What is Werner’s Theory of coordination compounds?

An explanation for the structure, origin, nature and theory of coordination compound bonding was provided by Werner in 1893. Werner’s Theory of coordination compounds is the name given to this hypothesis.

In 1913, Werner received the Nobel Prize in coordinate chemistry as the first inorganic chemist. The interaction between cobalt chloride and ammonia yielded a variety of complicated chemicals.

Postulates of Werner’s Theory

The postulates of Werner’s coordination compound theory are follows: 

  • There are two valencies for coordination complexes’ core metals.

Primary valency

  • CoCl3, NaCl, CuSO4, etc., are all examples of primary valencies that can be seen in metal salts.
  • It is now known as the metal’s oxidation number in more current parlance for primary valency.
  • It is possible to identify the primary valencies.
  • Outside of the coordinating area, these are written.
  • This is a non-directional and complex compound that doesn’t have any geometry.

Secondary valency

  • It is possible for metals to have both negative and neutral ions in their secondary valency.
  • The coordination number of the metal is referred to as this secondary valency in modern chemistry.
  • The coordination sphere is where secondary valencies are stored.
  • The complex’s geometry is clarified by these, which are directional in nature.
  • These can’t be ionised.
  • For every metal atom, there is a predetermined number of secondary valances. It signifies that the number of coordinations is predetermined.
  • Both the fundamental and secondary valencies of the metal atom must be satisfied for the metal atom to be complete. The primary valency is satisfied by a negative ion. Antimatter or neutral molecular structure on the other hand can satisfy the requirements of secondary valencies.
  • The secondary valencies point to a specific location in space. In fact, it is for this same reason that the coordinate compound has a specific geometry. Let’s have a look at the example of a metal ion with six secondary valances. Around the metal ion, they form octahedral clusters of atoms. Tetrahedral or square planar arrangements surround the centre metal ion in the case of ions with four secondary valencies, respectively. As a result, we can conclude that the secondary valency has a significant impact.

Structure and Properties explained using Werner’s Theory:

According to Werner, the following four complexes of Co (III) chloride with ammonia have the following structural and chemical properties:

  • CoCl3.6NH3 has three silver chloride precipitates, which are the primary valency, and six NH3 molecules, which are the secondary valency, according to his findings. As a result, the compound is now referred to as [Co(NH3)6] Cl3.
  • The remaining 1Cl– and 5NH3 ions serve as secondary valency in CoCl3. 5NH3 has primary valency, and the 2Cl– ions serve as secondary valency. So [Co(NH3)5Cl] Cl2 is the compound.
  • CoCl3.4NH3 has a main valency of 1Cl– and secondary valencies of 2Cl– and 4NH3. Consequently, the chemical is [Co(NH3)5 Cl2]. Cl
  • All 3Cl– and 3NH3 ions in CoCl3.3NH3 are secondary valencies. So [Co(NH3)5 Cl3] is the compound.
  • He uses dotted lines (…….) to symbolise primary valencies and solid lines (—) to represent secondary valencies.

Werner’s Theory of Coordinate Compounds is supported by the data.

1.Cryoscopic Measurements

The number of ions generated during the dissociation of an ionic molecule can be determined via cryoscopic measurements (i.e., measurements of depression in freezing point). In a colloidal solution, the freezing point is lowered by the number of particles in the mixture. The lower the freezing point, the more particles there are.

2.Electrical conductance measurements

Testing for electrical conductance involves counting the charged particles that are present in a solution to determine its conductance.

3.Precipitation reaction

When silver nitrate solution, containing chloride complex, is added. In the absence of a coordination sphere, chloride is precipitated out of solution There is a direct correlation between an increase in precipitate production and an increase in chloride ions outside of the sphere.

Werner’s Theory of Coordination compounds and Isomerism

After looking at the coordinated groups in space, Werner focused on their geometrical configurations in relation to the central cation. He was able to deduce the reason for these compounds’ optical and geometrical isomerism. Here are a few real-world examples:

  • [CoCl2(NH3)4]Cl complex

According to Werner’s theory, this complex can be divided into three distinct parts. These are octahedral, planar, trigonal prisms. For planar, trigonal, and octahedral structures, the number of potential isomers is 3, 3, and 2.

Because only two isomers of this chemical were isolated, it was established that its octahedral structure was determined by the geometry of its coordinating group. Werner believed that all six-coordinated complexes had octahedral geometry in the case of several other complexes in which the coordination number of the central atom was six.

He was also familiar with the geometry of complexes in which the central metal atom’s coordination number is 4. For such compounds, he proposed the Square Planar and Tetrahedral structures. Here is an illustration of what I mean.

  •  [PtCl2(NH3)2] complex

The metal here has a coordination number of 4, which is appropriate for the structure. According to Werner’s theory, the cis and trans forms of this compound are both isomeric. There are four ligands on the same plane, as seen by this diagram. Therefore it is recommended that the structure is either tetrahedral or square-planar in shape.

Limitations of Werner’s theory of coordination compounds

The limitations of Werner’s theory of coordination compounds are as follows:

  • It fails to account for coordination compounds’ magnetic, colour, and optical properties.
  • It failed to explain why coordination compounds aren’t formed by all components.
  • Coordination chemicals’ directional characteristics were not adequately explained.
  • There is no evidence to support this notion in terms of the stability of the complex.
  • However, complexes cannot be explained using this hypothesis.

Conclusion

Scientist Werner proposed his theory of coordination compounds in 1823, describing how complex compounds form and take on their final structure. This theory came to be known as Werner’s Theory of Coordination Compounds.

He was given the Nobel Prize and is known as the “Father of Coordination Chemistry” for his work on this idea. Many different kinds of experiments were carried out by Werner to arrive at his novel theory, which is now known as Werner’s Theory. 

Any metal in the coordinate compound has two valencies, according to this idea. Werner’s Theory and its many postulates, and its limitations, has been discussed in-depth in this article.