`[Fe(H_(2)O)_(6)]^(3+) and [Fe(CN)_(6)]^(3-)` differ in

Options

A. Oxidation number
B. Coordination number
C. Structure
D. Magnetic nature

Answer

To determine how the complexes \([Fe(H_2O)_6]^{3+}\) and \([Fe(CN)_6]^{3-}\) differ, we will analyze their oxidation states, coordination numbers, structures, and magnetic properties step by step.

### Step 1: Determine the Oxidation State
1. For \([Fe(H_2O)_6]^{3+}\):
- Let the oxidation state of Fe be \(X\).
- Water (\(H_2O\)) is a neutral ligand, contributing 0 to the charge.
- The overall charge of the complex is \(+3\).
- Therefore, we have the equation:
\[ X + 0 = +3 \implies X = +3 \]

2. For \([Fe(CN)_6]^{3-}\):
- Let the oxidation state of Fe be \(Y\).
- Each cyanide (\(CN^-\)) has a charge of \(-1\).
- The overall charge of the complex is \(-3\).
- Therefore, we have the equation:
\[ Y + 6(-1) = -3 \implies Y - 6 = -3 \implies Y = +3 \]

**Conclusion**: The oxidation state of Fe in both complexes is \(+3\).

### Step 2: Determine the Coordination Number
1. For \([Fe(H_2O)_6]^{3+}\):
- There are 6 water molecules coordinated to Fe.
- Therefore, the coordination number is \(6\).

2. For \([Fe(CN)_6]^{3-}\):
- There are 6 cyanide ligands coordinated to Fe.
- Therefore, the coordination number is also \(6\).

**Conclusion**: The coordination number for both complexes is \(6\).

### Step 3: Determine the Structure
- Both complexes have octahedral geometry due to the coordination number of \(6\).

**Conclusion**: Both complexes have the same octahedral structure.

### Step 4: Determine the Magnetic Nature
1. For \([Fe(H_2O)_6]^{3+}\):
- The electronic configuration of \(Fe^{3+}\) is \(3d^5\).
- Water is a weak field ligand, which does not cause pairing of electrons.
- Therefore, all five \(3d\) electrons remain unpaired.
- The number of unpaired electrons (\(n\)) is \(5\).
- The magnetic moment (\(\mu\)) can be calculated using:
\[ \mu = \sqrt{n(n + 2)} = \sqrt{5(5 + 2)} = \sqrt{35} \approx 5.916 \text{ Bohr magneton} \]

2. For \([Fe(CN)_6]^{3-}\):
- The electronic configuration of \(Fe^{3+}\) is still \(3d^5\).
- Cyanide is a strong field ligand, which causes pairing of electrons.
- Therefore, there is only \(1\) unpaired electron.
- The number of unpaired electrons (\(n\)) is \(1\).
- The magnetic moment (\(\mu\)) can be calculated using:
\[ \mu = \sqrt{n(n + 2)} = \sqrt{1(1 + 2)} = \sqrt{3} \approx 1.732 \text{ Bohr magneton} \]

**Conclusion**:
- \([Fe(H_2O)_6]^{3+}\) is strongly paramagnetic with a magnetic moment of approximately \(5.916\) Bohr magneton.
- \([Fe(CN)_6]^{3-}\) is weakly paramagnetic with a magnetic moment of approximately \(1.732\) Bohr magneton.

### Final Conclusion
The two complexes differ in their magnetic nature. Therefore, the correct answer is that they differ in **magnetic nature**.

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