Temperature dependent self-assembly of lanthanide coordination polymers based on a benzimidazolium dicarboxylate linker: synthesis, structure and luminescence properties

Five new coordination polymers, namely [Ln(L)(NO3)2]n (Ln = La (1), Pr (2) and Sm (3)), [Eu(L)(NO3)2<middle dot>1.5H2O]n (4) and [Tb(L)(OAc)2(H2O)<middle dot>3H2O]n (5) (HOAc = CH3COOH), were synthesised by reaction of lanthanide nitrates with 1,3-bis(4-carboxybenzyl)benzimidazolium chloride (H2L+Cl-) under solvothermal conditions. All the coordination polymers were characterised by powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, elemental analysis and single crystal X-ray diffraction. Complexes 1-5 exhibit two different 2-D structures due to the variation in reaction temperature. Complexes 1-4 are isostructural and crystallised in the monoclinic system, C2/c space group, showing a two-dimensional layer with Ln chains linked by L- ligands. Complex 5 crystallised in the P21/n space group, featuring a 2-D layer different from 1-4 with Tb dimers linked by L- ligands through carboxylates. Further, the luminescence properties of complexes 3-5 were investigated. In addition, the fluorescence lifetime and quantum efficiency of complex 4 were measured. Five two-dimensional complexes were obtained and the structures of 1-4 differ from that of 5 owing to the distinct coordination modes of the ligand H2L+Cl- at specific reaction temperatures. Further, the luminescence properties of complexes 3-5 were investigated. Additionally, the fluorescence lifetime of complex 4 was tested. (Image credit: Li-Xin You.)