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

Abstract

[Mn(II)(hfac)₂] and [Cu(II)(hfac)₂] formed 1:2 and 1:1 complexes with 3- and 4-(teri-butyloxyamino)pyridine (3- and 4NOPy) and 1-{3- and 4-(tert-butyloxyamino)phenyl}imidazole (3- and 4NOIm). The molecular and crystal structures 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 hexacoordinated structures in trans geometry and 1:1 complexes of Mn(II) with 4NOPy, 3-, and 4NOIm have cyclic dimer structures in cis coordination. Magnetic properties of the obtained fourteen complexes including meso-tetraarylporpyrinatochromium(III)C1 derivatives were investigated by magneto/susceptoinetry. Temperature dependence of the molar paramagnetic susceptibilities revealed that the coupling between the metal ion and the aminoxyl radicals through the aromatic rings in the complex ligated with 4NOPy were antiferromagnetic for Mn(II) and Cr(III) and ferromagnetic for Cu(II) complexes. The magnetic couplings opposite in sign to those of 4NOPy were obtained in the Cu(II) complex with 3NOIm and Cr(III)TPP complexes with 3NOPy.

Key Words:

• free radicals
• aminoxyl radicals
• manganese(II) complexes
• copper(II) complexes
• exchange coupling
• hybrid spin systems