Question

The total number of all possible isomers for the square planar complex with formula \[ \mathrm{K[M(NCS)(NO_2)(gly)]} \] is _____.

\[ \mathrm{(M = metal\ ion\ and\ gly = NH_2CH_2COO^-)} \]

Hint:

Important ambidentate ligands: \[ \mathrm{NO_2^-} \Rightarrow \mathrm{NO_2^- / ONO^-} \] \[ \mathrm{SCN^-} \Rightarrow \mathrm{SCN^- / NCS^-} \] Always check:
• linkage isomerism
• geometrical isomerism
• symmetry reduction while counting coordination compound isomers.

Answer 1

Correct Answer: 6

Step 1: Understanding the Concept:
This problem involves coordination chemistry, specifically the isomerism of square planar complexes.
The complex is of the type [M(a)(b)(CD)], where 'a' and 'b' are monodentate ligands and 'CD' is a bidentate unsymmetrical ligand.
Ligands present: 1. NCS\(^-\): An ambidentate ligand that can coordinate via Nitrogen (isothiocyanato, -NCS) or Sulfur (thiocyanato, -SCN).
2. NO\(_2^-\): An ambidentate ligand that can coordinate via Nitrogen (nitro, -NO\(_2\)) or Oxygen (nitrito, -ONO).
3. Glycinato (gly): An unsymmetrical bidentate ligand coordinating via Nitrogen and Oxygen.
Step 2: Key Formula or Approach:
To find the total number of isomers, we must consider both Geometrical Isomerism (GI) and Linkage Isomerism (LI).
Square planar complexes do not show optical isomerism (unless the ligands themselves are chiral) because they possess a plane of symmetry.
First, we determine the number of linkage combinations.
Then, for each combination, we determine the number of geometrical isomers.
Step 3: Detailed Explanation:
1. Linkage Isomerism:
The two ambidentate ligands lead to the following combinations:
- (M-NCS) and (M-NO\(_2\))
- (M-NCS) and (M-ONO)
- (M-SCN) and (M-NO\(_2\))
- (M-SCN) and (M-ONO)
There are 4 possible linkage combinations.
2. Geometrical Isomerism:
Let's analyze one specific linkage combination, say [M(NCS)(NO\(_2\))(gly)].
In a square planar geometry with an unsymmetrical bidentate ligand (N-O), and two monodentate ligands (A, B): The monodentate ligands A and B can be arranged relative to the N and O atoms of the glycinato ligand.
Possible arrangements: - A can be trans to N (which forces B to be trans to O).
- A can be trans to O (which forces B to be trans to N).
This results in 2 distinct geometrical isomers for each linkage combination.
3. Total Isomers:
Total isomers = (Number of linkage combinations) \(\times\) (Number of geometrical isomers per combination).
Total isomers = \( 4 \times 2 = 8 \).
Step 4: Final Answer:
Considering the linkage isomerism provided by the two ambidentate ligands and the geometrical isomerism due to the unsymmetrical bidentate ligand in a square planar environment, the total number of isomers is 8.