Observation of a Large Current on the Cyclic Voltammetry of Acylaminoferrocenes in the Solid State: An Efficient Electron-Transfer Pathway through Continuous NH···O=C Hydrogen-Bond Chains and π-Conjugation

Abstract

Abstract A series of crystal structures of acylaminoferrocenes, [(C5H5)Fe(C5H4NHCOR)] (R = CH3 (1), CH2CH3 (2), t-Bu (3), and CF3 (4)) revealed an unusually delicate dependence of the alkyl substituent structure on electron transfer through NH···O=C bonding and π-conjugation. The presence of strong intermolecular NH···O=C hydrogen bonds in the crystal was established by X-ray, IR, and CRAMPS. Compounds 1 and 2 are without steric or electrostatic hindrance, and both exhibit continuous and strong hydrogen-bond chains, or an effective π-electrons system. However, the hydrogen-bond chains in 3 and 4 are weak, or broken, by the bulkiness of t-Bu or the electrostatic repulsion of CF3. Solid-state cyclic voltammograms of 1–4 have revealed the electrochemical processes, which are critically dependent on the array and the strength of the hydrogen bonds. Although both 3 and 4 show typical reversible cyclic voltammograms, 1 and 2 exhibit irreversible redox behaviors and remarkably large current values, which indicate the presence of an effective electron transfer through the continuous hydrogen-bond chains.