Two sodium and lanthanide(III) MOFs based on oxalate and V-shaped 4,4′-oxybis(benzoate) ligands: Hydrothermal synthesis, crystal structure, and luminescence properties

Two lanthanide based metal-organic frameworks, [NaLn(oba)(ox)(H2O)] (LnEu(1) and Sm(2)) were obtained from 4,4′-oxybisbenzoic acid, sodium oxalate and corresponding lanthanide salts by hydrothermal synthesis. They were characterized by single-crystal X-ray diffraction, IR spectra, and photoluminescent spectra. The crystallographic data reveals that complexes 1 and 2 are isomorphous and isostructural, composed of three-dimensional framework built up of distorted tricapped trigonal EuO9 units, distorted octahedron NaO6 units, 4,4′-oxybis(benzoate) and oxalate. The carboxylate oxygen atoms of the 4,4′-oxybis(benzoate) and oxalate ligand are coordinated to lanthanide ions and sodium ions, resulting into two-dimensional inorganic sheets, which are further linked into three-dimensional network by organic ligands. Thermogravimetric analyses of 1–2 display a considerable thermal stability. Photoluminescent measurements indicated that europium complex 1 displayed strong red emission.