Tm. Barclay et al., Synthesis, structure, and magnetism of bimetallic manganese or nickel complexes of a bridging verdazyl radical, INORG CHEM, 40(22), 2001, pp. 5581-5584
Two binuclear metal-radical complexes, formed by the reaction of M(hfac)(2)
. 2H(2)O (M = Mn or Ni; hfac = hexafluoroacetylacetonate) with the 1,5-dime
thyl-3-(4,6-dimethylpyrimidin-2-yl)-6-oxoverdazyl radical (3), were synthes
ized. 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 = 17.14
3(3), c = 16.276(3) Angstrom, beta = 123.748(3)degrees, Z = 4. The compound
consists of two pseudo-octahedral Mn(H) ions, both bearing two hfac ancill
ary ligands, bridged by the bis(bidentate) radical 3. The temperature depen
dence of the magnetic susceptibility of 5 reveals moderate antiferromagneti
c exchange between each of the Mn(H) 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 m
agnetic susceptibility versus temperature behavior of 6 (whose molecular st
ructure 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.