Question

In isolated condition $C-C$ bond length of $C_2{H}_4$ is x, then the bond length of $C-C$ bond of $C_2{H}_4$ in Zeise's salt is :

• A. greater than x
• B. Less than x
• C. Equal to x
• D. None of these

Answer 1

The correct option is A greater than x


Ziese's salt is potassium trichloro(ethene)platinate(II) having formula $K\left[PtC{l}_3\right(C_2{H}_4\left)\right].H_{2}O$.

The Zeise’s salt has square planar geometry, where the three corners of the square are accommodated by the chloro ligand and one by the ethylene ligand. The alkene $C=C$ is at the ${90}^{\circ }$ to the $PtC{l}_3$ plane.

The bonding between the platinum and the ligands can be explained based on the Molecular orbital theory.

The olefin $C_2{H}_4$ has the pi bond. This pi-electron density of the olefin acts as a ligand and overlaps with the $\sigma$ orbital of the platinum atom. This establishes a $\sigma$ bond between the metal and the ligand.
In Zeise’s salt, the metal has the filled $d\pi$ orbital and the carbon atom of the ethylene has the empty $d{\pi }^{\ast }$ orbital.The back bonding takes place between the metal orbital and empty pi orbital of the ligand. In this bonding, the electrons are transferred from the metal to ligand.
Electrons are donated to antibonding orbital. Consequently the bond order decreases and hence the bond length of $C=C$ is greater than x.
Isolated $C-C$ bond length in $C_2{H}_4$ is around $1.34\stackrel{\circ }{A}$ and the bond length of $C-C$ bond in the Zeise’s salt is nearly $1.37\stackrel{\circ }{A}$.