Synthesis of lanthanide diphosphonates using <i>o</i>-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.