en.Wedoany.com Reported - Researchers at Graz University of Technology (TU Graz) have demonstrated that metal-organic framework (MOF) thin films possess a structure entirely different from previously assumed. This study, focusing on copper-terephthalate (Cu(bdc)) thin films, overturns a widely accepted structural model.
Due to their high porosity, MOFs are considered promising materials for innovative applications such as gas storage, carbon dioxide capture, or targeted drug delivery, a discovery that earned the Nobel Prize in Chemistry in 2025. The structure of MOFs in single-crystal form is relatively easy to determine, but the structure in thin films has largely remained a mystery, yet it determines the material's properties and potential applications.
A team led by Roland Resel and Egbert Zojer from the Institute of Solid State Physics at TU Graz, together with Paolo Falcaro and colleagues from the Institute of Physical Chemistry, and Christof Wöll from the Karlsruhe Institute of Technology (Karlsruher Institut für Technologie), published a paper in Advanced Functional Materials. Using Cu(bdc) thin films as an example, the researchers showed that all previously proposed structural models were incorrect and identified a structure that explains all observed properties: Cu(bdc) thin films are not porous but densely packed, and contain additional hydroxyl groups that were missing in most previous models.
"Our results indicate that many published structural models of MOF thin films are incorrect and need to be reassessed," said Egbert Zojer. This progress stems from combining complex quantum mechanical simulations with the rotating grazing-incidence X-ray diffraction (rotating-GIXD) method employed at the Elettra synchrotron radiation facility in Trieste. Unlike conventional methods, rotating-GIXD provides a nearly complete picture of the crystal periodicity, enabling the team to deduce the atomic structure of Cu(bdc) thin films. By combining quantum mechanical simulations with film density determined via X-ray reflectometry, the researchers ruled out a large number of structures proposed in previous literature and revealed the true identity of the film through simulations.
The now-identified non-porous structure explains why the thin films can barely load guest molecules, why they exhibit exceptionally high stability towards water, and why they possess magnetic properties impossible in previously assumed structures. The structure also confirms its ferromagnetic ground state, shifting its application potential towards physical phenomena that could be relevant in sensors, microelectronics, or magnetic storage systems. Furthermore, the structure contains copper oxide layers similar to those in high-temperature superconductors, and the potential applications arising from this form the basis for further research.
"Through our work, we have demonstrated that the reliable determination of MOF thin film structures is only possible through the combination of modern diffraction methods with theoretical modeling," noted Egbert Zojer. "The diffraction method spearheaded by Roland Resel's team, along with the software developed at TU Graz for analyzing synchrotron data, provided essential tools for this. This lays the foundation for elucidating the structures of other MOF thin films in the future and subsequently using them in a targeted manner for new applications in sensors and microelectronics."
