Syntheses,Crystal Structures And Photophysical Properties Of 3d-4f Coordination Polymers Based On Pyridine-2,5-dicarboxylic Acid

Using Ln^? ions and Co^?/Ni^? ions with 3d⁷/3d⁸ valence electron configurations as coordination central metal ions,12 kinds of Ni/Co-Ln coordination polymers have been designed and synthesized through hydrothermal method.Pyridine-2,5-dicarboxylate with multiple coordination sites is selected as the main ligand,and flexible oxalate is choosen as auxiliary ligand.Their chemical formulas are as follows:(1){[PrNi_0.5(2,5-pydc)(ox)(H₂O)₄]·2H₂O}_n(2){[Nd Ni_0.5(2,5-pydc)(ox)(H₂O)₄]·2H₂O}_n(3){[Gd Ni_0.5(2,5-pydc)(ox)(H₂O)₃]·H₂O}_n(4){[Tb Ni_0.5(2,5-pydc)(ox)(H₂O)₃]·H₂O}_n(5){[Dy Ni_0.5(2,5-pydc)(ox)(H₂O)₃]·H₂O}_n(6){[Er₂Ni(2,5-pydc)₃(ox)(H₂O)₄]·2H₂O}_n(7){[HoNi_0.5(2,5-pydc)(ox)(H₂O)₃]·H₂O}_n(8){[Pr Co_0.5(2,5-pydc)(ox)(H₂O)₄]·2H₂O}_n(9){[Nd Co_0.5(2,5-pydc)(ox)(H₂O)₄]·2H₂O}_n(10){[Tb Co_0.5(2,5-pydc)(ox)(H₂O)₃]·5H₂O}_n(11){[Gd Co_0.5(2,5-pydc)(ox)(H₂O)₃]·H₂O}_n(12){[Dy Co_0.5(2,5-pydc)(ox)(H₂O)₃]·H₂O}_nCrystal structures of polymers(1)-(6)and(8)-(10)have been determined by X-ray single-crystal diffraction,and it is proved that polymers(7),(11)and(12)are isomorphous with polymers(3)-(5)according to the powder XRD diffraction.Polymers(1)-(7)are Ni-Ln polymers with three different crystal structures,(1)and(2)exhibit 2D layers constructed by pyridine-2,5-dicarboxylate(2,5-pydc^2-)and oxalate(ox^2-),and further connected into the 3D infinite hydrogen bond network structures with O-H···O hydrogen bonds formed by carboxyl O atoms from oxalate and coordination water molecules.Polymers(3)-(7)are connected into3D network structures by coordination bonds,while 2,5-pydc^2-in polymer(6)adopts three coordination modes to coordinate with Ln^? and Ni^? ions,so the structure of(6)is quite different from the other 3D Ni-Ln polymers.For Co-Ln polymers,there are still three different crystal structures.Hereinto polymers(8)and(9)are isomorphic with polymers(1)and(2),polymers(11)and(12)are isomorphic with(3)-(5).Moreover,polymer(10)possesses the same crystal framework with(3)-(5),but the asymmetric unit of polymer(10)has four more lattice water molecules than them.At room temperature,the IR,UV-Vis-NIR absorption and Vis-region fluorescence excitation and emission spectra of 12 kinds of polymer crystals have been measured,and their spectra are analyzed and assigned.All polymers exhibit the LMCT emission of Ni^?/Co^?-ligand moiety,the characteristic luminescence of Ln^? ions in some polymers is weak and doesn't reach the expected sensitization effect.Some bands of Ln(?)ions present shift,split and broad,which may be attributed to that the internal energy levels of the system are tuned by the influence of Ni(?)or Co(?)ion and the crystal field,and this is also reflected by their UV-Vis-NIR absorption spectra.