Synthesis, structures and luminescent properties of a series of novel Sr(II)-Ln(III) (Ln = Eu, Gd, Tb) coordination polymers.

Eight novel Sr(II)-Ln(III) heteronuclear coordination polymers based on pyridine-2,6-dicarboxylic acid (H2pda) and imidazole (im) ligands, namely, [LnSr(pda)3(H2O)5]·Him·H2O (Ln = Eu (1), Gd (2), Tb (3)), [Ln2Sr(pda)6(H2O)5]·4Him·C2H5OH·nH2O (Ln = Eu (4), n = 5; Gd (5), n = 4), [LnSr(pda)3(H2O)4]·Him·3H2O (Ln = Gd (6), Tb (7)), and [GdSr(pda)3(H2O)5]·Him·C2H5OH·3H2O (8), have been prepared by employing different amounts of imidazole. X-ray crystal structure analysis reveals that these compounds exhibit a rich structural chemistry. Complexes 1-3 possess 2-D frameworks. Complexes 4-5, 6-7, and 8 exhibit three types of 1-D chain structure. The structures of the complexes could be rationally tuned via adding different amounts of imidazole. The luminescent properties of these complexes have been investigated. The results show that Eu(III) and Tb(III) complexes exhibit intense red and green luminescence emission which are characteristics of Tb(III) and Eu(III), respectively. Solid-state quantum yield and the lifetime of these complexes are also reported.