Explain why [CoCl₄]^2- (blue) and [Co(H₂O)₆]²⁺ (pink) have different colors. Which complex has its absorption bands at longer wavelengths?

Video transcript

All right. Hi, everyone. So this question says the NCO complex ions N IC 42 negative and NIH 362 positive have different colors. N IC 42 negative is blue. While ninh 362 positive is violet, explain this color difference and identify the complex that will absorb at longer wavelengths. Now, recall first and foremost, that the reason why these complex ions are going to have different colors is because their crystal fields splitting energy is different. Recall it chloride is considered a weak field ligand, which therefore is generally considered high spent. Now by contrast or rather as a result, right, the lien that contains chloride is going to adopt tetrahedral geometry. Whereas by contrast, the lien that contained ammonia is going to appear or is going to demonstrate octahedral geometry or is an octahedral complex. Now recall that the crystal field splitting energy or delta of a tetrahedral complex is much smaller than the delta value of an octahedral complex, which means that the splitting energy of N IC 42 negative is going to be smaller than the splitting energy of ninh 362 positive. And because the the crystal field splitting energy values are different, they will also appear different colors. No recall the the wavelength of light absorbed is not going to be the color that is observed when looking at the complex from the outside, right, because if a certain wavelength of light is absorbed, then it is the complementary color that will be observed when looking at the compound itself. So in this case, right N I cl 42 negative appears blue. It's so because its appearance is blue, the wavelength of light absorbed is going to correspond to the complementary color of blue in the color wheel, which if you recall is orange, which ranges in between approximately 600 to 650 nanometers. So also right, the ligand that contains ammonia appears violent and the complementary color of violet and the color wheel is going to be yellow, which means that the ligand that contains ammonia is going to absorb yellow light at a wavelength between about 560 to 600 nanometers. So because the color orange has a longer wavelength than the color yellow chloride is going to absorb at a longer wavelength and there you have it. So here is your final answer, right N IC 42 minus and or two negative and ninh 362 positive have different colors because the splitting energy or delta of N IC 42 negative is smaller than the splitting energy of N I NH 362 positive NCL 42 negative will absorb at longer wavelength. And so with that being said, thank you so very much for watching. And I hope you found this helpful.