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In a coordination compound, the so-called “crystalfield” gives rise to a differe

ID: 1757874 • Letter: I

Question

In a coordination compound, the so-called “crystalfield” gives rise to a difference in energy levels for someof the electrons in a transition metal ion. That is, electrons canoccupy one of two states, separated by the crystal field splittingenergy .

The octahedral complex [Cr(NH3 )6 ]3+ has a crystalfield splitting of o 2.16 eV, while[Co(NH3 )6 ]3+ has o 2.84eV.

What color are these compounds?

If a compound absorbs a certain color of light, it exhibits thecolor complementary to the color of absorbed light. Recallthat 1eV = 1.6e-19 J.


Explanation / Answer

The octahedral complex [Cr(NH3 )6 ]3+ has a crystalfield splitting of o = 2.16 eV. This ion has absorption bandat about 630 nm. The color is sky blue. While [Co(NH3 )6 ]3+ has o 2.84 eV. Which absorbs light primarily in the red region of thevisible spectrum.