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3.5.4 Transition Metals - Other applications of transition metal complexes

Specification

Students should:
  • understand the importance of variable oxidation states in catalysis; both heterogeneous and homogeneous catalysts
  • understand that Fe(II) in haemoglobin enables oxygen to be transported in the blood, and why CO is toxic.
  • know that the Pt(II) complex cisplatin is used as an anticancer drug
  • appreciate the benefits and risks associated with this drug
  • understand that [Ag(NH3)2]+ is used in Tollens' reagent to distinguish between aldehydes and ketones

Catalysis summary

Catalysts may be either in the same phase as the reactants (homogeneous) or in a different phase ( heterogeneous). Both types of catalysis depend on the ability of transition metals to change oxidation state providing a sink or source of electrons.

Biological importance of transition metals

Transition metals perform many functions in living systems. The essential minerals include copper, zinc, cobalt, molybdenum and iron. All of our red blood cells contain haemoglobin, a protein with four haem groups, each of which has an iron atom in the 2+ oxidation state at the centre of a chelating structure known as a porphyrin..

Haemoglobin

Carbon monoxide poisons haemoglobin by bonding tightly to the iron(II) atom. This prevents the atom binding to oxygen and effectively removes it from the game. The organism dies as oxygen cannot get to the areas where it is needed. The carbon monoxide bound complex is known as carboxyhaemoglobin. It is a cherry red complex, which is why people suffering from carbon monoxide poisoning are very red in the face.

Medicines

Transition metals are also implicated in some medicines, such as cis-platin, an anti cancer agent.