New NIR-emissive tetranuclear Er(III) complexes with 4-hydroxo-2,1,3-benzothiadiazolate and dibenzoylmethanide ligands: synthesis and characterization

摘要

New tetranuclear heteroleptic complexes [Er-4(dbm)(6)(O-btd)(4)(OH)(2)] (1) and [Er-4(dbm)(4)(O-btd)(6)(OH)(2)] (2) (O-btd = 4-hydroxo-2,1,3-benzothiadiazolate and dbm = dibenzoylmethanide) and their solvates with toluene, THF and CH2Cl2 were prepared using two synthetic approaches. The structures of the products were confirmed by single-crystal X-ray diffraction. Magnetic properties of 1 and 2 are in good agreement with X-ray data. The effective magnetic moment (mu(eff)) values at 300 K for 1 and 2 corresponds to a system of 4 non-interacting Er(III) ions in the ground state (4)J(15/2) with g = 6/5. At ambient temperature and upon excitation with lambda(exc) = 450 nm, complexes 1 and 2 exhibit luminescence at similar to 1530 nm, i.e. in the near infra-red (NIR) region. The luminescence intensity grows with increasing the number of the (O-btd) ligands in the complexes. This observation suggests (O-btd)-as a new efficient antenna ligand for the lanthanide-based NIR luminescence.