Acta Cryst. (2012). B68, 57-65 [ doi:10.1107/S0108768111051159 ]
Abstract: A series of alkali salts of hydrogen bromanilic acid trihydrates (K+, Rb+ and Cs+, potassium, rubidium and caesium 2,5-dibromo-4-hydroxy-3,6-dioxocyclohexa-1,4-dien-1-olate trihydrate), bromanilic acid tetrahydrate (Na+, disodium 2,5-dibromo-3,6-dioxocyclohexa-1,4-diene-1,4-diolate tetrahydrate) and bromanilic acid dihydrates (K+, Rb+ and Cs+, dipotasium, dirubidium and dicaesium 2,5-dibromo-3,6-dioxocyclohexa-1,4-diene-1,4-diolate dihydrate) were prepared and studied by single-crystal X-ray diffraction. Their crystal packings are dominated by quinoid ring stacking. The monoanionic quinoid rings pack face-to-face without offset and with short centroid separations (3.25-3.30 Å), while the dianionic rings form offset stacks (1.4-1.8 Å) with a larger centroid separation (3.8-4.1 Å).
Keywords: bromanilic acid; -stacking; quinoid rings; electron delocalization; X-ray structure; pseudosymmetry.
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