Synthesis, structures and luminescent properties of novel coordination polymers constructed by lanthanide salts and benzimidazole-5,6-dicarboxylic acid

Two three-dimensional (3D) novel lanthanide complexes with the H2Lbenzimidazole-5,6-dicarboxylate [Ln2L3(H2O)] [Ln = Eu (1), Tb (2)] and one two-dimensional (2D) novel lanthanide complex [Pr(L)(HL)H2O]·H2O (3) were synthesized by hydrothermal reaction at 180 °C and characterized by elemental analysis, infrared spectra and single-crystal X-ray diffraction. The result showed that complexes 1 and 2 are isostructural and build porous 3D networks by L2− groups linking Ln(III) atoms via tetradentate (bridging and bridging) and pentadentate (bridging/chelating and bridging) coordination modes. Complex 3 is a eight-coordinated Pr(III) chain complex, exhibiting a 2D polymeric network with parallel Pr-carboxylate chains along the crystallographic c-axis. In addition, it is found that in these structures, coordination modes of L2− and HL− are versatile and can adopt different conformations according to distinct dimensions of polymeric structures. The photoluminescent properties of 1, 2 and thermogravimetric analyses of the three complexes were discussed in detail.