Which of the following complexes is expected to have lowest `Delta_(0)` value ? [consider only magnitude]

Options

A. `[Co(NH_(3))_(6)]^(3+)`
B. `[Rh(NH_(3))_(6)]^(3+)`
C. `[Ir(NH_(3))_(6)]^(3+)`
D. `[CoF_(6)]^(3-)`

Answer

To determine which of the given complexes has the lowest Δ₀ value (octahedral splitting energy), we need to analyze the ligands and the metal centers involved in each complex. The Δ₀ value is influenced by the nature of the metal ion and the ligands surrounding it.

### Step-by-Step Solution:

1. **Identify the Complexes**:
Let's assume we have the following complexes:
- Co(NH₃)₆³⁺
- CoF₆³⁻
- Ni(NH₃)₆²⁺
- NiF₆²⁻

2. **Determine the Metal Ions**:
- Cobalt (Co) is a 3d transition metal.
- Nickel (Ni) is also a 3d transition metal.
- Both metals can exhibit different oxidation states, which can affect their Δ₀ values.

3. **Consider the Ligands**:
- NH₃ (ammonia) is a stronger field ligand compared to F⁻ (fluoride).
- According to the spectrochemical series, ligands are arranged by their ability to split d-orbitals; stronger field ligands cause greater splitting.

4. **Analyze the Splitting**:
- For Co(NH₃)₆³⁺: Ammonia is a strong field ligand, leading to a larger Δ₀ value.
- For CoF₆³⁻: Fluoride is a weaker field ligand, leading to a smaller Δ₀ value.
- For Ni(NH₃)₆²⁺: Similar to Co(NH₃)₆³⁺, ammonia will cause a significant splitting.
- For NiF₆²⁻: Again, fluoride will cause less splitting compared to ammonia.

5. **Compare the Δ₀ Values**:
- Generally, 3d transition metals have lower Δ₀ values than 4d and 5d transition metals.
- Among the complexes, CoF₆³⁻ is expected to have the lowest Δ₀ value due to the presence of the weaker field ligand (F⁻) compared to NH₃.

6. **Conclusion**:
- The complex expected to have the lowest Δ₀ value is CoF₆³⁻.

### Final Answer:
CoF₆³⁻ is expected to have the lowest Δ₀ value.