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

Co-crystals <b>1a</b>–<b>1d</b> and <b>1d′</b> have been prepared by slow evaporation of the solutions of mixtures of 1,3-adamantanedicarboxylic acid (<b>1</b>) and 1,3-di(pyridin-4-yl)propane (<b>a</b>), <i>E</i>-1,2-di(pyridine-4yl)diazene (<b>b</b>), (<i>E</i>)-2,2′-(ethene-1,2-diyl)dipyridine 1-oxide (<b>c</b>), and 1,7-phenanthroline (<b>d</b>), 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 <b>1c</b>. Because of the presence of N-oxide functionality, in <b>1c</b>, 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 <b>1c</b>. In addition, acid <b>1</b> and <b>d</b> form two different conformational polymorphs due to the variations in the conformations of the two −COOH groups that prevail on acid <b>1</b> but with a similar recognition pattern between the co-crystal formers.