Flavosemiquinone model systems. Part 3. Molecular and crystal structure of the cation radical salt 1,4,6,7-tetramethylquinoxalinium triiodide

Abstract

1,4,6,7-Tetramethylquinoxalinium cation radical 2represents the essential part of the isoalloxazine π system in N(1), N(5)-diprotonated cationic flavosemiquinones 1. The low-temperature X-ray crystal structure analysis of the stable radical salt of 2 with the sterically innocuous triiodide counterion has allowed us to examine intermolecular interactions between the aromatic cation radicals in the solid. Crystals of 2 I₃ are orthorhombic, space group Pnma., in a cell of dimensions a= 1150.7(1), b= 694.0(1), c= 2032.5(3) pm; R= 0.0323 for 2385 observed reflections. Although the planar cations form centrosymmetric pairs within the crystal lattice, their arrangement is only controlled by packing effects and not by any significant π–π interactions.