The least stable metal cabonyl as per the bonding considerations should be

Options

A. `Cr(CO)_(6)`
B. `Mn(CO)_(6)`
C. `Fe(CO)_(5)`
D. `Ni(CO)_(4)`.

Answer

To determine the least stable metal carbonyl based on bonding considerations, we will calculate the effective atomic number (EAN) for each metal carbonyl mentioned in the question. The EAN is calculated using the formula:

\[ \text{EAN} = Z - x + 2L \]

Where:
- \( Z \) is the atomic number of the metal.
- \( x \) is the oxidation state of the metal.
- \( L \) is the number of lone pairs donated by the ligands.

### Step-by-Step Solution:

1. **Calculate EAN for Cr(CO)6:**
- Atomic number of Chromium (Cr) = 24
- Oxidation state (x) = 0 (since CO is a neutral ligand)
- Number of CO ligands = 6 (each CO donates 1 lone pair)
- Total lone pairs = 6
- EAN = \( 24 - 0 + 2 \times 6 = 24 + 12 = 36 \)

2. **Calculate EAN for Mn(CO)6:**
- Atomic number of Manganese (Mn) = 25
- Oxidation state (x) = 0
- Number of CO ligands = 6
- Total lone pairs = 6
- EAN = \( 25 - 0 + 2 \times 6 = 25 + 12 = 37 \)

3. **Calculate EAN for Fe(CO)6:**
- Atomic number of Iron (Fe) = 26
- Oxidation state (x) = 0
- Number of CO ligands = 6
- Total lone pairs = 6
- EAN = \( 26 - 0 + 2 \times 6 = 26 + 12 = 36 \)

4. **Calculate EAN for Ni(CO)6:**
- Atomic number of Nickel (Ni) = 28
- Oxidation state (x) = 0
- Number of CO ligands = 6
- Total lone pairs = 6
- EAN = \( 28 - 0 + 2 \times 6 = 28 + 12 = 36 \)

5. **Compare EAN values:**
- EAN for Cr(CO)6 = 36
- EAN for Mn(CO)6 = 37
- EAN for Fe(CO)6 = 36
- EAN for Ni(CO)6 = 36

6. **Identify the least stable metal carbonyl:**
- The effective atomic number of Mn(CO)6 is 37, which is not equal to the nearest noble gas atomic number (36 for Krypton). Therefore, Mn(CO)6 is the least stable metal carbonyl.

### Conclusion:
The least stable metal carbonyl as per the bonding considerations is **Mn(CO)6**.

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