952505-03-2Relevant articles and documents
Tridentate facial ligation of tris(pyridine-2-aldoximato)nickel(II) and tris(imidazole-2-aldoximato)nickel(II) to generate NiIIFe IIINiII, MnIIINiII, Ni IINiII, and ZnIINiII and the electrooxidized MnIVNiII, NiIINiIII
Chaudhuri, Phalguni,Weyhermueller, Thomas,Wagner, Rita,Khanra, Sumit,Biswas, Biplab,Bothe, Eberhard,Bill, Eckhard
, p. 9003 - 9016 (2007)
Eight hetero- and homometal complexes 1-6, containing the metal centers NiIIFeIIINiII (1), MnIIINi II (2), NiIINiII (3a-c and 4), Zn IINiII (5), and ZnIIZnII (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 NiII 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 NiII2 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 IIINiII, exhibits a reduction of MnIII to MnII and two subsequent oxidations of MnIII 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 NiIINi III system resulting from the spin coupling, a spin quartet ground state, St = 3/2, has been confirmed by the X-band EPR measurements.
