In 1893, Swiss chemist Alfred Werner put up a novel theory to describe the bonding and structure of coordination molecules. He received the 1913 Nobel Prize in Chemistry for his groundbreaking breakthrough. Prior to Werner’s research, scientists struggled to understand how metal ions formed complex compounds by bonding with other molecules. His idea established the groundwork for contemporary coordination chemistry and offered clarity.
What Are Coordination Compounds?
Coordination compounds in order to understand Werner’s Theory.
The components of a coordination complex are:
A central metal atom or ion, usually a transition metal.
• Ions or molecules that provide the metal two electrons are known as surrounding ligands.
For example:
In the compound
[Co(NH3)6]Cl3, cobalt (Co) is the central metal ion, and ammonia (NH₃) molecules are the ligands.
Werner’s Theory: The Key Points
Werner’s Theory proposed four main ideas:
1.Primary and Secondary Valencies
Werner distinguished between two types of valencies in coordination compounds:
Primary Valency: This write to the oxidation state (or charge) of the central metal ion. It is satisfied by negatively charged ions (anions) and is ionisable.
Example: In [CoCl3(NH3)3], cobalt has a primary valency of +3, satisfied by 3 chloride ions.
Secondary Valency: This communicate to the number of ligand molecules or ions directly bonded to the metal ion. It is non-ionisable and forms the coordination sphere.
In the same example, cobalt exhibits a secondary valency of 6, satisfied by 3 ammonia molecules and 3 chloride ions.
2. Coordination Number
The number of ligand donor atoms that are directly bound to the core metal ion is known as the coordination number. For a specific metal in a given complex, this value is fixed.
For cobalt in [Co(NH3)6]Cl3, the coordination number is 6.
For platinum in [PtCl4]2−, the coordination number is 4.
3. Spatial Arrangement of Ligands
According to Werner’s Theory, certain geometries result from the ligands occupying specified places around the core metal ion.
Coordination Number 6: Octahedral geometry (e.g., [Co(NH3)6]3+).
Coordination Number 4: Can be either tetrahedral or square planar.
Tetrahedral: [NiCl4]2−
Square planar: [Pt(NH3)2Cl2]
4. Formation of Coordination Compounds
Werner proposed that metal ions can form stable coordination compounds by simultaneously satisfying both kinds of valencies.
For example:
In [Co(NH3)6]Cl3, 3 chloride ions satisfy the primary valency, while 6 ammonia molecules satisfy the secondary valency.
The 3 chloride ions remain outside the coordination sphere and can be precipitated as AgCl when treated with silver nitrate.
Explaining Isomerism in Coordination Compounds
The existence of isomers in coordination compounds was also explained by Werner’s Theory. In coordination compounds, two significant forms of isomerism are:
Geometrical Isomerism: Occurs when ligands occupy different positions around the metal ion.
Example: [Pt(NH3)2Cl2] has cis and trans isomers.
Optical Isomerism: Occurs when a complex can exist in two non-superimposable mirror images (enantiomers).
Example: [Co(en)3]3+
Real-Life Applications of Werner’s Theory
Coordination compounds, however, are found everywhere.
Medicinal Chemistry: Cisplatin, a coordination molecule based on platinum, is used to treat cancer.
Biological Systems: Iron is at the core of hemoglobin, the molecule in blood that carries oxygen.
Industrial Catalysts: A variety of coordination compounds serve as industrial process catalysts.
Why Is Werner’s Theory Important?
Because it clarified the structures and bonding in complex compounds, laid the groundwork for understanding isomerism and contributing in the development of contemporary theories of chemical bonding and coordination chemistry.
Final Thoughts
In summary, the foundation of coordination chemistry is Werner’s Theory of Coordination Compounds. Werner’s study cleared the path for numerous subsequent discoveries by elucidating the process by which metal ions form bonds with ligands and forecasting the spatial arrangement of these ligands.
Alfred Werner put forth Werner’s Theory in 1893, which describes the bonding and structure of coordination molecules. To explain how ligands attach to a central metal ion and create a coordination sphere, it presents the ideas of primary valency (oxidation state) and secondary valency (coordination number).
The term “primary valency” describes the core metal ion’s oxidation state. Anions can satisfy it and it is ionisable.
The coordination number, or secondary valency, is the number of ligand molecules or ions that are directly bonded to the metal ion. It forms the coordination sphere and is not ionisable.For instance, in [Co(NH3)6]Cl3, the main valency is satisfied by three Cl⁻ ions, whereas the secondary valency is satisfied by six NH₃ molecules.
The number of ligand donor atoms that are joined to the central metal ion in a coordination complex is known as the coordination number. The amount of ligand molecules or ions that are directly bound to the metal ion is counted to ascertain it.For example, in
[Co(NH3)6]3+, the coordination number is 6, while in [PtCl4]2−, the coordination number is 4.
The geometry of a coordination compound depends on the coordination number:
Coordination Number 6: Octahedral geometry (e.g., [Co(NH3)6]3+)
Coordination Number 4:
Tetrahedral geometry (e.g., [NiCl4]2−)
Square planar geometry (e.g., [Pt(NH3)2Cl2])
Werner’s Theory explains two major types of isomerism in coordination compounds:
Geometrical Isomerism: Occurs when ligands occupy different spatial positions around the metal ion (e.g., cis and trans isomers of [Pt(NH3)2Cl2]).
Optical Isomerism: Occurs when a compound exists in two non-superimposable mirror image forms (enantiomers), such as in [Co(en)3]3+.
Werner’s Theory is significant because:
It provided the first correct description of coordination compounds.
It explained the bonding and structure of metal complexes.
It laid the groundwork for modern theories like valence bond theory (VBT) and crystal field theory (CFT), which describe the behaviour of coordination compounds in greater detail.
Yes, There are numerous practical uses for coordination compounds:
Cisplatin: A coordination chemical based on platinum that is used to treat cancer.
Hemoglobin: An iron-based coordination complex that carries oxygen in blood.