Complexes of bis(hexafluoroacetylacetonato)copper(II) [Cu(hfac)(2)] ligated with 3- and 4-(N-oxyl-tert-butylamino)pyridines (3NOPy and 4NOPy) and N-{3- and 4-(N-oxyl-tert-butylamino)phenyl}imidazoles (3NOIm and 4NOIm) were prepared. The 1:2 complexes [Cu(hfac)(2)(3NOPy and 4NOPy)(2)] have hexacoordinated octahedral structures in which the two pyridyl nitrogen atoms are coordinated to the copper(II) ions in the trans configuration. The 1:1 complex [Cu(hfac)(2)(4NOPy)] has a distorted pentacoordinated pseudo-head-to-tail cyclic dimer structure in which the oxygen atom of the aminoxyl group of one complex is situated at a distance of 2.79 Å from the copper ion of the other complex. The magnetic properties of these and two other complexes, [Cu(hfac)(2)(3NOIm and 4NOIm)(2)], were investigated using a SQUID susceptometer. Temperature dependence studies of the chi(mol)Tvalues of [Cu(hfac)(2)(4NOPy)(2)] revealed that the two aminoxyl radicals interact ferromagnetically with the copper(II) ion (S = (1)/(2)) with an exchange parameter J/k(B) = 60.4 +/- 3.3 K to produce a quartet ground state (S = (3)/(2)). On the other hand, the chi(mol)T value of the isomeric [Cu(hfac)(2)(3NOPy)(2)] was nearly constant at 0.5 emu K mol(-)(1) in the temperature range 5-300 K. A rectangular four-spin model was fitted to the chi(mol)T vs T plot for complex [Cu(hfac)(2)(4NOPy)] to give J/k(B) = 58.6 and 58.5 K. Similarly, the J values for [Cu(hfac)(2)(3NOIm and 4NOIm)(2)] were negative and positive, respectively, but their absolute J values were too small to determine in both cases.

No abstract

4,4'-Bis(N-tert-butyloxylamino)-2,2'-bipyridine (4) and its 1:1 complexes with bis(hexafluoroacetylacetonato)manganese(II), -copper(II), and -zinc(II) were prepared. An X-ray structure analysis of free ligand 4 reveals that the molecule has a trans conformation with Ci symmetry and the aminoxyl radical center has a short contact of 2.36 A with one of the neighboring molecules. The three 1:1 complexes have mutually similar molecular structures in which the 2,2'-bipyridine moiety has a cis conformation and serves as a bidentate ligand and coordination geometry around the metal atom is a distorted octahedron. The EPR experiments for free ligand 4 and [Zn(hfac)2.4] in frozen solution suggested that the exchange couplings between the two aminoxyls (R) through the 2,2'-bipyridine rings are antiferromagnetic with JR-R/kB = -19.3 +/- 0.5 and -24.3 +/- 0.4 K, respectively. Isosceles triangular three-spin models were applied to the 1:1 magnetic metal complexes to give JR-M/kB = -19.1 +/- 0.2 K and JR-R/kB = -32.9 +/- 0.3 K for [Mn(hfac)2.4] and JR-M/kB = +73 +/- 18 K and JR-R/kB = -24.5 +/- 6.5 K for [Cu(hfac)2.4].