Q. 34.2( 5 Votes )
By crystal field
Crystal field splitting in octahedral coordination entities:
In octahedral coordination entities, there are six ligands surrounding the metal atom/ion. The d-orbitals get spilt into two sets- the t2g set and the eg set in crystal field splitting. The energy separation between the both is denoted
by o. The t2g orbitals are lower in energy, and eg orbitals are higher in energy. The assigning of the electron to the orbitals is done on the basis of o. and P(pairing energy).
Firstly. The electrons occupy t2g orbitals single. For the fourth electron, there can be two possibilities-
i. If o < P, the fourth electron enters one of the eg orbitals to give
t32g e1g configuration (This is the rule being followed in the above question)
ii. If o > P, the fourth electron enters one of the t2g orbitals to give t42g e0g configuration.
The orbital splitting energies are not enough to force pairing.
In the formation of the tetrahedral complex, the energy involved in the splitting of D - orbital is very small compared to the energy involved in octahedral splitting. Δt is very low. The orbital splitting energies are therefore not sufficient to force pairing. Hence low spin configurations are rarely observed in tetrahedral coordination entity formation
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