Crystal structures and packing of 4-cyanocubanecarboxylic acid, its methyl ester, and the solid solution of 1,4-dicyanocubane and 1,4-dibromocubane

The crystal structure of 4-cyanocubanecarboxylic acid contains the same syn-anti carboxyl group catemer that is found in other cubane monocarboxylic acids. The cyano groups are arranged according to the type-II geometry, in that they are 21 screw-axis related. Curiously, there is a 5% orientational disorder of the cyano and anti carboxyl groups. The ester of the title acid packs isostructurally with the corresponding chloro and fluoro analogs because of the importance of the C-H…O hydrogen bond patterns. 1,4-Dicyanocubane forms solid solutions with 1,4-dibromocubane, but, interestingly, the crystal structure of the solid solution is distinct from that of either component. The formation of these solid solutions seems to be governed by shape and size factors