Edexcel A Level Chemistry:复习笔记6.2.2 Transition Metal Complexes

Transition Metal Complexes


  • Transition element ions can form complexes which consist of a central metal ion and ligands
  • A ligand is a molecule or ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons to the bond
    • This is the definition of a Lewis base - electron pair donor
  • This means ligands have a negative charge or a lone pair of electrons capable of being donated
    • This definition may seem familiar: a ligand is the same as a nucleophile
  • Different ligands can form different numbers of dative bonds to the central metal ion in a complex
    • Some ligands can form one dative bond to the central metal ion
    • Other ligands can form two dative bonds, and some can form multiple dative bonds
  • Co-ordination number is number of co-ordinate bonds to the central metal atom or ion

Common Ligands

  • Water molecules frequently act as ligands. Each water molecule makes a single bond with the metal ion using one of the lone pairs on the oxygen atom
  • The lone pair is donated to the partially filled d-subshell of the transition metal ion

Table showing Examples of Common Monodentate Ligands


Representing complex ions

  • Square brackets are used to group together the ligands and metal ion in a representation of the geometrical arrangement
  • The overall charge on the complex ion is the sum of the oxidation states of all the species present
  • If the ligands are neutral then the overall charge will be the same as the oxidation state of the metal ion


Examples of complexes with monodentate ligands

Naming complexes

  • Complexes are named in the following way
  • If the overall ion is a cation then the nomenclature is:

Prefix for number of ligands/ligand name/element/oxidation number

  • The prefixes are the same ones used in organic chemistry: di, tetra, hexa for 2, 4 & 6 respectively (3 & 5 are rarely encountered except in mixed ligand complexes)
  • If the overall ion is an anion, the name of element is modified to have the name ending 'ate' and sometimes Latin word stems are used
    • tetrachlorcuprate(II)
    • hexaaquairon(II)
    • hexaamminecobalt(II)
    • tetracyanonickelate(II)Using the examples in the illustration above, the names are:
  • Notice in these examples that
    • cuprate( Latin - cuprum) and nickelate are used in place of copper and nickel as they are anions
    • Ammonia takes the prefix ammine as a ligand, which is spelt with a double 'm' unlike the functional group amine