How many isomers are possible for the complex `[Co(en)_(2)Cl_(2)]`(en=ethylene diamine )

Options

A. 4
B. 2
C. 6
D. 3

Answer

To determine the number of isomers for the complex \([Co(en)_{2}Cl_{2}]\) where \(en\) stands for ethylene diamine, we can follow these steps:

### Step 1: Identify the Coordination Number and Geometry
The complex \([Co(en)_{2}Cl_{2}]\) has cobalt (Co) as the central metal ion, with a coordination number of 6. This is because there are two bidentate ethylene diamine ligands (each donating 2 pairs of electrons) and two monodentate chloride ions.

**Hint:** The coordination number is determined by counting the number of donor atoms from ligands attached to the central metal ion.

### Step 2: Determine the Type of Isomerism
For coordination compounds, we can have geometric and optical isomerism. In this case, since we have bidentate ligands and monodentate ligands, we can expect both types of isomerism.

**Hint:** Geometric isomers arise from different arrangements of ligands around the central metal ion, while optical isomers are non-superimposable mirror images.

### Step 3: Identify Geometric Isomers
For the complex \([Co(en)_{2}Cl_{2}]\), we can have two geometric isomers:
1. **Cis Isomer:** The two chloride ions are adjacent to each other (90 degrees apart).
2. **Trans Isomer:** The two chloride ions are opposite each other (180 degrees apart).

**Hint:** Visualize the arrangement of ligands around the central metal to determine if they are adjacent (cis) or opposite (trans).

### Step 4: Identify Optical Isomers
Optical isomers occur when there is no plane of symmetry in the molecule. The cis isomer of \([Co(en)_{2}Cl_{2}]\) will have a non-superimposable mirror image, meaning it can exist as an optical isomer. The trans isomer will have a plane of symmetry and will not have an optical isomer.

**Hint:** Check for symmetry in the structure; if you can draw a line that divides the molecule into two identical halves, it has symmetry and won't have optical isomers.

### Step 5: Count the Total Number of Isomers
From the above analysis, we have:
- 2 geometric isomers (cis and trans)
- 1 optical isomer (from the cis form)

Thus, the total number of isomers for the complex \([Co(en)_{2}Cl_{2}]\) is 3.

**Final Answer:** The total number of isomers is **3**.