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. The EAN is defined as the number of electrons in the metal atom or ion plus the number of electrons donated by the ligands. The EAN should equal the atomic number of the nearest noble gas, which for the 4th period elements (like calcium, chromium, cobalt, and nickel) is Krypton (atomic number 36).

### Step-by-Step Solution:

1. **Identify the Complexes**: The complexes given are:
- Ca(EDTA)²⁻
- [Cr(en)₃]³⁺
- [CoBr₃]²⁻
- [Ni(DMG)₂]²⁻

2. **Calculate EAN for Each Complex**:

**a. For Ca(EDTA)²⁻**:
- Calcium (Ca) has an atomic number of 20, so it has 20 electrons.
- EDTA (Ethylenediaminetetraacetic acid) donates 12 electrons (6 donor atoms, each donating 2 electrons).
- Charge of EDTA is -4, so we consider Ca²⁺ (which has 20 - 2 = 18 electrons).
- EAN = 18 (from Ca²⁺) + 12 (from EDTA) = 30.
- **Result**: EAN = 30 (not equal to 36).

**b. For [Cr(en)₃]³⁺**:
- Chromium (Cr) has an atomic number of 24, so it has 24 electrons.
- Ethylenediamine (en) donates 4 electrons per molecule and there are 3 en ligands, so total = 4 x 3 = 12 electrons.
- Charge of Cr is +3, so we consider Cr³⁺ (which has 24 - 3 = 21 electrons).
- EAN = 21 (from Cr³⁺) + 12 (from en) = 33.
- **Result**: EAN = 33 (not equal to 36).

**c. For [CoBr₃]²⁻**:
- Cobalt (Co) has an atomic number of 27, so it has 27 electrons.
- Each bromide (Br) donates 1 electron and there are 3 Br ligands, so total = 1 x 3 = 3 electrons.
- Charge of Co is +2, so we consider Co²⁺ (which has 27 - 2 = 25 electrons).
- EAN = 25 (from Co²⁺) + 3 (from Br) = 28.
- **Result**: EAN = 28 (not equal to 36).

**d. For [Ni(DMG)₂]²⁻**:
- Nickel (Ni) has an atomic number of 28, so it has 28 electrons.
- Dimethylglyoxime (DMG) donates 4 electrons per molecule and there are 2 DMG ligands, so total = 4 x 2 = 8 electrons.
- Charge of Ni is +2, so we consider Ni²⁺ (which has 28 - 2 = 26 electrons).
- EAN = 26 (from Ni²⁺) + 8 (from DMG) = 34.
- **Result**: EAN = 34 (not equal to 36).

3. **Conclusion**: After calculating the EAN for all complexes, none of them match the EAN of 36, which is required to follow the EAN rule.

### Final Answer: None of the given complex species follow the EAN rule.