Synthesis and Characterization of Diferrocenyl Conjugates: Varying π-Conjugated Bridging Ligands and its Consequence on Electrochemical Communication

Organometallic wire-like complexes with ferrocenyl termini, conjugated with one and two units of thienylethynyl (M1 and M2) and thienyl (M3 and M4) groups, have been synthesized with a general formula of [Fc-C C-(Th-C C)(1-2)-Fc] and [Fc-(Th)(1-2)-Fc] (Fc = ferrocenyl, Th = thienyl) respectively. The diferrocenyl organometallic complexes have been characterized by various spectroscopic tools such as multinuclear NMR, FTIR, elemental analysis, and mass spectrometry. The electrochemical properties of these compounds have been investigated by cyclic (CV) and differential pulse voltammetry (DPV). The single reversible oxidation wave in diferrocenyl complexes with thienylethynyl spacers (M1 and M2) indicates the absence of intramolecular electrochemical communication between the two ferrocenyl termini. Interestingly, the diferrocenyl complexes with one and two thienyl spacers (M3 and M4) show two successive reversible one-electron oxidation waves, indicating electronic coupling between the two ferrocenyl (Fc) termini. The potential difference (Delta E-1/2) between the two redox centers is 160 mV and 130 mV, respectively, with the corresponding comproportionation constants (K-c) of 6.2 x 10(2) and 1.5 x 10(2). Upon mono-oxidation of M3 by [Cp2Fe][BF4], a broad and weak intervalence charge-transfer (IVCT) transition is observed in the NIR region of 1200-2200 nm.