Face-to-face stacking of quinoid rings of alkali salts of bromanilic acid

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).