Problem 46 - Chemistry An Atoms First Approach

Question

Draw all geometrical and linkage isomers of square planar \(\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2}(\mathrm{SCN})_{2}\)

Step-by-Step Solution

Answer

There are four isomers for the square planar complex \(\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2}(\mathrm{SCN})_{2}\): 1. Cis isomer with both thiocyanate ligands S-bound: \(\mathrm{Pt}(\mathrm{NH}_{3})_{2}(\mathrm{S}\mathrm{CN})_{2}\) 2. Cis isomer with both thiocyanate ligands N-bound: \(\mathrm{Pt}(\mathrm{NH}_{3})_{2}(\mathrm{N}\mathrm{CS})_{2}\) 3. Trans isomer with both thiocyanate ligands S-bound: \(\mathrm{Pt}(\mathrm{NH}_{3})_{2}(\mathrm{S}\mathrm{CN})_{2}\) 4. Trans isomer with both thiocyanate ligands N-bound: \(\mathrm{Pt}(\mathrm{NH}_{3})_{2}(\mathrm{N}\mathrm{CS})_{2}\)

Step 1: Identify the central atom and ligands

In this square planar complex, the central atom is Platinum (Pt), and there are two types of ligands: ammine (NH3) and thiocyanate (SCN).

Step 2: Draw the square planar complex

The initial complex consists of Platinum (Pt) surrounded by the ligands in a square planar arrangement. There are two ammine ligands and two thiocyanate ligands.

Step 3: Determine the possible geometrical isomers

Geometrical isomers are formed when the ligands are arranged differently around the central atom. In this case, there are two possibilities: 1. The ammine ligands are adjacent to each other (cis isomer). 2. The ammine ligands are opposite each other (trans isomer).

Step 4: Draw the geometrical isomers

For the square planar complex with the given formula, we have two geometrical isomers: 1. Cis isomer: The ammine ligands are adjacent to each other and the thiocyanate ligands are opposite each other in the square plane.  2. Trans isomer: The ammine ligands are opposite to each other and the thiocyanate ligands are also opposite each other in the square plane. 

Step 5: Determine the possible linkage isomers

Linkage isomers arise from different sites of attachment of ligands. In thiocyanate (SCN), there are two possible sites of attachment: sulfur (S) or nitrogen (N). Thus, the thiocyanate ligand can create two linkage isomers: S-bound or N-bound.

Step 6: Draw the linkage isomers for cis and trans isomers

Here are the possible linkage isomers for the cis and trans geometrical isomers: - Cis isomer: 1. Cis - Both thiocyanate ligands are S-bound: \(\mathrm{Pt}(\mathrm{NH}_{3})_{2}(\mathrm{S}\mathrm{CN})_{2}\) 2. Cis - Both thiocyanate ligands are N-bound: \(\mathrm{Pt}(\mathrm{NH}_{3})_{2}(\mathrm{N}\mathrm{CS})_{2}\) - Trans isomer: 1. Trans - Both thiocyanate ligands are S-bound: \(\mathrm{Pt}(\mathrm{NH}_{3})_{2}(\mathrm{S}\mathrm{CN})_{2}\) 2. Trans - Both thiocyanate ligands are N-bound: \(\mathrm{Pt}(\mathrm{NH}_{3})_{2}(\mathrm{N}\mathrm{CS})_{2}\) So, there are a total of four isomers for the given square planar complex: two geometrical isomers with each having two linkage isomers.