Abstract
Five new anilato-based, Ln(III)-containing, layered compounds have been prepared with the asymmetric ligand chlorocyananilato (C6O4(CN)Cl)2−; different Ln(III) ions Ce(III), Pr(III), Yb(III), and Dy(III); and the three different solvents H2O, dimethylsolfoxide (DMSO), and dimethylformamide (DMF). Compounds [Ce2(C6O4(CN)Cl)3(DMF)6]·2H2O (1), [Pr2(C6O4(CN)Cl)3(DMF)6] (2), [Pr2(C6O4(CN)Cl)3(DMSO)6] (3), [Yb2(C6O4(CN)Cl)3(DMSO)4]·2H2O (4) and [H3O][Dy(C6O4(CN)Cl)2(H2O)]·4H2O (5) show the important role that the Ln(III) size, as well as the size and shape of the solvent may play in the crystal structure of each compound. Compounds 1–4 present (6,3)-2D hexagonal lattices, with important differences in the coordination number and geometry of the Ln(III) ion, as well as in the distortion of the hexagonal cavities, depending on the Ln(III) and solvent size. Compound 5 (the only one prepared with water) presents a (4,4)-2D square lattice, where the Dy(III) ions are surrounded by four chelating anilato ligands. Compounds 2–4 are essentially paramagnetic, confirming the presence of weak (if any) magnetic coupling mediated by the anilato ligands when connecting Ln(III) ions. Compounds 2–4 showed a red shift and a broadening of the emission band of the ligand. Compound 4 also showed a strong emission band attributed to the Yb(III), suggesting an antenna effect of the ligand. An energy transfer diagram is proposed to explain these luminescent properties.
Highlights
The design of crystalline porous coordination polymers, or metal organic frameworks (MOFs) with different cavities sizes and shapes, is one of the hottest topics in Coordination Chemistry [1,2]
These compounds show the important role played by the size of the Ln(III) ion, as well as the size and shape of the coordinating solvent molecules, in determining the structure of the compounds
Compounds 1 and 2, prepared with the same solvent (DMF) but with different metal ions (Ce and Pr), show the important role of a small variation of the Ln(III) size: the larger Ce(III) ion allows a coordination number of nine, with a distorted tri-capped trigonal prismatic geometry that led to corrugated hexagonal layers with regular hexagonal cavities, whereas the slightly smaller Pr(III) ion gives rise to a distorted mono-capped square antiprism coordination geometry that generates rectangular cavities
Summary
The design of crystalline porous coordination polymers, or metal organic frameworks (MOFs) with different cavities sizes and shapes, is one of the hottest topics in Coordination Chemistry [1,2]. The very few examples reported, to date, with solvents other than water include [Pr2(C6O4Cl2)3(EtOH)6]·2EtOH [35], [Er2(C6O4Br2)3(DMSO)4]·2DMSO·2H2O [36], [Er2(C6O4Br2)3(DMF)6] [36], and the very recently reported series formulated as [Ln2(C6O4Br2)3(DMSO)n]·2DMSO·mH2O, with n = 6 and m = 0 when Ln = La-Gd, and n = 4 and m = 2 when Ln = Tb-Yb [38] These three compounds present the same (6,3)-2D topology, but the cavities are rectangular (in the EtOH and DMF cases) or have a very distorted hexagonal shape (in the DMSO compound), suggesting that the solvent plays an important role in the final structure. Further work to complete the series with all the Ln(III) ions and all the solvents is underway
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