American Chemical Society
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Synthesis, Structure, and Magnetism of Bimetallic Manganese or Nickel Complexes of a Bridging Verdazyl Radical

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journal contribution
posted on 2001-09-18, 00:00 authored by Tosha M. Barclay, Robin G. Hicks, Martin T. Lemaire, Laurence K. Thompson
Two binuclear metal−radical complexes, formed by the reaction of M(hfac)2·2H2O (M = Mn or Ni; hfac = hexafluoroacetylacetonate) with the 1,5-dimethyl-3-(4,6-dimethylpyrimidin-2-yl)-6-oxoverdazyl radical (3), were synthesized. The binuclear Mn complex 5 (i.e., 3[Mn(hfac)2]2) crystallizes in the monoclinic space group C2/c:  C30H17N6O9F24Mn2, a = 29.947(3), b = 17.143(3), c = 16.276(3) Å, β = 123.748(3)°, Z = 4. The compound consists of two pseudo-octahedral Mn(II) ions, both bearing two hfac ancillary ligands, bridged by the bis(bidentate) radical 3. The temperature dependence of the magnetic susceptibility of 5 reveals moderate antiferromagnetic exchange between each of the Mn(II) ions and the verdazyl radical (J = −48 cm-1). The S = 9/2 ground spin state of the complex was corroborated by low-temperature magnetization versus field measurements. In contrast, the magnetic susceptibility versus temperature behavior of 6 (whose molecular structure is presumed to be analogous to that of 5) indicates that the two Ni(II) ions are strongly ferromagnetically coupled to the verdazyl radical (J = +220 cm-1). The magnetization versus field behavior of 5 is consistent with an S = 5/2 ground-state species.