Question

Among the following statements A-D, the incorrect ones are:
A. Octahedral $Co\left(III\right)$ complexes with strong field ligands have high magnetic moments

B. When ${\Delta }_{\circ }<P$ the d- electron configuration of $Co\left(III\right)$ in an octahedral complex is $t_{2g}^4,e_g^2$.

C. Wavelength of light absorbed by $\left[Co\right(en{)}_3{]}^{3+}$ is lower than that of $[Co{F}_6{]}^{3-}$

D. If the ${\Delta }_{\circ }$ for an octahedral complex of $Co\left(III\right)$ is $18000{\text{cm}}^{-1}$, the ${\Delta }_t$ for its tetrahedral complex with the same ligand will be $16000{\text{cm}}^{-1}$.

• A. B and C only
• B. A and B only
• C. A and D only
• D. C and D only

Answer 1

The correct option is C A and D only

$C{o}^{3+}$ has $d^6$ electronic configuration. In the presence of strong field ligand, ${\Delta }_{\circ }>P$. Thus the splitting occurs as: $t_{2g}^6,e_g^0$; so the magnetic moment is zero.

According to the spectrochemical series, $en$ is a stronger ligand than $F$ and therefore promotes pairing. This implies that the ${\Delta }_{\circ }$ of en is more than the ${\Delta }_{\circ }$ of $F$.

${\Delta }_{\circ }=\frac{hc}{{\lambda }_{abs}}$
${\Delta }_t=\frac{4}{9}{\Delta }_{\circ }=8000{\text{cm}}^{-1}$