Sample Exercise
The complex ion trans-[Co(NH3)4Cl2]+ absorbs light primarily in the red region of visible spectrum (the most intense absorption is at 680 nm.) What is the color of the complex?
SOLUTION Because the complex absorbs red light, its color will be complementary to red. From Figure, we see that is green.
Practice Exercise
The [Cr(H20)6]2+ ion has an absorption band at about 630 nm. Which of the following color—sky blue, yellow, or deep red—is most likely to describe this ion? Answer: sky blue.