Why are low spin tetrahedral complexes not formed ?

Options

A. for tetrahedral complexes , the CFSE is lower than pairing energy
B. for tetrahedral complexes , the CFSE is higher than pairing energy
C. electrons do not go to `e_(g)` in case of tetrahedral complexes
D. tetrahedral complexes are formed by weak field ligands only .

Explanation

To understand why low spin tetrahedral complexes are not formed, we can analyze the situation step by step:

### Step 1: Understanding Crystal Field Theory (CFT)
Crystal Field Theory explains how the arrangement of ligands around a central metal ion affects the energy levels of the d-orbitals. In tetrahedral complexes, the d-orbitals split into two sets: the lower energy set (t2) and the higher energy set (e).

**Hint:** Recall that in tetrahedral complexes, the splitting of d-orbitals is different from octahedral complexes.

### Step 2: Energy Splitting in Tetrahedral Complexes
In tetrahedral complexes, the energy difference between the split d-orbitals (ΔT) is relatively small compared to octahedral complexes (Δoct). The splitting of d-orbitals in tetrahedral geometry is given by the relation ΔT = (4/9)Δoct.

**Hint:** Remember that the smaller the splitting energy, the less likely it is for electrons to pair up.

### Step 3: Pairing Energy
Pairing energy (P) is the energy required to pair two electrons in the same orbital. For low spin complexes to form, the crystal field stabilization energy (CFSC) must be greater than the pairing energy (P).

**Hint:** Think about the balance between CFSC and pairing energy when determining the spin state of a complex.

### Step 4: Comparison of CFSC and Pairing Energy
In tetrahedral complexes, the CFSC is lower than the pairing energy due to the small value of ΔT. This means that the energy gained from placing electrons in lower energy orbitals does not compensate for the energy cost of pairing.

**Hint:** Consider how the energy levels influence whether electrons will remain unpaired or pair up.

### Step 5: Conclusion on Low Spin Tetrahedral Complexes
Since the CFSC in tetrahedral complexes is lower than the pairing energy, electrons prefer to remain unpaired rather than pair up. Therefore, low spin tetrahedral complexes are not formed.

**Hint:** Reflect on how the geometry and ligand strength play a role in the formation of spin states in coordination complexes.

### Final Answer
Low spin tetrahedral complexes are not formed because the crystal field stabilization energy (CFSC) is lower than the pairing energy (P), leading to a preference for unpaired electrons.