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

A new series of bis­(ferrocenylethynyl)
complexes, 3–7, and a mono­(ferrocenylethynyl)
complex, 8, 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, ΔE1/2 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.