Tridentate facial ligation of tris(pyridine-2-aldoximato)nickel(II) and tris(imidazole-2-aldoximato)nickel(II) to generate NiIIFeIIINiII, MnIIINiII, NiIINiII, and ZhIINiII and the electrooxidized MnIVNiII, NiIINiIII, and ZnIINiIII species:: A magnetostructural, electrochemical, and EPR spectroscopic study

Eight hetero- and homometal complexes 1-6, containing the metal centers Ni '' Fel '' Ni '' (1), Mnl '' Ni '' (2), Ni '' Ni '' (3a-c and 4), Zn '' Ni '' (5), and Zn '' Zn '' (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato) nickel (11) and tris(l-methylimidazole-2-aldoximato)nickel(II) with three facially disposed pendent oxime 0 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. Binoclear 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 '' 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) complexes, 3a-c, and 4, demonstrates the effects of the remote substituents on the, spin coupling. The electrochemical measurements CV and square wave voltammograms (SOW) 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 '' Ni '', exhibits a reduction of Mn''' to Mn''' and two subsequent oxidations of Mn''' and Ni '' 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 '' Ni''' system resulting from the spin coupling, a spin quartet ground state, S = 3/2, has been confirmed by the X-band EPR measurements.