Mössbauer Spectroscopy Studies of Slow Paramagnetic Relaxation and Magnetic Interactions in Ferrocenium-Based Molecular Magnetic Materials

Abstract

Analogous to the quest for ever higher T c organic and inorganic superconductors, the search for molecular magnetic materials with high Curie and Neel temperatures continues unabated. By molecular, we will mean truly organic, primarily carbon-based materials, or perhaps polar organic solvent-soluble organometallic species. They should exhibit spontaneous magnetization to something approximating a bulk magnetically ordered state where such three-dimensional ordering occurs in zero applied field. We like to believe that some of the impetus for the current interest in this area came from our discovery1 that the charge transfer salt, decamethylferrocenium tetracyanoethyleneide, {DMFc+}{TCNE}− (alternatively [Fe(Cp*)2]+[TCNE]−), shows bulk ferromagnetism, with a Curie temperature T c = 4.8 K. This conclusion was confirmed by classical susceptibility, heat capacity,2 neutron diffraction, and zero- and applied-field Mossbauer spectroscopy measurements. A variety of paradigms have been proposed, tried, and recently discussed3 vis-a-vis rational approaches to isolation of such materials. There are clearly challenging synthetic chemistry and structural characterization problems remaining that must be mastered for continued advances in this area.