<i>De Novo</i> Synthesis of Single-Crystalline Multi-Module Chromium(III) Metal–Organic Frameworks for Water Adsorption

The robust Cr-(III) metal-organic frameworks (MOFs) have attracted considerable interest in water adsorptions. However, the synthesis of highly crystalline Cr-MOFs is complicated by the kinetically inert nature of Cr-(III). The main method for the preparation of Cr-MOFs now is postsynthetic metathesis, which is all consuming. Here, we report the <i>de novo</i> synthesis of a series of multi-module, single-crystalline Cr-MOFs at the micro scale (up to 6 μm). A dual-modulator (HF-pyridine) strategy is developed to modulate the multiple competitive coordination bonding in dual-ligand-based Cr-MOFs, with the secondary modulator of pyridine having the functional group of the secondary module of tripyridyl ligands, which thus acts as an additional inhibitor to nucleation. The high crystallinity has enabled the structure determination of a novel Cr-MOF (Cr-bpdc-tph) at atomic resolution by the continuous rotation electron diffraction (cRED) technique. Cr-bpdc-tph integrates both high porosity with a BET surface area up to 3191 m²/g and exceptional chemical resistance in extreme acidic and basic solutions (pH < 0 and pH > 14). The water adsorption results show that Cr-bpdc-tph has achieved an effective working efficiency of 76% within the relative humidity range of 45-65%.