Image description: Left: Top and side views of a section of a two-dimensional Cu2Si monolayer. Cu atoms copper colored, Si atoms grey. Right: Bonding structure of the Cu2Si monolayer. (a-c) Individual 4c-2e σ bonds. (d) Superimposition of 4c-2e σ bonds. Copper is orange, silicon is blue. LM Yang, et al., JACS 2015, 137, 2757. © 2015 American Chemical Society.
Two-dimensional materials have become a subject of great interest to researchers during the past decade. These materials, one of the most well-known of which is the carbon monolayer (one atom thick) graphene, have interesting properties that might make them useful for various applications, such as semiconductors, electronics, and composite materials.
Associate Professor Eric Ganz (Physics and Astronomy, College of Science and Engineering) and his collaborators recently published a paper in the Journal of the American Chemical Society about one of these materials. Two-dimensional materials with planar hypercoordinate motifs are extremely rare due to the difficulty in stabilizing the planar hypercoordinate configurations in extended systems. Hypercoordinate means more bonds than normal for a particular atom. The paper describes a two-dimensional monolayer that features planar hexacoordinate copper and planar hexacoordinate silicon. (Hexacoordinate means six atomic bonds.) The researchers used density function theory calculations to study and evaluate this material, Cu2Si. A section of the periodic infinite sheet is shown in the image.
The researchers’ computations showed that the Cu2Si monolayer is very stable, and the framework survives brief molecular dynamics annealing up to 900 K. Bond order analysis and partitioning reveals unusual four center 4c-2e σ bonds that stabilize the two-dimensional structure. (σ bonds are the strongest type of covalent chemical bond.)
The paper can be read on the JACS website (Yang, Li-Ming, Vladimir Bacic, Ivan A. Popov, Alexander I. Boldyrev, Thomas Heine, Thomas Frauenheim, and Eric Ganz. 2015. Two-dimensional Cu2Si monolayer with planar hexacoordinate copper and silicon bonding. Journal of the American Chemical Society 137 (7) (FEB 25): 2757-62.)
posted on May 27, 2015