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, FeCp2, in hexafluorobenzene, C6F6. This adduct demonstrates the remarkably strong interactions
between the five-membered aromatic rings of FeCp2 and the
six-membered aromatic ring of C6F6. These molecular
interactions are sufficiently strong and anisotropic to change the
temperature of the order–disorder transition of the ferrocene
molecule from below ca. 164 K to RT. No solvate adduct could be formed
between benzene and FeCp2. These observations will be of
particular relevance to the crystal engineering community, whose goal
is the design of solids with bespoke properties.