Chemistry - Coordination Chemistry Question with Solution | TestHub

The synergic bonding in Zeise's salt involves ethene (${\mathrm{C}}_2{\mathrm{H}}_4$) acting as a $\pi$-donor to Pt, and Pt back-donating electrons into the ${\pi }^{\ast }$ antibonding orbital of ethene. Therefore, ethene is both a $\pi$-donor and a $\pi$-acceptor.

Explanation:

In Zeise's salt, $\mathrm{K}[\mathrm{PtC}{\mathrm{l}}_3({\mathrm{C}}_2{\mathrm{H}}_4)]$, the bonding between platinum (Pt) and ethene (${\mathrm{C}}_2{\mathrm{H}}_4$) is a classic example of synergic bonding.

1. $\sigma$-donation (or $\pi$-donation): Ethene donates electron density from its filled $\pi$ bonding orbital to an empty $d$ orbital of platinum. This makes ethene a $\pi$-donor.

2. $\pi$-back donation: Platinum, in turn, donates electron density from its filled $d$ orbitals into the empty ${\pi }^{\ast }$ (antibonding) orbital of ethene. This makes ethene a $\pi$-acceptor.

This synergic effect strengthens the Pt-${\mathrm{C}}_2{\mathrm{H}}_4$ bond and weakens the C-C bond within ethene.

Therefore, ${\mathrm{C}}_2{\mathrm{H}}_4$ acts as both a $\pi$-donor and a $\pi$-acceptor.