Hydrothermal synthesis and characterization of two 2-D lanthanide-2,2′-bipyridine-3,3′-dicarboxylate coordination polymers based on zigzag chains

Two lanthanide coordination polymers, {[La2(bpdc)3(H2O)4]·(H2O)4}n (1) and {[Sm2(bpdc)3(H2O)2]·(H2O)5}n (2) (H2bpdc = 2,2′-bipyridine-3,3′-dicarboxylic acid) have been obtained by hydrothermal synthesis. Single-crystal X-ray diffraction shows that 1 and 2 are two-dimensional network structures based on the zigzag chains which are linked by bpdc ligands, forming the first examples of binary lanthanide polymers with bpdc. It is unprecedented that the adjacent zigzag chains are symmetrical in mirror images with the arraying form of ⋯ ABAB ⋯ . In 1 and 2, lanthanide ion are all nine-coordinate and bpdc ligands exhibit different kinds of coordination modes. The 1-D infinite water chain in 1 and pentameric water ring in 2 have been found between lattice water molecules. Thermo-gravimetric analyses of 1 and 2 display considerable thermal stability. Photoluminescent properties of 1 and 2 are discussed.