THE COMPETITION OF BASICITY AND STERIC FACTORS IN THE NITROXIDE DONORFUNCTIONS IN METAL-COMPLEXES - THE STUDY OF M(HFAC)(2) (M=CO, NI) ADDUCTS WITH 3-IMIDAZOLINE NITROXIDES

The similar nitroxides 2,2,5,5-tetramethyl-4-phenyl-3-imidazoline-1-ox yl (L(1)) and methyl-5,5-dimethoxy-4-phenyl-3-imidazoline-1-oxyl (L(2) ) form complexes of different composition on reaction with cobalt and nickel hexafluoroacetylacetonates : M(hfac)(2)L(2)(1) and M(hfac)(2)(H 2O)(2)L(2)(2). In the M(hfac)(2)L(2)(1) complexes the nitroxides are b onded to the metal ion through the nitroxide oxygen but the imine nitr ogen does not participate in coordination for steric reasons. In M(hfa c)(2)(H2O)(2)L(2)(2) the nitroxide moieties are H-bonded to the coordi nated water molecules through the imine nitrogen atoms and methoxy oxy gen 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)(2)L(2)(3), L(3) = 2,2-dimethyl-5-methoxy-4-phenyl-2H-imidazo l 1-oxide. The complexes M(hfac)(2)L(2)(1) demonstrate strong antiferr omagnetic coupling between the metal ion and nitroxides. Copyright (C) 1996 Elsevier Science Ltd