Face-to-face stacking of dianionic quinoid rings in crystals of alkali salts of 2,5-dihydroxyquinone in view of π-system polarization

Abstract

A series of alkali (M⁺ = K⁺, NH₄⁺, Rb⁺ and Cs⁺) salts of 2,5-dihydroxyquinone [M₂⁺ (C₆H₄O₄)²⁻] was prepared and their structures were determined by X-ray structure analysis. A less-common type of π-stacking of dianionic quinoid rings in face-to-face fashion (no offset) is observed. However, in the potassium salt of this series the stacking motif of the dianionic quinoid rings is in a herring-bone pattern, usually observed in the stacking of aromatics. The different types of crystal structures, induced by varied cations, are discussed in terms of the relative energies calculated by the DFT method. The structural features observed were reproduced by the calculations. The stacking of the quinoid rings is assisted by dispersion interactions.