Question

The crystal field splitting energy CFSE $\left(In{\Delta }_{0}units\right)$ for $[Co{F}_6{]}^{3-}$ will be:

• A. $-1.6{\Delta }_0$
• B. $-2.4{\Delta }_0$
• C. $-0.4{\Delta }_0$
• D. $+0.6{\Delta }_0$

Answer 1

The correct option is C $-0.4{\Delta }_0$

$F^{-}$ a `weak ligand The crystal field splitting will be small and hence maximum number of electrons will be unpaired (high spin complex).
$C{o}^{3+}$ has 6 d electrons and in a weak field they will be distributed between $t_{2g}$ and $e_g$ orbitals as follows.

$\begin{array}{ccc}\text{Orbital type}& \text{Distribution}& \text{CFSE}\\ e_g:& \underset{–}{\uparrow }\underset{–}{\uparrow }& 2x+0.6{\Delta }_0=1.2{\Delta }_0\\ t_{2g}:& \underset{–}{\uparrow \downarrow }\underset{–}{\uparrow }\underset{–}{\uparrow }& 4x-0.4{\Delta }_0=-1.6{\Delta }_0\end{array}$ $=-0.4{\Delta }_0$