Co-Crystallization of Stereoisomers of N,N'-Bis(2-phenyl-5-hydroxymethyl-1,3-dioxan-5-yl)ethanediamide

X-ray analysis has revealed that two stereoisomers of the title compound, C₂₄H₂₈N₂O₈, co-crystallize in form (I). The unit cell of (I) contains equal numbers of the N,N′-bis­(trans-2-phenyl-5-hydroxymethyl-1,3-dioxan-5-yl)ethanediamide, (Ia), and the N,N′-bis­(cis-2-phenyl-5-hydroxymethyl-1,3-dioxan-5-yl)ethanediamide, (Ib), stereoisomers, each lying about crystallographic inversion centres. Fractional crystallization of this mixture afforded crystals (II) containing only molecules of stereoisomer (Ia), also with crystallographic inversion symmetry. The stereoisomer (Ia) is Z-shaped in (I) and (II), whereas (Ib) is maximally extended. In both (I) and (II), the molecules are linked about inversion centres by O-H...O hydrogen bonds.

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