Chemical and Thermal Stability of Isotypic Metal-Organic Frameworks: Effect of Metal Ions

Chemical and thermal stabilities of isotypic metal-organic frameworks (MOFs) like Al-BDC (Al-benzenedicarboxylate called MIL-53-Al), Cr-BDC (MIL-53-Cr) and V-BDC (MIL-47-V), after purification to remove uncoordinated organic linkers, have been compared to understand the effect of the central metal ions on the stabilities of the porous MOF-type materials. Chemical stability to acids, bases, and water decreases in the order of Cr-BDC > Al-BDC > V-BDC, suggesting stability increases with increasing inertness of the central metal ions. However, thermal stability decreases in the order of Al-BDC > Cr-BDC > V-BDC, and this tendency may be explained by the strength of the metal-oxygen bond in common oxides like Al2O3, Cr2O3, and V2O5. In order to evaluate precisely the stability of a MOF, it is necessary to remove uncoordinated organic linkers that are located in the pores of the MOF, because a filled MOF may be more stable than the same MOF after purification.