Systematic and Dramatic Tuning on Gas Sorption Performance in Heterometallic Metal-Organic Frameworks

摘要

Despite their having much greater potential for compositional and structural diversity, heterometallic metal-organic frameworks (MOFs) reported so far have lagged far behind their homometallic counterparts in terms of CO_2 uptake performance. Now the power of heterometallic MOFs is in full display, as shown by a series of new materials (denoted CPM-200s) with superior CO_2 uptake capacity (up to 207.6 cm~3/g at 273 K and 1 bar), close to the all-time record set by MOF-74-Mg. The isosteric heat of adsorption can also be tuned from -16.4 kJ/mol for CPM-200-Sc/Mg to -79.6 kJ/mol for CPM-200-V/Mg. The latter value is the highest reported for MOFs with Lewis acid sites. Some members of the CPM-200s family consist of combinations of metal ions (e.g., Mg/Ga, Mg/Fe, Mg/V, Mg/Sc) that have never been shown to coexist in any known crystalline porous materials. Such previously unseen combinations become reality through a cooperative crystallization process, which leads to the most intimate form of integration between even highly dissimilar metals, such as Mg~(2+) and V~(3+). The synergistic effects of heterometals bestow CPM-200s with the highest CO_2 uptake capacity among known heterometallic MOFs and place them in striking distance of the all-time CO_2 uptake record.