Preparation and structures of biferrocenes with alicyclic substituents: Order–disorder of substituents in the crystal structures of cyclohexenylbiferrocene and its charge-transfer salt

Biferrocene derivatives with cyclohexyl, cyclohexenyl, and cyclopentenyl substituents were prepared and crystallographically characterized. The cyclohexenyl substituents exhibited twofold disorder in the crystals. A charge-transfer salt of 1′-cyclohexenylbiferrocene with [Ni(mnt)2] was prepared. The biferrocenium cation in this salt was in a valence-trapped state owing to electrostatic interactions with the anion. The cyclohexenyl substituent in the [Ni(mnt)2] salt exhibited no disorder because of closer packing of the salt.