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Wednesday, September 04, 2019
1:00 PM - 2:00 PM
CNLS Conference Room (TA-3, Bldg 1690)

Seminar

Delocalized Chemical Bonding in Novel Materials

Alexander I. Boldyrev
Utah State University

Electronic structure in 2D- and 3D-materials are usually discussed in terms of band structure, similar to MOs in clusters and molecules. However, band picture cannot say anything about local environment, which is essential for understanding defects, catalysis and many other properties of such materials. In 2008 we introduced a newmethod Adaptive Natural Density Natural Partitioning (AdNDP)1 for molecules andclusters and in 2013 we developed Solid State Adaptive Natural Density Partitioning (SSAdNDP)2 method for extended 1D-, 2D-, and 3D- systems with periodic boundary conditions. These methods allow us for the first time to partition bonding in complicated molecules, clusters and solids simultaneously in localized bonding and delocalized bonding. In this presentation I will discuss applications of these methods to newmaterials. We begin with the analysis of chemical bonding in the 2D-new materials, such as graphene and borophane. Then, we will discuss Na8BaPb6, Na8BaSn6, and Na8EuSn6 Zintl Phases. Our SSAdNDP analyses reviled that such multiply charged anions indeed contain 6 π-electrons delocalized over five atoms of the five-membered rings. Sunís family of all-metal antiaromatic complexes, [Ln(h4-Sb4)3]3- (Ln=La, Y, Ho, Er, Lu), have been identified by the AdNDP as the first examples of antiaromatic species, where the Ln3+ ions facially coordinated by three cyclo-Sb4 units containing 4 delocalized π- electrons. Sunís complex [Au2Sb16]4- containing two quasi-planar AuSb4 moieties are examples of σ-aromatic species with 6 σ-electrons due to the interaction of the Au atom with four neighboring Sb atoms in a delocalized manner. Thus, the [Au2Sb16]4- anion is the first solid-state all-metal σ-aromatic cluster featuring six delocalized σ-electrons. Other examples of delocalized bonding will be also discussed, including 3c-2e bonds insupertetrahedral aluminum − a new allotropic ultralight crystalline form of aluminum, 8c-2e bonds in sodium vacancies in the high-pressure Na2He compound, 6c-2e and 5c-2e bonds in oxygen vacancies in the bulk and on the surface of MgO crystal and other cases. We believe that both AdNDP1,3 and SSAdNDP2 methods present powerful tools for deciphering chemical bonding in new 2D- and 3D-materials.

Host: Ping Yang/Enrique Batista