Sum of oxidation state (magnitude) and coordination number of cobalt in \(Na[Co(bpy)Cl_4]\) is____ .
(Given : bpy =
)
(Given : bpy =
)
Correct Answer: 9
Approach Solution - 1
To determine the sum of the oxidation state (magnitude) and coordination number of cobalt in \( Na[Co(bpy)Cl_4] \), follow these steps:
- Identify the Ligands: In the complex \( Na[Co(bpy)Cl_4] \), the ligands are bipyridine (bpy) and chloride ions (Cl-).
- Oxidation State Calculation:
- Sodium (Na) has an oxidation state of +1.
- Bipyridine (bpy) is a neutral ligand, contributing 0 to the oxidation state.
- Chloride ions (Cl-) have an oxidation state of -1. There are four chloride ions contributing a total of -4.
- Let the oxidation state of cobalt (Co) be x. The sum of the oxidation states equals 0:
\[+1 + x + 0 + (-4) = 0\]
Simplifying, we get: \(x - 3 = 0\).
Therefore, \(x = +3\).
- Coordination Number: The coordination number of cobalt is determined by the number of ligand donor atoms bonded to it.
- Each bipyridine ligand binds through two nitrogen atoms, contributing 2 to the coordination number.
- Each chloride ion (Cl) contributes 1 to the coordination number. With four chloride ions, this adds up to 4.
- Thus, the total coordination number is \(2 + 4 = 6\).
- Sum Calculation:
The sum of the oxidation state magnitude (3) and coordination number (6) is:
\[3 + 6 = 9\]
- Verification: The calculated value (9) falls within the provided range (9, 9).
Therefore, the answer is 9.
Approach Solution -2
\(Na [Co(bpy)Cl_4]\)
Oxidation state of cobalt = \(+ 3\)
Coordination number of cobalt = \(6\)
[As bpy is bidentate]
So, sum = \(9\)
Therefore, the answer is \(9\).
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Concepts Used:
Werner’s Theory of Coordination Compounds
In 1893 Werner produced a theory to explain the structures, formation and nature of bonding in the coordination compounds. This theory is known as Werner’s theory of coordination compounds.
Postulates of Werner's Theory:
The important postulates as observed by Alfred Werner throughout his experiments are as follows:
- The complex/ coordination compounds contain a central metal atom.
- The metal atoms in a coordination compound generally show two types of valency: primary valency and secondary valency.
- The primary valencies denote the oxidation state. They are ionizable and are satisfied by the negative ions.
- Secondary valencies denote the coordination number. They are non-ionizable and are fixed for every metal atom. The secondary valency is generally satisfied by the neutral molecules or negative ions.
- The metal atoms should satisfy both primary and secondary valencies.
- The secondary valency of the atom basically shows the geometry/ polyhedra of the particular coordination compound.
Limitations of Werner’s Theory:
- Though Werner explained some properties of the coordination compound, he failed to explain the colour of the coordinate compound.
- He could not explain the magnetic and optical properties of coordination compounds.
- He could not answer the question, why does the coordination sphere have a definite geometry.