Synthesis of new forms of carbon compounds

Under the leadership of Prof. Dr. Leonid Dubrovinsky from the Bavarian Geoinstitute and Prof. Dr. Natalia Dubrovinskaia from the Laboratory of Crystallography at the University of Bayreuth, researchers have synthesized new carbon compounds which have structural elements similar to those of complex organic molecules, but deprotonated (i.e. do not contain hydrogen).

To do this, the researchers used diamond anvil cells that compressed the tiny calcium carbide crystals to pressures in the three-digit gigapascal range and simultaneously heated them to temperatures of around 3,000 °C. These conditions correspond to those at a depth of 2.900 km in the Earth's interior. The change in pressure and temperature caused the calcium carbide to form two new carbides: high-pressure polymorph of CaC₂ and Ca₃C₇.

Although the high-pressure polymorph of CaC₂ has the same chemical composition as the starting material, it differs from it in the spatial arrangement of the atoms and in its chemical properties. The polymorph possesses carbon chains that can exist under conditions that far exceed those known for the existence of conventional organic compounds. The formation of such compounds under the conditions in the interior of planets could even have played a role in the origin of life, because they could be the origin of hydrocarbons.

The compound with the chemical formula Ca₃C₇ has never been observed before, so that its synthesis and structure elucidation represent a significant step forward in understanding the behaviour of carbon-based materials under extreme conditions.

Prof. Dr. Leonid Dubrovinsky, the lead researcher of the study, explained: "Our findings not only expand the boundaries of known carbon chemistry but also provide a new perspective on how complex carbon structures could exist in the deep Earth and potentially in other planetary bodies"

"The similarities between these high-pressure carbides and deprotonated metal-organic compounds open up exciting possibilities for designing novel materials with unique electronic, magnetic, and optical properties," added Prof. Dr. Natalia Dubrovinskaia.

The research work was carried out in international collaboration by scientists from the Bavarian Geoinstitute and the Laboratory of Crystallography at the University of Bayreuth, the German Electron Synchrotron (DESY), the University of Cologne, the University of Edinburgh, Goethe University Frankfurt, the University of Chicago, the European Synchrotron Radiation Facility and Linköping University.