A series of adducts formed by association of the uranyl ion, UO22+, with either nitronyl nitroxide substituted pyridine and triazole ligands or their imino nitroxide counterpart are described. The stability of the radical unit in the vicinity of the U centre appeared to be dependent on whether this unit is directly involved or not in the coordination to the metal ion. The crystal structures of both types of compounds have been determined by X-ray diffraction. The temperature dependence of the magnetic behaviours in the solid state for the paramagnetic compounds revealed substantial exchange interaction among the spin carriers in the crystal.