In theoretical chemistry, the charge-shift bond is a proposed new class of chemical bonds that sits alongside the three familiar families of covalent, ionic, and metallic bonds where electrons are shared or transferred respectively.[1][2] The charge shift bond derives its stability from the resonance of ionic forms rather than the covalent sharing of electrons which are often depicted as having electron density between the bonded atoms. A feature of the charge shift bond is that the predicted electron density between the bonded atoms is low. It has long been known from experiment that the accumulation of electric charge between the bonded atoms is not necessarily a feature of covalent bonds.[3]
An example where charge shift bonding has been used to explain the low electron density found experimentally is in the central bond between the inverted tetrahedral carbon atoms in [1.1.1]propellanes. Theoretical calculations on a range of molecules have indicated that a charge shift bond is present, a striking example being fluorine, F2, which is normally described as having a typical covalent bond.[2] The charge shift bond (CSB) has also been shown to exist at the cation-anion interface of protic ionic liquids (PILs).[4] The authors have also shown how CSB character in PILs correlates with their physicochemical properties.
- ^ Sini, Gjergji; Maitre, Philippe; Hiberty, Philippe C.; Shaik, Sason S. (1991). "Covalent, ionic and resonating single bonds". Journal of Molecular Structure: THEOCHEM. 229: 163–188. doi:10.1016/0166-1280(91)90144-9. ISSN 0166-1280.
- ^ a b Shaik, Sason; Danovitch, David; Wei, Wu & Hiberty, Phillippe.C. (2014) [1st. Pub. 2014]. "Chapter 5: The Valence Bond Perspective of the Chemical Bond". In Frenking, Gernod & Shaik, Sason (eds.). The Chemical Bond. Wiley-VCH.[failed verification]
- ^ Dunitz, Jack D.; Seiler, Paul (1983). "The absence of bonding electron density in certain covalent bonds as revealed by x-ray analysis". Journal of the American Chemical Society. 105 (24): 7056–7058. doi:10.1021/ja00362a007. ISSN 0002-7863.
- ^ Patil, Amol Baliram; Bhanage, Bhalchandra Mahadeo (2016). "Modern ab initio valence bond theory calculations reveal charge shift bonding in protic ionic liquids". Physical Chemistry Chemical Physics. 18 (23): 15783–15790. Bibcode:2016PCCP...1815783P. doi:10.1039/C6CP02819E.