Which of the following molecules is not tetrahedral ?

Options

A. `[Pt(en)_(2)]^(2+)`
B. `[Ni(CO)_(4)]`
C. `[Zn(NH_(3))_(4)]^(2+)`
D. `[NiCl_(4)]^(2-)`

Answer

To determine which of the following molecules is not tetrahedral, we need to analyze the coordination geometry of each complex based on the ligands and the central metal ion's electronic configuration. Let's break down the analysis step by step.

### Step 1: Identify the complexes
We have the following complexes to analyze:
1. [Pt(C2H4)Cl2]
2. [Ni(CO)4]
3. [Zn(NH3)4]²⁺
4. [NiCl4]²⁻

### Step 2: Analyze the first complex [Pt(C2H4)Cl2]
- Platinum (Pt) in this complex is in the +2 oxidation state.
- The electronic configuration of Pt²⁺ is [Xe] 4f¹⁴ 5d⁶.
- Ethylene diamine (C2H4) is a strong field ligand and will cause pairing of electrons.
- The geometry of this complex is square planar (DSP² hybridization), not tetrahedral.

### Step 3: Analyze the second complex [Ni(CO)4]
- Nickel (Ni) in this complex is in the 0 oxidation state.
- The electronic configuration of Ni is [Ar] 4s² 3d⁸.
- Carbon monoxide (CO) is a strong field ligand and promotes hybridization to form SP³.
- The geometry of this complex is tetrahedral.

### Step 4: Analyze the third complex [Zn(NH3)4]²⁺
- Zinc (Zn) in this complex is in the +2 oxidation state.
- The electronic configuration of Zn²⁺ is [Ar] 3d¹⁰.
- Ammonia (NH3) is a neutral ligand and does not cause pairing.
- The geometry of this complex is tetrahedral (SP³ hybridization).

### Step 5: Analyze the fourth complex [NiCl4]²⁻
- Nickel (Ni) in this complex is in the +2 oxidation state.
- The electronic configuration of Ni²⁺ is [Ar] 3d⁸.
- Chloride (Cl⁻) is a weak field ligand and does not cause pairing.
- The geometry of this complex is tetrahedral (SP³ hybridization).

### Conclusion
From the analysis, the only complex that is not tetrahedral is [Pt(C2H4)Cl2], which has a square planar geometry.

### Final Answer
**The molecule that is not tetrahedral is [Pt(C2H4)Cl2].**

---