Effect of Different Synthesis Approaches on Structural and Thermal Properties of Lanthanide(III) Metal-Organic Frameworks Based on the 1H-Pyrazole-3,5-Dicarboxylate Linker

The impact of different synthetic procedures such as: hydrothermal, mechanochemical and precipitation on the structure and thermal properties of coordination polymers of 1H-pyrazole-3,5-dicarboxylic acid (H(3)pdca) with selected lanthanide ions was determined. The prepared complexes of the general formula: Ln(2)(Hpdca)(3).nH(2)O, where Ln = Eu(III), Nd(III), Tb(III) and Er(III); n = 6 or 7 were fully investigated by: elemental analysis, Energy-Dispersive X-Ray (ED-XRF) and infrared (ATR-FTIR) spectroscopy, powder as well as single-crystal X-ray diffraction methods and thermal analysis (TG-DSC and TG-FTIR) in various atmospheres. It was proved that all used strategies offer high yields of reactions along with crystallinity of the obtained products. The X-ray diffraction methods allowed to conclude that the complexes with the same metal ions exhibit the same crystal structure despite different synthesis routes. On the other hand, the coordination polymers of Eu(III), Tb(III) and Er(III) prepared under different conditions are isomorphous. Only neodymium(III) compounds have a different crystal structure. Thermal stability of the produced complexes was correlated with the synthesis conditions, in particular with the way of energy supply. It was found that the highest thermal stability was exhibited by the complexes prepared under the hydrothermal conditions. Additionally, based on the volatile products of metal complexes decomposition, the mechanism of their pyrolysis was proposed in relation to their structures.

Automated summary

The impact of different synthetic procedures on the structure and thermal properties of coordination polymers of 1H-pyrazole-3,5-dicarboxylic acid with lanthanide ions was investigated. The complexes exhibited high yields of reactions and crystallinity. The Eu(III), Tb(III), and Er(III) coordination polymers prepared under different conditions were found to be isomorphous, while only the neodymium(III) compounds had a different crystal structure. The thermal stability of the produced complexes was correlated with the synthesis conditions, with those prepared under hydrothermal conditions showing the highest stability.