Coordination Compounds: A Brief Overview
Coordination compounds are chemical substances formed by the combination of a central metal atom or ion with neutral molecules or anions called ligands. These ligands are attached to the central metal ion through coordinate covalent bonds, where the ligand donates a pair of electrons to the metal ion.
Key Components of Coordination Compounds
- Central Metal Ion: The central atom or ion is usually a transition metal or a post-transition metal.
- Ligands: Ligands can be neutral molecules (like water, ammonia) or anions (like chloride, cyanide). They are classified based on the number of donor atoms they have:
- Monodentate: One donor atom (e.g., H₂O, NH₃)
- Bidentate: Two donor atoms (e.g., ethylenediamine (en))
- Polydentate: More than two donor atoms (e.g., EDTA)
Nomenclature of Coordination Compounds
The naming of coordination compounds follows specific rules:
Ligands:- Anionic ligands end in "-ido" (e.g., chloride becomes chlorido).
- Neutral ligands are named as they are (e.g., water, ammonia).
- Prefixes like "di-", "tri-", "tetra-" indicate the number of ligands of a particular type.
- The name of the metal ion is given in its oxidation state.
- If the metal ion is in its common oxidation state, it is not indicated.
- If the compound has an overall charge, it is indicated as a superscript.
Example: [Co(NH₃)₆]³⁺ is named hexaamminecobalt(III) ion.
Isomerism in Coordination Compounds
Coordination compounds can exhibit different types of isomerism:
Geometric Isomerism:- Cis-trans isomerism: Ligands are arranged in a cis or trans configuration around the central metal ion.
- Facial (fac) and meridional (mer) isomerism: For octahedral complexes with three bidentate ligands.
Optical Isomerism:
- Chiral complexes that are not superimposable on their mirror image.
Applications of Coordination Compounds
Coordination compounds have a wide range of applications:
- Catalysis: Many industrial processes use coordination compounds as catalysts.
- Medicinal Chemistry: Drugs like cisplatin are coordination compounds used in cancer treatment.
- Dyes and Pigments: Coordination compounds are used to produce colorful substances.
- Analytical Chemistry: They are used in complexometric titrations and colorimetric analysis.
