Three-center two-electron bond

A three-center two-electron bond is an electron deficient atomic orbitals form three molecular orbitals: one bonding, one non-bonding, and one anti-bonding. The two electrons go into the bonding orbital, resulting in a net bonding effect and constituting a chemical bond among all three atoms. In many common bonds of this type, the bonding orbital is shifted towards two of the three atoms instead of being spread equally among all three. When visualised in 3D, it looks like a banana, and hence a 3-center-2-electron bond is often called a banana bond.