Influence of Solvent in Crystal Engineering: A Significant Change to the Order-Disorder Transition in Ferrocene.

We present the structure of a novel solvate adduct formed by dissolving ferrocene, FeCp, in hexafluorobenzene, CF. This adduct demonstrates the remarkably strong interactions between the five-membered aromatic rings of FeCp and the six-membered aromatic ring of CF. These molecular interactions are sufficiently strong and anisotropic to change the temperature of the order-disorder transition of the ferrocene molecule from below ca.