In π back bonding, the electrons move from an atomic orbital on one atom to a π* anti-bonding orbital on another atom or ligand. The electrons from the metal are used to bond to the ligand in order to release the metal from excess negative charge.
- Back bonding is dative(coordinate) π- bonding.
- For it to occur, the essential requirement is
Presence of vacant orbital and lone pair orbital on two directly bonded atoms respectively.
If we examine the structure of OF2, both are second period elements so these elements have “no” d- orbitals (their valence orbitals are only one 2s orbital and three 2p -orbitals.)
Each fluorine here, forms one sigma bond and has three lone pairs. Oxygen atom is involved in two sigma bonds and has two lone pairs. So as you can see, no vacant orbital is available to accept lone pair and form coordinate bond. Hence no back bonding in such cases.