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Endowing Porphyrinic Metal–Organic Frameworks with High Stability by a Linker Desymmetrization Strategy
Summary:
The authors from the University of Science and Technology of China developed two highly stable porphyrinic metal–organic frameworks, USTC-9(Fe) and USTC-9(In), via a linker-desymmetrization strategy; the Fe variant exhibits outstanding CO₂-cycloaddition activity (96.4 % conversion, 70 °C, 1 atm CO₂) and extreme chemical stability (2 M HCl to pH 12).
Background:
1. Traditional porphyrinic MOFs such as PCN-600 collapse after routine activation because their symmetrical linkers offer insufficient steric protection; previous stabilization attempts required extra components that clogged pores.
2. The authors proposed desymmetrizing the TCPP linker to create interlocked, chair-shaped TmCPP linkers, generating thickened pore walls without sacrificing porosity.
Research Content:
1. Synthesis
– Cluster precursor: Fe₂MnO(OOCCH₃)₆ (or Fe₃O analogue) + H₂TmCPP in DMF/HNO₃/TFA, 160 °C, 10 h.
– Post-synthetic ion exchange affords USTC-9(Fe) and USTC-9(In) single crystals.
2. Characterizations
1) BET surface areas: 2294 m² g⁻¹ (USTC-9-Fe) and 2067 m² g⁻¹ (USTC-9-In); uniform ~17 Å mesopores (DFT).
2) SEM reveals rod-shaped crystals (2–3 µm long).
3) NH₃-TPD shows higher Lewis acidity for Fe variant (126 °C vs 106 °C desorption peak).
3. Application
– CO₂ cycloaddition to epibromohydrin: USTC-9(Fe) 96.4 % conversion (70 °C, 1 atm CO₂, TBAB co-catalyst); retains activity after five cycles.
– Both MOFs survive 24 h in 3 M HCl, pH 12 NaOH, and common organic solvents without structural loss.
4. Mechanism
– Interlocked TmCPP linkers create steric hindrance and mutual π–π buttressing, suppressing linker rotation and capillary collapse.
– Open Fe³⁺/In³⁺ sites act as Lewis acids to activate epoxides; Br⁻ from TBAB performs nucleophilic ring-opening, followed by CO₂ insertion and cyclization.
Outlook:
This work delivers a general “linker-desymmetrization” blueprint for stabilizing porphyrinic MOFs while preserving high porosity, opening avenues for robust catalysts and sorbents under harsh conditions.
Endowing Porphyrinic Metal–Organic Frameworks with High Stability by a Linker Desymmetrization Strategy
Authors: Wentao Han, Xing Ma, Jingxue Wang, Fucheng Leng, Chenfan Xie, Hai-Long Jiang
DOI: 10.1021/jacs.3c00957
Link: https://pubs.acs.org/doi/10.1021/jacs.3c00957
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