The number of unpaired electrons in central metal of cobalt ferrocyanide, `Co_2[Fe(CN)_6]` is

Options

A. 0
B. 2
C. 1
D. 3

Answer

To determine the number of unpaired electrons in the central metal of cobalt ferrocyanide, `Co_2[Fe(CN)_6]`, we will follow these steps:

### Step 1: Identify the oxidation states of the metals in the complex.
- The complex `Co_2[Fe(CN)_6]` contains cobalt (Co) and iron (Fe).
- The cyanide ion (CN) has a charge of -1, and there are 6 cyanide ions, contributing a total charge of -6.
- Let the oxidation state of iron (Fe) be \( x \). The total charge of the coordination entity must equal the charge contributed by the cobalt ions and the cyanide ions.

### Step 2: Set up the equation for the oxidation state of iron.
- The total charge of the complex is neutral, so we can write:
\[ 2(+2) + x + 6(-1) = 0 \]
Simplifying this gives:
\[ 4 + x - 6 = 0 \implies x - 2 = 0 \implies x = +2 \]
- Therefore, iron is in the +2 oxidation state.

### Step 3: Determine the electronic configuration of Fe²⁺.
- The atomic number of iron (Fe) is 26. The electronic configuration of neutral Fe is:
\[ [Ar] 3d^6 4s^2 \]
- For Fe²⁺, we remove two electrons from the 4s subshell:
\[ \text{Fe}^{2+}: [Ar] 3d^6 4s^0 \]

### Step 4: Analyze the effect of the ligand on electron pairing.
- The cyanide ion (CN⁻) is a strong field ligand, which means it will cause pairing of electrons in the d-orbitals.
- The 3d subshell can hold a maximum of 10 electrons. For 6 electrons in the 3d subshell, the arrangement will be:
- The electrons will pair up due to the strong field nature of CN⁻.

### Step 5: Draw the electron configuration for 3d.
- The distribution of the 6 electrons in the 3d subshell will be:
\[ \uparrow\downarrow \quad \uparrow\downarrow \quad \uparrow\downarrow \]
- All electrons are paired.

### Step 6: Count the number of unpaired electrons.
- Since all 6 electrons in the 3d subshell are paired, the number of unpaired electrons in Co²⁺ is:
\[ \text{Number of unpaired electrons} = 0 \]

### Final Answer:
The number of unpaired electrons in the central metal of cobalt ferrocyanide, `Co_2[Fe(CN)_6]`, is **0**.

---