Amongst $\mathrm{TiF}_{6}^{2-}, \mathrm{CoF}_{6}^{3-}, \mathrm{Cu}_{2} \mathrm{Cl}_{2}$ and…

Amongst $\mathrm{TiF}_{6}^{2-}, \mathrm{CoF}_{6}^{3-}, \mathrm{Cu}_{2} \mathrm{Cl}_{2}$ and $\mathrm{NiCl}_{4}^{2-}$, which are the colourless species?
(atomic number of $\mathrm{Ti}=22, \mathrm{Co}=27, \mathrm{Cu}=29, \mathrm{Ni}=28$ )
  1. $\mathrm{Cu}_{2} \mathrm{Cl}_{2}$ and $\mathrm{NiCl}_{4}{ }^{2-}$
  2. $\mathrm{TiF}_{6}^{2-}$ and $\mathrm{CoF}_{6}^{3-}$
  3. $\mathrm{CoF}_{6}{ }^{3-}$ and $\mathrm{NiCl}_{4}^{2-}$
  4. $\mathrm{TiF}_{6}^{2-}$ and $\mathrm{Cu}_{2} \mathrm{Cl}_{2}$

Solution

$\operatorname{In}\left[\mathrm{TiF}_{6}ight]^{2-}$ and $\mathrm{Cu}_{2} \mathrm{Cl}_{2} \Rightarrow \mathrm{Ti}^{4+}$ and $\mathrm{Cu}^{+}$
Both ion do not have any unpaired electron in d orbital to (promote) transition. Hence no
absorption of energy is there.
So they are colorless species.

Asked in: JEE-TOPICTESTS-CHEMISTRY

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