A neutron diffraction study of the crystal structure of ferrocene

Abstract

The structure of ferrocene was refined with data measured at 173 and 298 K (space group P21/a, Z = 2) to final R's = 0.030 and 0.018, resp. The positions of all H atoms were varied in the refinements. The cyclopentadienyl ligands are significantly nonplanar, with the H atoms displaced toward the Fe, in agreement with the results of earlier electron diffraction studies (Bohn and Haaland, 1966; Haaland and Nilsson, 1968). The structure is disordered, as indicated by Willis's original neutron diffraction measurements (1960). Refinements were carried out by 3 procedures: (1) conventional refinement with anisotropic thermal parameters introduced for all atoms, (2) extension of (1) to include 3rd- and 4th-order thermal tensors for C and H atoms, and (3) refinement with the cyclopentadienyl ligands assumed to occupy 2 disordered positions. Based upon the results of these refinements and rigid-body-motion analyses of the thermal parameters, it appears that the disorder of the cyclopentadienyl rings results from the presence of mols. in different orientations randomly distributed throughout the crystal. A similar conclusion was reached from x-ray diffraction data (Seiler and Dunitz, 1979).