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
Pathogenic bacteria hitchhiking to North and Baltic Seas?
22.07.2016 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
Unconventional quasiparticles predicted in conventional crystals
22.07.2016 | Max-Planck-Institut für Chemische Physik fester Stoffe
Munich Physicists have developed a novel electron microscope that can visualize electromagnetic fields oscillating at frequencies of billions of cycles per second.
Temporally varying electromagnetic fields are the driving force behind the whole of electronics. Their polarities can change at mind-bogglingly fast rates, and...
Breakup of continents with two speed: Continents initially stretch very slowly along the future splitting zone, but then move apart very quickly before the onset of rupture. The final speed can be up to 20 times faster than in the first, slow extension phase.phases
Present-day continents were shaped hundreds of millions of years ago as the supercontinent Pangaea broke apart. Derived from Pangaea’s main fragments Gondwana...
Scaffolding and specialised workers help with the delivery – Heidelberg biochemists gain new insights into biogenesis
A type of scaffolding on which specialised workers ply their trade helps in the manufacturing process of the two subunits from which the ribosome – the protein...
Scientists at the Helmholtz Zentrum München have developed a new mass spectrometry imaging method which, for the first time, makes it possible to analyze hundreds of metabolites in fixed tissue samples. Their findings, published in the journal Nature Protocols, explain the new access to metabolic information, which will offer previously unexploited potential for tissue-based research and molecular diagnostics.
In biomedical research, working with tissue samples is indispensable because it permits insights into the biological reality of patients, for example, in...
Chemists at the University of Basel have succeeded in using computer simulations to elucidate transient structures in proteins. In the journal Angewandte Chemie, the researchers set out how computer simulations of details at the atomic level can be used to understand proteins’ modes of action.
Using computational chemistry, it is possible to characterize the motion of individual atoms of a molecule. Today, the latest simulation techniques allow...
15.07.2016 | Event News
15.07.2016 | Event News
11.07.2016 | Event News
22.07.2016 | Information Technology
22.07.2016 | Physics and Astronomy
22.07.2016 | Life Sciences