13. 1 Why are complexes colored?

13.1: Why are complexes colored?

CU2+   +  6 ligands -> ligands will have dative covalent bonds with a central transition metal ion, and they are going to form a complex

If you were to shine a light through the above complex, the light comes out on the other side, but in a different color

Copper[]       [] [] [] [] [] 4s1     3d10

Cu 2+[]         [] [] [] [] [] 4s0     3d9

IMPORTANT: These ligands will interact with the central transition metal ion, and the d-orbital of that central transition metal ion will split so that 2 of the 3d orbitals now have higher energy than the other 3

A partially filled orbital will have colored complexes 

If orange light went through the complex, it would be absorbed because it promoted an electron from a lower 3d to a higher 3d orbital (so now the complex looks blue because it is on the opposite side of the color wheel in your data booklet)

If the d-orbital is full or empty, no electronic promotion can take place, so the complex appears white or colorless since no colored light will be absorbed. 

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