A series of rare earth coordination polymer constructed from paddle-wheel building blocks

Three coordination polymers, Ln2(bpdc)3(phen)2(H2O)2 (Ln=Nd(1), Eu(2), and Tb (3); bpdc=2,2′-bipyridine-3,3′-dicarboxylate; phen=1,10-phenanthroline), were obtained by hydrothermal reaction of Ln2O3 with 2,2′-bipyridine-3,3′-dicarboxylate acid, and 1,10-phenanthroline. They were characterized by single-crystal X-ray diffraction, IR spectra, and photoluminescent spectra. The crystallographic data of 1–3 indicated that they were isostructural. Both complexes contained paddle-wheel building blocks, formed by bpdc and phen ligands. These paddle-wheel secondary building units (SBUs) were further connected to form two-dimensional (2-D) metal organic framework (MOF) networks by 2,2′-bipyridine-3, and 3′-dicarboxylate linkers. A three-dimensional (3-D) supramolecular structure was formed by π–π aromatic interactions between adjacent 2-D infinite networks. Photoluminescent measurements indicated that europium compound 2 and terbium compound 3 were strong, red and green emitters, respectively.