Heterogeneous Acetalization of Benzaldehyde over Lanthanide Oxalate Metal-Organic Frameworks

Lanthanides (Ln) from the f-blocks of the periodic table have gained significant interest due to their unique characteristics, including magnetism, photoluminescence, and catalysis. In this study, a series of lanthanide metal-organic frameworks [Ln-MOFs, Ln = Eu(III), Tb(III), Nd(III), Er(III), Ho(III), Gd(III), Pr(III), and Dy(III)] were constructed based on oxalic acid and lanthanide metals as the building blocks. These MOFs were comprehensively characterized using various analytical and spectroscopic techniques, including powder X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, nitrogen adsorption-desorption, and Raman spectroscopy. The magnetic properties of the investigated materials were examined, revealing both antiferromagnetic and ferromagnetic interactions within the Ln-Ox MOFs. The catalytic activities of Ln-Ox MOFs were evaluated through the heterogeneous acetalization of benzaldehyde with methanol. Reaction yields by the reported catalysts varied up to 90% depending on the MOF's metal center, and the product was confirmed by gas chromatography-mass spectrometry. Recycling experiments have confirmed the stable regeneration of Ln-Ox MOFs in which the product yields remained the same over four consecutive cycles. The hydrothermal synthesis of these MOFs paves the way for a diverse array of materials showcasing unique lanthanide properties, making them suitable for various applications.