The competition of basicity and steric factors in the nitroxide donor functions in metal complexes: The study of M(hfac) 2(M = Co, Ni) adducts with 3-imidazoline nitroxides

Abstract

The similar nitroxides 2,2,5,5-tetramethyl-4-phenyl-3-imidazoline-1-oxyl (L 1) and 2,2-dimethyl-5,5-dimethoxy-4-phenyl-3-imidazoline-1-oxyl (L 2) from complexes of different composition on reaction with cobalt and nickel hexafluoroacetylacetonates: M(hfac) 2L 2 1 and M(hfac) 2 (H 2O) 2L 2 2. In the M(hfac) 2L 2 1 complexe the nitroxides are bonded to the metal ion through the nitroxide oxygen but the imine nitrogen does not participate in coordination for steric reasons. In M(hfac) 2(H 2O) 2L 2 2 the nitroxide moieties are H-bonded to the coordinated water molecules through the imine nitrogen atoms and methoxy oxygen atoms. The nitroxide L 2 is unstable in the presence of Co(hfac) 2 and on removal of water decomposes to yield the adduct with nitrone Co(hfac) 2L 2 3, L 3 = 2,2-dimethyl-5-methoxy-4-phenyl-2 H-imidazol 1-oxide. The complexes M(hfac) 2L 2 1 demonstrate strong antiferromagnetic coupling between the metal ion and nitroxides.