Tridentate Facial Ligation of Tris(pyridine-2-aldoximato)nickel(II)and Tris(imidazole-2-aldoximato)nickel(II)To Generate Ni~(II)Fe~(III)Ni~(II),Mn~(III)Ni~(II),Ni~(II)Ni~(II),and Zn~(II)Ni~(II)and the Electrooxidized Mn~(IV)Ni~(II),Ni~(II)Ni~(III),an

摘要

Eight hetero-and homometal complexes 1-6,containing the metal centers Ni~(II)Fe~(III)Ni~(II)(1),Mn~(III)Ni~(II)(2),Ni~(II)Ni~(II)(3a-c and 4),Zn~(II)Ni~(II)(5),and Zn~(II)Zn~(II)(6),are described.The tridentate ligation property of the metal complexes tris-(pyridine-2-aldoximato)nickel(II)and tris(1-methylimidazole-2-aldoximato)nickel(II)with three facially disposed pendent oxime O atoms has been utilized to generate the said complexes.Complex 1 contains metal centers in a linear arrangement,as is revealed by X-ray diffraction.Complexes were characterized by various physical methods including cyclic voltammetry(CV),variable-temperature(2-290 K)magnetic susceptibility,electron paramagnetic resonance(EPR)measurements,and X-ray diffraction methods.Binuclear complexes 2-6 are isostructural in the sense that they all contain a metal ion in a distorted octahedral environment MN3O3 and a second six-coordinated Ni~(II)ion in a trigonally distorted octahedral NiN6 geometry.Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers.The order of the strength of exchange coupling in the isostructural Ni_2~(II)complexes,3a-c,and 4,demonstrates the effects of the remote substituents on the spin coupling.The electrochemical measurements CV and square wave voltammograms(SQW)reveal two reversible metal-centered oxidations,which have been assigned to the Ni center ligated to the oxime N atoms,unless a Mn ion is present.Complex 2,Mn~(III)Ni~(II),exhibits a reduction of Mn~(III)to Mn~(II)and two subsequent oxidations of Mn~(III)and Ni~(II)to the corresponding higher states.These assignments of the redox processes have been complemented by the X-band EPR measurements.That the electrooxidized species[3a]~+,[3b]~+,[3c]~+,and[4]~+contain the localized mixed-valent Ni~(II)Ni~(III)system resulting from the spin coupling,a spin quartet ground state,S_t=3/2,has been confirmed by the X-band EPR measurements.