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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