Crystal Structures of Ferrocene Derivatives Containing Iron Atoms in Anomalous Electronic States

Abstract

Some ferrocene derivatives have been shown by Mossbauer spectroscopy to give an anomalous electronic state when treated with an oxidant or a Lewis acid. Two typical compounds among them, dibutylbiferricinium triiodide and iodotetramethyl[ 2 ] ferrocenophanium triiodide were subjected to an X-ray structural analysis, in order to clarify the mechanism for the formation of the unique electronic state in terms of the molecular strupture, conformation and counter anions in a solid.
Crystal str ucture of dibutylbiferricinium triiodide, which is known to exhibit temperaturedependent mixed valence state in Mössbauer spectrum, was determined at 150, 298 and 363 K. The averaged-valence state appeared in Mössbauer spectrum was attributed to an anisotropic molecular structure and interaction between iron atoms and iodide ions, which were slightly different from those in the trapped valence state observed at a lower temperature.
A part of iodotetramethyl[ 2 ] ferrocenophanium triiodide showed a lar ge quadrupole splitting in its Mössbauer spectrum, while the rest of the species showed the quadrupole splitting as small as that of ferricinium species. X-ray structural studies of a single crystal of this compound indicate that there are two kinds of iron atoms present at 298 K; i. e., 85% of iron atoms have a bond formation with iodide ions in a distance of 2.64Å and 15% of them are in the ferricinium state.