Tridentate facial ligation of tris(pyridine-2-aldoximato)nickel(II) and tris(imidazole-2-aldoximato)nickel(II) To generate NiIIFeIIINiII, MnIIINiII, NiIINiII, and ZnIINiII 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(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 MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) 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(II)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 (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 NiIINiIII system resulting from the spin coupling, a spin quartet ground state, S(t) = 3/2, has been confirmed by the X-band EPR measurements.
Chaudhuri
Phalguni
P
Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany. chaudhuri@mpi-muelheim.mpg.de
Weyhermüller
Thomas
T
Wagner
Rita
R
Khanra
Sumit
S
Biswas
Biplab
B
Bothe
Eberhard
E
Bill
Eckhard
E
D004563:Electrochemistry / Q000379:methods*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008280:Magnetics; D008345:Manganese / Q000737:chemistry*; D008670:Metals; D008956:Models, Chemical; D008968:Molecular Conformation; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010091:Oximes; D010100:Oxygen / Q000737:chemistry; D013053:Spectrophotometry / Q000379:methods; D013696:Temperature; D013816:Thermodynamics; D014961:X-Ray Diffraction; D015032:Zinc / Q000737:chemistry*
D008024:Ligands; D008670:Metals; D009942:Organometallic Compounds; D010091:Oximes; C525755:tris(imidazole-2-aldoximato)nickel(II); C525756:tris(pyridine-2-aldoximato)nickel(II); D008345:Manganese; D009532:Nickel; D007501:Iron; D015032:Zinc; D010100:Oxygen