Electrochemically Driven Swinging of a Nitrobenzyl Pendant Arm in a Nickel Scorpionand Complex.

A radical anion -NO 2 .- is formed upon an electrochemically reversible one-electron reduction of the square-planar Ni II complex of N-nitrobenzylcyclam. The -NO 2 .- group goes to occupy an axial position of the metal ion, thus establishing a significant electronic interaction with the metal center. In particular, the ESR spectrum supports the occurrence of an electron transfer from -NO 2 .- to the metal, which therefore presents a significant Ni I character. On re-oxidation, the nitrobenzyl side chain detaches and the Ni II complex is restored, providing an example of a fully reversible redox driven intramolecular motion.