An article by Alexandrova group, recently published in a leading international chemistry journal, designated as a “Very Important Paper (VIP)” by evaluators.
The article, “Origin of Extraordinary Stability of Square-Planar Carbon Atoms in Surface Carbides of Cobalt and Nickel” was published in the Mar. 24, 2015 online issue of Angewandte Chemie International Edition, a journal of the German Chemical Society. The ‘VIP’ designation means that the paper is among the top five percent of articles selected by the journal’s referees.
Professor Anastassia Alexandrova explains the research discussed in the article:
Among a few unusual systems where C atoms are tetracoordinated square planar, rather than tetrahedral, the least understood ones are surface carbides of transition metals, featuring also the peculiar p4g reconstruction. Despite the strange coordination, stabilities of these carbides are so high that they compete with those of diamond and graphite.
TOC graphics shows us out for the count.. but not of stars, of electrons in surface alloys.
In this article, we provide a new rationalizing bonding model for these structures, which further allows us to predict several new carbides, borides, and nitrides of Co, Ni, Cu, Rh, Pd, and Ag, with analogous structures, and predictable degrees of surface reconstruction. We show that the square planar main group elements (C, B, and N) promote local 2-D aromaticity in the surface; regardless of the system composition, it is always the same set of s-radial and p-states that bind the main group element to the metal and are responsible for aromaticity. The aromatic arrangement is so powerful that the required number of electrons is adjusted by using the void M4 squares as electron reservoirs. Depletion of the population of antibonding states in M4 leads to Peierls instability and p4g reconstruction. Hence, generally, electron-poor binary surface alloys of this kind reconstruct strongly, whereas electron-rich systems reconstruct less or do not reconstruct. This work, for the first time, dares to extend the concept of local aromaticity to surface chemistry, and it is proven to be predictive in the design of new surface alloys.
The Alexandrova group also had a VIP paper published in the journal in 2012. Learn more here.