Lanthanide Coordination Polymers with Tetrafluoroterephthalate as a Bridging Ligand: Thermal and Optical Properties

By slow diffusion of triethylamine into a solution of 2,3,5,6-tetrafluoroterephthalic acid (H(2)tfBDC) and the respective lanthanide salt in EtOH/DMF single crystals of seven nonporous coordination polymers, (2)(infinity) [Ln(tfBDC)(NO3)(DMF)(2)]center dot DMF (Ln(3+) = Ce, Pr, Nd, Sm, Dy, Er, Yb; C2/c, Z = 8) have been obtained. In the crystal structures, two-dimensional square grids are found, which are composed of binuclear lanthanide nodes connected by tfBDC(2-) as a linking ligand. The coordination sphere of each lanthanide cation is completed by a nitrate anion and two DMF molecules (CN = 9). This crystal structure is unprecedented in the crystal chemistry of coordination polymers based on nonfluorinated terephthalate (BDC2-) as a bridging ligand; as for tfBDC(2-), a nonplanar conformation of the ligand is energetically more favorable, whereas for BDC2-, a planar conformation is preferred. Differential thermal analysis/thermogravimetric analysis (DTA/TGA) investigations reveal that the noncoordinating DMF molecule is released first at temperatures of 100-200 degrees C. Subsequent endothermal weight losses correspond to the release of the coordinating DMF molecules. Between 350 and 400 degrees C, a strong exothermal weight loss is found, which is probably due to a decomposition of the tfBDC(2-) ligand. The residues could not be identified. The emission spectra of the (2)(infinity)[Ln(tfBDC)(NO3)(DMF)(2)]center dot DMF compounds reveal intense emission in the visible region of light for Pr, Sm, and Dy with colors from orange, orange-red, to warm white.