Chiral Lanthanum Metal-Organic Framework with Gated CO2 Sorption and Concerted Framework Flexibility

Francoise M Amombo Noa; Erik Svensson Grape; Michelle Åhlén; William E Reinholdsson; Christian R Göb; François-Xavier Coudert; Ocean Cheung; A Ken Inge; Lars Öhrström

doi:10.1021/jacs.2c02351

Chiral Lanthanum Metal-Organic Framework with Gated CO₂ Sorption and Concerted Framework Flexibility

J Am Chem Soc. 2022 May 18;144(19):8725-8733. doi: 10.1021/jacs.2c02351. Epub 2022 May 3.

Authors

Francoise M Amombo Noa¹, Erik Svensson Grape², Michelle Åhlén³, William E Reinholdsson¹, Christian R Göb⁴, François-Xavier Coudert⁵, Ocean Cheung³, A Ken Inge², Lars Öhrström¹

Affiliations

¹ Chemistry and Biochemistry, Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-41296 Gothenburg, Sweden.
² Department of Materials and Environmental Chemistry, Stockholm University, Stockholm SE-10691, Sweden.
³ Nanotechnology and Functional Materials, Department of Material Sciences and Engineering, Uppsala University, SE-751 21 Uppsala, Sweden.
⁴ Rigaku Europe SE, Hugenottenallee 167, Neu-Isenburg D-63263, Germany.
⁵ Chimie ParisTech, PSL University, CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France.

Abstract

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, cpb^6-: [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.