A cationic radical lanthanide organic tetrahedron with remarkable coordination enhanced radical stability

Rare–earth supramolecular compounds, such as lanthanide organic polyhedrons (LOPs), are of particular interest due to their many possible applications in various fields. Here we report the first syntheses of Ln4(L•+)4–type (Ln, lanthanides; L•+, radical ligand) radical–bridged lanthanide organic tetrahedrons by self–assembly of face–capping triphenylamine (TPA)–cored radical ligand with different lanthanide ions. Remarkable coordination enhanced radical stability has been observed, with half–life times (t1/2) for L1•+, La4(L1•+)4, Eu4(L1•+)4, Gd4(L1•+)4, Tb4(L1•+)4 and Lu4(L1•+)4 estimated to be 53 min, 482 min, 624 min, 1248 min, 822 min and 347 min, respectively. The TPA radical in Ln4(L1•+)4 containing paramagnetic Ln ions (Ln = EuIII, GdIII and TbIII) is observed to be more stable than that in Ln4(L1•+)4 (Ln = LaIII and LuIII) constructed by diamagnetic Ln ions. This difference in radical stability is possibly due to the magnetic interactions between paramagnetic LnIII ions and L1•+ ligands, as confirmed by electron paramagnetic resonance (EPR) in La4(L)4 (L = L1 and L1•+) and Tb4(L)4 (L = L1 and L1•+), and magnetic susceptibility measurements in Tb4(L)4 (L = L1 and L1•+). Our study reveals the coordination of radical ligands with lanthanide ions can improve the radical stability, which is crucial for their applications.