Which of the given complex species is following EAN rule ?

Options

A. `[Ca(EDTA)]^(2-)`
B. `[Cr(en)_3]^(3+)`
C. `[CoBr("trien")]^+`
D. `[Ni("dmg)_2]`

Answer

To determine which of the given complex species follows the Effective Atomic Number (EAN) rule, we will calculate the EAN for each complex using the formula:

\[ \text{EAN} = Z + 2 \times \text{Coordination Number} - \text{Oxidation State} \]

Where:
- \( Z \) is the atomic number of the metal.
- The coordination number is the number of ligand atoms that are bonded to the metal.
- The oxidation state is the charge of the metal ion.

### Step-by-Step Solution:

1. **Calcium EDTA (Ca(EDTA)²⁻)**:
- Atomic number of Calcium (Ca) = 20
- Coordination number of EDTA = 6 (as it is a hexadentate ligand)
- Oxidation state of Calcium = +2 (since EDTA has a -4 charge and the overall charge is -2, Ca must be +2)

\[ \text{EAN} = 20 + 2 \times 6 - 2 = 20 + 12 - 2 = 30 \]
- 30 is not the atomic number of a noble gas (the nearest noble gas is Argon with atomic number 18 or Krypton with atomic number 36). Thus, **does not obey EAN rule**.

2. **Chromium (EN)₃ (Cr(EN)₃)³⁺**:
- Atomic number of Chromium (Cr) = 24
- Coordination number of Ethylenediamine (EN) = 2 (as it is a bidentate ligand)
- Oxidation state of Chromium = +3 (since the complex is +3)

\[ \text{EAN} = 24 + 2 \times 6 - 3 = 24 + 12 - 3 = 33 \]
- 33 is not the atomic number of a noble gas. Thus, **does not obey EAN rule**.

3. **Cobalt (Br)₃(Trien)⁺ (Co(Br)₃(Trien))**:
- Atomic number of Cobalt (Co) = 27
- Coordination number of Trien = 3 (as it is a tridentate ligand)
- Oxidation state of Cobalt = +2 (since the overall charge is +1 and Br is -1)

\[ \text{EAN} = 27 + 2 \times 6 - 2 = 27 + 12 - 2 = 37 \]
- 37 is not the atomic number of a noble gas. Thus, **does not obey EAN rule**.

4. **Nickel (DMG)₂ (Ni(DMG)₂)**:
- Atomic number of Nickel (Ni) = 28
- Coordination number of DMG = 2 (as it is a bidentate ligand)
- Oxidation state of Nickel = +2 (since DMG is -2 overall)

\[ \text{EAN} = 28 + 2 \times 4 - 2 = 28 + 8 - 2 = 34 \]
- 34 is not the atomic number of a noble gas. Thus, **does not obey EAN rule**.

### Conclusion:
None of the given complexes follow the EAN rule.