Coordination Compounds 2 Question 29

####31. The octahedral complex of a metal ion $M^{3+}$ with four monodentate ligands $L _1, L _2, L _3$ and $L _4$ absorb wavelengths in the region of red, green, yellow and blue, respectively. The increasing order of ligand strength of the four ligands is

(2014 Main)

(a) $L _4<L _3, L _2<L _1$

(b) $L _1<L _3<L _2<L _4$

(c) $L _3<L _2<L _4<L _1$

(d) $L _1<L _2<L _4<L _3$

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Answer:

Correct Answer: 31. (c)

Solution:

  1. Arrange the complex formed by different ligands $L _1, L _2, L _3$ and $L _4$, according to wavelength of their absorbed light, then use of the following relation to answer the question.

Ligand field strength $\propto$ Energy of light absorbed

$$

$$

Wavelength of absorbed light decreases.

$\therefore$ Increasing order of energy of wavelengths absorbed reflect greater extent of crystal field splitting, hence, higher field strength of the ligand.

Energy blue $\left(L _4\right)>$ green $\left(L _2\right)>$ yellow $\left(L _3\right)>\operatorname{red}\left(L _1\right)$

$\therefore \quad L _4>L _2>L _3>L _1$ in field strength of ligands.



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