A metal complex is a chemical species made up of a central metal atom or ion that is bonded to surrounding molecules or ions called ligands.
Key Features of a Metal Complex:
- Central metal
- Usually a transition metal, because they can form multiple bonds using their d orbitals.
- Can be in different oxidation states.
- Ligands
- Atoms, ions, or molecules that donate electron pairs to the metal.
- Examples: H₂O, NH₃, CO, Cl⁻, CN⁻, PPh₃.
- Coordinate (dative) bonds
- The metal accepts electrons into its empty orbitals from ligands.
- This forms coordinate covalent bonds.
- Geometry
- The shape depends on the metal and the number/type of ligands.
- Common geometries: octahedral, tetrahedral, square planar.
Examples
- [Fe(CN)₆]⁴⁻ → hexacyanoferrate(II) complex (octahedral).
- [Cu(NH₃)₄]²⁺ → tetraamminecopper(II) complex (square planar or distorted tetrahedral).
- [Ni(CO)₄] → nickel carbonyl (tetrahedral, stable organometallic complex).
In simple terms:
A metal complex is like a “team” where a metal center is surrounded by “helpers” (ligands) that donate electrons to it, making the structure stable and giving it special reactivity.