What is the relationship between Einstein's theory of relativity and the distinctive color of gold?

As an elemental metal, gold It has long been valued for its relative rarity, as well as its unparalleled malleability and chemical inertness, which means it can be easily turned into jewelry and coins that do not react with chemicals in the environment and do not tarnish over time. Now, a team of researchers from Stanford Found a way to create and stabilize a An extremely rare form of goldwhich has lost two negatively charged electrons, is called Au 2+.

The substance that stabilizes this elusive copy of the valuable element is A Perovskite halideA metal from the oxide group. This class of crystalline materials is very promising different applications, Including solar cells, light sources and more efficient electronic components, indicates the work published in Nature chemistry.

Surprisingly, Au 2+ 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 Au 2+ ; At first I didn't even believe it. The creation of this first-of-its-kind Au 2+ perovskite is exciting.

The gold atoms in it have strong similarities to the copper atoms found in high-temperature superconductors, and heavy atoms with unpaired electrons, such as Au 2+, look interesting, with magnetic effects not seen in lighter atoms.

“Halide perovskites have really attractive properties for many everyday applications, so we were looking to expand this family of materials,” explained Kurt Lindquist, the study’s lead author who conducted the research as a doctoral student at Stanford University and now works as an inorganic chemistry researcher at Princeton University. The unprecedented Au 2+ perovskite could open interesting new horizons“.

An additional major reason for its value is the color of the gold of the same name. No other metal in its pure state has such a rich and distinctive tone.. The basic physics behind the famous appearance also explains why Au 2+ is so rare.

The main reason is relativistic effects, which were originally postulated in the book The famous theory of Albert Einstein. We've learned that when objects move very quickly and approach a significant fraction of the speed of light, they become heavier.

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 makes Gold absorbs blue light and thus appears yellow to our eyes.

Because of the arrangement of gold's electrons, and thanks to relativity, the atom naturally appears as Au 1+ and Au 3+, losing one or three electrons, respectively, and neglecting Au 2+. The number 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 metal.

With the right molecular configuration, Au 2+ can withstand, and Lindquist said he found the new perovskite that hosts Au 2+ while working on a larger project focused on magnetic semiconductors for use in electronic devices.

He mixed a salt called cesium chloride and Au 3+ chloride in water and added hydrochloric acid to the solution “with a little vitamin C,” Lindquist said. In the resulting reaction, it, as an acid, donates an electron (negatively charged) to the combined Au 3+ that forms Au 2+.

Interestingly, Au 2+ 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, extensive testing was performed 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 Yong Li, professor of applied physics and photonic sciences, and Edward Solomon, the Munro E. Spaght Professor of Chemistry and professor of photonic sciences, contributed to the study of the behavior of Au2+.

Experiments finally confirmed the presence of Au 2+ in perovskites, and in the process added a chapter to the centuries-old history of chemistry and physics involving Linus Pauling, who won the 1954 Nobel Prize in Chemistry and the Nobel Prize in Chemistry. Peace in 1962.

Early in his career, he worked on gold perovskites containing the Au 1+ and Au 3+ forms. Coincidentally, Pauling also later studied the structure of vitamin C, one of the components needed to produce stable perovskites containing the elusive Au 2+ .

We love Linus Pauling's connection to our work. The composition of this perovskite makes a good story. For this reason, in the future they will seek to study the new material further and modify its chemistry. The hope is that it can be used in applications that require magnetism and conduction, where electrons jump from Au 2+ to Au 3+ in the perovskite.

*Himamala Karunadasa He is an associate professor of chemistry in the Stanford School of Humanities and Sciences and lead author of the study