Suitably-aligned f atomic orbitals can overlap to form a φ molecular orbital (a φ bond)
Inchemistry, phi bonds (φ bonds) are covalentchemical bonds, where six lobes of one involved atomic orbitaloverlap six lobes of the other involved atomic orbital. This overlap leads to the formation of a bonding molecular orbital with three nodal planes which contain the internuclear axis and go through both atoms.
The Greek letter φ in their name refers to f orbitals, since the orbital symmetry of the φ bond is the same as that of the usual (6-lobed) type of f orbital when seen down the bond axis.
There was one possible candidate known in 2005 of a molecule with phi bonding (a U−U bond, in the molecule U2).[1] However, later studies that accounted for spin orbit interactions found that the bonding was only of fourth order.[2][3][4] Experimental evidence for phi bonding between a thorium atom and cyclooctatetraeneinthorocene has been supported by computational analysis, though this mixed-orbital bond has strong ionic character and is not a traditional covalent phi bond.[5]
