JEE MAIN - Chemistry (2014 (Offline) - No. 18)
The octahedral complex of a metal ion M3+ with four monodentate ligands L1, L2, L3 and L4 absorb wavelengths in the region of red, green, yellow and blue, respectively. The increasing order of ligand strength of the four ligands is :
L3 < L2 < L4 < L1
L1 < L2 < L4 < L3
L4 < L3 < L2 < L1
L1 < L3 < L2 < L4
Forklaring
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For a given metal ion, weak filed ligands create a complex with smaller $$\Delta $$, which will absorbs light of longer $$\lambda $$ and thus lower frequency. Conservely, stronger filled ligands create a larger $$\Delta ,$$ absorb light of shorter $$\lambda $$ and thus higher $$v.i.e.$$ higher energy.
$$\mathop {{\mathop{\rm Re}\nolimits} d}\limits_{\lambda = 650\,nm} \,\,\mathop { < Yellow}\limits_{570\,\,nm} \,\,\mathop { < Green}\limits_{490\,nm} < \mathop {Blue}\limits_{450\,nm} $$
So order of ligand strength is
$${L_1} < {L_3} < {L_2} < {L_4}$$