Question

In which of the following complexes the CFSE, \(\Delta_0\) will be equal to zero?

• A. \([Fe(NH_3)_6]Br_2\)
• B. \([Fe(en)_3]Cl_3\)
• C. \(K_4[Fe(CN)_6]\)
• D. \(K_3[Fe(SCN)_6]\)

Hint:

To determine CFSE, consider the electronic configuration of the metal ion and use the crystal field theory. If the d-electron configuration is such that the electrons are evenly distributed between the \(e_g\) and \(t_2\)g orbitals, the CFSE will be zero.

Answer 1

The Correct Option is D

For complex \(K_3[Fe(SCN)_6]\): E.C. of \(Fe^{3+}\) - [Ar] \(3d^5\) W.F.L.

Calculation of CFSE: \[ \text{CFSE} = (-0.4 \times 3 + 0.6 \times 2) \Delta_0 = 0 \Delta_0 \] Thus, the CFSE is zero for \(K_3[Fe(SCN)_6]\).