Stable Metal-Organic Frameworks with Group 4 Metals: Current Status and Trends.

Group 4 metal-based metal-organic frameworks (M-MOFs), including Ti-, Zr-, and Hf-based MOFs, are one of the most attractive classes of MOF materials owing to their superior chemical stability and structural tunability. Despite being a relatively new field, M-MOFs have attracted significant research attention in the past few years, leading to exciting advances in syntheses and applications. In this outlook, we start with a brief overview of the history and current status of M-MOFs, emphasizing the challenges encountered in their syntheses. The unique properties of M-MOFs are discussed, including their high chemical stability and strong tolerance toward defects. Particular emphasis is placed on defect engineering in Zr-MOFs which offers additional routes to tailor their functions. Photocatalysis of M-MOF is introduced as a representative example of their emerging applications. Finally, we conclude with the perspective of new opportunities in synthesis and defect engineering.