The complex that violates the Sidgwicks’s rule of EAN is

Options

A. Potassium ferrocyanide
B. Hexamine cobalt (III) Chloride
C. Tetramine copper (II) sulphate
D. Potassium dichloridodioxalato cobaltate (III)

Answer

To determine which complex violates Sidgwick's rule of Effective Atomic Number (EAN), we will analyze each given complex step-by-step.

### Step 1: Understand the EAN Rule
The Effective Atomic Number (EAN) is calculated using the formula:
\[ \text{EAN} = Z - n + 2 \times CN \]
Where:
- \( Z \) = atomic number of the central metal atom
- \( n \) = oxidation state of the metal
- \( CN \) = coordination number (the number of ligand donor atoms coordinated to the metal)

According to Sidgwick's rule, the EAN of a complex should be equal to the atomic number of the nearest noble gas. For transition metals, this is typically 36 (the atomic number of Krypton).

### Step 2: Analyze Each Complex

#### A. Potassium Ferrocyanide \((K_4[Fe(CN)_6])\)
1. Identify the oxidation state of Iron (Fe):
- Let oxidation state = \( x \)
- Charge balance: \( 4(+1) + x + 6(-1) = 0 \)
- \( 4 + x - 6 = 0 \) → \( x = +2 \)

2. Calculate EAN:
- Atomic number of Fe = 26
- EAN = \( 26 - 2 + 2 \times 6 = 26 - 2 + 12 = 36 \)

#### B. Hexamine Cobalt \(([Co(NH_3)_6]Cl_3)\)
1. Identify the oxidation state of Cobalt (Co):
- Let oxidation state = \( +3 \) (as given)
- Coordination number = 6

2. Calculate EAN:
- Atomic number of Co = 27
- EAN = \( 27 - 3 + 2 \times 6 = 27 - 3 + 12 = 36 \)

#### C. Tetramine Copper \(([Cu(NH_3)_4]SO_4)\)
1. Identify the oxidation state of Copper (Cu):
- Let oxidation state = \( +2 \) (as given)
- Coordination number = 4

2. Calculate EAN:
- Atomic number of Cu = 29
- EAN = \( 29 - 2 + 2 \times 4 = 29 - 2 + 8 = 35 \)

#### D. Potassium Dichlorido Dioxylate Cobaltate \((K_3[CoCl_2(C_2O_4)_2])\)
1. Identify the oxidation state of Cobalt (Co):
- Let oxidation state = \( +3 \) (as given)
- Coordination number = 6 (2 from oxalate and 2 from chloride)

2. Calculate EAN:
- Atomic number of Co = 27
- EAN = \( 27 - 3 + 2 \times 6 = 27 - 3 + 12 = 36 \)

### Conclusion
The only complex that does not follow the EAN rule (not equal to 36) is **C. Tetramine Copper**, which has an EAN of 35.

### Final Answer
The complex that violates the Sidgwick’s rule of EAN is **C. Tetramine Copper**.