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.