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Face-to-face π-stacking in the multicomponent crystals of chloranilic acid, alkali hydrogenchloranilates, and water

The multicomponent crystals of chloranilic acid (CA) and its alkali salt of monochloranilate trihydrate [RbHCA∙0.5H2CA∙3H2O and CsHCA∙0.5H2CA∙3H2O] and cocrystals with urea [NaHCA∙2(NH2)2CO and Cs2CA∙(NH2)2CO] were prepared and their crystal structures determined. In the crystal structures of RbHCA∙0.5H2CA∙3H2O and CsHCA∙0.5H2CA∙3H2O molecules of neutral choranilic acid and its monoanion stack face-to-face in the sequence ∙∙∙HCA-∙∙∙H2CA∙∙∙HCA-∙∙∙ with very short centroid-centroid separation distances (<3.30 Å) with an offset of 0.27 Å within a triplet. In an infinite stack of triplets, interactions between two mono anions are characterised by the centroid-centroid separation distances of ~3.50 Å and offset of 1.5 Å. Two novel cocrystals with urea reveal anion stacks similar to those of aromatic rings. A Cambridge Structural Database search was used to spot preferences of chloranilic acid and its anions for π-stacking.

π∙∙∙π interactions ; hydrogen bonds ; chloranilic acid ; Cambridge Structural Database ; quinones

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