What is the electronic configuration of the Ti3+ ion? Explain why the electronic absorption spectrum of [Ti(OH2)6]3+ consists of an absorption with a shoulder rather than a single absorption.
The Correct Answer and Explanation is:
Correct Answer:
- The electronic configuration of the Ti³⁺ ion is [Ar] 3d¹.
- The electronic absorption spectrum of [Ti(H₂O)₆]³⁺ shows an absorption with a shoulder rather than a single absorption because of ligand field splitting and vibronic coupling in the octahedral complex.
Explanation
Titanium in its ground state has an atomic number of 22, with an electronic configuration of [Ar] 4s² 3d². When it loses three electrons to become Ti³⁺, two electrons are removed from the 4s orbital and one from the 3d orbital, resulting in the configuration [Ar] 3d¹. This means the Ti³⁺ ion has one electron in the 3d orbital.
In the complex ion [Ti(H₂O)₆]³⁺, the Ti³⁺ ion is surrounded by six water molecules, forming an octahedral geometry. In an octahedral field, the five degenerate 3d orbitals split into two energy levels: the lower energy t₂g orbitals (dxy, dxz, dyz) and the higher energy eₙ orbitals (dx²−y², dz²).
Since Ti³⁺ has only one 3d electron, this electron occupies a t₂g orbital. The absorption of light promotes this electron from a t₂g to an eₙ orbital. This type of electronic transition is known as a d-d transition.
The absorption spectrum of [Ti(H₂O)₆]³⁺ is not sharp because of several factors:
- Vibronic coupling: The electronic transition occurs simultaneously with vibrational transitions of the complex. This interaction produces a band rather than a single line.
- Jahn-Teller distortion: Although weak for d¹ systems, slight distortions from perfect octahedral symmetry may cause a splitting of the eₙ or t₂g levels, leading to an absorption peak with a shoulder.
Therefore, instead of one sharp absorption, the complex shows a broadened peak with a shoulder, reflecting the complex electronic and vibrational interactions within the coordination compound.
