Structural insights into new luminescent 2D lanthanide coordination polymers using an N, N′-disubstituted benzimidazole zwitterion. Influence of the ligand

Metal-Organic Framework vs. Coordination Polymer—Influence of the Lanthanide on the Nature of the Heteroleptic Anilate/Terephtalate 3D Network

Metal-organic frameworks (MOFs), whose definition has been regularly debated, are a sub-class of coordination polymers (CPs) which may feature both an overall 3D architecture and some degree of porosity. In this context, MOFs based on lanthanides (Ln-MOFs) could find many applications due to the combination of sorption properties and magnetic/luminescent behaviors. Here we report rare examples of 3D Ln-CPs based on anilate linkers, obtained under solvothermal conditions using a heteroleptic strategy. The three compounds of formula [Yb2(μ-ClCNAn)2(μ-F4BDC)(H2O)4]·(H2O)3 (1), [Er2(μ-ClCNAn)2(μ-F4BDC)(H2O)4]·(H2O)4 (2) and [Eu2(μ-ClCNAn)2(μ-F4BDC)(H2O)6] (3) have been characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and optical measurements. Structural characterization revealed that compounds 1 and 2 present an interesting MOF architecture with extended rectangular cavities which are only filled with water molecules. On the other hand, compound 3 shows a much more complex topology with no apparent cavities. We discuss here the origins of such differences and highlight the crucial role of the Ln(III) ion nature for the topology of the CP. Compounds 1 and 2 now offer a playground to investigate the possible synergy between gas/solvent sorption and magnetic/luminescent properties of Ln-MOFs.

New Ln-MOFs based on mixed organic ligands: synthesis, structure and efficient luminescence sensing of the Hg2+ ions in aqueous solutions

In view of Hg²⁺ ion sensing by luminescence, a series of new, phenanthroline-decorated 3D lanthanide metal organic frameworks (Ln-MOFs) valorising an original combination of four different lanthanides and two organic ligands, i.e. thiobis(4-methylene-benzoic acid) (H₂tmba) and 1,10-phenanthroline (phen), have been successfully synthesized, namely {[Ln₄(tmba)₆(phen)₄]·m(H₂O)(phen)}_n [Ln = Ce, m = 3 (1); Pr, m = 1 (2); Eu, m = 3 (3); and Tb, m = 3 (4)]. Compounds 1-4 were characterised by single-crystal X-ray diffraction, elemental and thermogravimetric analyses, and powder X-ray diffraction. The luminescence properties of complexes 3 and 4 were thoroughly investigated. It is herein proved that compound 3 sensitively and selectively acts as an excellent luminescent probe for the detection of Hg²⁺ ions in waters, with a detection limit of 1.00 μM. As additional assets, 3 displays superb stability over a wide pH range (3-12) of the aqueous media, as well as convenient recycling after completion of the detection experiments. The rationale for the observed luminescence quenching effect of mercury might be a strong interaction arising between Hg²⁺ ions and the carboxylate oxygen atoms of the tmba^2- ligand. The results open new perspectives for applications in environmental remediation.