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Verdazyl Radicals as Oligopyridine Mimics:  Structures and Magnetic Properties of M(II) Complexes of 1,5-Dimethyl-3-(2,2‘-bipyridin-6-yl)-6-oxoverdazyl (M = Mn, Ni, Cu, Zn)

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journal contribution
posted on 05.03.2003, 00:00 by Tosha M. Barclay, Robin G. Hicks, Martin T. Lemaire, Laurence K. Thompson
The verdazyl radical 1,5-dimethyl-3-(2,2‘-bipyridin-6-yl)-6-oxoverdazyl (3) was prepared, and its homoleptic metal complexes M(3)22+·2X- (5, M = Mn(II); 6, M = Ni(II); 7, M = Cu(II); 8, M = Zn(II); X = ClO4, PF6) were characterized by single-crystal X-ray diffraction and variable-temperature magnetic susceptibility measurements. Relevant crystallographic parameters are as follows:  5, monoclinic space group Pna21, a = 18.755(4) Å, b = 11.154(3) Å, c = 16.594(4) Å, α = 90.00°, β = 90.00°, γ = 90.00°, V = 3471.4(13) Å3, and Z = 4; 7, triclinic space group P1̋, a = 9.4638(18) Å, b = 9.8442(19) Å, c = 18.769(4) Å, α = 103.746(3)°, β = 92.925(3)°, γ = 94.869(3)°, V = 1687.8(6) Å3, and Z = 2; 8, triclinic space group P1̋, a = 9.4858(14) Å, b = 9.7919(14) Å, c = 18.889(3) Å, α = 104.196(3)°, β = 92.855(3)°, γ = 94.216(3)°, V = 1692.1(4) Å3, and Z = 2. In all cases, the two verdazyl-based ligands bind almost perpendicular to each other in meridional positions, yielding pseudooctahedral metal complexes whose general structural features are strongly reminiscent of metal bis(terpyridine) complexes. The intramolecular metal−verdazyl magnetic exchange coupling is strongly ferromagnetic in 6 (JNi-vd= +240 cm-1), and strongly antiferromagnetic in 5 (JMn-vd= −93 cm-1). Complex 7 exhibits weak ferromagnetic coupling (JCu-vd = −4.5 cm-1). Intramolecular radical−radical coupling in the zinc complex 8 was found to be weakly antiferromagnetic (Jvd-vd = −8 cm-1). Intramolecular radical−radical exchange was generally weak in the four metal complexes, ranging from −10 cm-1 (for 5) to +2 cm-1 (for 7). The low-temperature magnetic behavior of 7 and 8 is complex, possibly arising from a combination of intra- and intermolecular interactions.

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