A case study of the inflexible bis-hydrazone butane-2,3-dione bis[(fluoren-9-ylidene)hydrazone]

The crystal structure of the fluorenone-based bis-hydrazone butane-2,3-dione bis[(fluoren-9-ylidene)hydrazone], C₃₀H₂₂N₄, consists of two fluorene subunits connected by a conjugated =N-N=C-C=N-N= chain. The compound was synthesized by condensation between fluorenone and hydrazine in acetic acid. Although the molecule contains bulky fluorenyl moieties on the termini of the conjugated chain, no polymorphs or solvated phases were obtained. Two methyl groups were found to be located in trans positions with respect to one another, thereby providing extra stability to the rigid bis-hydrazone.