COMPLEX IONS

• WHAT ARE COMPLEX IONS?

  when transition metal ions form co-ordinate bonds by accepting electron pairs from other ions or molecules called ligands
• WHAT ARE LIGANDS?

  particles with a lone pair of electrons that bond to metals by co-ordinate bonds

  -> are Lewis bases (electron donors)
• WHAT IS THE CO-ORDINATION NUMBER?

  number of co-ordinate bonds from ligands to metal ions

  -> 6 = octahedral

  -> 4 = square planar/ tetrahedral

  -> 2 = linear
• WHAT ARE AQUA IONS?

  • dissolve salt of transition metal in water
  • positively charged metal ion surrounded by water molecules acting as ligands
• WHAT ARE THE TYPES OF LIGAND?

  UNIDENTATE

  • form one co-ordinate bond to metal ion
  • e.g. Cl-, OH-, CN-, H2O and NH3

  BIDENTATE

  • form two co-ordinate bonds to metal ion
  • e.g. 1,2-diaminoethane, ethanedioate ion and benzene-1,2-diol

  MULTIDENTATE

  • form more than two co-ordinate bonds to metal ion
  • e.g. EDTA (4-) forms 6 bonds
• WHAT ARE CHELATES?

  complex ions with polydentate ligands, which allow d-block metal ions to be removed from solution
• WHAT IS THE CHELATE EFFECT?

  • when a ligand is added to a solution of transition metal salt
  • EDTA (4-) replaces all water ligands in an aqua ion
  • e.g. [Cu(H2O)6] (2+) (aq) + EDTA (4-) (aq) -> [CuEDTA] (2-) (aq) + 6H2O (l)
  • occurs due to an increased number of particles in forward reaction
  • causing an entropy increase
  • so the chelate complex is favoured
• HAEMOGLOBIN?

  • Fe (2+) ion
  • co-ordination number of 6
  • first 4 taken up by porphyrin
  • 5th taken up by N atom
  • 6th can take up O2 ligand
  • Fe (2+) to O2 bond is weak as O2 is not a very good ligand allowing it to be easily given up to cells
  • therefore better ligands bind more strongly causing suffocation (e.g. CN- or CO)
• SHAPE OF LIGANDS?

  larger ligands lead to fewer ligands fitting around central metal ion
• TYPES OF ISOMERISM THAT CAN OCCUR?

  GEOMETRIC

  • occur in octahedral or square planar molecules
  • e.g. cisplatin is a successful anti-cancer drug whereas transplatin is not (Pt(NH3)2Cl2)

  OPTICAL

  • non-superimposable mirror images that rotate a plane of polarised light in opposite directions
  • occurs when there are two or more bidentate ligands

  IONISATION

  • occurs when a compound can exist with different numbers of molecules either acting as ligands or existing as negative ions