Trans metals

• Bidentate ligands are able to form two coordinate bonds to the central metal ion. Ethanedioate ions and Ethane-1,2-diamine are common bidentate ligands
• Bidentate ligands can replace two unidentate ligands while the coordination number remains at six
• Physical properties of transition metals

  • Similar atomic radius, high densities, high melting and boiling points
• The Cl- ligand is much larger than the NH3 and H2O ligands, resulting in a change in coordination number for that complex
• Special chemical properties of transition metals

  • Form complexes
  • Form coloured ions
  • Variable oxidation states
  • Good catalysts
• Coordination Number is equal to the number of coordinate bonds formed around the central metal ion. Silver complexes have a coordination number of 2 and platinum complexes commonly have a coordination number of 4
• Complexes formation

  Consist of a central metal ion or atom surrounded by ligands
• Ligand Substitution Reactions

  Ligands NH3 and H2O can be exchanged without a change in coordination number via a ligand substitution reaction
• Complexes can be represented in formulas using square brackets
• Ligands


  Molecules or ions with a lone electron pair that can form a coordinate bond to the central metal ions by donating this electron pair
• Common ligands

  • Cl-, H2O, NH3
• Multidentate ligands are able to form up to six coordinate bonds to the central metal ion. The most common multidentate ligand is EDTA (ethylenediaminetetraacetic acid)
• Haem, a component of haemoglobin, is another common multidentate ligand that consists of six coordinate bonds around a central Fe2+ ion
• Carbon monoxide is toxic to humans as it replaces the oxygen in the haem complex, preventing it from being transported around the body
• The transition metals are elements in the d-block of the periodic table with a partially filled d-orbital. They lose electrons to form positive ions with the s-orbital electrons being removed first
• With copper complexes and NH3 in excess, the substitution is incomplete and the complex formed has a combination of water and ammonia ligands, resulting in a deep blue solution
• The Chelate Effect in ligand substitution reactions: Positive entropy change is favourable as it means a more stable complex is being formed
• Toxicity of carbon monoxide

  • It replaces the oxygen in the haem complex, preventing it from being transported around the body
• The greater the entropy change, the more negative the free energy change (∆G) will be, making the reaction more favourable
• Tetrahedral complexes form with larger ligands such as Cl​-, with a bond angle of 109.5​o
• Platinum and Nickel complexes form in a square planar shape with a bond angle of 90​o
• Cisplatin

  • It is the cis isomer of a square planar complex of platinum, commonly used as a cancer therapy drug
• Silver complexes always have a linear shape with a bond angle of 180​o
• Substituting unidentate ligands with bidentate or multidentate ligands is known as the chelate effect
• Optical Isomerism is shown by octahedral complexes with bidentate ligands
• Haem complex

  • Consists of six coordinate bonds around a central Fe​2+​ ion, transports oxygen around the body
• Enthalpy change (∆H) for ligand substitution reactions is very small as the bonds being formed are very similar to the bonds that were broken, resulting in an overall enthalpy change near zero
• Cis-trans Isomerism is shown by octahedral complexes with different types of unidentate ligands
• Colour arises because of how substances absorb and reflect light. When white light shines on a substance, some of the wavelengths of light are absorbed but the remaining wavelengths are reflected
• Transition metal ions can be identified by their colour, which depends on the coordination number of the complex, type of ligand bonded to the ion, and the oxidation state
• Cells in the natural world are chiral, so only one isomer of the drug will be the correct orientation to 'fit' the cells, therefore only this single isomer will work and cure the disease
• Transition metal complexes with H​2​O and NH​3 ​ligands commonly form octahedral complexes with a bond angle of 90​o
• Cisplatin can cause serious side effects such as hair loss, meaning it has to be administered in small amounts to try and reduce these effects
• pH of the reaction conditions

  Determines whether a transition metal is oxidised or reduced
• Colorimetry


  1. Analytical technique that uses the absorption of visible light to determine the concentration of coloured ions by measuring absorbance

  2. Calibration graph is produced by measuring solutions of known concentrations to calibrate the colorimeter on a graph of relative absorbance against concentration
• Catalysts provide an alternative reaction path with a lower activation energy and allow equilibrium to be reached faster
• Vanadium oxidation states

  • +5 - VO2+ yellow
  • +4 - VO2+ blue
  • +3 - V3+ green
  • +2 - V2+ violet
• Types of catalysts

  • Heterogeneous
  • Homogeneous
• Colour

  • Depends on the coordination number of the complex, type of ligand bonded to the ion, and the oxidation state
• Variable oxidation states are a key chemical property of transition metals