A neutron diffraction study of the crystal structure of ferrocene

The structure of ferrocene has been refined with singlecrystal neutron diffraction data measured at temperatures of 173 and 298 K [Fe(^ 5-C 5H 5) 2, C 1 0 H 1 0 Fe, space group PI J a, Z = 2]. The positions of all H atoms have been varied in the refinements. The cyclopentadienyl ligands are found to be significantly non-planar, with the H atoms displaced toward the Fe atom, in agreement with the results of earlier electron diffraction studies [Bohn & Haaland (1966). J. Organomet. Chem. 5, 470-476; Haaland & Nilsson (1968). Acta Chem. Scand. 22, 2653-2670]. The crystal structure is dis* Research carried out at Brookhaven National Laboratory under contract with the US Department of Energy and supported by its Office of Basic Energy Sciences. t To whom correspondence should be addressed. ordered, as indicated by Willis's original neutron diffraction measurements [Willis (1960\Acta Cryst. 13,1088; (1961). AERE Report R3708, Harwell, Oxfordshire, England]. In the present work, refinements were carried out by three procedures: {A) conventional refinement with anisotropic thermal parameters introduced for all atoms, (.B) extension of (A) to include thirdand fourthorder thermal tensors for C and H atoms, and (C) refinement with the cyclopentadienyl ligands assumed to occupy two 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 molecules in different orientations randomly distributed throughout the crystal. A similar conclusion has been reached from X-ray diffraction data [Seiler & Dunitz (1979). Acta Cryst. B35, 10681074]. FUSAO TAKUSAGAWA AND THOMAS F. KOETZLE 1075