Intramolecular and intermolecular dynamics in the two crystal phases of ferrocene carboxaldehyde

Incoherent quasi-elastic and inelastic neutron scattering experiments have been performed on crystalline ferrocene carboxaldehyde in both its ordered (T < 317 K) and disordered (317 < T/K < 396) phases. The unsubstituted ring is found to be undergoing five-fold jump reorientations between indistinguishable positions at all temperatures within range of the experimental resolution (T > 170 K), with an energy barrier of 17 ± 4 kJ mol^-1. The molecular motions in the disordered phase are found to be complex and involve internal rotation plus whole-molecule rotational and translational components, consistent with structural work. They are associated with time-scales in the range 10^-10 -10^-12 s and a range of energy barriers up to 20 kJ mol^-1.