Six two-dimensional (2D) coordination polymers (CPs), namely, poly[{μ5-3,3-[(5-carboxylato-1,3-phenylene)bis(oxy)]dibenzoato-κ6O1:O1':O3,O3':O5:O5'}bis(N,N-dimethylformamide-κO)lanthanide(III)], [Ln(C21H11O8)(C3H7NO)2]n, with lanthanide/Ln = cerium/Ce for CP1, praseodymium/Pr for CP2, neodymium/Nd for CP3, samarium/Sm for CP4, europium/Eu for CP5 and gadolinium/Gd for CP6, have been prepared by solvothermal methods using the ligand 3,3'-[(5-carboxy-1,3-phenylene)bis(oxy)]dibenzoic acid (H3cpboda) in the presence of Ln(NO3)3. The complexes were characterized by single-crystal X-ray and powder diffraction, IR spectroscopy, elemental analysis and thermogravimetric analysis (TGA). All the structures of this family of lanthanide CPs are isomorphous with the triclinic space group P-1 and reveal that they have the same 2D network based on binuclear LnIII units, which are further extended via interlayer C-H...π interactions into a three-dimensional supramolecular structure. The carboxylate groups of the cpboda3- ligands link adjacent LnIII ions and form binuclear [Ln2(RCOO)4] secondary building units (SBUs), in which each binuclear LnIII SBU contains four carboxylate groups from different cpboda3- ligands. Moreover, with the increase of the rare-earth Ln atomic radius, the dihedral angles between the aromatic rings gradually increase. Magnetically, CP6 shows weak antiferromagnetic coupling between the GdIII ions. The solid-state luminescence properties of CP2, CP5 and CP6 were examined at ambient temperature and CP5 exhibits characteristic red emission bands derived from the Eu3+ ion (CIE 0.53, 0.31), with luminescence quantum yields of 22%. Therefore, CP5 should be regarded as a potential optical material.
Keywords: coordination polymer; crystal structure; lanthanide; luminescence; magnetism; polycarboxylic acid.