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.

An example of a purely organic compound with four-center two-electron bonding is the adamantyl dication.^[3]

[edit] References

v • d • e Chemical bonds Intramolecular ("strong") Covalent bonds Sigma bond · Pi bond · Delta bond Double bond · Triple bond · Quadruple bond · Quintuple bond · Sextuple bond 3c-2e · 3c-4e · 4c-2e Agostic bond · Bent bond · Dipolar bond · Pi backbond Conjugation · Hyperconjugation · Aromaticity · Hapticity · Antibonding Ionic bonds cation-pi bond · salt bond Metallic bonds Metal aromaticity Intermolecular ("weak") Hydrogen bond Dihydrogen bond · Dihydrogen complex · Low-barrier hydrogen bond · Symmetric hydrogen bond Other noncovalent van der Waals force · London dispersion force · Mechanical bond · Halogen bond · Aurophilicity · Intercalation · Stacking · Entropic force · Chemical polarity Note: the weakest strong bonds are not necessarily stronger than the strongest weak bonds