Look at the colors of the isomeric complexes in Figure 21.12, and predict which is the stronger field ligand, nitro (-NO₂) of nitrito (-ONO). Explain. 

Video transcript

All right. Hi, everyone. So this question says to consider the isomeric complexes. Conh 35 SCN two positive and conh 35 N CS two positive. The complex ion co NH 35 SCN two positive is violet colored. While CNH 35 N CS two positive is orange colored. Determine which ligand is a stronger field ligand. Tho S the N or ISO N CS justify your answer. All right. So recall the strength of a given ligand is dependent on its crystal field splitting energy or delta value. Now, the crystal field splitting energy is the energy required to complete the electronic transition from lower energy D orbitals to higher energy D orbitals. Now, the splitting energy is naturally influenced by the nature of the ligand itself, meaning that strong field ligands, we have higher delta values whereas Wakefield ones will have lower delta values. Now, we can also compare energy as a function of absorption wavelength because recall also that E which stands for energy is equal to h multiplied by C divided by LAMBDA. Now, lambda refers to the wavelength of light absorbed by the complex itself. And it just so happens that energy and wavelength are inversely proportional to each other in which as one value increases, the other one must decrease. So in other words, the larger the energy required or meaning the larger the delta value, the shorter the wavelength of absorption must be. Now, we are given information about the colors of these complexes. But that doesn't mean that it's the same color that is being absorbed, right? Because recall that when one delta value is absorbed by a complex, the color that is observed is going to be complimentary two, the color that is absorbed. So because we're given the colors observed, we have to find the complementary color to find the wavelength absorbed. So if I scroll down to open up some space for myself, right, the Tho Cyano complex or SCN is going to be violet in color. Now, recall it according to the color wheel, the complementary color of violet is going to be yellow, which means that the absorption band of the thoon ligand was yellow ranging between 560 to 600 nanometers and the Iso Thone or N CS complex was orange in color. Now, according to the color wheel, the complementary color of orange happens to be blue. So the absorption band of the Iso Oyono ligand ranges between 430 to 490 nanometers. So this means that the absorption band of the iso cyano ligand is shorter than that of the Tho cion li which means that the isothiocyanate ligand is considered stronger field because it has a shorter wavelength of absorption and there you have it. So our final answer is that is SOO or NCS is a stronger field ligand because CNH 35 N CS two positive has an absorption band at shorter wavelengths compared to CNH three SCN two positive. So with that being said, thank you so very much for watching. And I hope you found this helpful.