Frequently Asked Question

The visible absorption spectrum of [Ni(NH3)6]2+ exhibits three peaks, indicating electronic transitions within the d-orbitals of the nickel(II) ion. Here's how we can analyze this using an Orgel diagram:
1. Nickel(II) Electronic Configuration: Ni2+ has a d8 configuration ([Ar] 3d8). In an octahedral field, the d-orbitals split into two sets: the lower energy t2g set (dxy, dyz, dxz) and the higher energy eg set (dz2, dx2-y2).
2. Orgel Diagram: An Orgel diagram is a simplified energy level diagram for d-orbitals in a specific ligand field. It helps visualize possible electronic transitions. For octahedral Ni2+ (d8), the Orgel diagram shows:

Two electrons in the eg set (higher energy).

Six electrons in the t2g set (lower energy).
3. Electronic Transitions: The observed absorption peaks correspond to electronic transitions from the lower energy t2g orbitals to the higher energy eg orbitals.

365 nm: This high-energy transition likely corresponds to a 3T1g(F) → 3T1g(P) transition, a spin-allowed transition involving a change in both spin multiplicity and orbital angular momentum.

600 nm: This transition likely corresponds to a 3A2g(F) → 3T1g(F) transition, a spin-allowed transition involving a change in orbital angular momentum but not in spin multiplicity.

940 nm: This lowest energy transition likely corresponds to a 3A2g(F) → 3T2g(F) transition, a spin-allowed transition involving a change in orbital angular momentum but not in spin multiplicity.
The exact assignment of peaks can be further confirmed by analyzing the intensity and shape of the absorption bands, as well as comparing the experimental spectrum to theoretical calculations.