Co-Crystals of 1,3-Adamantanedicarboxylic Acid with N-Oxide and Aza Compounds

Co-crystals 1a–1d and 1d′ have been prepared by slow evaporation of the solutions of mixtures of 1,3-adamantanedicarboxylic acid (1) and 1,3-di(pyridin-4-yl)propane (a), E-1,2-di(pyridine-4yl)diazene (b), (E)-2,2′-(ethene-1,2-diyl)dipyridine 1-oxide (c), and 1,7-phenanthroline (d), as the case may be. The structures of the complexes are determined by the single crystal X-ray diffraction method. The structure analysis reveals that in all the complexes the basic recognition between the co-crystal formers is through O–H···N/C–H···O pairwise hydrogen bonds except in 1c. Because of the presence of N-oxide functionality, in 1c, the co-crystal formers are held together by O–H···O/C–H···O pairwise hydrogen bonds. Further, while all the structures form stacked sheets arrangement in the three-dimensional packing, within the two-dimensional arrangement contrast differences are found with a notable observation being the host network with voids in the structure of 1c. In addition, acid 1 and d form two different conformational polymorphs due to the variations in the conformations of the two −COOH groups that prevail on acid 1 but with a similar recognition pattern between the co-crystal formers.