Magnetic Tunability in RE-DOBDC MOFs via NO_x Acid Gas Adsorption

The magnetic susceptibility of NOx-loaded RE-DOBDC (rare earth (RE): Y, Eu, Tb, Yb; DOBDC: 2,5-dihydroxyterephthalic acid) metal–organic frameworks (MOFs) is unique to the MOF metal center. RE-DOBDC samples were synthesized, activated, and subsequently exposed to humid NOx. Each NOx-loaded MOF was characterized by powder X-ray diffraction, and the magnetic characteristics were probed by using a VersaLab vibrating sample magnetometer (VSM). Lanthanide-containing RE-DOBDC (Eu, Tb, Yb) are paramagnetic with a reduction in paramagnetism upon adsorption of NOx. Y-DOBDC has a diamagnetic moment with a slight reduction upon adsorption of NOx. The magnetic susceptibility of the MOF is determined by the magnetism imparted by the framework metal center. The electronic population of orbitals contributes to determining the extent of magnetism and change with NOx (electron acceptor) adsorption. Eu-DOBDC results in the largest mass magnetization change upon adsorption of NOx due to more available unpaired f electrons. Experimental changes in magnetic moment were supported by density functional theory (DFT) simulations of NOx adsorbed in lanthanide Eu-DOBDC and transition metal Y-DOBDC MOFs.