Delta bond

This overlap leads to the formation of a bonding molecular orbital with two nodal planes which contain the internuclear axis and go through both atoms.

This type of bonding is observed in atoms that have occupied d orbitals with low enough energy to participate in covalent bonding, for example, in organometallic species of transition metals.

The δ notation was introduced by Robert Mulliken in 1931.

[5][6] The first compound identified as having a δ bond was potassium octachlorodirhenate(III).

Cotton reported that there was δ-bonding as part of the rhenium–rhenium quadruple bond in the [Re2Cl8]2− ion.