Synthesis of a magnetic polyvinylferrocene-tetracyano ethylene complex

A polymeric magnet was produced by reacting polyvinylferrocene (PVFE) with tetracyanoethylene (TCNE). Fourier transform infrared spectroscopy (FTIR) reveals that the Fe +2 of the ferrocene pendant group of the polymer has been oxidized to the Fe+3 state in the magnet, as confirmed by the shift of the out-of-plane bending band of the C-H bonds in the cyclopentadiene rings from 816 cm-1 to 851 cm-1, as well as the shift of the metal ion ligand vibration in the ferrocene moiety from 480 cm -1 to 552 cm-1. The proton nuclear magnetic resonance (NMR) spectrum shows shifts of the aromatic H atoms of the ferrocene rings from 4.05 ppm in the PVFE to 4.15 ppm in the PVFE/TCNE complex, consistent with the removal of electron density from the vicinity of the cyclopentadiene rings. The inverse of the mass magnetization vs. temperature curve yields a Curie temperature, Tc, near 2° K. It is possible to extrapolate several values of theta around 170° K, indicating the presence of more than one type of magnetic domain. The fitting of the magnetization data to the Brillouin function results in three possible fits. The 57Fe Mossbauer spectroscopy showed one of the magnetic species is a superparamagnet. At 2° K the magnetization curve exhibits the hysteresis characteristic of the ferromagnetic state with coercive fields of 200--5000 G. Computer modeling suggests that the cyclopentadiene rings are oriented at an angle of 32° in the PVFE/TCNE complex. This model implies that there is but one TCNE molecules available to oxidize each iron center PVFE, leading to the Fe+3 state, the magnetism and the ring distortion in the PVFE/TCNE complex. In contradistinction, the cyclopentadiene rings are parallel in the diamagnetic complex formed by the reaction of ferrocene with TCNE with more than two TCNE molecules competing for the electron on each iron center. Here, iron is not oxidized by TCNE. These geometrical features provide a very likely explanation of the differences in their magnetic behaviors and will be discussed extensively herein. The potential applications of this and future magnetic polymers of high molecular weight will also be discussed.