Question

Consider the following two complex ions : ${\left[Co{F}_6\right]}^{3-}$ and ${\left[Co{\left(C_2{O}_4\right)}_3\right]}^{3-}$. Which of the following statement(s) is/are false?
I. Both are octahedral.
II. ${\left[Co{\left(C_2{O}_4\right)}_3\right]}^{3-}$ is diamagnetic while ${\left[Co{F}_6\right]}^{3-}$ is paramagnetic.
III. Both are outer orbital complexes.
IV. In both the complexes, the central metal is in the same oxidation state.

• A. Both (II) and (III)
• B. (II), (III) and (IV)
• C. Only (III)
• D. Both (III) and (IV)
• E. (I), (II) and (IV)

Answer 1

Answer: (C)

Only (III)

All statements are true except (III), that both are outer orbital complexes. In fact,
In both the given complexes, the central metal is in the same oxidation state,
i.e. $+3$
${\left[Co{F}_6\right]}^{3-}$ due to weal ligand $\left(F\right)$ does not go for pairing and show outer octahedral orbital complex $\left({sp}^3{d}^2\right)$. As it has five unpaired electrons, therefore, it is paramagnetic in nature.
While ${\left[Co{\left(C_2{O}_4\right)}_3\right]}^{3-}$ due to strong bidentate ligand, go for pairing and forms inner octahedral orbital complex $\left(d^2{sp}^3\right)$. As it does not have unpaired electrons, therefore it is diamagnetic in nature.