The central metal ion is the most important part of a coordination complex. Its main roles are:
1. Bonding with ligands
- The metal ion acts as an electron-pair acceptor (Lewis acid).
- Ligands donate electron pairs to form coordinate (dative) bonds with the metal.
- This is what holds the complex together.
2. Determines geometry
- The size and coordination number of the metal decide the shape of the complex.
- Examples:
- 6 ligands → octahedral
- 4 ligands → tetrahedral or square planar
3. Influences properties
- Color: Transition metals can absorb light due to d-orbital splitting.
- Magnetism: Depends on the arrangement of d-electrons in the metal.
- Reactivity/Catalysis: Metal ions can speed up reactions by providing sites for reactants.
4. Stabilizes the complex
- The positive charge of the metal ion attracts negatively charged or neutral ligands, making the complex stable.
Simple way to remember:
- The metal is like the “center of a hub”: it holds the ligands, decides the shape, gives color and magnetism, and helps in reactions.