Syntheses, structures, and luminescent properties of three novel two-dimensional lanthanide coordination polymers with mixed aromatic carboxylate ligands

Three novel two-dimensional (2-D) coordination polymers {[Ln (bpdc) (BDC) _0.5 (DMF) (H ₂O)]•1.5H ₂O} _n [Ln = Tb (1), Sm (2), Gd (3); H ₂bpdc = 2,4′- biphenyldicarboxylic acid; H ₂BDC = 1,4-benzenedicarboxylic acid, and DMF = N,N′-dimethylformamide] have been successfully synthesized by the reactions of metal source Ln(NO ₃) ₂•5H ₂O with mixed aromatic carboxylate ligands named, H ₂bpdc and H ₂BDC in the mixed solution of DMF and H ₂O. Complexes 1-3 were characterized by element analyses, IR spectroscopy and single-crystal X-ray diffraction. The results reveal that three complexes are isostructural. In the molecular structure of 1, the neighboring Tb ³⁺ cations are connected by the edge sharing fashion from two three-bridging μ ₃-oxygen atoms to construct a dinuclear polyhedron. The adjacent dinuclear units are linked by two bpdc ^2- ligands to form an infinite double zigzag chain containing quadrangular grids. These chains are linked by BDC ^2-, which acted as pillar to form a 2-D layered structure containing (4, 4) networks. The solid-state luminescent properties of complexes 1 and 2 were investigated at room temperature. Complexes 1 and 2 have displayed their characteristic emissions and decay lifetimes.