Oxo-centred Trinuclear Acetate Complexes Containing Mixed-metal Clusters

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Crystal structure of a chromium(III)iron(III)nickel(II) complex and magnetic properties of a dichromium(III)magnesium(II) complex


The crystal structure of [CrIIIxFeIII2-xNi IIO(O2CCH3)6(py) 3]·py 1 (x = ca. 0.7, py = pyridine), has been determined at 25°C. Although the molecule has no crystallographically imposed symmetry, the metal atoms form an almost equilateral triangle, M⋯M 3.274(3), 3.284(4), 3.281(3) Å, with the O atom less than 0.006 Å from the M3 plane, and the Cr, Fe, and Ni atoms extensively disordered over the three metal sites. The corresponding Cr2Mg, Cr2Ni, and Fe2Ni complexes are isomorphous with 1. The structure differs from that of the rhombohedral FeIII2MII (MII = Mn, Fe, Co or Zn) and CrIII2MII (MII = Mn, Fe or Co) analogues in the orientations of the pyridine rings. The planes of the pyridine ligands in 1 are approximately perpendicular to the M3 plane, and the non-coordinated pyridine molecule lies approximately in this plane. (This contrasts with the rhombohedral complexes, where the ligand pyridine rings are approximately parallel with the M3 plane and the non-co-ordinated pyridine lies with its plane on the three-fold axis of the M3O system.) The magnetic susceptibility of [CrIII2MgO(O2CCH3) 6(py)3]·py has been measured between 5 and 300 K, and fitted by use of an exchange hamiltonian -2JS1·S2, giving JCrCr = -17 cm-1, a value considerably smaller than that (ca. -26 cm-1) of the Cr2Ni and Cr2Co analogues.



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