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Solvent-Assisted Metal Metathesis: A Highly Efficient and Versatile Route towards Synthetically Demanding Chromium Metal–Organic Frameworks
Summary:
The authors from the Institute of Crystalline Materials, Shanxi University, developed robust Cr(III)-based metal–organic frameworks (Cr-MOFs) with high porosity and exceptional chemical stability via a solvent-assisted metal metathesis strategy, achieving efficient and versatile synthesis from Fe(III)-MOF precursors.
Background:
1. To address the difficulty in direct synthesis of Cr-MOFs due to the kinetic inertness of Cr–O bonds, previous researchers attempted postsynthetic routes such as reductive labilization–metathesis and direct metal exchange, but these methods suffered from harsh conditions, incomplete exchange, and poor generalizability.
2. The authors proposed an innovative solvent-assisted metal metathesis approach using coordinating solvents (e.g., acetone) to achieve nearly complete and mild exchange of Fe(III) by Cr(III) in diverse Fe-MOFs.
Research Content:
1. Synthesis:
The authors synthesized a series of Cr-MOFs (e.g., Cr-SXU-1, Cr-MIL-100, Cr-MIL-142A/C, Cr-PCN-333, and Cr-PCN-600) by treating corresponding Fe(III)-MOFs with CrCl₃·6H₂O in acetone at 60–100 °C for 4 h per cycle (3–5 cycles).
2. Characterizations:
1) BET surface area: Cr-SXU-1 showed 4036 m² g⁻¹ (N₂ at 77 K); Cr-MIL-100, Cr-MIL-142A, Cr-MIL-142C, and Cr-PCN-333 exhibited 1764, 1581, 1823, and 2071 m² g⁻¹, respectively.
2) PXRD confirmed retention of crystallinity and isostructural conversion; SEM/TEM-like optical images revealed single-crystal to single-crystal transformation.
3) TG analysis demonstrated thermal stability up to 420 °C; PXRD after 48 h in 3 M HCl or pH 11/12 solutions verified exceptional chemical stability.
3. Application:
Cr-SXU-1 maintained porosity after PEI functionalization and showed enhanced CO₂ uptake at 273 K, indicating potential for gas storage/separation.
4. Mechanism:
The carbonyl group of acetone coordinates to Fe(III) and Cr(III), facilitating ligand exchange; electron-donating methyl groups and low steric hindrance of acetone enhance exchange efficiency, as supported by IR shifts of ν(C=O).
Outlook:
This work provides a general, mild, and scalable route to robust Cr-MOFs, overcoming previous synthetic barriers and expanding the toolbox for stable porous materials in catalysis, gas separation, and environmental remediation.
Solvent-Assisted Metal Metathesis: A Highly Efficient and Versatile Route towards Synthetically Demanding Chromium Metal–Organic Frameworks
Authors: Jun-Hao Wang, Ying Zhang, Mian Li, Shu Yan, Dan Li, Xian-Ming Zhang
DOI: 10.1002/anie.201701217
Link: https://onlinelibrary.wiley.com/doi/10.1002/anie.201701217
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