Lanthanide-based F-MOFs: Structure, hydrolytic stability, spectral and magnetic properties

• Published in: Journal of solid state chemistry 2024-11, Vol.339, p.124949, Article 124949
• Main Authors: Princík, D., Zeleňák, V., Gyepes, R., Čižmár, E., Zeleňáková, A., Hrubovčák, P., Zelenka, T., Elečko, J., Macko, J., Lubal, P., Bednarčík, J., Dutková, E.
• Format: Article
• Language: English
• Subjects: Coordination polymer; Fluorinated MOFs; Hydrophobicity; Lanthanides; Magnetic properties; Metal-organic frameworks
• ISSN: 0022-4596
• DOI: 10.1016/j.jssc.2024.124949

A series of five novel lanthanide-based fluorinated metal-organic frameworks (Ln-F-MOFs) have been synthesized under solvothermal conditions by the reaction of 3,3′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-dicarboxylic acid (H2L) and lanthanide Ln(III) ions (Ln(III)La, Ce, Pr, Nd and Eu). Powder X-ray diffraction (PXRD) analysis revealed that all prepared complexes are isostructural. A single-crystal X-ray crystallographic study of one representative of the isostructural group, namely {[La2(L)3(DMF)2(H2O)2]}n showed, that compound crystallizes in a triclinic system with space group P-1. The lattice parameter values are a = 8.563(2) Å, b = 13.199(3) Å, c = 16.008(4) Å, α = 104.588(7) °, β = 92.904(7) ° and γ = 92.717(7) °, with two formula units in the unit cell. The overall structure is formed by 2D polymeric layers, which are arranged into a semi-3D supramolecular structure through hydrogen bonds and other intramolecular interactions. The study of the hydrophobic properties of the complexes showed that the complexes exhibit surface hydrophobicity with a “rose petal effect” and a contact angle of approximately 107°. However, the structures are not hydrolytically stable in the long term and the structure starts to delaminate after two days in water. This is a manifestation of the fact that the complexes do not form a 3D polymer network, it is made up of 2D layers connected only by weak non-bonding interactions. The photoluminescence properties of the Ln(III) complexes are determined by the characteristic 5d-4f or 4f-4f electron transitions for the individual lanthanide ions. The magnetic properties of Nd(III), Pr(III) and Eu(III) variants were studied. The magnetic properties of {[Pr2(L)3(DMF)2(H2O)2]}n are characterized by the presence of a low-lying quasi-doublet with 15.6 cm−1 energy splitting, whereas Eu(III) variant is nonmagnetic at low temperatures, but the magnetic 7F1 state is accessible by thermal excitation. For Nd(III) complex, the X-band EPR measurements were performed. Since 1D channels with dimensions of 4.90 × 7.23 Å2 are present within the structure, the adsorption of N2, CO2 and H2 gases was also studied. Five novel isostructural lanthanide-based fluorinated metal-organic frameworks (Ln-F-MOFs) constructed from the ligand 3,3′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-dicarboxylic acid (H2L) and Ln(III) ions (La, Ce, Pr, Nd and Eu) has been synthesized. Structure channels lined with fluorine atoms enable a water-repellent effect, confirme