Comprehensive structural analysis of bromine-substituted ferrocenyl chalcones

A structural analysis is developed for five bromine-substituted ferrocenyl chalcones; the crystal structures of three of these compounds are reported for the first time. 3-(4-Bromophenyl)-1-ferrocenylprop-2-en-1-one (1), 3-(3-bromophenyl)-1-ferrocenylprop-2-en-1-one (2), 3-(2-bromophenyl)-1-ferrocenylprop-2-en-1-one (3), 1-(4-bromophenyl)-3-ferrocenylprop-2-en-1-one (4) and 1-(3-bromophenyl)-3-ferrocenylprop-2-en-1-one (5), all [Fe(C₅H₅)(C₁₄H₁₀BrO)], were synthesized via a base-catalyzed Claisen-Schmidt condensation between the corresponding ketone and aldehyde, yielding three compounds (1-3) with ferrocene attached to the carbonyl group (System 1) and two (4 and 5) with ferrocene attached to the alkene directly (System 3). Also, the position of the Br atom in the aromatic ring changes in each compound. The effect of these two parameters is evaluated considering distinct compound features, crystal packing and supramolecular features. The compounds crystallize in multiple space-group types, namely, P2₁/n (1), P2₁2₁2₁ (2), P2₁/c (3), Pca2₁ (4) and P1 (5). The majority of the intermolecular interactions arise from the ferrocene units and aromatic rings; for all compounds, the role of bromine in the crystal packing is evident by the presence of H...Br/Br...H, C...Br/Br...C and Br...Br intermolecular interactions. The position of the Br atom has effects on the crystal density, as well as the exhibited bromine interactions. The enone connectivity in System 3 for para- and meta-substituted ferrocenyl chalcones enables shorter interactions and more participation of the enone in short contacts in comparison to System 1. This is confirmed by Hirshfeld surface analysis (red spots for short contacts) and via generated two-dimensional fingerprint plots (unique features and green regions). In addition, the title compounds were analyzed by ¹H NMR, ¹³C NMR and IR spectroscopy, and melting-point analysis.