Question:

The octahedral complex of a metal ion $M^{3+} $ with four monodentate ligands $L_1,L_2,L_3 \, and \, L_4 $ absorb wavelengths in the region of red, green, yellow and blue, respectively. The increasing order of ligand strength of the four ligands is

Updated On: Jun 29, 2024
  • $L_4 < L_3, L_2 < L_1 $
  • $L_1 < L_3 < L_2 < L_4 $
  • $L_3 < L_2 < L_4 < L_1 $
  • $L_1 < L_2 < L_4 < L_3 $
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The Correct Option is B

Solution and Explanation




The energy of red light is less than that of violet light

So energy order is

Red $
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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.