17A3-4. Transition metals

• Aqueous solutions of transition metal ions


  Usually coloured
• Colour of aqueous ions and other complex ions


  Consequence of the splitting of the energy levels of the d-orbitals by ligands
• Visible light is made up of a limitless number of colours
• Complementary colours


  Colours opposite each other on a colour wheel
• When white light is passed through a solution containing a transition metal complex


  Some wavelengths of light are absorbed by the complex, so the light emerging will contain proportionately more of the complementary colour
• Ions with completely filled 3d energy levels or no electrons in 3d energy levels


  Not coloured
• Colour in transition metal complexes

  1. Electrons in lower energy 3d level absorb energy from visible spectrum and move to higher energy level

  2. Amount of energy absorbed depends on energy difference between levels
• Octahedral complexes


  • Most common ligands are water, ammonia and hydroxide ion
  • Complexes have six-fold coordination
• Octahedral complexes


  • [Mn(H2O)6]2+
  • [Fe(H2O)4(OH)2]
  • [Cr(OH)6]3-
• Tetrahedral complexes


  Formed with relatively large ligands like Cl-
• Tetrahedral complex


  • [CuCl4]2-
• Linear complex


  Reactive ion present in Tollens' reagent (ammoniacal silver nitrate)
• Complexes with six ligands are usually octahedral, with four ligands are usually tetrahedral, and with two ligands are usually linear