Question

The complex ion that will lose its crystal field stabilization energy upon oxidation of its metal to $+3$ state is:

• A. $\left[Fe\right(phen{)}_3{]}^{2+}$
• B. $\left[Zn\right(phen{)}_3{]}^{2+}$
• C. $\left[Ni\right(phen{)}_3{]}^{2+}$
• D. $\left[Co\right(phen{)}_3{]}^{2+}$

Answer 1

The correct option is A $\left[Fe\right(phen{)}_3{]}^{2+}$

By oxidation of $F{e}^{2+}$ into $F{e}^{3+}$, the CFSE value decrease.

(2) $\left[Zn\right(phen{)}_3{]}_2\stackrel{-e^{-}}{\to }\left[Zn\right(phen{)}_3{]}^{3+}$

$Z{n}^{2+}$: $3d^{10}$ $Z{n}^{3+}$: $3d^9$

C.F.S.E $=0$ C.F.S.E=$-0.6{\Delta }_o$

By oxidation of $Z{n}^{2+}$ into $Z{n}^{3+}$ , the CFSE value increase.

(3) $\left[Ni\right(phen{)}_3{]}^{2+}\stackrel{-e^{-}}{\to }\left[Ni\right(phen{)}_3{]}^{3+}$

$N{i}^{2+}$: $3d^8$ $N{i}^{3+}$: $3d^7$

C.F.S.E $=-1.2{\Delta }_0$ C.F.S.E $=-1.8{\Delta }_0$

By oxidation of $N{i}^{2+}$ into $N{i}^{3+}$ , the CFSE value increase.

(4) $\left[Co\right(phen{)}_3{]}^{2+}\stackrel{-e^{-}}{\to }\left[Co\right(phen{)}_3{]}^{3+}$

$C{o}^{2+}$: $3d^7$ $C{o}^{3+}$: $3d^6$

$C.F.S.E=-1.8{\Delta }_0$ $C.F.S.E=-2.4{\Delta }_0$

By oxidation of $C{o}^{2+}$ into $C{o}^{3+}$ , the CFSE value increase.