The crystal packing modes of three sterically overcrowded imidazole derivatives

The crystal packing of racemic 4-cyclohexylamino-5-hydroxy-1,5-diphenyl-Δ³-imidazolin-2-one resembles the bilayered packing arrangements with alternating hydrophilic and hydrophobic layers observed in the crystal structures of lipids. The hydrophobic layers of the imidazolinone are built up individually by phenyl and cyclohexyl groups. In contrast, the corresponding 4-tert-butylamino derivative crystallizes optically resolved in a non-bilayer layer structure. This crystal packing is similar to the host-lattice of the inclusion compound formed by 9-(4-tert-butylphenyl)fluoren-9-ol and dioxane [Csöregh, Weber, Nassimbeni, Gallardo, Dörpinghaus, Ertan & Bourne (1993). J. Chem. Soc. Perkin Trans. 2, pp. 1775–1781]. The major building units of 4-tert-butylamino-1,5-diphenylimidazole are centrosymmetrical dimers in which the molecules display a `yin-and-yang'-like self-complementarity. The dimers pack in columns, which form a distorted hexagonal pattern.

-1