Flexible metal–organic frameworks with a range of pore sizes are made by threading through molecular ligands
The ability to ‘thread’ a molecular ligand through a metal–organic framework (MOF) to alter the pore size of the material — and yet allow the MOF to retain its crystallinity and principal structural features — has been demonstrated in a new study by A*STAR.
MOFs are three-dimensional, coordination networks comprising metal ions and organic molecules and usually are crystalline, porous materials with many applications including storage of gases such as hydrogen and carbon dioxide. While ‘threaded’ MOFs have been synthesized in the past, they remain challenging to easily and reliably produce.
Inclusion of molecular ligands creates a flexible, interpenetrated MOF — similar to stitching a thread through fabric to make a new pattern. Use of bridging ligands of varying lengths potentially could lead to materials with many different properties in terms of gas adsorption, gas separation and catalysis.
Now, Andy Hor and colleagues at the A*STAR Institute of Materials Research and Engineering and the National University of Singapore show how solvate molecules adhering to the surface of the channels on a cadmium-based coordination polymer can be replaced with nitrogen-containing ligands that form a bridge between two metal ions of the MOF. These dipyridyl ligands of lengths varying from 0.28 to 1.10 nanometers are then threaded through the pores of the framework to form flexible MOF structures with different porosities (see image).
A surprise for the researchers came when long dipyridyl ligands that were expected to cause structural collapse of the framework were accommodated by slippage of two-dimensional layers within the structure. “Our observation that within these crystals, two side-by-side layers can slip or slide across to create space for guests suggests that these MOFs are actually smarter than we thought because they can respond to external stimuli without losing their crystallinity,” says Hor.
The researchers used the solvent diethylformamide (DEF), rather than the less bulky dimethylformamide solvate, to create cadmium-based double layers with large enough channels to permit the dipyridyl ligands to thread through. They also replaced other DEF solvates within the structure with water to minimize congestion.
“We hope to apply a similar approach to other MOFs — using a range of metals and organic molecules — and to test the boundaries for creating adaptable three-dimensional materials,” says Hor. “We could introduce different functional organic moieties to the present MOF and create materials with magnetic, electronic and photonic functionalities.” Also, the dynamic nature of these MOFs makes them attractive candidates for selective gas adsorption materials.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering. More information about the group’s research can be found at the Porous Materials Laboratory webpage.
 Zhang, Z.-X. Ding, N.-N., Zhang, W.-H., Chen, J.-X., Young, D. J. & Hor, T. S. A. Stitching 2D polymeric layers into flexible interpenetrated metal–organic frameworks within single crystals. Angewandte Chemie International Edition 53, 4689–4632 (2014).
Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern
20.07.2018 | Princeton University
Relax, just break it
20.07.2018 | DOE/Argonne National Laboratory
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences