁺, M²⁺, and acetate ions in aqueous solution gives *3H2O (M=Mg, Mn, Co, Ni, or Zn), which on crystallisation from pyridine (py) is converted into .Reaction of chromium(II) acetate with metal(II) acetate in pyridine in the presence of air gives (M=Mg, Co, or Ni), and with in pyridine in the absence of air gives (M=Mn or Fe) and .The compounds with co-ordinated pyridine have been examined crystallographically and magnetically.The Cr2Mg, Cr2Ni, Fe2Ni, and CrFeNi compounds crystallise in the monoclinic system, space group Cc or C2/c, Z=4, but the other seven compounds are rhombohedral and isomorphous with *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 Cr2Co and Cr2Ni compounds (4.2-60 K), for the Fe2Mn and Fe2Ni compounds (4.2-295 K), and for the Fe2Ni(aquo) and Fe2Mg compounds (80-295 K) have been fitted by use of an exchange Hamiltonian to yield values of the exchange parameters J 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 J_FeFe in the Fe2Mg, Fe2Mn, and Fe2Ni compounds and of J_CrCr in the Cr2Co and Cr2Ni compounds are approximately twice their values in the cations ⁺ (M=Cr or Fe), indicating that the μ₃-O atom provides the main superexchange pathway.Diffuse-reflectance and solution spectra (6000-40000 cm^-1) 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 Fe(III)2Fe(II) and Cr(III)Fe(III)Fe(II) compounds at ca. 7000 cm^-1 is assigned to intervalence transfer.The room-temperature spectra of Cl (M3=Cr(III)3, Cr(III)2Fe(III), Cr(III)Fe(III)2, or Fe(III)3; L=H2O or py) have also been obtained, and intense absorption bands at ca. 19000 and 26000 cm^-1 are tentatively assigned to simultaneous (Cr³⁺, Fe³⁺) double excitations.