Synthesis and magnetic properties of nitronyl nitroxide radicals carrying a purine ring

2-(Purin-8-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide (Pu-NN) was designed and synthesized. Two crystalline phases (α- and β-phases) exhibiting different IR spectral patterns at the v_NH region were obtained depending on the crystallizing condition. The temperature dependences of the magnetic susceptibility of these two phases followed Curie-Weiss law with θ = - 5.7 K (α-phase) and θ = - 0.3 K (β-phase) implying intermolecular antiferromagnetic interaction, which were quite different from that of parent benzimidazole derivative, 2-(benzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H- imidazolyl-1-oxyl-3-oxide that formed a 1-D ferromagnetic chain induced by an intermolecular hydrogen bonding.