Concomitant and conformational polymorphism, conformational isomorphism, and phase relationships in 4-cyanopyridine·4,4′-biphenol cocrystals

The 2:1 co-crystal of 4-cyanopyridine and 4,4′-biphenol exists in at least two polymorphic forms. Single-crystal X-ray crystallographic analysis of forms I and II revealed conformational differences in the 4,4′-biphenol molecules, but O-H⋯ N(pyridine) supramolecular heterosynthons sustain both forms, suggesting that O-H⋯N(pyridine) interactions are favored over competing O-H⋯N(cyano) interactions. These conformational polymorphs crystallize concomitantly, and conformational isomorphism is also observed in this co-crystal. Experimental conditions that induce transformations between form I and form II are described. The structural differences between form I and II are discussed in the broader context of conformational polymorphism.