Structural and Magnetic Study of Fluorinated Gadolinium Metal–Organic Frameworks

Gadolinium-based metal–organic frameworks (MOFs) are attractive due to their potential magnetic applications such as magnetic refrigeration, magnetic resonance imaging, and quantum information science. In this work, Gd3+-based MOFs containing binuclear metal nodes and fluorinated hexaclusters have been prepared exhibiting paramagnetic behavior, and their crystal structures were obtained. A two-dimensional MOF (Gd-BCA-2D) having the sql topology was prepared by the hydrothermal reaction of Gd3+ and bicinchoninic acid (BCA). A fluoro-bridged hexacluster-based MOF (Gd-BCA-3D) having the fcu topology was prepared using 2,6-difluorobenzoic acid as the fluorinating agent. By adding copper(II) to the synthesis, the biquinoline nitrogens of BCA rotate to the cis orientation, resulting in a new mixed-metal MOF (CuGd-BCA-3D) with the flu topology. Investigation of the magnetic properties of these fluoro-bridged MOFs revealed a weak antiferromagnetic exchange between nearest-neighbor Gd3+ ions. Additionally, europium analogues were used to characterize the luminescent properties. Emissions spectra of Eu-BCA-2D and Eu-BCA-3D exhibit an efficient sensitization of Eu3+ ions by the BCA ligand.