Chiral Lanthanum Metal-Organic Framework with Gated CO
2 Sorption and Concerted Framework Flexibility.
J Am Chem Soc 2022;
144:8725-8733. [PMID:
35503249 PMCID:
PMC9122260 DOI:
10.1021/jacs.2c02351]
[Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
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A metal–organic
framework (MOF) CTH-17 based
on lanthanum(III) and the conformationally chiral linker 1,2,3,4,5,6-hexakis(4-carboxyphenyl)benzene,
cpb6–: [La2(cpb)]·1.5dmf was prepared
by the solvothermal method in dimethylformamide (dmf) and characterized
by variable-temperature X-ray powder diffraction (VTPXRD), variable-temperature
X-ray single-crystal diffraction (SCXRD), and thermogravimetric analysis
(TGA). CTH-17 is a rod-MOF with new topology och. It has high-temperature stability with Sohncke space groups P6122/P6522 at 90
K and P622 at 300 and 500 K, all phases characterized
with SCXRD and at 293 K also with three-dimensional (3D) electron
diffraction. VTPXRD indicates a third phase appearing after 620 K
and stable up to 770 K. Gas sorption isotherms with N2 indicate
a modest surface area of 231 m2 g–1 for CTH-17, roughly in agreement with the crystal structure. Carbon
dioxide sorption reveals a gate-opening effect of CTH-17 where the structure opens up when the loading of CO2 reaches
approximately ∼0.45 mmol g–1 or 1 molecule
per unit cell. Based on the SCXRD data, this is interpreted as flexibility
based on the concerted movements of the propeller-like hexatopic cpb
linkers, the movement intramolecularly transmitted by the π–π
stacking of the cpb linkers and helped by the fluidity of the LaO6 coordination sphere. This was corroborated by density functional
theory (DFT) calculations yielding the chiral phase (P622) as the energy minimum and a completely racemic phase (P6/mmm), with symmetric cpb linkers representing
a saddle point in a racemization process.
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