Probing the Electronic Properties of a Trinuclear Molecular Wire Involving Isocyanoferrocene and Iron(II) Phthalocyanine Motifs

A new
trinuclear iron­(II) complex involving two isocyanoferrocene ligands
axially coordinated to iron­(II) phthalocyanine, (FcNC)2FePc [Fc = ferrocenyl; Pc = phthalocyaninato(2−) anion], was
isolated and characterized using a variety of spectroscopic methods
as well as single-crystal X-ray diffraction. The redox behavior of
the above molecular wire was investigated through electrochemical,
spectroelectrochemical, and chemical oxidation approaches and compared
to that of the bis­(tert-butylisocyano)­iron­(II) phthalocyanine
reference compound, (t-BuNC)2FePc. For
both complexes, the first oxidation involves the phthalocyanine ligand
and results in the formation of a red phthalocyanine cation-radical-centered
[(RNC)2FePc]+ species, as evidenced by their
UV–vis and electron paramagnetic resonance spectra. Despite
the ∼11.5 Å distance between the isocyanoferrocene iron
centers, the second and third oxidation potentials for (FcNC)2FePc are separated by ∼80 mV, which is indicative of
a weak long-range metal–metal coupling in this system. Spectroscopic
signatures of the mixed-valence [(FcNC)2FePc]2+ dication were obtained using spectroelectrochemical and chemical
oxidation approaches. These experimentally assessed characteristics
were also correlated with the electronic structure, redox properties,
and spectroscopic signatures predicted by density functional theory
(DFT) and time-dependent DFT analyses.