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

A series of alkali (M+ = K+, NH4+, Rb+ and Cs+) salts of 2, 5-dihidroxyquinone [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 potassium salt of this series stacking motif of dianionic quinoid rings is herring-bone, usually observed in 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 quinoid rings is assisted by dispersion interactions.

2; 5-dihidroxyquinone; face-to-face π-stacking; quinoid rings; electron delocalisation; X-ray structure; DFT calculations

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