Octahedral complexes of copper(II) undergo structural distortion (Jahn-Teller). Which one of the given copper(II) complexes will show the maximum structural distortion?
(en – ethylenediamine;H2N−CH2−CH2−NH2)
(en – ethylenediamine;H2N−CH2−CH2−NH2)
[Cu(H2O)6]SO4
[Cu(en)(H2O)4]SO4
cis−[Cu(en)2Cl2]
trans−[Cu(en)2Cl2]
The Correct Option is D
Approach Solution - 1
The phenomenon of structural distortion in octahedral complexes, particularly in copper(II) complexes, is described by the Jahn-Teller effect. This effect occurs due to the presence of degenerate electronic states in a non-linear molecular system, leading to removal of degeneracy via geometric distortion.
In the case of copper(II) (Cu2+), which typically has an electronic configuration of [Ar] 3d9 4s0, the distortion usually occurs to relieve the degeneracy in the eg orbitals (dz2 and dx2-y2).
Let's analyze each option to determine which one will show the maximum structural distortion:
[Cu(H2O)6]SO4: Water is a weak field ligand. This complex will exhibit some distortion due to the Jahn-Teller effect, though typical distortion isn't as strong as in complexes with other ligands.
[Cu(en)(H2O)4]SO4: The ethylenediamine (en) is a bidentate ligand, which provides stronger ligand field stabilization compared to water. However, with only one bidentate and four water molecules, the symmetry is not significantly disrupted. Still, some distortion is present due to the weaker nature of the H2O ligands.
cis−[Cu(en)2Cl2]: In this complex, two ethylenediamine ligands bind at two different points, creating a chelate. This complex also has two chloride ions. The cis configuration allows some symmetry, but the Jahn-Teller distortion occurs to some extent, less pronounced.
trans−[Cu(en)2Cl2]: Here, the strong bidentate chelate en and two chloride ions create an octahedral structure. The trans configuration disrupts the symmetry more robustly than the cis arrangement. Due to the stronger unequal ligand distribution, this configuration exhibits a significant amount of Jahn-Teller distortion.
The trans−[Cu(en)2Cl2] complex experiences the maximum Jahn-Teller distortion due to the significant reduction in symmetry, two strong bidentate ligands, and optimal geometric arrangement of the ligands interacting with the d-orbital electrons primarily responsible for the Jahn-Teller effect.
Therefore, the correct answer is:
trans−[Cu(en)2Cl2]
This detailed analysis illustrates that the geometric configuration and ligand type considerably influence the structural properties of transition metal complexes, specifically the Jahn-Teller effect in octahedral complexes of copper(II).
Approach Solution -2
John teller distortion: Any non-linear compound remove its degeneracy to attain the stability.
Extent of John teller distortion depends upon metal ion as well as nature of ligand.
Stronger the ligand, more will be the John Teller distortion and more will be the stability.
Hence, Trans [Cu(en)2Cl2] will exhibit maximum John Teller distortion.
So, the correct option is (D): Trans - [Cu(en)2Cl2].
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Concepts Used:
Coordination Compounds
A coordination compound holds a central metal atom or ion surrounded by various oppositely charged ions or neutral molecules. These molecules or ions are re-bonded to the metal atom or ion by a coordinate bond.
Coordination entity:
A coordination entity composes of a central metal atom or ion bonded to a fixed number of ions or molecules.
Ligands:
A molecule, ion, or group which is bonded to the metal atom or ion in a complex or coordination compound by a coordinate bond is commonly called a ligand. It may be either neutral, positively, or negatively charged.