Which of the following is not isostructural with `SiCl_(4)` ?

Options

A. `SO_(4)^(2-)`
B. `PO_(4)^(3-)`
C. `NH_(4)^(+)`
D. `SCl_(4)`

Answer

To determine which of the following species is not isostructural with SiCl4, we first need to understand the structure of SiCl4.

### Step 1: Identify the structure of SiCl4
SiCl4 (silicon tetrachloride) has a tetrahedral molecular geometry. This means that the silicon atom is at the center, and the four chlorine atoms are positioned at the corners of a tetrahedron.

### Step 2: Analyze the options
We will analyze each of the given options to see if they also have a tetrahedral structure.

1. **SO4^2- (sulfate ion)**:
- The sulfate ion has a central sulfur atom bonded to four oxygen atoms, with a tetrahedral arrangement. Therefore, SO4^2- is isostructural with SiCl4.

2. **PO4^3- (phosphate ion)**:
- The phosphate ion has a central phosphorus atom bonded to four oxygen atoms, also arranged tetrahedrally. Thus, PO4^3- is isostructural with SiCl4.

3. **NH4+ (ammonium ion)**:
- The ammonium ion has a central nitrogen atom bonded to four hydrogen atoms, arranged tetrahedrally. Therefore, NH4+ is isostructural with SiCl4.

4. **SCl4 (sulfur tetrachloride)**:
- The sulfur atom in SCl4 has four chlorine atoms bonded to it, but it also has one lone pair of electrons. This results in a seesaw molecular geometry (or distorted tetrahedral), which is not the same as the perfect tetrahedral structure of SiCl4.

### Conclusion
The species that is not isostructural with SiCl4 is **SCl4**.

### Summary of Steps:
1. Identify the structure of SiCl4 (tetrahedral).
2. Analyze SO4^2-, PO4^3-, and NH4+ for tetrahedral structure (they are isostructural).
3. Analyze SCl4 for its structure (it has a seesaw shape due to the lone pair).
4. Conclude that SCl4 is not isostructural with SiCl4.