Reactions of Transition Metal Complexes

Reactions of Transition Metal Complexes

Understanding Transition Metal Complexes

  • Transition metal complexes involve a central metal ion surrounded by multiple ligands.
  • Ligands are ions or molecules that donate a pair of electrons to a central metal ion to form a dative or coordinate bond.
  • The resulting unit is called a coordination compound, with typically a charged or neutral entity.

Identifying Ligands

  • Ligands can be anions like Cl-, neutral molecules like H2O, or more complex entities like NH3 or CN-.
  • They are named as amine for NH3, aqua for H2O, chloro for Cl-, and cyano for CN-.
  • Ligands that can form more than one bond to the central metal ion are referred to as polydentate or multidentate ligands.

Reactions of Transition Metal Complexes: Substitution

  • One of the key reactions is the substitution reaction, where one or more ligands in the complex ion is replaced by another ligand.
  • A good example is the reaction of an aqua complex with hydroxide ions to form a hydroxo complex.
  • In the process of substitution, the coordination number and oxidation state of the central metal ion should remain unchanged.

Reactions of Transition Metal Complexes: Redox Reactions

  • The other important reaction is the redox reaction, involving a change in the oxidation state of the transition metal.
  • In redox reactions, the transition metal ion is typically either oxidised or reduced.
  • For example, a manganate(VII) ion (MnO4-) can reduce to a manganese(II) ion (Mn2+) in acidic conditions.

Importance of Colour in Transition Metal Complexes

  • Understanding the colour changes during reactions of transition metal complexes can aid in identifying the complex ion involved.
  • Different complex ions of the same transition metal can have different colours because the different ligands cause the d-orbitals to split by differing amounts.
  • When an absorption of light leads to an electron transitioning from a lower to a higher energy d-orbital, this energy corresponds to a particular wavelength of light, thus giving the complex ion its characteristic colour.