Isostructural lanthanide-based metal-organic frameworks: structure, photoluminescence and magnetic properties

A series of the anhydrous lanthanide-based metal-organic frameworks (Ln-MOFs) were successfully synthesized under hydrothermal conditions of Ln(III) ions with 3,4'-oxybis(benzoate) (3,4'-oba), oxalate (ox) and 1,10-phenanthroline (phen). Structural analyses revealed that they are isostructural 3D open-frameworks with the formula of [Ln(3,4'-oba) (phen)(ox)(0.5)](n) (Ln = Sm for 1, Eu for 2, Gd for 3, Tb for 4, and Dy for 5) and the topology of {3(3) . 4(3) . 5(8) . 6}. Within the 3D structure, the [LnO(6)N(2)] units are bridged by ox to form [Ln2ox] dimers and then are further connected by 3,4'-oba ligands. These complexes feature high chemical stabilities in common solvents, boiling water, and acidic (pH = 3) and alkaline (pH = 13) solutions and high thermal stability even up to 400 degrees C. The photoluminescence and magnetic properties were studied. Especially, 2 shows bright red emission with a high luminescence efficiency of 40.51%. We mainly discuss the luminescence properties of 2 in common solvents and inorganic ions. It shows luminescence stability in common solvents and the ability to detect ammonia and Fe3+ ions under a long excitation wavelength (350 nm). Significantly, magnetic studies reveal that the Dy-MOF, 5, shows a typical singlemolecule magnetic behavior. Under zero dc field, compound 5 shows temperature and frequency dependent out-of-phase (chi '' M) signals, indicating the existence of slow magnetic relaxation.