Question

The number of d-d transition(s) expected for the complex [Cu(NH3)2(H2O)]²⁺ is

• A. 1
• B. 2
• C. 3
• D. 4

Hint:

For a d⁹ configuration in a metal complex, only one d-d transition is possible due to the presence of one unpaired electron.

Answer 1

The Correct Option is C

The given question asks about the number of d-d transitions expected in the complex ion [Cu(NH₃)₂(H₂O)]²⁺.

1. The complex ion in question is [Cu(NH₃)₂(H₂O)]²⁺. Copper in this complex has an oxidation state of +2, which means the electronic configuration of Cu²⁺ is [Ar] 3d⁹.
2. The d-orbitals in Cu²⁺ experience splitting in an octahedral or distorted-tetrahedral field provided by the ligands NH₃ and H₂O. Although the complex has only three ligands, the structure is roughly distorted-tetrahedral due to coordination ability and electron count.
3. In an octahedral or tetrahedral field, the five degenerate d-orbitals split into two sets of orbitals at different energy levels. This splitting allows for the possibility of electronic transitions between these d-orbitals, known as d-d transitions.
4. For [Cu(NH₃)₂(H₂O)], having a 3d⁹ configuration, there is one unpaired electron in the d-orbital. This electron can transition among the partially filled d-orbitals.
5. The transitions depend on whether there are electrons available for excitation from one energy level to another. In many cases involving Cu²⁺, especially when low-symmetry fields are present such as in this distorted geometry, multiple transitions can occur.
6. Thus, due to the electronic configuration and the geometric arrangement of ligands, three possible d-d transitions are expected as a result of the multiple ways in which electrons can be excited within split d-orbital levels.

Based on the above reasoning, the correct answer is 3.