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A research team associated with Prof. Sebastian Henke’s group in the Department of Chemistry and Chemical Biology at TU Dortmund University, in cooperation with partners at Ruhr Universität Bochum, has investigated the extraordinarily responsive behavior of porous metal-organic framework compounds. These can, depending on conditions of their physical environment, crumple up like a piece of paper and unfold again. The findings, which are highly relevant for applications such as energy storage or molecular separation, were recently published in the renowned scientific journal Nature Communications.
Metal-organic frameworks, MOFs for short, are synthetic materials. Composed of organic and inorganic molecules, they have a porous, open structure. Some MOFs have responsive properties; that is, they change their crystal structure depending on conditions of their physical environment. Thus the size and shape of the pores can change, for example, if one varies the chemical composition of the ambient atmosphere or exerts mechanical pressure. Among other things, this responsiveness enables MOFs to store gases very efficiently or to separate molecules from one another.
Doctoral candidate Roman Pallach from Prof. Sebastian Henke’s group has now discovered a new form of responsiveness in MOFs: Through targeted chemical modification of the organic MOF building blocks, the networks of pores no longer switch back and forth between two ordered, crystalline states, but rather between an ordered state and one that is very complex and disordered. The modified building blocks generate competing interactions within the network structures, so that the disordered state is preferred when guest molecules – stored gases, for example – are absent in the pores.
“When we remove the guest molecules from the pores, the network is, in a sense, frustrated, and it can only fold up in a disordered manner,” says Prof. Sebastian Henke. “With these MOFs, folding up while maintaining the order is not possible.”
Investigation with X-ray scattering methods
In cooperation with Dr. Julian Keupp from Prof. Rochus Schmid’s research group at Ruhr Universität Bochum and members of Physical Chemistry Prof. Rasmus Linser’s group at TU Dortmund University, the scientists conducted theoretical and experimental studies of the MOFs’ responsive behavior and were able to gain deep insights into the structure and temperature-dependent dynamics of the disordered state. In addition to computer simulations and spectroscopic techniques, they used sophisticated X-ray scattering methods at Dortmund’s synchrotron radiation source DELTA, at the German Electron Synchrotron DESY in Hamburg, and at the Diamond Light Source near Oxford, UK.
The findings of the interdiscplinary research team were recently published in the renowned scientific journal Nature Communications. The project was funded in part within the framework of the joint Excellence Cluster RESOLV of Ruhr Universität Bochum and TU Dortmund University.
R. Pallach, J. Keupp, K. Terlinden, L. Frentzel-Beyme, M. Kloß, A. Machalica, J. Kotschy, S. K. Vasa, P. A. Chater, C. Sternemann, M. T. Wharmby, R. Linser, R. Schmid, S. Henke, Nat. Commun. 2021, 12, 4097: Frustrated Flexibility in Metal-Organic Frameworks. DOI: 10.1038/s41467-021-24188-4
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The campus of TU Dortmund University is located close to interstate junction Dortmund West, where the Sauerlandlinie A 45 (Frankfurt-Dortmund) crosses the Ruhrschnellweg B 1 / A 40. The best interstate exit to take from A 45 is “Dortmund-Eichlinghofen” (closer to South Campus), and from B 1 / A 40 “Dortmund-Dorstfeld” (closer to North Campus). Signs for the university are located at both exits. Also, there is a new exit before you pass over the B 1-bridge leading into Dortmund.
To get from North Campus to South Campus by car, there is the connection via Vogelpothsweg/Baroper Straße. We recommend you leave your car on one of the parking lots at North Campus and use the H-Bahn (suspended monorail system), which conveniently connects the two campuses.
TU Dortmund University has its own train station (“Dortmund Universität”). From there, suburban trains (S-Bahn) leave for Dortmund main station (“Dortmund Hauptbahnhof”) and Düsseldorf main station via the “Düsseldorf Airport Train Station” (take S-Bahn number 1, which leaves every 15 or 30 minutes). The university is easily reached from Bochum, Essen, Mülheim an der Ruhr and Duisburg.
You can also take the bus or subway train from Dortmund city to the university: From Dortmund main station, you can take any train bound for the Station “Stadtgarten”, usually lines U41, U45, U 47 and U49. At “Stadtgarten” you switch trains and get on line U42 towards “Hombruch”. Look out for the Station “An der Palmweide”. From the bus stop just across the road, busses bound for TU Dortmund University leave every ten minutes (445, 447 and 462). Another option is to take the subway routes U41, U45, U47 and U49 from Dortmund main station to the stop “Dortmund Kampstraße”. From there, take U43 or U44 to the stop “Dortmund Wittener Straße”. Switch to bus line 447 and get off at “Dortmund Universität S”.
The AirportExpress is a fast and convenient means of transport from Dortmund Airport (DTM) to Dortmund Central Station, taking you there in little more than 20 minutes. From Dortmund Central Station, you can continue to the university campus by interurban railway (S-Bahn). A larger range of international flight connections is offered at Düsseldorf Airport (DUS), which is about 60 kilometres away and can be directly reached by S-Bahn from the university station.
The H-Bahn is one of the hallmarks of TU Dortmund University. There are two stations on North Campus. One (“Dortmund Universität S”) is directly located at the suburban train stop, which connects the university directly with the city of Dortmund and the rest of the Ruhr Area. Also from this station, there are connections to the “Technologiepark” and (via South Campus) Eichlinghofen. The other station is located at the dining hall at North Campus and offers a direct connection to South Campus every five minutes.
The facilities of TU Dortmund University are spread over two campuses, the larger Campus North and the smaller Campus South. Additionally, some areas of the university are located in the adjacent “Technologiepark”.