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A visible absorption spectrum of [ni(nh3)6]2+ has peaks at 365, 600 and 940 nm. Construct an Orgel diagram for nickel(ii) in an octahedral ligand field and use it to assign each observed peak to an electronic transition. b. Calculate the wavenumber of each absorption band and evaluate the crystal field splitting parameter,
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## Orgel Diagram and Electronic Transitions:
1. Orgel Diagram:
Nickel(II) has a d8 electron configuration. In an octahedral field, the d orbitals split into two sets: the lower energy t2g orbitals (dxy, dyz, dxz) and the higher energy eg orbitals (dz2, dx2-y2).
The Orgel diagram shows the possible electronic transitions between these orbitals. Since Ni(II) is d8, the ground state configuration is t2g6 eg2.
2. Electronic Transitions:
365 nm: This corresponds to the highest energy transition, likely from the t2g level to the eg level (t2g6 eg2 → t2g5 eg3). This is a spin-allowed transition.
600 nm: This is a lower energy transition, potentially from the t2g level to the eg level with a different spin state (t2g6 eg2 → t2g5 eg3). It could be a spin-forbidden transition but still observable due to spin-orbit coupling.
940 nm: This is the lowest energy transition, possibly involving a change in spin state, potentially a transition within the t2g level (t2g6 eg2 → t2g5 eg3). It's likely spin-forbidden but can occur due to spin-orbit coupling.
3. Crystal Field Splitting Parameter (Δo):
Calculate the wavenumbers:
365 nm = 27,397 cm-1
600 nm = 16,667 cm-1
940 nm = 10,638 cm-1
Assign Δo: The highest energy transition (365 nm) is likely the best representation of Δo (the crystal field splitting energy). So, Δo ≈ 27,397 cm-1.
Note: The exact nature of the transitions can be complex and further analysis like Tanabe-Sugano diagrams may be required to definitively assign each peak.
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