REDETERMINATION OF THE COBALTOCENE CRYSTAL-STRUCTURE AT 100-K AND 297-K - COMPARISON WITH FERROCENE AND NICKELOCENE

The molecular and crystal structures of the monoclinic modification of cobaltocene CP2Co (P2(1)/n, Z = 2) was determined at 100 K and 297 K with new sets of X-ray diffraction data (MoKalpha radiation, 3995 and 6534 reflections, refinement to R = 0.026 and 0.030 using 1061 and 1299 independent observable reflections, respectively). At 297 K the structure is disordered (similar to the isomorphous ferrocene and nickelocene) with two distinct orientations of the ring, differing in occupancy factors (80% and 20%) and by a rotation angle in the ring plane of approximately 34-degrees. Just as for nickelocene but in contrast to ferrocene, no sharp phase transition was found on cooling CP2Co to 100 K, but an essential ordering of the Cp-ring position was detected with a decrease of the contribution of the second minor orientation to nearly 10%. On the basis of a careful analysis of the molecular geometry, crystal packing, and anisotropic atomic displacement parameters, a dynamic temperature-dependent nature of the disorder in CP2Co is assumed.