Question

In the formation of octahedral complex ligands approach towards ___ and ___ orbital of central metal.
(A) ${d_z}^2,d_{x^2-y^2}$
(B) $d_{x^2-y^2},d_{xy}$
(C) $d_{xy},d_{yz}$
(D) $d_{z^2},d_{xz}$

Answer 1

Hint: One needs to know the shapes of different d-orbitals in order to know which orbitals are approached at the time of formation of the octahedral complex. The shape of an octahedral complex is as below where black dots represent ligands.

Complete step by step answer:
- Generally, as we know ligands are negatively charged, neutral or in less occurrence cases positively charged as well. Regardless to all these changes, all ligands have high electron density.
- According to the Aufbau principle, Electrons are filled from lower to higher energy orbitals. For an octahedral case, this tends to be $d_{xy},d_{yz},d_{xz}$.
Let us understand the basic concept of crystal field theory.
In simple words, it describes the breaking of orbital degeneracy in transition metal complexes due to the presence of ligands. This theory describes the strength of the metal ligand bonds, because the strength of the system is altered based on the metal ligand bond.
- Whenever ligands approach the central metal, they always tend to approach in such a way that the repulsion among them is the lowest. Generally a molecule with octahedral geometry approaches the metal ion along the x, y and z axes. Due to which the electrons in the $d_{z^2}$ and $d_{x^2-y^2}$ orbitals experience greater repulsion. Therefore, generally it requires more energy to have an electron in these orbitals. This causes a splitting in the energy levels of the d orbital.
- For octahedral complexes, the crystal field splitting is denoted by ${\mathrm{\Delta }}_0$ .
- The energies of the $d_{z^2}$ and $d_{x^2-y^2}$ orbitals increases due to greater interactions with the ligands.
- The energies of $d_{xy},d_{yz},d_{xz}$ orbitals decrease with respect to the normal energy level and become more stable.
Hence, in the formation of octahedral complex ligands approach towards $d_{z^2}$ and $d_{x^2-y^2}$ orbital of central metal.

- So, option (A) is the required answer.



Note: Remember that ligands that cause a metal to have small crystal field splitting, which leads to high spin are called weak-field ligands and ligands that produce large crystal field splitting, which leads to low spin are called strong field ligands.