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Theory of Coordination: Blomstrand-Jorgensen Chain Theory

Theory of Coordination: Blomstrand-Jorgensen Chain Theory

In 1850-1870 problems pose about how the structure of complex compounds. At that time organic chemists found that carbon atoms always have a valence of four and organic compounds have a chain structure. For example: CH3(CH2)3Cl structure CH3-CH2-CH2-CH2-Cl.
Based on this, Blomstrand (Sweden, 1869) proposed a chain theory for complex metal structures. Because each element has a fixed valence, Blomstrand and Jorgensen state that in the cobalt (III) complex there are only three bonds. The Chain Theory proposed by Blomstarnd-Jorgensen is one of the main efforts to explain the bonds formed in complex compounds.
Blomstrand and Jorgensen proposed his theory based on the reaction of the formation of AgCl in the complex compound CoCl3. x NH3 using silver nitrate reagent.
CoCl3. 6 NH3 (yellow orange)   + AgNO3 (excess)       → 3 AgCl
CoCl3. 5 NH3 (pink)                  + AgNO3 (excess)       → 2 AgCl
CoCl3. 4 NH3                             + AgNO3 (excess)       → 1 AgCl
CoCl3. 3 NH3                             + AgNO3 (excess)       →      -
Based on the mole ratio of AgCl formed, Blomstrand-Jorgensen proposed a structure for each CoCl3. 6 NH3; CoCl3. 5 NH3; CoCl3. 4 NH3 and CoCl3. 3 NH3 complex as structures I, II, III and IV in the figure below.
According to Blomstrand-Jorgensen, Cl atoms that are bound directly to Co are very strong and difficult to release so that they cannot be deposited using a solution of silver nitrate, while Cl which are bound indirectly to Co are easily released so that they can easily be deposited using a silver nitrate solution. The experimental results for the reaction of CoCl3. 6 NH3, CoCl3. 5 NH3, CoCl3. 4 NH3 according to the theoretical structure proposed by Blomstrand-Jorgensen, but Blomstrand-Jorgensen did not succeed in reacting the compound CoCl3. 3 NH3 with a solution of silver nitrate so that Blomstrand-Jorgensen could not explain the structure which is suitable for CoCl3. 3 NH3 structural compounds. However, Jorgensen can make IrCl3. 3 NH3 compounds which cannot deliver electricity and do not form AgCl deposits when mixed with a silver nitrate solution.

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