Charge-shift bonding and its manifestations in chemistry

Abstract

Electron-pair bonding is a central chemical paradigm. Here, we show that alongside the two classical covalent and ionic bond families, there exists a class of charge-shift (CS) bonds wherein the electron-pair fluctuation has the dominant role. Charge-shift bonding shows large covalent–ionic resonance interaction energy, and depleted charge densities, and features typical to repulsive interactions, albeit the bond itself may well be strong. This bonding type is rooted in a mechanism whereby the bond achieves equilibrium defined by the virial ratio. The CS bonding territory involves, for example, homopolar bonds of compact electronegative and/or lone-pair-rich elements, heteropolar bonds of these elements among themselves and with other atoms (for example, the metalloids, such as silicon and germanium), hypercoordinated molecules, and bonds whose covalent components are weakened by exchange-repulsion strain (as in [1.1.1]propellane). Here, we discuss experimental manifestations of CS bonding in chemistry, and outline new directions demonstrating the portability of the new concept.

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Figure 1: Valence bond computed energies (E) as functions of the interatomic distances (R) for some bonds.
Figure 2: Some ELF representations of electron density in a few typical cases.
Figure 3: Correlation of the charge-shift/covalent bond character with the repulsive/attractive nature of the covalent interaction, and with the electronegativities of the bonded atoms.

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Correspondence to Sason Shaik or Wei Wu or Philippe C. Hiberty.

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Shaik, S., Danovich, D., Wu, W. et al. Charge-shift bonding and its manifestations in chemistry. Nature Chem 1, 443–449 (2009). https://doi.org/10.1038/nchem.327

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