Synthesis of lanthanide diphosphonates using o-xylylenediphosphonic acid as a ligand: photoluminescence and catalytic properties

Four new lanthanide(III) diphosphonates, namely [Ln(HL)(H2O)]n (Ln = Gd (1), Tb (2), Dy (3), and Ho (4)), have been synthesized under hydrothermal conditions using multifunctional ligand o-xylylenediphosphonic acid (H4L). Structural characterizations have been carried out using elemental analysis, inductively coupled plasma optical emission spectroscopy (ICP-OES), fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), single-crystal X-ray diffraction (SCXRD), and powder X-ray diffraction (PXRD). The single-crystal X-ray analysis revealed that compounds have a similar core structure except for 2. Nine-coordinated polymers 1, 3, and 4 are isostructural and form two-dimensional (2D) coordination polymers in which each pair of Ln(III) ions is bridged by phosphonate oxygen atoms. Compound 2 features a 2D framework in which each terbium ion is seven-coordinated by six phosphonic oxygen atoms from four phosphonate ligands and an aqua ligand. The photoluminescent and catalytic properties of the 1–4 have been investigated. The effect of vessel size on crystal quality has also been examined.