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Coordination Polymers with Tetrafluoroterephthalate as Bridging Ligand

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posted on 02.11.2011, 00:00 by Christiane Seidel, Ruth Ahlers, Uwe Ruschewitz
Seven nonporous coordination polymers with tetrafluoroterephthalate (tfBDC2–) as a bridging ligand were synthesized and structurally characterized. Homoleptic 3[Tl2(tfBDC)] (P1̅, Z = 1, 1) contains six-coordinated Tl centers, which are connected by the tfBDC2– ligand to form a three-dimensional (3D) network. Upon heating it decomposes at approximately 200 °C. Nine-coordinated PbO9 polyhedra are found in 2[Pb(tfBDC)(H2O)3]·1/2 H2O (P1̅, Z = 1, 2), which forms a layer-like structure. These layers are held together by hydrogen bonds involving water molecules. These water molecules are released by heating to 70–100 °C. 1[MII(tfBDC)(H2O)4] (P1̅, Z = 1; MII = Zn (3), Co (4), Ni (5)) contains almost undistorted MIIO6 octahedra with the carboxylate groups of the tfBDC ligands in trans coordination so that a chain-like structural unit is formed. These chains are further connected by hydrogen bonds. Upon heating, these water molecules are released in two steps at 100 and 200 °C. 3[Mn2(tfBDC)2(DMF)2(EtOH)] (P21, Z = 2, 7) is isostructural to the known Zn compound (6). Both compounds contain dimeric [MIIO6]2 units, which are connected by tfBDC2– ligands to form a 3D network. All compounds are unprecedented in the crystal chemistry of coordination polymers with nonfluorinated terephthalate (BDC2–) as bridging ligand. This is mainly because the planar conformation found for BDC2– is energetically less favorable for perfluorinated tfBDC2–.