Magnetic and structural properties of monoradicals and diradicals based on thienyl-substituted nitronyl nitroxide

Magnetic properties of monoradicals and diradicals based on thienyl-substituted nitronyl nitroxide (NN) were investigated by measuring temperature and magnetic-field dependences of magnetization. The magnetic behavior of the monoradical 3-benzo[b]thienyl NN (3-BTHNN) is interpreted in terms of the quasi-2D ferromagnetic Heisenberg model with the coupling constant J/k=+0.16 K and J′/k=+0.02 K, while the alternating antiferromagnetic (AFM) intermolecular interactions are observed in the monoradicals, 2- and 3-thienyl NN (2- and 3-THNN). In contrast, the magnetic behavior of the diradicals, 2,3- and 2,5-bis(NN)thiophene (2,3- and 2,5-THBNN), is explained by quite strong AFM intramolecular interactions between the two spin centers, each located on the two NN moieties. We discuss here the origin of the magnetic interactions observed in these radicals by considering their molecular and crystal structures determined by the X-ray diffraction techniques.