New 3D Lanthanide Phosphonates: Syntheses, Crystal Structure, Thermal Stability, Luminescence, and Magnetism

Hydrothermal reactions of lanthanide oxide or lanthanide chloride with 3-ammonium-1-hydroxy­propylidene-1,1-diphosphonic acid (+H3N­CH2CH2C­(OH)­(PO3H2)­(PO3H–), H4L) afforded seven new lanthanide phosphonates, namely, [Ln(HL)] (Ln = Eu (1), Tb (2), Sm (3), Gd (4), Er (5), Nd (6), and Pr (7)). Compounds 1–7 are characterized by single-crystal X-ray diffraction, powder XRD, elemental analysis, IR spectroscopy, and thermogravimetric analysis (TGA). Compounds 1–5 crystallize in the orthorhombic Pnma space group, whereas compounds 6 and 7 crystallize in the monoclinic P2(1)/c space group. Compounds 1–7 exhibit a similar 3D open framework with eight-membered ring channels, which are occupied by organic pendants of CH2CH2NH3. TGA and PXRD reveal that compound 1 is thermally stable up to 350 °C under an air atmosphere. It is interesting that compounds 1 and 2 display bright red and green luminescence, respectively, which can be further enhanced obviously upon cooling to 10 K. It is worth noting that the bright red emission of compound 1 can be preserved after heat-treatment at 350 °C under an air atmosphere. Compounds 6 and 7 can give off NIR luminescence and near UV emission, respectively. Furthermore, the magnetic properties of solids 1 and 3–6 have also been studied.