First examples of ternary lanthanide 2,2′-bipyridine-3,3′-dicarboxylate coordination polymers with zigzag chains structures assembled from lanthanide ions, 2,2′-bipyridine-3,3′-dicarboxylate and 1,10-phenanthroline

Four lanthanide coordination polymers, [{Ln2(bpdc)3(phen)2(H2O)2} · (H2O)6]n (Ln = Sm (1); Eu (2); Gd (3), Tb (4)), were self-assembled from 2,2′-bipyridine-3,3′-dicarboxylic acid (H2bpdc),1,10-phenanthroline(phen) and corresponding lanthanide oxides by hydrothermal synthesis. Compounds 1–4 are found to be isomorphous and isostructural. Single-crystal X-ray diffraction studies show that compounds 1–4 are all of one-dimensional zigzag chain structures and extend to two-dimensional networks through π–π interactions and hydrogen bonds. The pyridyl nitrogen atoms of the 2,2′-bipyridyl unit in the bpdc ligand are uncoordinated in an anti-conformation along the central C–C bond of the ligand. Thermogravimetric analysis of 1–4 showed an obvious thermal stability indicating that the coordination habit of the metal ions with bpdc and phen has an effect on the overall framework. Photoluminescence measurement indicates that compound 2 and compound 4 are strong red and green emitters, respectively.