The geometry of `Ni(CO)_4` and `Ni(PPH_3)_2Cl_2` are

Options

A. square planar and tetrahedral respectively
B. Both tetrahedral
C. tetrahedral and square planar
D. Both square planar

Answer

To determine the geometries of the coordination compounds `Ni(CO)_4` and `Ni(PPh_3)_2Cl_2`, we will analyze the hybridization and oxidation states of nickel in each complex.

### Step 1: Analyze `Ni(CO)_4`

1. **Identify the oxidation state of nickel**:
- Carbon monoxide (CO) is a neutral ligand, so it does not contribute any charge. Therefore, the oxidation state of nickel in `Ni(CO)_4` is 0.

2. **Determine the electron configuration of nickel**:
- The atomic number of nickel (Ni) is 28. Its electron configuration is `[Ar] 3d^8 4s^2`.

3. **Consider the ligand field**:
- CO is a strong field ligand, which means it will cause pairing of electrons in the d-orbitals.

4. **Hybridization**:
- In the presence of strong field ligands like CO, the 4s electrons will also participate in hybridization. The configuration will be `3d^10` (after pairing) and `4s^0`, leading to `sp^3` hybridization.

5. **Geometry**:
- `sp^3` hybridization corresponds to a tetrahedral geometry.

### Step 2: Analyze `Ni(PPh_3)_2Cl_2`

1. **Identify the oxidation state of nickel**:
- In this complex, PPh₃ (triphenylphosphine) is a neutral ligand, and Cl is a negatively charged ligand. Since there are two Cl ligands, the total charge contributed by Cl is -2. Therefore, the oxidation state of nickel in `Ni(PPh_3)_2Cl_2` is +2.

2. **Determine the electron configuration of nickel**:
- For Ni in the +2 oxidation state, the electron configuration is `[Ar] 3d^8` (removing two electrons from the 4s orbital).

3. **Consider the ligand field**:
- PPh₃ is a weak field ligand, which means it does not cause pairing of electrons in the d-orbitals.

4. **Hybridization**:
- With the configuration `3d^8`, the electrons will occupy the d-orbitals without pairing. Therefore, the hybridization remains `sp^3`.

5. **Geometry**:
- `sp^3` hybridization also corresponds to a tetrahedral geometry.

### Conclusion:
Both `Ni(CO)_4` and `Ni(PPh_3)_2Cl_2` exhibit tetrahedral geometry.

### Summary of Geometries:
- `Ni(CO)_4`: Tetrahedral
- `Ni(PPh_3)_2Cl_2`: Tetrahedral