The metal-dependent regiospecificity in the exchange coupling of manganese(II), copper(II), and chromium (III) ions with the aminoxyl radical attached as a substituent on the aromatic base ligands

[Mn(II)(hfac)(2)] and [Cu(II)(hfac)(2)] formed 1:2 and 1:1 complexes with 3 - and 4-(tert-butyloxyamino)pyridine (3- and 4NOPy) and 1-{3- and 4-(tert-b utyloxyamino)phenyl}imidazole (3- and 4NOIm). The molecular and crystal str uctures for seven of them were investigated by X-ray analyses to show that the 1:2 complexes of Mn(II) and Cu(II) with 3- and 4NOPy have hexacoordinat ed structures in trans geometry and 1:1 complexes of Mn(II) with 4NOPy, 3-, and 4NOIm have cyclic dimer structures in cis coordination. Magnetic prope rties of the obtained fourteen complexes including meso-tetraarylporpyrinat ochromium(III)Cl derivatives were investigated by magneto/susceptometry. Te mperature dependence of the molar paramagnetic susceptibilities revealed th at the coupling between the metal ion and the aminoxyl radicals through the aromatic rings in the complex ligated with 4NOPy were antiferromagnetic fo r Mn(II) and Cr(III) and ferromagnetic for Cu(II) complexes. The magnetic c ouplings opposite in sign to those of 4NOPy were obtained in the Cu(II) com plex with 3NOIm and Cr(III)TPP complexes with 3NOPy.