Madrid, 2 (European Press)
For the first time, researchers from Stanford University have found a way to create and stabilize an extremely rare form of gold that has lost two negatively charged electrons, called Au2+.
The material that stabilizes this elusive version of the precious element is halide perovskite, a class of crystalline materials that shows great promise for a variety of applications, including solar cells, light sources and more efficient electronics.
Surprisingly, Au2+ perovskite is quick and easy to prepare using ingredients that are commercially available at room temperature.
“It was a real surprise that we were able to synthesize a stable material containing Au2+; I couldn’t believe it at first,” Himamala Karunadasa, associate professor of chemistry in Stanford’s School of Humanities and Sciences and lead author of the study, said in a statement. Published in Nature Chemistry. “The creation of this first-of-its-kind Au2+ perovskite is exciting. The gold atoms in perovskites have strong similarities to the copper atoms in high-temperature superconductors, and heavy atoms with unpaired electrons, such as Au2+, exhibit ‘cold magnet’ effects. They cannot be seen. In the lighter atoms.”
“Halide perovskites have attractive properties for many everyday applications, so we were looking to expand this family of materials,” said Kurt Lindquist, the study’s lead author who conducted the research as a doctoral student at Stanford University. Princeton. . “This unprecedented Au2+ perovskite could open up interesting new horizons.”
As an elemental metal, gold has long been valued for its relative rarity, as well as its unparalleled malleability and chemical inertness, meaning it can be easily transformed into jewelry and coins that do not react with chemicals in the environment and do not tarnish. time. An additional major reason for its value is the color of the gold of the same name; It can be said that no other metal in its pure state has such a rich and distinctive tone.
The basic physics behind gold’s famous appearance also explains why Au2+ is so rare, Karunadasa explained.
The main reason is relativistic effects, which were originally postulated in Albert Einstein’s famous theory of relativity. “Einstein taught us that when objects move very quickly and approach a significant fraction of the speed of light, objects become heavier,” Karunadasa said.
This phenomenon also applies to particles and has profound consequences for “massive” heavy elements, such as gold, whose atomic nuclei contain a large number of protons. Together, these particles exert an enormous positive charge, forcing negatively charged electrons to orbit the nucleus at extremely high speeds. As a result, the electrons become heavy and surround the nucleus closely, diluting its charge and allowing the outermost electrons to deflect more than in conventional metals. The rearrangement of electrons and their energy levels causes gold to absorb blue light and thus appear yellow to our eyes.
Because of the arrangement of gold’s electrons, and thanks to relativity, the atom naturally appears as Au1+ and Au3+, losing one or three electrons, respectively, and neglecting Au2+. (The “2+” indicates a net positive charge due to the loss of two negatively charged electrons, and the chemical symbol “Au” for gold comes from “aurum,” the Latin word for gold.)
Researchers at Stanford University found that with the right molecular configuration, Au2+ can persist. Lindquist said he “stumbled upon” the new Au2+-hosting perovskite while working on a larger project focused on magnetic semiconductors for use in electronic devices.
Lindquist mixed a salt called cesium chloride and Au3+ chloride in water and added hydrochloric acid to the solution “with a little vitamin C,” he said. In the resulting reaction, vitamin C (an acid) donates an electron (negatively charged) to the combined Au3+ that forms Au2+. Interestingly, Au2+ is stable in solid perovskite but not in solution.
“In the lab, we can make this material using very simple ingredients in about five minutes at room temperature,” Lindquist said. “We ended up with a very dark green powder, almost black, that is surprisingly heavy because of the gold it contains.”
Realizing that they might have found new chemical debris, so to speak, Lindquist performed several tests on the perovskite, including spectroscopy and X-ray diffraction, to investigate how it absorbs light and to characterize its crystal structure. Stanford research groups in physics and chemistry led by Young Li, professor of applied physics and photonic sciences, and Edward Solomon, Monroe E. Professor of Chemistry, contributed to the study. Spaght, professor of photonic sciences, is studying the behavior of Au2+.