Coordination chemistry is a branch of chemistry that focuses on coordination compounds, which are chemical species consisting of a central metal atom or ion surrounded by molecules or ions called ligands. These ligands are bound to the metal through coordinate (dative covalent) bonds, where the ligand donates a pair of electrons to the metal.
Here’s a structured breakdown:
1. Central Metal Atom or Ion
- Usually a transition metal (like Fe, Cu, Ni, Co) because they have empty d orbitals that can accept electron pairs from ligands.
- The metal can be in various oxidation states, affecting the properties of the complex.
2. Ligands
- Molecules or ions that donate electron pairs to the metal.
- Can be monodentate (donate one pair, e.g., NH₃, Cl⁻) or polydentate (donate multiple pairs, e.g., EDTA).
- Ligands determine the geometry and stability of the complex.
3. Coordinate (Dative Covalent) Bond
- A bond where both electrons come from the ligand.
- Example: In [Fe(CN)₆]³⁻, each CN⁻ donates a pair of electrons to Fe³⁺.
4. Properties of Coordination Compounds
- Colorful: Due to d-d electron transitions in transition metals.
- Magnetic: Some complexes are paramagnetic or diamagnetic depending on unpaired electrons.
- Catalytic activity: Many act as catalysts in reactions (e.g., in industrial or biological processes).
5. Applications
- Medicine: Cisplatin (anticancer drug).
- Industry: Catalysts for hydrogenation or polymerization.
- Biological systems: Hemoglobin and chlorophyll are natural coordination compounds.
In short, coordination chemistry studies the formation, structure, bonding, and reactivity of metal-ligand complexes.