The crystal field theory assumes interaction between metal ion and the ligands as a purely electrostatic and ligands are supposed to be point charges.
Q. Amongst the following complexes which has square planar geometry?

Options

A. `[RhCl(CO)(P Ph_(3))_(2)]`
B. `K_(2)[Cu(SCN)_(4)]`
C. `K_(2)[Ni(PH_(3))_(2)Cl_(2)]`
D. `MnO_(4)^(2-)`

Answer

To determine which complex has a square planar geometry among the given options, we can follow these steps:

### Step 1: Understand Coordination Numbers and Ligand Strength
- Coordination number refers to the number of ligand atoms that are bonded to a central metal atom in a complex.
- The geometry of the complex can depend on the coordination number and the strength of the ligands (strong field vs. weak field).

**Hint:** Remember that strong field ligands can lead to different geometries compared to weak field ligands, especially in coordination number 4.

### Step 2: Identify the Coordination Number
- For coordination number 4, the geometry can be either tetrahedral or square planar depending on the nature of the ligands.
- Strong field ligands typically lead to square planar geometry, while weak field ligands lead to tetrahedral geometry.

**Hint:** Look for strong field ligands in the options provided to identify potential square planar complexes.

### Step 3: Analyze the Electronic Configuration
- Check the electronic configuration of the metal ions in the complexes.
- For example, if we consider Rhodium (Rh), which is a 4d element, and has an electronic configuration of 4d^8 in its +1 oxidation state, it can lead to square planar geometry when hybridized as dsp².

**Hint:** Pay attention to the oxidation states of the metal ions and their corresponding electronic configurations.

### Step 4: Evaluate Each Complex
- Evaluate each complex based on the metal ion and the ligands present:
- **Rhodium Complex:** With Rh in a +1 oxidation state and strong field ligands, it can exhibit square planar geometry.
- **Copper Complex:** Copper in +2 oxidation state with weak field ligands will likely be tetrahedral.
- **Nickel Complex:** Nickel in +2 oxidation state with weak field ligands will also be tetrahedral.
- **Manganate Complex (MnO4²⁻):** This complex will also show tetrahedral geometry.

**Hint:** Compare the ligand field strength and coordination number for each complex to determine the geometry.

### Step 5: Conclusion
- After evaluating the complexes, we find that only the complex with Rhodium exhibits square planar geometry due to the presence of strong field ligands and the appropriate electronic configuration.

**Final Answer:** The complex with square planar geometry is the one containing Rhodium (Rh).