Synthesis and luminescence of binuclear lanthanide complexes with 4,6-bis(diphenylphosphino)pyrimidine dioxide as a bridging ligand

Abstract

Five new isostructural binuclear complexes [Ln2L2(H2O)2(NO3)6] (Ln = Sm, Eu, Gd, Tb, and Dy) based on 4,6-bis(diphenylphosphino)pyrimidine dioxide (L) have been synthesized, and their luminescence properties have been studied. The complexes consist of two nine-coordinated Ln(III) atoms linked by two L ligands in the O,O´-bridging manner. The Gd3+ complex possesses ligand-centered emission, while its Tb3+ and Eu3+ analogs exhibit metal-centered phosphorescence only. At the same time, the Sm3+ and Dy3+ complexes show both metal- and ligand-centered emission. In the complexes studied, the ligand L sensitizes the Tb3+ emission most effectively due to the relatively high triplet energy level (23900 cm−1). Moreover, mixed-metal complexes [Tb2xEu2(1-x)L2(H2O)2(NO3)6] (x = 0.9, 0.8, 0.6, 0.4, 0.2) have been synthesized, whose emission color can be tuned from green to yellow and red through adjusting of the Tb/Eu ratio.