A note from Dr. Haas: You have already read about some of the factors that effect the strength of the ligand field in octahedral complexes in the previous subsection, Section 4.1. For this reading assignment, please go back and focus some time to review the parts of Section 4.1 that discuss how the metal ion identity can effect d-orbital splitting. Specifically, these are the sections that are relevant:
- In 4.1.1: Crystal Field Theory (click), there is a brief summary of three factors that affect the d-orbital splitting in octahedral complexes (and it is true regarless of whether you're using LFT or CFT). These are the three factors we'll focus on in the next two class meetings.
- In 4.1.2: Ligand Field Theory, there is a more robust explanation for the effect of the metal ion on d-orbital splitting.
Summary of metal ion properties that effect \(\Delta_o\)
- Position on the periodic table (period or shell number)
The splitting of the d-orbitals in any ligand field increases as shell number increases going down the periodic table. In general, with octahedral ligand fields, the 3d metal ions can be either weak-field or strong-field depending on other factors. With octahedral complexes, the 4d and larger metal ions are generally strong-field.
- Oxidation state (charge of the metal ion)
As the positive charge on a metal ion increases, the strength of the field also increases. The charge on a 3d metal ion can contribute to whether it is weak-field or strong-field (and thus high-spin or low-spin for d4-d7 metal ions). In the 3d metal ions in an octahedral ligand field, the +3 metal ions tend to be strong-field (and thus low spin) complexes. The +2 metal ions in this series are usually weak-field; but we cannot make a good prediction about this without knowing about the identity of the ligands.