Mechanistic study on electrochemical reduction of calix[4]quinone in acetonitrile containing water

Abstract

The mechanism of electrochemical reduction of calix[4]quinones (CQs) is of vital importance, as their reduction products, calix[4]hydroquinones (CQH(8)s), are known to self-assemble organic nanotubes, which in turn self-assemble novel metal nanostructures by a self-synthetic process of electrochemical reduction of solvated metals. We therefore conducted detailed studies of electrochemical reduction of CQ in rigorously dried acetonitrile (CH3CN) and in CH3CN containing varied amounts of water as well as perchloric acid. CQ undergoes a series of reversible one electron reductions in dry CH3CN leading to anion radicals of each of p-benzoquinone units followed by formation of dianions. However, a series of following chemical-electrochemical reactions with protons takes place after the initial electron transfer in CH3CN containing water. The final product of this series of reactions is identified as CQH(8) via an eight electron, eight proton reaction. The intermediate species are identified, and the reaction mechanism is elucidated using transient electrochemical, electrochemical quartz crystal microbalance and spectroelectrochemical measurements. The present results could be utilized to fine control the self-assembling reaction of nanotubes by electrochemical processes and to design electrochemically controllable nanomechanical devices.