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Vapor-Phase Metalation by Atomic Layer Deposition in a Metal–Organic Framework
Summary:
The authors from Northwestern University & Warsaw University of Technology developed NU-1000, a mesoporous Zr-MOF with spatially oriented –OH groups, and achieved quantitative vapor-phase metalation (Zn²⁺/Al³⁺) via atomic layer deposition (AIM), delivering Lewis-acid catalysts for Knoevenagel condensation with no metal leaching.
Background:
1. Condensed-phase MOF metalation suffers from solvent coordination, purification steps and uneven metal distribution.
2. The team proposed AIM – self-limiting, vapor-phase ALD inside MOF pores – obtaining atomically dispersed, open metal sites.
Research Content:
1. Synthesis:
Solvothermal reaction of ZrCl₄ + H₄TBAPy + benzoic acid in DEF/DMF → NU-1000; activated by HCl/DMF to expose terminal –OH; AIM carried out with ZnEt₂ or AlMe₃ at 110–140 °C.
2. Characterizations:
1) BET 2320 m² g⁻¹ (NU-1000) → 1580/1160 m² g⁻¹ after AIM; 30 Å mesopores shrink to ~27 Å.
2) SEM 2–5 µm crystals; EDX linescans show uniform Zn/Al across single crystal.
3) DRIFTS: –OH peaks (3674 & 3655 cm⁻¹) vanish after AIM; ICP gives 0.5 Zn/Zr and 1.4 Al/Zr.
3. Application:
Zn-AIM & Al-AIM catalyze ethyl cyanoacetate + benzaldehyde Knoevenagel condensation (active), while NU-1000 is inactive; post-catalysis ICP confirms no metal leaching.
4. Mechanism:
Self-limiting ALD surface reaction: –OH + M–R → –O–M–R + RH; only channel-pointing –OH react with ZnEt₂, whereas AlMe₃ accesses all terminal –OH, creating single-site Lewis acids.
Outlook:
AIM provides a solvent-free, scalable route to install multiple metals or clusters inside stable MOFs, opening generic avenues for catalysis, separations and sorption technologies.
Vapor-Phase Metalation by Atomic Layer Deposition in a Metal–Organic Framework
Authors: Joseph E. Mondloch, Wojciech Bury, David Fairen-Jimenez, Stephanie Kwon, Erica J. DeMarco, Mitchell H. Weston, Amy A. Sarjeant, SonBinh T. Nguyen, Peter C. Stair, Randall Q. Snurr, Omar K. Farha, Joseph T. Hupp
DOI: 10.1021/ja4050828
Link: https://pubs.acs.org/doi/10.1021/ja4050828
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