Lanthanide complexes with disulfide ligand generated in situ: Syntheses, crystal structures and fluorescent properties

Five new lanthanide complexes [Ln2(DTDN)4(phen)4]·7H2O·2H3O+ (Ln = Nd (1), Sm (2), Eu (3), Tb (4), Dy (5), H2DTDN = 2,2′-dithiodinicotinic acid, phen = 1,10-phenanthroline) have been solvothermally synthesized and characterized by single-crystal X-ray diffraction, elemental analyses, IR spectra, and TG analyses. By in situ oxidation of 2-mercaptonanicotinic acid (2-H2MN), the expected ligand H2DTDN was generated. All crystals are isostructural and crystallize in monoclinic system with space group C2/c. The metal center is eight-coordinated completely by four carboxylic oxygen atoms from four different DTDN2− ligands, and four nitrogen atoms from two phen molecules with a distorted square-antiprismatic geometry. The structures can be considered as two-dimensional (2D) structures and further linked by hydrogen bonds into the final trinodal 4-connected network. Photoluminescence studies revealed that complexes 2–5 exhibit strong fluorescent emission bands in the solid state at room temperature.