Introduction

In this perticular article we are going to discuss about Inner and outer orbital Octahedral complexes. We will also going to understand the concept of octahedral complexes and their inner and outer orbital complexes in detail.

Octahedral complexes- 

(A) Inner orbital complexes :

let us discuss inner orbital complexing taking some example:

1. {CO(CN)₆}³⁻ ion :

 In this complexes , oxidation state of Cobalt is +3. The velence shell electronic configuration of CO³⁺ is 3d⁶ magnetic measurements indicate that {CO(CN)₆}³⁻ is diamagnetic . All six 3d electrons are therefore paired and occupy three of the five 3d- orbitals. The CN⁻ ligands are strong and therefore cause pairing of 3d electron. The vacant two 3d-orbitals combine with the vacant 4s and 4p orbitals to form six d²sp³ hybrid orbitals. These six hybrid orbitals overlap with six filled orbitals of ligands, one on each of the ligands and thus six coordinate covalent bonds are formed.

2. {CO(NO₂)₆}⁴⁻ ion :

In this complex ion, oxidation state of Cobalt is +2 and its velence shell electronic configuration is 3d⁷. Magnetic measurements indicate that this complex ion is paramagnetic corresponding to presence of one unpaired electron. The NO⁻₂ ligands are strong, they therefore, cause pairing of metal 3d-electrons. Pauling suggested that two vacant 3d- orbital are made available by promotion of an unpaired electron from a 3d-orbitals to 5s orbital so that CO²⁺ion gets d²sp³ hybridized.

The presence of an unpaired electron in 5s orbital is supported by the fact that, 5s-orbital has very high energy and Hence the electron present in it is loosely bound and can be removed easily. Experimentally it is also observed that {CO(NO₂)₆}⁴⁻ is oxidised by air or H₂O₂ easily to give {CO(NO₂)₆}³⁻. This indicates that the complex {CO(NO₂)₆}⁴⁻ is unstable in air. Thus this complex should be prepaired in inert atmosphere.

3.{Mn(CN)₆}³⁻ ion :

In this complex ion, oxidation states of Mn is +3 and its velence shell electronic configuration is 3d⁴. Magnetic measurements show that this complex ion is paramagnetic corresponding to two unpaired electrons. Hence All the four electrons occupy just three of the five 3d-orbitals leaving  two 3d-orbitals vacant. These two vacant 3d-orbitals combine  with the vacant 4s and 4p. Orbital to give six d²sp³ – hybrid orbitals. These hybrid orbitals form bonds with ligands by accepting six pairs of electrons, one pair from each of the six ligands. Since CN⁻ is a strong ligands and has a tendency to pair up the d-electrons on metal but it causes pairing of two electrons only leaving two electrons as unpaired. If all the electrons become paired, then it will violet the Hund’s rule of maximum multiplicity.

4.{Cr(CN)₆}³⁻ ion 

In this complex ion, oxidation state of Cr is +3 and its velence shell electronic configuration is 3d³. Magnetic measurements show that this complex ion is paramagnetic corresponding to the presence of three unpaired electrons. All the three 3d- electrons occupy just three of the five 3d-orbitals as vacant. These two vacant orbitals combine with the vacant 4s and 4p-orbitals to give six d²sp³ hybrid orbitals. These six hybrid orbitals form bonds with ligands by accepting six lone pair of ligands, one pair from each of the six ligands. The three orbitals of the metal cation have three unpaired electrons and are degenerate. Thus even in the presence of strong ligands pairing will not occur. If pairing of electrons occur, then it will violet Hund’s rule of maximum multiplicity.

5.{V (NH₃)₆}³⁺ ion :

In this complex ion, oxidation state of vanadium is +3 and its velence shell electronic configuration is 3d². And Magnetic measurements indicate that this complex ion is paramagnetic corresponding to two unpaired electrons. All the two 3d-electrons occupy just two of the five 3d-orbitals leaving three 3d-orbitals vacant two of which combine with the vacant 4s and 4p orbitals to give six d²sp³-hybrid orbitals. The d²sp³- hybrid orbitals form bonds with the ligands accepting six pairs of electrons. One pair from each of the six ligands. Out of three 3d-unhyroidized orbitals, two orbitals have two unpaired electrons one unpaired electron in each and one orbitals remains vacant. These three unhybridized 3d-orbitals are degenerate. Consequently even in the presence of strong ligands pairing of electrons will not occur. If pairing of electrons occurs, then it will violet Hund’s rule of maximum multiplicity.

(B) Outer orbital octahedral complexes

In outer orbital complexes the central metal cation is sp³d² hybridized. In sp³d² hybridization, d-orbitals of outer shell (i.e., nd-orbitals) are involved. Let us discuss the Complexes by taking some examples-

1. [CoF₆]³⁻ Ion :- In this complex ion, oxidation state of Cobalt is +3 and its velence shell electronic configuration is 3d⁶. Magnetic moment measurements show that this complex is paramagnetic corresponding to four unpaired electrons. Also, F⁻ is the weak ligand, there will be no, pairing of 3d-electrons of the metal cation. Thus there is no vacant 3d orbital and none of 3-orbitals is available to accept electron pairs from the ligands. Consequently the vacant 4s, 4p and two of the five 4d-orbitals combine to give six sp³d² hybridization. These hybrid orbitals form bonds by accepting six pairs of electrons, one pair from each of the six ligands.

Inner and outer orbital Octahedral complexes

 

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