Aqua and ammine 3d metal complexes with the anion-radical of difurazanopyrazine

Abstract

Two approaches are proposed for obtaining heterospin complexes with an anion-radical of difurazanopyrazine L – a paramagnetic derivative of 4H,8H-bis(1,2,5-oxadiazolo)[3,4-b:3′,4′-e]pyrazine. Aqua 3d metal complexes [ML₂(H₂O)₄]·2H₂O (M = Ni and Co) were synthesized using saturated solutions of reagents with a large excess of M(NO₃)₂. Ammine complexes [ML₂(NH₃)₄] (M = Ni and Cu) were obtained from the reaction of M(NO₃)₂ with NaL(H₂O)₃ in a stoichiometric ratio in the presence of concentrated aqueous ammonia (28%). In all complexes, metal ions coordinate L via N atoms of the pyrazine ring. Molecules of the complexes are linked into a framework by hydrogen bonds. It was found that in [ML₂(NH₃)₄] strong antiferromagnetic exchange interactions are realized between anion-radicals from neighboring molecules, determining the magnetic behavior of the phase as a whole. Whereas in [ML₂(H₂O)₄]·2H₂O, the exchange interactions are ferromagnetic in nature. This is due to the presence of water molecules in the structure, which provide a displacement of the complex molecules relative to each other and, as a consequence, a weakening of the interactions between adjacent L.