Inner orbital octahedral complex

Let’s discuss inner orbital complexing taking an example, [Co(CN)6]3-  ion

  • In this complex oxidation state of cobalt is +3

             Valence shell electronic configuration is

  • Magnetic moment measurement indicates that  [Co(CN)6]3-C ion is diamagnetic(given). So that all the d-electrons arranged in such a way, that no unpaired electron is left in the d-orbital. 
  • In other words as CN  ion is a strong ligand, it causes the pairing of 3d-electrons.


  •  Here two vacant 3d-orbital combine with the vacant 4s and 4p orbital to form six  d2sp3

     hybrid orbital. 

  • Then six hybrid orbital overlap with six filled orbital of  CN ligand, one on each of the ligand and thus six coordinate covalent bonds are formed which gives d2sp3  hybridization.
  • As inner d-orbitals are involved in hybridization, it gives inner orbital octahedral geometry.

Test your understanding:

    Explain hybridisation in, 
     [Co(NO2)6]4-   (one unpaired electron) 
     [Mn(CN)6]3-    (two unpaired electron)
     [Cr(CN)6]3-C   (paramagnetic corresponding to three unpaired electron)

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