Modern technology makes extensive use of ion exchangers. For example, they are commonly used to decalcify water by binding calcium ions and releasing sodium ions in return. Good exchangers tend to be materials with high surface areas, such as resins, zeolites, or clays. German scientists have now demonstrated that the compact, crystalline structures of intermetallic compounds, in which the diffusion pathways for efficient materials transport are actually absent, can also exchange ions. In the journal Angewandte Chemie, they report the full replacement of the chloride ions in Bi12Rh3Cl2 crystals by bismuth atoms.
The team working with Michael Ruck at the Technical University of Dresden noticed this unexpected phenomenon while researching bismuth subhalides. Subhalides are compounds that have fewer halogen ions than pure ionic metal halides. This results in regions that contain direct bonds between metal atoms. Subhalides with bismuth and rhodium are known to have intermetallic substructures that range from clusters to three-dimensional networks. Bi12Rh3Cl2 contains intermetallic networks consisting of edge-sharing [RhBi8] cubes and antiprisms.
The researchers planned to “pull” the halogen atoms out without destroying the intermetallic regions under gentle conditions using an n-butyllithium solution. The chloride ions were extracted just as the scientists hoped, even though they seemed to be tightly enclosed by the narrow channels of the intermetallic network. Even more surprisingly, the resulting voids in the crystal structure were filled by bismuth atoms. The bismuth atoms came from barely noticeable chemical decomposition of the surface of the crystal.
The resulting product is Bi12Rh3Bi2, a metastable superconductor with a structure identical to that of the subchloride. During the reaction, the morphology of the crystal remains unchanged. “The transformation must be based on efficient transport of chloride ions out and bismuth ions into the network,” says Ruck. Crystallographic studies revealed a small change in the torsion angle of the [RhBi8] antiprisms. “The antiprisms act as hinges in the network,” explains Ruck. “Transient changes in the angle allow wide diffusion pathways to open up parallel to all of the intermetallic strands. Since the diffusion paths intersect, the transport system is three-dimensional.”
Although the intermetallic network only changes very slightly, the electronic properties are significantly different: the subchloride only demonstrates metallic conductivity along special directions that are insulated by nonconducting parts of the structure. In the intermetallic compound, in contrast, the conducting strands are metallically connected through the additional bismuth atoms. They are thus electrically connected, resulting in a three-dimensional metal.
About the Author
Professor Dr. Michael Ruck conducts research and teaches chemistry and food chemistry at the Technical University of Dresden. He works in the area of solid-state chemistry and is particularly interested in metallic compounds and low-temperature synthesis of materials. He is also a Fellow of the Max Planck Institute of the Chemical Physics of solids in Dresden.
Author: Michael Ruck, Technische Universität Dresden (Germany), http://www.cpfs.mpg.de/
Title: The Topochemical Pseudomorphosis of a Chloride into a Bismuthide
Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.201309460
| Angewandte Chemie
Transport of molecular motors into cilia
28.03.2017 | Aarhus University
Asian dust providing key nutrients for California's giant sequoias
28.03.2017 | University of California - Riverside
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
29.03.2017 | Materials Sciences
29.03.2017 | Physics and Astronomy
29.03.2017 | Earth Sciences