Heteroradical Salts Based on Paramagnetic Derivatives of Difurazanopyrazine and <i>N</i>-Alkylpyridinium Nitronyl Nitroxides

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 [NNp/mR]I iodides as a cation-radical source in the reaction with NaL(H2O)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 [NNpMe](L)x(HL)1–x·H2O containing both the paramagnetic anion L and its reduced form anion HL. It was found that the use of [NNp/mR]NO3 nitrates allows to avoid the reduction of L, and heteroradical salts [NNp/mR]L can be easily obtained. A single crystal XRD study showed that the solid phases of [NNp/mR]L salts form crystals formed by quartets of anions and cations {NNp/mR···L···L···NNp/mR}. 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 [NNmMe]L·H2O structure, alternating cationic and anionic radicals are ferromagnetically coupled and form magnetic chains, which are linked into layers by OH2O···NL hydrogen bonds. The [NNp/mR]L heteroradical salts represent a new type of paramagnet based on organic fragments with fixed charge and spin states.