Four-center two-electron bond

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A four-center two-electron bond is a type of chemical bond in which four atoms share two electrons in bonding which is unusual because in ordinary chemical bonds two atoms share two electrons (2c-2e bonding). This type of bonding is postulated in certain cluster compounds. For instance, the borane B₆H₇^- anion, is a B₆H₆^2- octahedron with an additional proton attached to one of the triangular faces. ^[1]. As a result the octahedron is distorted and a BBBH rhomboid ring can be identified in which this 4c-2e bonding takes place. This type of bonding is associated with electron deficient rhomboid rings in general ^[2] and is a relatively new research field, fitting in with the already well established three-center two-electron bonds and three-center four-electron bonds.

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v • d • e Chemical bonds "Strong" Covalent bonds & Antibonding Sigma bonds: 3c-2e (bent bond) · 3c-4e (Hydrogen bond, Dihydrogen bond, Agostic interaction) · 4c-2e Pi bonds: π backbonding · Conjugation · Hyperconjugation · Aromaticity · Metal aromaticity Delta bond: Quadruple bond · Quintuple bond · Sextuple bond Coordinate covalent bond · Hapticity Ionic bonds Cation-pi interaction · Salt bridge Metallic bonds - "Weak" Hydrogen bond Dihydrogen bond · Dihydrogen complex · Low-barrier hydrogen bond · Symmetric hydrogen bond · Hydrophile Other noncovalent van der Waals force · Mechanical bond · Halogen bond · Aurophilicity · Intercalation · Stacking · Entropic force · Chemical polarity other Disulfide bond · Peptide bond · Phosphodiester bond Note: the weakest strong bonds are not necessarily stronger than the strongest weak bonds