Question

The magnitude of CFSE (Crystal field stabilization energy,${\Delta _0}$) can be related to the configuration of d-orbitals in a coordination entity as?
(A) If ${\Delta _0} < P$, the configuration is ${t_{2g}}^3{e_g}^1$ = Weak field ligand and high spin complex
(B) If ${\Delta _0} > P$, the configuration is ${t_{2g}}^3{e_g}^1$ = Strong field ligand and high spin complex
(C) If ${\Delta _0} > P$, the configuration is ${t_{2g}}^4{e_g}^0$ = Strong field ligand and high spin complex
(D) If ${\Delta _0} = P$, the configuration is ${t_{2g}}^4{e_g}^0$ = Strong field ligand and high spin complex

Answer 1

When pairing energy is higher than CSFE then the electrons arranged in a way that the complex formed is a low spin complex. When pairing energy is lower than CFSE, it results in formation of a high spin complex.

Complete step by step solution:
Crystal field stabilization energy is the energy difference between the ${t_{2g}}$ orbitals and ${e_g}$ orbitals. The magnitude of the crystal field stabilization energy in comparison with the Pairing energy of the electrons (shown as P) decides whether the complex will be high spin or low spin.
- High spin complex stands for a complex which has a high value of spin quantum number. Same way, a low spin complex has a lower value of spin quantum number.
- When the electronic field of ligands is strong, it has a tendency to form low spin complexes. In that case, the formation of a high spin complex is not favored. When the ligand field is weak, the complex formed has a tendency to form high spin complexes. Here, low spin complex formation is not favored.
- In option (A), it is said that ${\Delta _0} < P$. That means pairing of electrons will not occur because its pairing energy is higher than CFSE. So, electronic configuration will be ${t_{2g}}^3{e_g}^1$. So, this complex is called a high spin complex. The ligand field is weak here. So, this option is correct.
- In option (B), it is given that ${\Delta _0} > P$, so electronic configuration should be ${t_{2g}}^4{e_g}^0$ which is not given. So, this option is not correct.
- In option (C), it is given that ${\Delta _0} > P$. So, all things will be like option (A) but the ligand field cannot be a strong field because here a high spin complex is formed. So, this option is also wrong.
- In option (D), it is given that ${\Delta _0} = P$, but the electronic configuration is of high spin complex and it is given that the ligand field is strong which is not possible. So, this option is also wrong.

Therefore the correct answer of this question is (A).

Note: Remember that when the ligand field is strong, the complex formed is always a low spin complex. When the ligand field is weaker, the complex formed is always a high spin complex.