MOFs with bridging or terminal hydroxo ligands: Applications in adsorption, catalysis, and functionalization

Metal-organic frameworks (MOFs) are popular porous materials prepared from metallic species and organic linkers via the formation of coordination bonds. The applications and potentiality of MOFs can be further improved by their functionalization, such as the introduction of functional groups into pristine MOFs. Among these functional groups, the –OH group is interesting because of its polarity and weak acidity for hydrogen bonding and acid catalysis, respectively, for example. The hydroxyl group can be loaded onto both the linker and metal sites. In this review, the –OH groups on the metallic species of MOFs are discussed because various MOFs contain hydroxo groups as ligands. MOFs bearing hydroxo ligands (MOF-HLs) are attractive because no functionalized linker (that is useful for MOFs with –OH on the linkers) or modification/functionalization is required during their preparation, unlike MOFs composed of other functional groups, such as –NH₂, –SO₃H, and –COOH. In this work, MOF-HLs have been reviewed for the first time in terms of their preparation, analysis, and applications (in adsorption, catalysis, and further functionalization). After a summary of this discussion, the future prospects for MOF-HLs are provided for further study in their relevant fields.