First-ever solid-state iron-bismuth compound created

The first-ever solid-state material reported to contain iron-bismuth bonds, FeBi₂, has been prepared by a team led by Danna E. Freedman of Northwestern University (ACS Cent. Sci. 2016, DOI: 10.1021/acscentsci.6b00287).

Iron and bismuth each react with multiple elements across the periodic table but are largely immiscible with each other, despite the fact that iron readily combines with all of the other group 15 elements to form superconducting materials. Chemists currently don’t understand the lack of reactivity between iron and bismuth.

Freedman and colleagues created FeBi₂ by combining the two elements in a diamond anvil cell at 30 gigapascals and 1,500 K. In the crystal structure, each iron atom is coordinated by eight bismuth atoms arranged into squares above and below the iron. The squares of bismuth atoms sit twisted relative to each other.

The high pressure stabilizes the Fe–Bi bonds in the material, which is also held together by Bi–Bi bonds. The Fe–Bi bond lengths are 0.2719 nm, while the Bi–Bi interactions range from 0.2948 to 0.3419 nm.

The researchers were able to decompress the FeBi₂ down to 3 GPa before it decomposed. That behavior suggests that there might be a way to quickly cool and slowly decompress the material to study and perhaps even use it at ambient pressure—0.0001 GPa—and low temperature, the researchers say.