Magnetism in organic radical ion salts based on imidazolyl and benzimidazolyl nitronyl nitroxide

Abstract

Radical ion salts of the neutral organic radicals, 2-imidazolyl nitronyl nitroxide (2-IMNN) and 2-benz- imidazolyl nitronyl nitroxide (2-BIMNN), and a diradical cation salt of pyridine-2,6-diylbis(nitronyl nitroxide) (2,6-PYBNN), were prepared. The radical ion salts of 2-BIMNN, Li + (2-BIMNN) .- and (2-BIMNN) .+ BF 4 - , exhibit strong antiferromagnetic interactions with exchange coupling constants J/k = -42 K and -510 K, respectively, while the 2-IMNN salts show Curie-Weiss behaviour with Weiss constants θ = -9.0 K for Li + (2-IMNN) .- and θ = -1.8 K for (2-IMNN) .+ Cl - , indicating weak interactions. The diradical cation salt (2,6-PYBNN) ..+ Cl - shows intramolecular ferromagnetic interaction with J/k = +4.7 K and intermolecular antiferromagnetic interaction with θ = -0.7 K, which is remarkably reduced from J/k = -57 K observed in the diradical 2,6-PYBNN.