Inorganic chemistryLesson 2 of 2 in the course Transition Metals and Coordination Chemistry

Crystal Field Splitting, Spin States, Magnetism, and Color

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Crystal field theory (CFT) helps explain why transition-metal coordination compounds have characteristic structures, colors, and magnetic properties. This lesson introduces the electrostatic model and explains how an octahedral arrangement of ligands splits the metal's d-orbital energies.

CFT treats ligands as point charges or dipoles whose electrons repel electrons in the unhybridized d orbitals of the central metal ion. The model focuses on the energies and arrangements of the metal's d electrons rather than directly describing metal–ligand bonds. In its pure form, CFT does not account for covalent bonding, so it gives one useful part of the explanation of coordination compounds rather than the whole picture.

All flashcards

What is crystal field theory?
A model that explains selected properties of transition-metal complexes by considering electrostatic interactions between ligand electrons and the metal ion's d electrons.
What does degenerate mean for a set of orbitals?
The orbitals have equal energy. The five d orbitals of an isolated metal ion are degenerate in the basic model.
Which d orbitals form the octahedral e_g set?
The d_z² and d_x²−y² orbitals. Their lobes point along the axes toward the six octahedral ligand positions.
Which d orbitals form the octahedral t₂g set?
The d_xy, d_xz, and d_yz orbitals. Their lobes point between the axes and between the ligands.
What is Δ_oct?
It is the crystal field splitting in an octahedral complex: the energy gap between the lower-energy t₂g set and the higher-energy e_g set.

Quiz questions

  1. What interaction is central to the basic crystal field theory model?Answer: Electrostatic repulsion between ligand electrons and electrons in the metal d orbitals.
  2. What does it mean for the five d orbitals of an isolated metal ion to be degenerate?Answer: They have the same energy.
  3. Which orbitals make up the e_g set in an octahedral complex?Answer: d_z² and d_x²−y².
  4. Why are the e_g orbitals higher in energy than the t₂g orbitals in an octahedral complex?Answer: Their lobes point directly toward the ligands, so they experience greater repulsion.
  5. What does Δ_oct represent?Answer: The energy difference between the e_g and t₂g sets in an octahedral field.

Based on Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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