Charge‐Shift Bonding: A New and Unique Form of Bonding

• Published in: Angewandte Chemie International Edition Vol. 59; no. 3; pp. 984 - 1001
• Main Authors: Shaik, Sason, Danovich, David, Galbraith, John Morrison, Braïda, Benoît, Wu, Wei, Hiberty, Philippe C.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 13-01-2020; Wiley-VCH Verlag
• Edition: International ed. in English
• Subjects: Benzene; bond theory; charge-shift bonds; Chemical bonds; Chemical Sciences; Covalence; covalent bonds; Electron density; ionic bonds; Molecular orbitals; Organic chemistry; Resonance; Resonant interactions; valence bonds; charge-shift bonds; valence bonds; covalent bonds; bond theory; ionic bonds
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201910085

Charge‐shift bonds (CSBs) constitute a new class of bonds different than covalent/polar‐covalent and ionic bonds. Bonding in CSBs does not arise from either the covalent or the ionic structures of the bond, but rather from the resonance interaction between the structures. This Essay describes the reasons why the CSB family was overlooked by valence‐bond pioneers and 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 all show the distinction of CSBs vis‐à‐vis covalent and ionic bonds. Furthermore, the covalent–ionic resonance energy can be quantified from experiment, and hence has the same essential status as resonance energies of organic molecules, e.g., benzene. The Essay ends by arguing that CSBs are a distinct family of bonding, with a potential to bring about a Renaissance in the mental map of the chemical bond, and to contribute to productive chemical diversity.
New description of valence bonding: The vertices of the triangle in the figure are labeled with the three variables of electron‐pair bonding, Φcov , Φion , and REcs (charge‐shift resonance energy), which lead to three families of valence bonding, covalent, ionic, and charge‐shift bonding, respectively. A variety of tricky bonding situations such as dative bonds, coordinative bonds, 3e‐bonds, and hypervalent bonds can be best described by charge‐shift bonding.