Hydrothermal reactions: From the synthesis of ligand to new lanthanide 3D-coordination polymers

• The ligand 2,5-piperazinedione-1,4-diacetic acid was synthetized using the hydrothermic method and characterized.
• Two new 3D-coordination polymers with this ligand containing Gd3+ and Eu3+ ions were also obtained.
• The compounds are isostructural and the typical luminescent properties were observed in both structures.

The organic ligand 2,5-piperazinedione-1,4-diacetic acid (H2PDA) was synthesized under hydrothermal conditions starting from the iminodiacetic acid and catalyzed by oxalic acid. The X-ray powder diffraction data indicates that the compound crystallizes in the P21/c monoclinic system as reported in the literature. The ligand was also characterized by elemental analysis, magnetic nuclear resonance, infrared spectroscopy and thermogravimetric analysis. Two new coordination networks based on lanthanide ions were obtained with this ligand using hydrothermal reaction. In addition to single-crystal X-ray diffraction, the compounds were characterized by infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and elemental analysis. Single-crystal XRD showed that the compounds are isostructural, crystallizing in P21/n monoclinic system with chemical formula [Ln(PDA)1.5(H2O)](H2O)3 (Ln=Gd3+(1) and Eu3+(2)).The luminescence properties of both compounds were studied. In the compound (1), a broad emission band was observed at 479 nm, redshifted by 70 nm in comparison of the free ligand. In (2), the typical f–f transition was observed with a maximum peak at 618 nm, related with the red emission of the europium ions. Computational methods were performed to simulate the crystal structure of (2). The theoretical calculations of the intensity parameters are in good agreement with the experimental values.

Scheme of obtaining the ligand 2,5-piperazinedione-1,4-diacetic acid (H2PDA) and two new isostructural 3D-coordination polymers [Ln(PDA)1.5(H2O)](H2O)3 (Ln=Gd3+ and Eu3+) by hydrothermal synthesis.Figure optionsDownload as PowerPoint slide