Effect of C-H...X interactions (X = O, S, [small pi]) in the supramolecular arrangements of 3-ferrocenyl-methoxybenzo[b]thiophene isomers

Two regioisomers, 3-ferrocenyl-6-methoxybenzo[b]thiophene (IV) and 3-ferrocenyl-4-methoxybenzo[b]thiophene (V), were isolated after an acid-catalysed intramolecular electrophilic cyclisation of 1-ferrocenyl-2-[3-(methoxyphenyl)thio]ethanone. This paper analyses the effect of the different positioning of the methoxy group in the benzothiophene ring on the molecular and crystal structures of both molecules. In isomer IV this group is more exposed to interactions with adjacent molecules than in V; thus, while in IV the COMe-H...OOMe intermolecular interactions determine the crystal packing, in V the overall assembly results from an interplay of the CCp-H...OOMe, CCp-H...S and CCp-H/[small pi] interactions. The supramolecular analysis provides an explanation for the spontaneous solid state separation of these regioisomers and their different physical properties, such as their melting points and their ability to interact with supports during chromatographic separations.