Which of the following is a high spin complex ?

Options

A. `[Co(NH_(3))_(6)]^(3+)`
B. `[Fe(CN)_(6)]^(4-)`
C. `[Ni(CN)_(4)]^(2-)`
D. `[FeF_(6)]^(3-)`

Answer

To determine which of the given complexes is a high spin complex, we need to analyze the ligands and the oxidation states of the metal ions involved in each complex. Here's a step-by-step breakdown of the solution:

### Step 1: Identify the complexes and their ligands
We have four complexes to consider:
1. \( \text{Co(NH}_3\text{)}_6^{3+} \)
2. \( \text{Fe(CN)}_6^{4-} \)
3. \( \text{Ni(CN)}_4^{2-} \)
4. \( \text{FeF}_6^{3-} \)

### Step 2: Determine the oxidation states of the metal ions
1. **Cobalt in \( \text{Co(NH}_3\text{)}_6^{3+} \)**:
- Let the oxidation state of Co be \( x \).
- \( x + 0 = +3 \) (NH3 is a neutral ligand)
- Therefore, \( x = +3 \).

2. **Iron in \( \text{Fe(CN)}_6^{4-} \)**:
- Let the oxidation state of Fe be \( x \).
- \( x + 6 \times (-1) = -4 \) (CN is a -1 ligand)
- Therefore, \( x = +2 \).

3. **Nickel in \( \text{Ni(CN)}_4^{2-} \)**:
- Let the oxidation state of Ni be \( x \).
- \( x + 4 \times (-1) = -2 \)
- Therefore, \( x = +2 \).

4. **Iron in \( \text{FeF}_6^{3-} \)**:
- Let the oxidation state of Fe be \( x \).
- \( x + 6 \times (-1) = -3 \)
- Therefore, \( x = +3 \).

### Step 3: Analyze the ligands and their field strength
- **NH3**: A strong field ligand that causes electron pairing (low spin).
- **CN-**: A very strong field ligand that also causes electron pairing (low spin).
- **F-**: A weak field ligand that does not cause electron pairing (high spin).

### Step 4: Determine the electron configurations
1. **Cobalt \( \text{Co}^{3+} \)**:
- Electronic configuration: \( [Ar] 3d^6 \)
- With NH3 (strong field), it pairs electrons: \( (↑↓)(↑↓)(↑)(↑)(↑) \) → Low spin.

2. **Iron \( \text{Fe}^{2+} \)**:
- Electronic configuration: \( [Ar] 3d^6 \)
- With CN- (strong field), it pairs electrons: \( (↑↓)(↑↓)(↑)(↑)(↑) \) → Low spin.

3. **Nickel \( \text{Ni}^{2+} \)**:
- Electronic configuration: \( [Ar] 3d^8 \)
- With CN- (strong field), it pairs electrons: \( (↑↓)(↑↓)(↑↓)(↑)(↑) \) → Low spin.

4. **Iron \( \text{Fe}^{3+} \)**:
- Electronic configuration: \( [Ar] 3d^5 \)
- With F- (weak field), it does not pair: \( (↑)(↑)(↑)(↑)(↑) \) → High spin.

### Conclusion
The only complex that forms a high spin configuration is \( \text{FeF}_6^{3-} \).

### Final Answer
The correct option is **4. \( \text{FeF}_6^{3-} \)**.

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