Why t2g level energy is lower as compare to eg in octahedral complexes?

All Answers (9) Show full discussion

• 
  Ganesh Hegde · Karnatak University, Dharwad

  eg orbitals in octahedral field directly face the ligands, hence due to strong repulsion between ligand field and electrons in these orbitals raises its energy. Where as t2g orbitals are not directed towards ligand field hence though the energy increases from the earlier degenerate level, it will be less than the eg level.

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  eg orbitals in octahedral field directly face the ligands, hence due to strong repulsion between ligand field and electrons in these orbitals raises its energy. Where as t2g orbitals are not directed towards ligand field hence though the energy increases from the earlier degenerate level, it will be less than the eg level.

  Oct 30, 2011
• 
  Vivek Kumar

  Thanks sir

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  Thanks sir

  Oct 31, 2011
• 
  Mkm Nair Nair · Maharaja's College

  Eg orbitals are axial and the ligands are approaching the metal ion axially in an octahedral complex. T2g orbitals are arranged in between axes and affected less. So more affected eg is raised in energy and t2g is lowered in energy to keep conservation of energy principle.

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  Eg orbitals are axial and the ligands are approaching the metal ion axially in an octahedral complex. T2g orbitals are arranged in between axes and affected less. So more affected eg is raised in energy and t2g is lowered in energy to keep conservation of energy principle.

  Nov 29, 2011
• 
  Ali Sudais jan · Middle East Technical University

  The first and third answers are the best and there is no space for any reply now..

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  The first and third answers are the best and there is no space for any reply now..

  Mar 15, 2012
• 
  Asit R Sarkar · University of Kalyani

  I would like to add something more. In an octahedral complex, six donors from six ligands, each with a pair of electron will form six sigma bonds with the central metal ion/atom. We can consider that the donors approach along the Cartesian coordinates (x,y and z axes), the direction of the metal sigma vacant orbitals (eg), the metal being at the origin. Since, t2g orbitals lie in between the Cartesian axes, the inter-electronic repulsion will be less compared to eg orbital, which lies along the axes. Hence, t2g orbital will be of lower energy compared to eg orbital for octahedral complexes. I will be happy to give further clarification, if needed.

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  I would like to add something more. In an octahedral complex, six donors from six ligands, each with a pair of electron will form six sigma bonds with the central metal ion/atom. We can consider that the donors approach along the Cartesian coordinates (x,y and z axes), the direction of the metal sigma vacant orbitals (eg), the metal being at the origin. Since, t2g orbitals lie in between the Cartesian axes, the inter-electronic repulsion will be less compared to eg orbital, which lies along the axes. Hence, t2g orbital will be of lower energy compared to eg orbital for octahedral complexes. I will be happy to give further clarification, if needed.

  Apr 4, 2012
• 
  Ali Sudais jan · Middle East Technical University

  nice answer Sir Asit R Sarkar

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  nice answer Sir Asit R Sarkar

  Jun 12, 2012
• 
  Richard Norman · Sam Houston State University

  Most of the answers thus far (with the exception of Asit Sarkar) have focused on essentially a crystal field approach to bonding in octahedral metal complexes. In a spherical environment, the d orbitals are degenerate (they have the same energy). When an octahedral arrangement of ligands is present, the orbitals separate into two symmetrically different groups--the eg and t2g groups. The eg group has the proper symmetry to interact with the ligand orbitals, and you get a bonding and an antibonding interaction. The bonding interaction results in the lower energy orbitals (essentially the ligand orbitals) being stabilized (moving to still lower energy), and the higher energy orbitals (essentially the metal orbitals) begin destabilized (moving to still higher energy). The lower energy orbitals are sigma bonding and the higher energy orbitals are sigma antibonding orbitals. This results in the eg metal orbitals moving above the t2g orbitals. The t2g orbitals are the incorrect symmetry to participate in sigma interactions with the ligands. However, they are the correct symmetry to participate in pi interactions with the ligands. Since pi interactions in metal complexes are weaker than sigma interactions, in a simple metal complex in an octahedral environment, the eg level of the metal atom will always be higher than the t2g level.

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  Most of the answers thus far (with the exception of Asit Sarkar) have focused on essentially a crystal field approach to bonding in octahedral metal complexes. In a spherical environment, the d orbitals are degenerate (they have the same energy). When an octahedral arrangement of ligands is present, the orbitals separate into two symmetrically different groups--the eg and t2g groups. The eg group has the proper symmetry to interact with the ligand orbitals, and you get a bonding and an antibonding interaction. The bonding interaction results in the lower energy orbitals (essentially the ligand orbitals) being stabilized (moving to still lower energy), and the higher energy orbitals (essentially the metal orbitals) begin destabilized (moving to still higher energy). The lower energy orbitals are sigma bonding and the higher energy orbitals are sigma antibonding orbitals. This results in the eg metal orbitals moving above the t2g orbitals. The t2g orbitals are the incorrect symmetry to participate in sigma interactions with the ligands. However, they are the correct symmetry to participate in pi interactions with the ligands. Since pi interactions in metal complexes are weaker than sigma interactions, in a simple metal complex in an octahedral environment, the eg level of the metal atom will always be higher than the t2g level.

  Jun 14, 2012
• 
  Patel Ketan ·

  all the ans.are appropriate on its own places. high school>graduate> Post graduate level .

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  all the ans.are appropriate on its own places. high school>graduate> Post graduate level .

  Jun 25, 2012
• 
  Sanjay Gaikwad · BJS Chemistry

  The lobes of eg are along the x,y,z,-x,-y and -z axis while the lobes of t2g are in between the axis. the approach of six ligand along the axis direction, hence it increases the energy therefore t2g level is lower than that of eg in octahedral complex.

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  The lobes of eg are along the x,y,z,-x,-y and -z axis while the lobes of t2g are in between the axis. the approach of six ligand along the axis direction, hence it increases the energy therefore t2g level is lower than that of eg in octahedral complex.

  Jun 26, 2012