Bis(fulvalene)diiron, Its Mono- and Dications. Intramolecular Exchange Interactions in a Rigid System

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Biferrocenylene [bis(fulvalene)diiron, BFD] was synthesized by two independent routes: an Ullman coupling of dibromoferrocene and the reaction of the fulvalene dianion with ferrous chloride. It was chemically oxidized to the mixed valence monocation and to the dication. These derivatives were characterized by optical, Mössbauer, ESR, and X-ray photoelectron spectra and magnetic susceptibility. The Mössbauer spectra of the mixed valence salts at 298 and 77 K indicate that both iron atoms are equivalent. X-Ray photoelectron spectra similarly attest to this equivalence. An asymmetry in the intensity of the Mössbauer lines is due to a Karyagin effect. The Mössbauer spectrum of the dication shows a quadrupole splitting of 3.0 mm/s which is unusually large for a ferrocenium-type derivative. The magnetic susceptibility of BFD (2,3) picrate, measured in the 2-300 K range, follows a Curie law with a room temperature moment very close to the spin-only value. The dicationic fluoroborate salt is diamagnetic. The ESR spectra of the monocationic picrate and fluoroborate salts are characterized by narrow lines and a small rhombic anisotropy. An absorption in the near-infrared centered at 1550 nm is observed in the spectra of the monocations, but not the neutral or dicationic derivatives. The assignment of this band is discussed with respect to the results of the other physical measurements. © 1976, American Chemical Society. All rights reserved.