Complex ions

• • A complex ion is a metal ion surrounded by coordinately bonded ligands.
  • A coordinate bond (or dative covalent bond) is a covalent bond in which both electrons in the shared pair come from the same atom, ion or molecule.
  • In a complex ion, they come from the ligands. So, a ligand is an atom, ion or molecule that donates a pair of electrons to a central metal ion.

  
• Monodentate ligands:

  
• Bidentate ligands: Ethane-1,2- diamine

  
• Multidentate ligands:


  • Has 6 lone paris (two on nitrogen atoms and 4 on oxygen atoms)
  • It can form 6 coordinate bonds with a metal ion
  • Complex ions with multidenate ligands are called chelates.

  
• Shapes of complex ions

  • The shape of a complex ion depends on its coordination number. This is the number of coordinate bonds that are formed with the central metal ion.
  • The usual coordination numbers are 6 and 4.
  • Many octahedral complex ions are hexaaqua complexes. This means there are six water ligands around the central ion.

  Six coordinate bonds:

  
• Shapes of complex ions (2)

  Four coordinate bonds:

  Complex ions with four coordinate bonds usually have a tetrahedral shape and 109.5° bond angles.

  
• Shapes of complex ions (3)

  • But in a few complexes, four coordinate bonds form a square planar shape.
  • All of the bond angles in a square planar structure are 90°.