Question

3. Consider the following possible ligands. For which of these do you expect back-bonding to be significant in their complexes? For those that you do not expect to participate in back-bonding, explain why.

H2       CO       Br2       O2       NO

Answer 1

CO and NO ligands are good enough in back bonding

arbonyl Complexes are compounds that contain carbon monoxide as a coordinated ligand. We can describe the bonding of CO to a metal as consisting of two components. The first component is a two electron donation of the lone pair on carbon (coordination exclusively through the oxygen is extremely rare) into a vacant metal d-orbital. This electron donation makes the metal more electron rich, and in order to compensate for this increased electron density, a filled metal d-orbital may interact with the empty pi* orbital on the carbonyl ligand to relieve itself of the added electron density. This second component is called pi-backbonding or pi-backdonation

NO ligand can be viewed as derivatives of the nitrosyl cation, NO⁺. The nitrosyl cation is isoelectronic with carbon monoxide, thus the bonding between a nitrosyl ligand and a metal follows the same principles as the bonding in carbonyl complexes. The nitrosyl cation serves as a two-electron donor to the metal and accepts electrons from the metal via back-bonding

H2 and O2 also participating backbonding but not significantly

Br2 will not participate in back bonding since it dont have empty orbital