Département de chimie moléculaire

Abstract We previously reported the multireversible redox behavior of bis(triple-helicate) pentanuclear complexes of the type [{M(μ-bpp)3}2M(μ3-X)]n+ (M=Mn, Fe with X=O and Co with X=OH) with rigid tetradentate binucleating 3,5-bis(pyridine-2-yl)pyrazole (bpp−) ligand. In this article, we focus on the nickel derivative of this family, [{NiII(μ-bpp)3}2NiII3(μ-OH)]3+ (13+), which exhibits up to five reversible or quasi-reversible one-electron waves in CH3CN solution. The two one-electron oxidized species as well as the one-electron reduced species with respective compositions of 4NiII1NiIII (14+), 3NiII2NiIII (15+) and 1NiI4NiII (12+), were quantitatively generated by bulk electrolyses and spectroscopically characterized highlighting the high stability of this family of complexes in several redox states. In addition to the initial complex 13+, the mixed-valence 12+ was also successfully characterized by single-crystal X-ray diffraction, allowing to locate the sites of successive reversible one-electron events. 12+ is an unusual example of a multinuclear complex including the low-valent Ni(I) state.