- Determine oxidation states and assign d-electron counts for transition metals in complexes.
- Derive the d-orbital splitting patterns for octahedral, elongated octahedral, square pyramidal, square planar, and tetrahedral complexes.
- For octahedral and tetrahedral complexes, determine the number of unpaired electrons and calculate the crystal field stabilization energy.
- Know the spectrochemical series, rationalize why different classes of ligands impact the crystal field splitting energy as they do, and use it to predict high vs. low spin complexes, and the colors of transition metal complexes.
- Use the magnetic moment of transition metal complexes to determine their spin state.
- Understand the origin of the Jahn-Teller effect and its consequences for complex shape, color, and reactivity.
- Understand the extra stability of complexes formed by chelating and macrocyclic ligands.
Coordination compounds (or complexes) are molecules and extended solids that contain bonds between a transition metal ion and one or more ligands. In forming these coordinate covalent bonds, the metal ions act as Lewis acids and the ligands act as Lewis bases. Typically, the ligand has a lone pair of electrons, and the bond is formed by overlap of the molecular orbital containing this electron pair with the d-orbitals of the metal ion.
- 4.9: Magnetic Susceptibility and the Spin-only Formula
- Paramagnetic compounds arr characterized by an attraction to an external magnetic field e.g., molecular oxygen. The magnitude of paramagnetism is measured in terms of the magnetic moment, where the larger the magnetic magnitude, the greater the paramagnetism of the compound.
- 4.10: Jahn-Teller Distortions
- The Jahn-Teller effect is a geometric distortion of a non-linear molecular system that reduces its symmetry and energy. This distortion is typically observed among octahedral complexes where the two axial bonds can be shorter or longer than those of the equatorial bonds. This effect can also be observed in tetrahedral compounds. This effect is dependent on the electronic state of the system.
- 4.14: Ligand Field Theory
- Ligand field theory (LFT) describes the bonding, orbital arrangement, and other characteristics of coordination complexes. It represents an application of molecular orbital theory to transition metal complexes. A transition metal ion has nine valence atomic orbitals: five nd, one (n+1)s, and three (n+1)p orbitals. These orbitals are of appropriate energy to form bonding interaction with ligands.
- 4.15: The 18-electron Rule
- The 18-electron rule is used primarily for predicting and rationalizing formulae for stable metal complexes, especially organometallic compounds. The rule is based on the fact that the valence shells of transition metals consist of nine valence orbitals (one s orbital, three p orbitals and five d orbitals), which collectively can accommodate 18 electrons as either bonding or nonbonding electron pairs.