A structural systematic study of semi-rigid ferrocene derivatives as a 3 × 3 metallocene isomer grid: p-/m-/o-(FcC6H4)CONH(p-/m-/o-C6H4)CO2Et, [Fc = (η5-C5H5)Fe(η5-C5H4)]

• Comprehensive chemical and structural study of an organometallic 3 × 3 isomer grid.
• Trends correlating physicochemical data with crystal and molecular structure.
• Examination of structural variability with substituent position.
• Variable aggregation highlights the unpredictable nature of molecular assembly.

The nine ethyl 4-/3-/2-{[(4-/3-/2-ferrocenylphenyl)carbonyl]amino}benzoates, {4-/3-/2-FcC6H4-CONH-(4-/3-/2-C6H4)CO2Et, where Fc = (η5-C5H5)Fe(η5-C5H4)} have been synthesised by coupling either the para-, meta- or ortho(ferrocenyl)benzoic acids (FcC6H4COOH), or their acid chlorides (FcC6H4COCl) with ethyl p-/m-/o-aminobenzoates, H2NC6H4CO2Et using (i) 1,3-dicyclohexylcarbodiimide (DCC), 1-hydroxybenzotriazole (HOBt) or (ii) acid chloride coupling reactions. The isomers were characterised by spectroscopic techniques; single crystal X-ray diffraction structures of all nine isomers are reported and reveal the inherent linearity of the para–para substituted isomer (pp) compared to the twisted geometry of the ortho–ortho system (oo). Intra-/intermolecular interactions and distinct patterns of molecular aggregation are evaluated and correlated with physicochemical measurements showing distinct trends. A rich and somewhat congested amide…amide hydrogen bonding is noted in (mp) and (mm), contrasting with a lack of amide…amide interactions in (pp) and (pm) and unexpected amide…ester hydrogen bonding in dimers of (om). The series highlights the unpredictable nature of molecular assembly.

The unpredictable nature of self-assembly is revealed in a variety of hydrogen bonding motifs (depending on substituent position), as highlighted by the congested amide…amide interactions in (mm) (graphic), and contrasting with their absence in (pp) and the cyclic amide…ester interactions in hydrogen bonded dimers of (om).Figure optionsDownload as PowerPoint slide