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VIDEO: CH. 19 Magnetism

Jun 17, 2025

Overview

This lecture explains how the magnetic properties of transition metal complexes are determined by the arrangement of electrons in split d orbitals, focusing on crystal field theory and the role of ligands.

Magnetic Properties and d Orbitals

  • Magnetic properties depend on the number of unpaired electrons in the metal ion's d orbitals.
  • D orbitals in complexes split into higher-energy (eg) and lower-energy (t2g) sets due to crystal field theory.
  • The energy difference between these sets is the crystal field splitting energy, Ξ” (Delta).
  • Ligands provide electrons and form coordinate covalent bonds with the metal ion.

Electron Configuration in Complex Ions

  • Electrons fill the lower-energy t2g orbitals before the higher-energy eg orbitals.
  • There are two possible electron filling patterns: pairing in lower orbitals or moving to higher orbitals.
  • The choice depends on the relative size of the crystal field splitting energy (Ξ”) and the electron pairing energy.
  • If pairing energy is higher than Ξ”, electrons occupy higher orbitals (high spin); if lower, they pair in lower orbitals (low spin).

Magnetic Types: Diamagnetic vs. Paramagnetic

  • Diamagnetic complexes have all electrons paired and are weakly repelled by magnetic fields.
  • Paramagnetic complexes have at least one unpaired electron and are attracted to magnetic fields.
  • The electron spin direction (parallel or anti-parallel) affects the complex’s magnetic behavior.

Ligands, Oxidation States, and Magnetism

  • The type of ligand affects Ξ”: weak-field ligands have small Ξ” (favor high spin), strong-field ligands have large Ξ” (favor low spin).
  • Oxidation state determines the number of d electrons to place in the crystal field diagram.
  • High spin complexes maximize unpaired electrons (paramagnetic); low spin complexes minimize unpaired electrons (often diamagnetic).
  • The combination of ligand strength, metal oxidation state, and electron configuration determines observed magnetic (and color) properties.

Key Terms & Definitions

  • Crystal Field Splitting Energy (Ξ”) β€” Energy gap between split d orbitals (eg and t2g) in the presence of ligands.
  • High Spin Complex β€” Complex with the most unpaired electrons due to small Ξ” and weak-field ligands.
  • Low Spin Complex β€” Complex with the fewest unpaired electrons due to large Ξ” and strong-field ligands.
  • Diamagnetic β€” No unpaired electrons; repelled by magnetic fields.
  • Paramagnetic β€” At least one unpaired electron; attracted to magnetic fields.
  • Ligand β€” Molecule or ion that donates electrons to a metal ion in a complex.
  • Electron Pairing Energy β€” Energy required to pair two electrons in the same orbital.

Action Items / Next Steps

  • Review assigned examples illustrating high spin and low spin configurations.
  • Understand how to determine magnetic properties from electron filling diagrams.

Full transcript