Speaker
Description
In recent years, lanthanide-based metal-organic frameworks (Ln-MOFs) have been gaining increasing attention due to their unique physicochemical properties and broad application potential. Ln-MOF materials are porous coordination polymers composed of lanthanide cations linked by organic ligands through coordination bonds [1]. Due to their partially filled $4f$ orbitals, lanthanides exhibit a strong tendency to form coordination polymers with high coordination numbers and diverse topologies, even when identical ligands are used. This structural flexibility enables the formation of extensive, highly organized networks with optimized properties for specific applications. Owing to the unique arrangement of electrons in $4f$ orbitals, Ln-MOF compounds find one of their key areas of application in magnetism [2].
In this work, we focused on the synthesis of new MOF materials prepared by coordinating the organic ligand H$_4$MTA with lanthanide ions. Solvothermal synthesis successfully yielded coordination polymers LnMTA (Ln = Nd(III), Sm(III), Eu(III)). The preparation of orange needle-shaped crystals of {[Ln$_4$(MTA)$_3$]$\cdot x$H$_2$O$\cdot y$DMF}$_n$ (LnMTA) was based on a hydrothermal reaction of Ln(NO$_3$)$_3\cdot 6$H$_2$O ($0.045$ mmol) with H$_4$MTA ($0.09$ mmol) in a DMF medium at $80$ °C for $6$ days. The synthesized coordination polymers were characterized using available physicochemical methods.The structure of the NdMTA complex was determined by single-crystal X-ray diffraction measurements. SC-XRD analysis revealed that the NdMTA complex crystallizes in an orthorhombic crystal system, where each MTA$^{4-}$ ion chelates four central neodymium atoms. The structure contains two types of cavities with dimensions of approximately $16.09\times 10.61$ Å$^2$ and $12.97\times 14.11$ Å$^2$ along the a-crystallographic axis. Based on PXRD analysis, it was confirmed that the prepared materials NdMTA, SmMTA and EuMTA are isostructural.The presence of the MTA$^{4-}$ ligand and solvent molecules within the cavities of the complex was confirmed by IR spectroscopy. Thermogravimetric analysis demonstrated that the porous complex undergoes desolvation upon heating to $150$ °C. The dehydrated form of LnMTA exhibits high thermal stability, maintaining its integrity up to $350$ °C. Magnetic properties were investigated using a SQUID based magnetometer in external dc field up to $5$ T and in the temperature range of $2 – 300$ K. Correlation between crystal structure of complexes and magnetic properties will be presented.
Acknowledgements
This work was supported by VEGA 1/0442/25 and APVV-20-0512. Funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V05-00008 (VVGS-ESGV-2923).
References
[1] W. Lu et al., “Tuning the structure and function of metal–organic frameworks via linker design,” Chem. Soc. Rev., vol. 43, no. 16. Royal Society of Chemistry (RSC), pp. 5561–5593, 2014. https://doi.org/10.1039/c4cs00003j
[2] S. Su et al., “Lanthanide Anionic Metal–Organic Frameworks Containing Semirigid Tetracarboxylate Ligands: Structure, Photoluminescence, and Magnetism,” Crystal Growth & Design, vol. 12, no. 4. American Chemical Society (ACS), pp. 1808–1815, Mar. 13, 2012. https://doi.org/10.1021/cg201283a
