Coordination Compounds 2 Question 19
####21. Homoleptic octahedral complexes of a metal ion ’ $M^{3+}$, with three monodentate ligands $L _1, L _2$ and $L _3$ absorb wavelengths in the region of green, blue and red respectively. The increasing order of the ligand strength is
(2019 Main, 9 Jan II)
(a) $L _1<L _2<L _3$
(c) $L _3<L _1<L _2$
(b) $L _2<L _1<L _3$
(d) $L _3<L _2<L _1$
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Answer:
Correct Answer: 21. (b)
Solution:
- In homoleptic complexes, the metal atom/ion is linked to only one type of ligand. Assuming, ligands are neutral, the octahedral complexes of $M^{3+}$ can be,
$$ \begin{array}{lccc} & {\left[M\left(L _1\right) _6\right]^{3+},\left[M\left(L _2\right) _6\right]^{3+}} & \text { and } & {\left[M\left(L _3\right) _6\right]^{3+}} \ \lambda _{\text {Absorption }}^{\text {(I) }} & \text { (II) } & \text { (III) } \ \text { Soeen } & \text { Blue } & \text { Red (wavelength) } \ \lambda _{\text {III }}^{L _3}>\lambda _{\text {I }}^{L _1}>\lambda _{\text {II }}^{L _2} \end{array} $$
We know, ligand strength $\propto \Delta _{\text {absorption }}^{\circ}$
So, the increasing order of the ligand strength will be, $L _3<L _1<L _2$
