Question

What is a pi-acid ligand?

Answer 1

Pi-acid ligand

• Ligands that are able to accept electron density from the metal atom into its own empty $\pi$ or $\pi$^* orbital are known as pi-acid or$\pi$ -acceptor ligands.
• The intensity of crystal field splitting energy is increased by this form of interaction and is thus known as strong field ligands

Example of pi-acid ligand

• Carbon monoxide $(\mathrm{CO})$ is an example of a pi-acid ligand.
• It is a good $\pi$-acceptor ligand due to the empty $\pi$^* orbital of carbon monoxide$(\mathrm{CO})$ .
• Carbon monoxide$(\mathrm{CO})$ accepts electron density from the metal d-orbital to its empty $\pi$^* orbital.
• The electronic configuration of $(\mathrm{CO})$ by molecular orbital diagram is given as ${\left(\mathrm{\sigma }1\mathrm{s}\right)}^2{(\mathrm{\sigma }\ast 1\mathrm{s})}^2{\left(\mathrm{\sigma }2\mathrm{s}\right)}^2{(\mathrm{\sigma }\ast 2\mathrm{s})}^2{\left(\mathrm{\pi }2\mathrm{px}\right)}^2{\left(\mathrm{\pi }2\mathrm{py}\right)}^2{\left(\mathrm{\sigma }2\mathrm{pz}\right)}^2$.
• An example of $\pi$– acid ligand complex is tetra carbonyl nickel $\mathrm{Ni}{\left(\mathrm{CO}\right)}_4$.