What is a coordination compound?

A coordination compound (also called a coordination complex) is an inorganic compound in which a central metal atom or ion is bonded to molecules or ions called ligands through coordinate (dative covalent) bonds.

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Key Points

1. Central Metal Atom or Ion
   • Usually a transition metal (like Fe, Cu, Co, Ni).
   • Can have different oxidation states.
2. Ligands
   • Molecules or ions that donate a pair of electrons to the metal.
   • Can be neutral (NH₃, H₂O, CO) or anionic (Cl⁻, CN⁻, OH⁻).
   • Can attach one (monodentate) or more (polydentate, chelating) donor atoms.
3. Coordinate Bond
   • The metal-ligand bond is a coordinate covalent bond, where the ligand provides both electrons.
4. Charge
   • The complex may be neutral, positively charged, or negatively charged.

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Examples

1. [Cu(NH₃)₄]²⁺ – Tetraamminecopper(II)
   • Metal: Cu²⁺
   • Ligand: NH₃
   • Charge: +2
2. [Fe(CN)₆]³⁻ – Hexacyanoferrate(III)
   • Metal: Fe³⁺
   • Ligand: CN⁻
   • Charge: -3
3. [Co(H₂O)₆]³⁺ – Hexaaquacobalt(III)
   • Metal: Co³⁺
   • Ligand: H₂O

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Importance of Coordination Compounds

• Found in biological systems (hemoglobin, chlorophyll).
• Used in catalysis and industrial processes.
• Many are colored and used as dyes or pigments.

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