MOSCOW, May 25. /TASS/. Russian and Chinese scientists have found numerous unusual compounds forbidden by classical chemistry in potassium (K) - chlorine (Cl) system, the Skoltech press service reported.

In the end of 2013, scientists have shown that numerous compounds forbidden by classical chemistry become stable at elevated pressure. This was proven for the example of a simple and well-understood system: Na-Cl, where such bizarre compounds as Na3Cl and NaCl7 were discovered. Since then, the list of "forbidden" compounds stabilized by pressure rapidly grew and now scientists found even greater variety of unusual compounds in K - Cl system,

"If simple systems like Na-Cl or K-Cl show such complex and counterintuitive chemistry, it only means that there is a lot about chemistry that remains to be discovered and understood", said the project leader and Professor at Skolkovo Institute of Science and Technology (Russia), Stony Brook University (USA) and MPTI (Russia), Artem Oganov.

Scientists found a great variety of "forbidden" compounds stabilized by pressure, including K3Cl, K2Cl, K3Cl2 etc. All of these compounds (except KCl3 phases) are metallic, while classical chemistry predicts that potassium chlorides can only be ionic. These compounds were first predicted using Oganov’s evolutionary algorithm USPEX, and then confirmed in Goncharov’s laboratory using high-pressure experiments in diamond anvil cells.

Two more surprises were uncovered. First, it was predicted and then experimentally proven that previously unknown compound KCl3 can exist at nearly ambient conditions. Secondly, a whole family of two-dimensional metallic compounds was discovered, with structures similar to normal KCl, but with an extra atomic layer of K atoms, along which electrical current can pass.

"Working on Na-Cl and K-Cl compounds was very exciting. I knew we are exploring the limits of chemical intuition, but was surprised by how far beyond it the results turned out to be", said Professor at China Agricultural University Weiwei Zhang.

"This work shows just how powerful the modern theory is. When we started working together, I was very skeptical about these crazy predictions made by USPEX method, but as we went on, was shocked by just how reliable these predictions are, no matter how crazy they appear at first", said one of the coauthors, Professor at Carnegie Institution of Washington (USA), Alex Goncharov.

Results of the study were published in the Scientific Reports journal.