Assembly of imidazolyl-substituted nitronyl nitroxides into ferromagnetically coupled chains

New nitronyl nitroxides, namely, 2-(4,5-dimethylimidazol-2-yl)-and 2-(4,5-dichloroimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl, were prepared in crystalline form. According to single-crystal X-ray data, intra-and intermolecular hydrogen bonds are formed between NH groups of the imidazole cycles and O atoms of the nitroxide moieties. The intermolecular H-bonds contribute to the alignment of molecules into chains along the a-axis; this alignment causes short intrachain contacts between O and C atoms carrying spin density of opposite signs. Such an arrangement of nitroxides induces ferromagnetic intrachain interactions (J ≈ 10 cm ^{− 1} ) between neighboring radicals.