Enriching Transmetalation Routes to Stable and Highly Porous Crystals of Chromium-Based Metal–Organic Frameworks

Among the rich chemical and structural diversity of metal–organic
frameworks (MOFs), those based on trivalent chromium (Cr(III)-MOFs)
have attracted significant interest due to their typically high stability.
However, their synthesis as highly crystalline materials remains challenging
due to chromium’s relative inertness, ability to adopt multiple
oxidation states, and intricate electronic interactions with ligands.
This study presents an innovative transmetalation approach from cobalt-
and indium-based MOFs, expanding beyond the previously reported routes,
mostly limited to iron-based MOF precursors. Moreover, the transmetalation
can be performed on cations with varied accessibility in clusters
with diverse connectivity (6 to 9). By expanding the library of possible
metal precursors, we additionally overcome some limitations encountered
with the traditional iron-based MOFs while increasing the structural
diversity of highly porous Cr-MOFs. Specifically, Co-sod-ZMOF-307 and In-soc-MOF-1, when transformed to their
chromium analogs, exhibit significantly enhanced stability and porosity
compared to their initial as-synthesized forms. Cr-soc-MOF-1 (from In), for instance, shows a substantial increase in porosity,
reaching 1.9 cm3/g, with a BET of 5668 m2/g,
while Cr-sod-ZMOF-307 (from In) stands as one of the
most porous Cr-MOFs reported, with pore volume reaching 2.4 cm3/g.