Physical Chemistry Seminar: Professor Sason Shaik, Hebrew University of Jerusalem
Physical Chemistry Seminar: Professor Sason Shaik, Hebrew University of Jerusalem (Host: Dick Zare)
**This seminar is only available for virtual attendance.**
"Charge-Shift Bonding: A New and Unique Class of Electron-Pair Bonds"
About the Seminar
Charge-shift bonds (CSB) constitute a new class of bonds different than covalent/polar-covalent and ionic-bonds. Bonding in CSB is not contributed by either the covalent or the ionic structures of the bond, but rather by the resonance interaction between the structures. This talk describes the reasons why the CSB family was overlooked by valence-bond pioneers. It then demonstrates that the unique status of CSBs is not theory-dependent. Thus, Valence-bond (VB), molecular-orbital (MO), and Energy-Decomposition-Analysis (EDA), as well as a variety of electron-density theories; Electron-Localization Function (ELF), Atoms in Molecules (AIM), and Electron-Stress Tensor (EST) approaches; all these show the distinction of CSB vis-à-vis covalent and ionic bonds. Furthermore, the covalent-ionic resonance energy can be quantified from experiment, and hence having the same essential status as resonance energies of iconic molecules, e.g., benzene. The talk then demonstrates how a variety of bond types -- dative-bonds, coordinative-bonds, and hypervalent-bonds, including 3-electron-bonds -- are CSBs. Subsequently, some experimental manifestations of CSBs are discussed, including recent experimental articulations of the concept. The talk ends by arguing that the definition of CSB as a distinct family of bonding fulfills the necessary conditions for making such a claim. The distinction between covalent-bonds and CSBs is thus fundamental, with a potential to bring about a Renaissance in the mental-map of the chemical bond, and to contribute to productive chemical diversity.
About the Speaker
Sason Shaik is a Saerree K. and Louis P. Fiedler Emeritus Professor of Chemistry at the Hebrew University. His main interests are in bonding, chemical reactivity, metalloenzymes, two-state reactivity and electric field effects in chemistry. Alongside a variety of computational tools, he uses valence bond theory as a conceptual frame, and has developed a number of new paradigms and concepts using this theory. His main recent awards/distinctions are the Schrödinger Medal (WATOC 2007); the August-Wilhelm-von-Hofmann-Medal (the German Chemical Society, 2012); Membership in the International Academy of Quantum Molecular Science (2015); The Gold Medal of the Israel Chemical Society (2017); Associate Membership in the Fench Academy of Sciences (2021). He also writes essays on history, the chemical bond as the heartland of chemistry, science and friendship, chemistry as a central pillar of human culture, etc.
(1978) Ph.D.: With N.D. Epiotic, The University of Washington, Seattle
(1979) Postoc: With R. Hoffmann, Cornell Unversity, Ithaca.
(1980-1988): Lecturer-to-Full Prof.: Ben-Gurion University, Beer-Sheva, Israel
(1992- today): Prof.: The Hebrew University of Jerusalem, Israel
(1995-2017): Director of the Lise Meitner-Minerva Center for Computational quantum Chemistry.
Image Credit: Sara Shaik