On the basic of stability of complex ion in the solution, complexes may be of two types, perfect and imperfect complexes. The stability depends upon the extent of dissociation which in turn depends upon charge on central metal atom, basic nature of ligand, chelation, and nature of metal ion and ligand according to HSAB principle.
Qgt Which one of the following does not follow EAN rule?

Options

A. `Fe(CO)_(5)`
B. `V(CO)_(6)`
C. `K_(4)[Fe(CN)_(6)]`
D. `Mn_(2)(CO)_(10)`

Answer

To solve the question of which complex does not follow the Effective Atomic Number (EAN) rule, we need to analyze each option based on the EAN concept. The EAN rule states that the effective atomic number of a metal in a complex should equal the atomic number of the nearest noble gas configuration.

### Step-by-Step Solution:

1. **Understand the EAN Rule**:
- The EAN is calculated by adding the number of valence electrons of the central metal atom to the number of electrons donated by the ligands.
- If the total equals the atomic number of the nearest noble gas, the complex follows the EAN rule.

2. **Analyze Each Complex**:
- **Option 1: Fe(CO)5**
- Atomic number of Iron (Fe) = 26
- CO is a neutral ligand and donates 2 electrons per ligand.
- Total electrons from 5 CO ligands = 5 × 2 = 10 electrons.
- EAN = 26 (Fe) + 10 (from CO) = 36 (which corresponds to Krypton, a noble gas).
- **Conclusion**: Follows EAN rule.

- **Option 2: V(CO)4**
- Atomic number of Vanadium (V) = 23
- CO donates 2 electrons per ligand.
- Total electrons from 4 CO ligands = 4 × 2 = 8 electrons.
- EAN = 23 (V) + 8 (from CO) = 31 (which does not correspond to any noble gas).
- **Conclusion**: Does not follow EAN rule.

- **Option 3: Fe(CN)6^4-**
- Atomic number of Iron (Fe) = 26
- CN^- is a bidentate ligand and donates 2 electrons per ligand.
- Total electrons from 6 CN^- ligands = 6 × 2 = 12 electrons.
- EAN = 26 (Fe) + 12 (from CN) = 38 (which corresponds to Xenon, a noble gas).
- **Conclusion**: Follows EAN rule.

- **Option 4: Mn2(CO)10**
- Atomic number of Manganese (Mn) = 25
- Each CO donates 2 electrons, and there are 10 CO ligands.
- Total electrons from 10 CO ligands = 10 × 2 = 20 electrons.
- EAN = 25 (for 1 Mn) + 25 (for the second Mn) + 20 (from CO) = 70.
- This does not correspond to any noble gas.
- **Conclusion**: Does not follow EAN rule.

3. **Final Answer**:
- The complex that does not follow the EAN rule is **V(CO)4**.