Heteroradical Salts Based on Paramagnetic Derivatives of Difurazanopyrazine and N-Alkylpyridinium Nitronyl Nitroxides

Abstract

The effective approach to the synthesis of heteroradical organic salts based on the paramagnetic difurazanopyrazine derivative and pyridinium-substituted nitronyl nitroxides has been proposed. It was demonstrated that the use of [NN p/m R]I iodides as a cation-radical source in the reaction with NaL(H 2 O) 3 (where L is the anion-radical of bis (1,2,5-oxadiazolo)[3,4-b:3′,4′-e]pyrazine) results in reducing L and the formation of solid solutions [NN p Me](L) x (HL) 1−x •H 2 O containing both the paramagnetic anion L and its reduced form anion HL. It was found that the use of [NN p/m R]NO 3 nitrates allows to avoid the reduction of L, and heteroradical salts [NN p/m R]L can be easily obtained. A single crystal XRD study showed that the solid phases of [NN p/m R]L salts form crystals formed by quartets of anions and cations {NN p/m R•••L•••L•••NN p/m R}. Within the quartets, the distances between the anion-radical planes of L are ∼3.3 Å, which ensures the presence of antiferromagnetic exchange interactions between them and determines the magnetic properties, in general. It was found that in the [NN m Me]L•H 2 O structure, alternating cationic and anionic radicals are ferromagnetically coupled and form magnetic chains, which are linked into layers by O H2O •••N L hydrogen bonds. The [NN p/m R]L heteroradical salts represent a new type of paramagnet based on organic fragments with fixed charge and spin states.