Which of the following is paramagnetic ?

Options

A. `V(CO)_(6)`
B. `Fe(CO)_(5)`
C. `Fe_(2)(CO)_(9)`
D. `Cr(CO)_(6)`

Answer

To determine which of the given carbonyl compounds is paramagnetic, we need to analyze the electronic configurations of the metals in each compound and how they interact with the carbonyl ligands. Let's go through the compounds one by one.

### Step 1: Analyze Vanadium Hexacarbonyl (V(CO)6)
- **Atomic Number of Vanadium (V)**: 23
- **Electronic Configuration**: [Ar] 3d³ 4s²
- In the presence of carbonyl (CO), which is a strong field ligand, the electrons will pair up.
- After pairing, the configuration becomes:
- 3d: ↑↓ ↑↓ ↑ (3 electrons in 3d orbitals)
- 4s: ↑↓ (2 electrons in 4s orbitals)
- **Hybridization**: D2-sp3
- **Unpaired Electrons**: 1 (in 3d)
- **Conclusion**: Vanadium hexacarbonyl is **paramagnetic**.

### Step 2: Analyze Iron Pentacarbonyl (Fe(CO)5)
- **Atomic Number of Iron (Fe)**: 26
- **Electronic Configuration**: [Ar] 3d⁶ 4s²
- Upon interaction with carbonyl, the electrons will pair up:
- After pairing, the configuration becomes:
- 3d: ↑↓ ↑↓ ↑↓ (6 electrons in 3d orbitals)
- 4s: ↑↓ (2 electrons in 4s orbitals)
- **Hybridization**: dsp³
- **Unpaired Electrons**: 0 (all are paired)
- **Conclusion**: Iron pentacarbonyl is **diamagnetic**.

### Step 3: Analyze Di-Iron Nonacarbonyl (Fe2(CO)9)
- This compound also contains iron, so we can use the same electronic configuration as above.
- **Unpaired Electrons**: 0 (as in Fe(CO)5)
- **Conclusion**: Di-iron nonacarbonyl is **diamagnetic**.

### Step 4: Analyze Chromium Hexacarbonyl (Cr(CO)6)
- **Atomic Number of Chromium (Cr)**: 24
- **Electronic Configuration**: [Ar] 3d⁵ 4s¹
- In the presence of carbonyl, the electrons will pair up:
- After pairing, the configuration becomes:
- 3d: ↑↓ ↑↓ ↑ (5 electrons in 3d orbitals)
- 4s: ↑↓ (1 electron in 4s orbitals)
- **Hybridization**: D2-sp3
- **Unpaired Electrons**: 0 (all are paired)
- **Conclusion**: Chromium hexacarbonyl is **diamagnetic**.

### Final Conclusion
Among the given compounds, only **Vanadium hexacarbonyl (V(CO)6)** is paramagnetic due to the presence of one unpaired electron.

### Summary of Results:
- **Vanadium hexacarbonyl**: Paramagnetic
- **Iron pentacarbonyl**: Diamagnetic
- **Di-iron nonacarbonyl**: Diamagnetic
- **Chromium hexacarbonyl**: Diamagnetic

Thus, the correct answer is **Vanadium hexacarbonyl**.