Supramolecular aggregation in 4,4′-bipyridin-1,1′-ium dichloride, 4,4′-bipyridin-1,1′-ium dinitrate and 4,4′-bipyridin-1-ium bromide

4,4′-Bipyridin-1,1′-ium dichloride [C₁₀H ₁₀Cl₂N₂ (I)] and 4,4′-bipyridin-1, 1′-ium dinitrate [C₁₀H₁₀N₄O₆ (II)] have been prepared and the crystal structures determined at 90.0 (2) K. Molecules of (I) are linked by two chlorine-bridged, three-centered N - H⋯Cl hydrogen bonds into chains along the b axis. The chains are coupled by weak C - H⋯Cl interactions into a molecular ladder along the c direction. In (II) each nitrate is coordinated to four bipyridinium ions through the interplay of the N - H⋯O and C-H⋯O contacts, resulting in a three-dimensional zigzag sheet on the ab plane. The sheets stack along the c axis. In 4,4′-bipyridin-1-ium bromide monohydrate [C₁₀H ₉N²⁺·Br^-·H₂O (III)] the bipyridinium ions are linked by three-center N - H·N′ hydrogen bonds in a head-to-tail fashion to form chains along the b axis. The chains are linked by C - H⋯Br and C - H⋯OH₂ into a three-dimensional framework.