Which complex ion has cis and trans isomer ?

Options

A. `[PdCl_(3)NH_(3)]^(-)`
B. `[Pd(CN)_(5)NH_(3)]^(-)`
C. `[PtCl_(2)(CN)_(2)]^(2-)`
D. `[Pt(C_(2)O_(4))_(2)]^(2-)`

Answer

To determine which complex ion has cis and trans isomers, we need to analyze the given options based on their geometrical arrangements and the types of ligands involved.

### Step-by-Step Solution:

1. **Understand the Concept of Geometrical Isomerism**:
- Geometrical isomerism occurs in coordination compounds when ligands can be arranged differently in space. The most common forms are cis (where similar ligands are adjacent) and trans (where similar ligands are opposite).

2. **Evaluate the First Option: [PdCl3(NH3)]^-**:
- Palladium (Pd) in this complex has a coordination number of 4, which typically leads to a square planar geometry.
- In a square planar arrangement with three Cl and one NH3, there is no possibility for cis-trans isomerism because the Cl ligands cannot be arranged in a way that allows for different spatial orientations.
- **Conclusion**: This option does not exhibit cis-trans isomerism.

3. **Evaluate the Second Option: [Pd(CN)5(NH3)]^-**:
- Here, palladium has a coordination number of 6, leading to an octahedral geometry.
- In an octahedral complex with five CN and one NH3, the arrangement does not allow for cis-trans isomerism because all CN ligands are identical and cannot be positioned to create distinct isomers.
- **Conclusion**: This option does not exhibit cis-trans isomerism.

4. **Evaluate the Third Option: [PtCl2(CN)2]^{2-}**:
- Platinum (Pt) has a coordination number of 4, resulting in a square planar geometry.
- In this complex, there are two Cl and two CN ligands. The Cl ligands can be arranged in two ways:
- **Cis**: Both Cl ligands are adjacent to each other.
- **Trans**: The Cl ligands are opposite each other.
- This arrangement allows for the formation of both cis and trans isomers.
- **Conclusion**: This option exhibits cis-trans isomerism.

5. **Evaluate the Fourth Option: [Pt(C2O4)]^{2-}**:
- In this case, the oxalate (C2O4) acts as a bidentate ligand, and platinum again has a coordination number of 4, leading to a square planar geometry.
- However, since the oxalate ligand occupies two coordination sites, it does not allow for the formation of cis-trans isomers.
- **Conclusion**: This option does not exhibit cis-trans isomerism.

### Final Answer:
The complex ion that has cis and trans isomers is **[PtCl2(CN)2]^{2-}** (Option 3).