Modulating Geometric Frustration in COFs through Linker Flexibility for Enhanced Glucosamine and Galactosamine Adsorption
Year: 2026
Type: preprint
Abstract: Geometric frustration remains largely unexplored in covalent organic frameworks (COFs), where reticular synthesis typically relies on highly symmetric and geometrically compatible building blocks. Departing from these conventional geometrical constraints can introduce additional accessible and reactive sites, providing opportunities to tune material properties for applications such as catalysis, sensing, and adsorption. Herein, we introduce geometric frustration into COFs using an asymmetric tetradentate thiophene-based aldehyde linker possessing unconventional bite angles of approximately 68°, 69°, 68°, and 154°. Condensation of this linker with three linear diamines of varying rigidity, namely 1,4-phenylenediamine, trans-1,4-cyclohexanediamine, and benzidine, yielded the corresponding COFs THPD, THCH, and THBZ. Structural characterization using PXRD, BET analysis, FT-IR spectroscopy, and solid-state NMR revealed significant structural disorder within the frameworks. To further elucidate their structural organization, multiple sulfur-orientation-dependent structural models were constructed and analyzed using periodic density functional theory (DFT) calculations. Correlating linker distortion, quantified through root-mean-square deviation (RMSD), with relative framework energies revealed stabilization through intermediate distortion states rather than fully relaxed geometries. The aromatic linker-based systems accumulate substantially larger strain energies than the cyclohexanediamine-based framework, demonstrating that linker flexibility governs strain accommodation within the COFs. These distortions strongly influence framework accessibility and amino sugar adsorption, with the moderately frustrated THCH framework exhibiting significantly enhanced guest uptake relative to the more rigid frustrated systems and a non-frustrated reference COF. Collectively, this work demonstrates that geometric frustration can be systematically embedded and modulated within COFs through linker design, while establishing RMSD-based structural analysis as a quantitative tool for identifying and comparing geometrically frustrated systems.
Source: ChemRxiv
Institution: Martin Luther University Halle-Wittenberg
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
Funder: Deutsche Forschungsgemeinschaft
OpenAlex ID: W7219625935