Flattening of a Bent Sulfonated MOF Linker: Impact on Structures, Flexibility, Gas Adsorption, CO2/N2 Selectivity, and Proton Conduction

Monika Szufla; Anna Krawczuk; Gabriela Jajko; Paweł Kozyra; Dariusz Matoga

doi:10.1021/acs.inorgchem.3c02553

Flattening of a Bent Sulfonated MOF Linker: Impact on Structures, Flexibility, Gas Adsorption, CO₂/N₂ Selectivity, and Proton Conduction

Inorg Chem. 2024 Jan 8;63(1):151-162. doi: 10.1021/acs.inorgchem.3c02553. Epub 2023 Dec 20.

Authors

Monika Szufla^{1

2}, Anna Krawczuk³, Gabriela Jajko^{1

2}, Paweł Kozyra¹, Dariusz Matoga¹

Affiliations

¹ Faculty of Chemistry, Jagiellonian University, Gronostajowa 2, 30-387 Kraków, Poland.
² Doctoral School of Exact and Natural Sciences, Jagiellonian University, ul. prof. S. Łojasiewicza 11, 30-348 Kraków, Poland.
³ Institut für Anorganische Chemie, Georg-August-Universität Göttingen, Tammannstr. 4, 37077 Göttingen, Germany.

PMID: 38117683
DOI: 10.1021/acs.inorgchem.3c02553

Abstract

Rational design of organic building blocks provides opportunities to control and tune various physicochemical properties of metal-organic frameworks (MOFs), including gas handling, proton conduction, and structural flexibility, the latter of which is responsible for new adsorption phenomena and often superior properties compared to rigid porous materials. In this work, we report synthesis, crystal structures, gas adsorption, and proton conduction for a flexible two-dimensional cadmium-based MOF (JUK-13-SO3H-SO2) containing a new sulfonated 4,4'-oxybis(benzoate) linker with a blocking SO₂ bridge. This two-dimensional (2D) MOF is compared in detail with a previously reported three-dimensional Cd-MOF (JUK-13-SO3H), based on analogous, but nonflat, SO₂-free sulfonated dicarboxylate. The comprehensive structure-property relationships and the detailed comparisons with insights into the networks flexibility are supported by five guest-dependent structures determined by single-crystal X-ray diffraction (XRD), and corroborated by spectroscopy (IR, ¹H NMR), powder XRD, and elemental/thermogravimetric analyses, as well as by volumetric adsorption measurements (for N₂, CO₂, H₂O), ideal adsorbed solution theory (IAST), density-functional theory (DFT+D) quantum chemical and grand-canonical Monte Carlo (GCMC) calculations, and electrochemical impedance spectroscopy (EIS) studies. Whereas both dynamic MOFs show moderate proton conductivity values, they exhibit excellent CO₂/N₂ selectivity related to the capture of CO₂ from flue gases (IAST coefficients for 15:85 mixtures are equal to ca. 250 at 1 bar and 298 K). The presence of terminal sulfonate groups in both MOFs, introduced using a unique prechlorosulfonation strategy, is responsible for their hydrophilicity and water-assisted proton transport ability. The dynamic nature of the MOFs results in the appearance of breathing-type adsorption isotherms that exhibit large hysteresis loops (for CO₂ and H₂O) attributed to strong host-guest interactions. Theoretical modeling provides information about the adsorption mechanism and supports interpretation of experimental CO₂ adsorption isotherms.