Synthesis, Structure, and Magnetism of Bimetallic Magnanese or Nickel Complexes of a Bridging Verdazyl Radical

摘要

Two binuclear metal-radical complexes, formed by the reaction of M(hfac)_2·2H_2O (M = Mn or Ni; hafc = 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: C_(30)H_(17)N_6O_9F_(24)Mn_2, a = 29.947(3), b = 17.143(3), c = 16.276(3) A,#beta# = 123.748(3) deg, 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 moleuclar strucure 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.