π-Stacking of quinoid rings in crystals of alkali diaqua hydrogen chloranilates

Abstract

The alkali diaqua complexes of hydrogen chloranilic acid of [KHCA(H₂O)₂], [RbHCA(H₂O)₂] and [CsHCA(H₂O)₂], and the salt of NH₄HCA·2H₂O were prepared and their crystal structures determined. The homologues of lithium and sodium are not stable, but their analogues [LiHCAEtOH] and [Na₅HCA(CA)₂(H₂O)₁₀] were obtained. All crystal structures studied, with exception of [LiHCAEtOH], reveal 3D-hydrogen bond networks with pronounced π⋯π interactions between anions supported by attractive polar interactions; the shortest separation distance between the centroids [3.229(2) Å] of the hydrogen chloranilate rings in a face-to-face stack is observed in the structure of [KHCA(H₂O)₂]. The analysis presented is focused on noncovalent interactions, in particular, the influence of cations and hydrogen bonds on the π-stacking of quinoid rings.