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Chapter 20: Problem 28

Transition metal complexes containing CN \(^{-}\) ligands are often yellow, whereas those containing \(\mathrm{H}_{2} \mathrm{O}\) ligands are often green or blue. Explain.

Short Answer

Expert verified
The color of transition metal complexes is affected by the ligands attached to the metal atom. CN- is a strong-field ligand that causes a large splitting in the d orbitals, absorbing light in the blue region and releasing yellow light. On the other side, H2O is a weak-field ligand that causes less splitting in the d orbitals, absorbing light in the red region and releasing green or blue light.

Step by step solution

01

Understand Energy Transition in Electronic Structure

The color of a transition metal complex is determined by the d orbital electron transitions in the central metal atom. When the light is shone onto the compound, certain wavelengths are absorbed to promote an electron from a lower energy level to a higher energy level. This corresponds to a particular wavelength of light, and its complementary color is what we observe.
02

Understand Ligand Impact

In a metal complex, ligands also play an important role. They affect the energy difference between d orbitals because they have different electric fields, influencing the splitting of d orbitals. Some ligands can cause a greater splitting than others.
03

Apply to Cyanide and Water Ligands

Cyanide (CN-) is a strong-field ligand and causes a large splitting in the d orbitals of the metal to which it is bound. As a result, the energy required for the electronic transition (ΔE=hf) is high, corresponding to light in the blue region of the spectrum. Therefore, the color seen in the complementary color (yellow). Water (\(\mathrm{H}_{2} \mathrm{O}\)) is a weak-field ligand and causes less splitting of the d orbitals. This corresponds to lower energy light, specifically from the longer wavelength (red) region, hence the observed color of the complex is its complementary color (green or blue).

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Most popular questions from this chapter

Oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\), is sometimes used to clean rust stains from sinks and bathtubs. Explain the chemistry underlying this cleaning action.

Compounds containing the \(\mathrm{Sc}^{3+}\) ion are colorless, whereas those containing the \(\mathrm{Ti}^{3+}\) ion are colored. Explain.

Complete these statements for the complex ion \(\left[\mathrm{Co}(\mathrm{en})_{2}\left(\mathrm{H}_{2} \mathrm{O}\right) \mathrm{CN}\right]^{2+}\) (a) The term "en" is the abbreviation for ____ (b) The oxidation number of \(\mathrm{Co}\) is _____(c) The coordination number of \(\mathrm{Co}\) is ____ (d) _____ is a bidentate ligand.

A student in 1895 prepared three chromium coordination compounds having the same formulas of \(\mathrm{CrCl}_{3}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\) with these properties: Write modern formulas for these compounds and suggest a method for confirming the number of \(\mathrm{Cl}^{-}\) ions present in solution in each case. (Hint: Some of the compounds may exist as hydrates, which are compounds that have a specific number of water molecules attached to them. The \(\mathrm{Cr}\) has a coordination number of 6 in all three compounds.)

The absorption maximum for the complex ion \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}\) occurs at \(470 \mathrm{nm}\). (a) Predict the color of the complex and (b) calculate the crystal field splitting in kilojoules per mole.
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