Spectroscopic studies of metal complexes with redox-active hydrogenated Schiff bases

Synthesis and spectroscopic (IR, UV-visible, ESR) characterization of metal(II) complexes M(Lx')2, (where M = Co(II), NI(II), VO(II), Pd(II), Lx' = L1', L2', L3' are monoanion of unsubstituted, 5-Cl and 5-Br substituted-2-hydroxybenzylamine) with redox-active N-(3,5-ditert-butyl-4-hydroxyphenyl)-2-hydroxybenzylamine ligands as well as radical species generated from these compounds by the oxidation with PbO2 are reported. ESR studies indicate that the VO(Lx')2 and Ni(Lx')2 complexes, in opposite to their salicylaldimine precursors, are more readily oxidized with lead dioxide and results in the formation of the indophenoxyl type stable radical. The formed radical species are very similar to each other and quite different from those of the salicylaldimine analogous according to their g-factors and hyperfine coupling constants. The nine line radical spectra observed in the oxidation of Co(Lx')2, on standing under vacuum, gradually converted to the signals characteristic of the low-spin Co(II) (g(x,y) = 2.276, g(z) = 1.998, A(xy)Co = 122.7 G, A(z)Co = 150 G) and radical containing Co(III) intermediate with g(x,y) = 2.015, A(xy)Co = 4.66 G, g(z) = 1.989, A(z)Co = 10 G were also observed.