Département de chimie moléculaire

Four bis-phenolate complexes [ZnIIL], [NiIIL], [CuIIL] and [CoIIL] (H2L = 2,2'-[2,2']bipyridinyl-6-yl-bis-4,6-di-tert-butylphenol) were synthesized. The Cu(II) and Ni(II) complexes were characterized by x-ray diffraction, showing a metal ion within a square planar geometry, slightly distorted towards tetrahedral. The cyclic voltammetry (CV) curve of [ZnIIL] consists of a single bi-electronic reversible wave at 0.06 V vs. Fc/Fc+. The electrochem. generated dication is a diradical species [ZnIIL√√]2+ that exhibits the typical phenoxyl $π$-$π$* band at 395 nm. It is EPR-silent due to magnetic interactions between the phenoxyl moieties. The CV curves of [NiIIL] and [CuIIL] exhibit two distinct ligand-centered 1-electron oxidn. waves. The 1st one is obsd. at E1/21 = 0.38 and 0.40 V for the Ni and Cu complex, resp., and corresponds to the formation of M(II)-coordinated phenoxyl radicals. Accordingly, [NiIIL√]+ exhibits a strong absorption band at 960 nm and an (S = 1/2) EPR signal centered at giso = 2.02. [CuIIL√]+ is EPR-silent, in agreement with a magnetic coupling between the metal and the radical spin. In contrast with the other complexes, [CoIIL] was found to react with dioxygen (mostly in the presence of pyridine), giving rise to a stable (S = 1/2) superoxo radical complex [CoIIIL(Py)(O2√)]. One-electron oxidn. of [CoIIL] at -0.01 V affords a diamagnetic Co(III) complex [CoIIIL]+ that is inert towards O2 binding, whereas two-electron oxidn. leads to the paramagnetic phenoxyl radical species [CoIIIL√]2+ whose EPR spectrum features an (S = 1/2) signal at giso = 2.00. [on SciFinder(R)]