Multireversible Redox Processes in a Self‐Assembled Nickel Pentanuclear Bis(Triple‐stranded Helicate): Structural and Spectroscopic Characterizations in the Ni II 5 and Ni I Ni II 4 Redox States

We previously reported the multireversible redox behavior of bis(triple‐helicate) pentanuclear complexes of the type [{M( μ ‐bpp) 3 } 2 M( μ 3 ‐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, [{Ni II ( μ ‐bpp) 3 } 2 Ni II 3 ( μ ‐OH)] 3+ ( 1 3+ ), which exhibits up to five reversible or quasi‐reversible one‐electron waves in CH 3 CN solution. The two one‐electron oxidized species as well as the one‐electron reduced species with respective compositions of 4Ni II 1Ni III ( 1 4+ ), 3Ni II 2Ni III ( 1 5+ ) and 1Ni I 4Ni II ( 1 2+ ), 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 1 3+ , the mixed‐valence 1 2+ was also successfully characterized by single‐crystal X‐ray diffraction, allowing to locate the sites of successive reversible one‐electron events. 1 2+ is an unusual example of a multinuclear complex including the low‐valent Ni(I) state.