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Issue 9, 2016
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Eight rare earth metal organic frameworks and coordination polymers from 2-nitroterephthlate: syntheses, structures, solid-state luminescence and an unprecedented topology

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Abstract

Eight novel lanthanide metal organic frameworks (MOFs) and coordination polymers (CPs), La2(NTA)3(OH2)6 (1), [Nd(NTA)(HNTA)(OH2)2]·3H2O (2), [Nd2(NTA)3(OH2)2](H2O)3·2H2O (3), and [Ln2(NTA)3(OH2)2](H2O)2 (Ln = Sm (4), Eu (5), Gd (6), Tb (7), Er (8)), (H2NTA = 2-nitroterephthalic acid), have been synthesized under hydrothermal and slow evaporation conditions. The compounds are characterized by X-ray crystallography, elemental analyses, infrared spectroscopy and thermogravimetric analyses (TGA). Compounds 1–8 feature varying coordination modes of the NTA ligand, including two modes that are being reported for the first time. Compound 2 was crystallized by slow evaporation and features a supramolecular 3-D framework involving H-bonds and π–π stacking interactions. In compounds 1 and 3–8, which were made under hydrothermal conditions, non-covalent interactions are secondary and the 3-D network is built from strong covalent bonds. Compounds 1, 3, and 4–8 form a 3,4,5-c network having point symbol {42.6}2{42.84}{43.6.86}2, a 4,4,6-c net with point symbol {42.84}{44.62}2{48.67}2 and an unprecedented 4,4,6-c net with point symbol {42.64}{43.63}2{48.66.8}2 respectively. The topologies are further simplified as parallel packing of rod-like SBUs; 1 and 2 form a distorted pcu network, 3 forms the nbo topology and 4–8 form the hex type topological network. From the crystal structure, solvent accessible voids for 2 and 3 are 138 Å3 [13%] and 864 Å3 [25%] of unit cell volume respectively. TGA data suggest that the framework in compounds 1, 2, 3, 5 and 7 are thermally stable up to 300 °C. Photoluminescence studies on compounds 5 and 7 indicate that NTA does not efficiently sensitize Eu3+ and Tb3+ emission due to alternate deactivation pathways available to the ligand. However, direct excitation in the visible region at 466 nm leads to red emission at room temperature in compound 5, the spectral profile of which suggests a lowering of the crystal field symmetry around Eu3+ and a quadrupolar contribution to the 5D07F2 peak. Emission from direct excitation of Tb3+ however is still quenched possibly due to back energy transfer to the ligand. This study is the second and most extensive report of lanthanide-based coordination networks involving nitroterephthalic acid and demonstrates its versatility as a building block for Ln-CPs and Ln-MOFs whose structures can be simplified as linked rod-shaped SBUs.

Graphical abstract: Eight rare earth metal organic frameworks and coordination polymers from 2-nitroterephthlate: syntheses, structures, solid-state luminescence and an unprecedented topology

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Publication details

The article was received on 14 Mar 2016, accepted on 08 Jun 2016 and first published on 08 Jun 2016


Article type: Paper
DOI: 10.1039/C6NJ00822D
New J. Chem., 2016,40, 7338-7349

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    Eight rare earth metal organic frameworks and coordination polymers from 2-nitroterephthlate: syntheses, structures, solid-state luminescence and an unprecedented topology

    J. A. Smith, M. A. Singh-Wilmot, K. P. Carter, C. L. Cahill, A. J. Lough and C. S. Knee, New J. Chem., 2016, 40, 7338
    DOI: 10.1039/C6NJ00822D

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