Four series of lanthanide coordination polymers based on the tetrabromobenzene-1,4-dicarboxylate ligand: structural
Suwadee Jiajaroen1,2, Winya Dungkaew3, Filip Kielar4
1Thammasat University Research Unit in Multifunctional Crystalline Materials and Applications (TU-MCMA), Faculty of Science and Technology, Thammasat University, Pathum Thani 12121, Thailand. kc@tu.ac.th.
Abstract:
Four series of lanthanide-based coordination polymers (LnCPs), namely [Ln(Br4bdc)1.5(MeOH)3] (1Ln; Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy), [Ln2(Br4bdc)2(NO3)2(MeOH)4] (2Ln; Ln = Ce, Pr, Nd, Sm), [Ln(Br4bdc)(NO3)(MeOH)] (3Ln; Ln = Gd, Tb, Dy), and [Ln2(Br4bdc)3(H2O)2.3(MeOH)2.7] (4Ln; Ln = Gd, Tb, Dy) have been synthesized by reacting hydrated lanthanide(III) salts with tetrabromobenzene-1,4-dicarboxylic acid (H2Br4bdc) in different solvents under solvothermal conditions. The structural diversity found in the system mainly resulted from the effects of anions, solvents, and the variation in the ionic radii of the lanthanide(III) ions. Compounds in series 1Ln feature a two-dimensional (2D) layered structure with sql topology based on {(Ln(COO)2)2(μ-COO)2} secondary building units (SBUs). Compounds in series 2Ln and 3Ln comprise, respectively, infinite uniform and alternate chains of {Ln(COO)2} SBUs that are assembled into a similar network topology to 1Ln. Meanwhile, compounds in series 4Ln feature 3D coordination networks of a pcu α-Po topological net consisting of binuclear {Ln2(COO)3} SBUs. The formation of polymeric networks in series 1Ln-4Ln is facilitated by the numerous coordination sites of the ligand Br4bdc2- and the fact that its bromine atoms can participate in the formation of various types of intermolecular interactions. The solid-state photoluminescence studies on Eu- (1Eu) and Tb- (1Tb, 3Tb, 4Tb) containing compounds indicate that the Br4bdc2- ligands can efficiently sensitize Eu3+ and Tb3+ emission. Notably, such compounds exhibit highly sensitive fluorescence sensing for acetone, water, and Fe3+ ions via the fluorescence quenching effect. As the representatives of the series, activated 1Eu, 2Pr, 3Tb, and 4Tb show the maximum CO2 uptake capacities of 170.4, 273.7, 255.3, and 303.5 cm3 g-1, respectively, at 50 bar and 298 K with good repeatability of the adsorption-desorption properties. Magnetic studies indicate that the Gd- and Dy-based compounds 1Gd, 1Dy, 3Gd, 3Dy, and 4Gd show simple paramagnetic behaviours, whereas compound 4Dy exhibits weak ferromagnetic interactions.
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