Analysis of the configuration and hydrogen-bonding interactions in the crystal structure of 5,8-dimethoxy-2,3-bis(2-pyridinio)quinoxaline perchlorate dihydrate

The perchlorate salt of diprotonated 5,8-dimethoxy-2,3-bis(2-pyridyl)quinoxaline, [C₂₀H₁₈N₄O₂]·(ClO₄)₂ ·(H₂O)₂ (1), has been prepared and characterized by ¹H NMR, IR, UV–Vis, and elemental analysis, and established by X-ray diffraction technique. In the crystal structure of the title compound, two pyridinio rings form dihedral angles of 38.7(6)° and 26.5(5)° with the mean quinoxaline plane, and a dihedral angle of 52.7(6)° with each other. It is unexpected that the favorite orientation of two protonated pyridyl rings is such that their nitrogen donors are opposite to each other (trans–trans configuration). The most striking feature of this structure resides in the fact that numerous hydrogen-bonding interactions are observed, resulting in a novel double-chain supramolecular architecture along crystallographic [111] direction. There exist significant face-to-face – stacking interactions between the interchain neighboring pyridinio rings, which may further stabilize this structure.