Hydrated Ions as Examples of a Coordination Complex

The Chemistry of Art > 5. Complexes > Hydrated Ions as Examples of a Coordination Complex >

Describe hydrated ions as examples of a coordination complex or a complex ion and identify examples

• For many metal cations, (particularly transition metals) the water molecules bond to them
  • Via co-ordinate covalent bonds from the oxygen atom
• Vacant orbitals in the transition metals can be filled be any molecules or anions that have a lone pair of electrons to donate

Complexes:

• A complex ion has
  • A central metal cation
  • Surrounded by a group of anions or molecules
  • These are known as ligands
• Compounds that contain complex ions are called coordination compounds

Ligands:

• Examples include
  • Anions (E.g Cl^– or CN^–)
  • Polar molecules (E.g H₂O or NH₃)
• Co-ordinate covalent bonds form between the ligands and the transition metal ion
  • Uses the lone pair electrons of the ligand

Hydrated coordinate examples:

• Cobalt (II) Chloride hexahydrate (CoCl₂.6H₂O)
• Magnesium sulphate heptahydrate (MgSO₄.7H₂O)
• Sodium tetraborate decahydrate (Na₂B₄O₇.10H₂O_
• Calcium sulphate dihydrate (CaSO₄.2H₂O)

How to draw the above

• Co-ordiantes of cation will be told to you
• Draw a Lewis dot structure of the ligands to figure out how many dentates it has (Due to electronegativeity etc)
• Draw the negative polar end towards the centre and connect with an arrow to indicate a co-ordinate bond has taken place