Long-Range Intramolecular Electronic Communication in Bis(ferrocenylethynyl) Complexes Incorporating Conjugated Heterocyclic Spacers: Synthesis, Crystallography, and Electrochemistry

A new series of bis­(ferrocenylethynyl) complexes, <b>3</b>–<b>7</b>, and a mono­(ferrocenylethynyl) complex, <b>8</b>, have been synthesized incorporating conjugated heterocyclic spacer groups, with the ethynyl group facilitating an effective long-range intramolecular interaction. The complexes were characterized by NMR, IR, and UV–vis spectroscopy as well as X-ray crystallography. The redox properties of these complexes were investigated using cyclic voltammetry and spectroelectrochemistry. Although there is a large separation of ∼14 Å between the two redox centers, Δ<i>E</i>_1/2 values in this series of complexes ranged from 50 to 110 mV. The appearance of intervalance charge-transfer bands in the UV–vis–near-IR region for the monocationic complexes further confirmed effective intramolecular electronic communication. Computational studies are presented that show the degree of delocalization across the Fc–CC–CC–Fc (Fc = C₅H₅FeC₅H₄) highest occupied molecular orbital