Three electronic transitions at 14900, 22700
and 34400 cm-l are observed in the absorption
spectrum of [CrF6]3-. The Ao value (in cm-)
and the corresponding transition are -
(A) 7800 and 4A2g
(B) 14900 and 4A2g → 4T2g
(C) 14900 and 4T2g → 4Tig
(D) 7800 and 4T29
4T1g (F)
4T 28
Answers
Explanation:
Calculation of Δo: In the UV-visible spectra of [Cu(H2O)6]2+, the broad band at 12000 cm−1 is due to spin- allowed 2Eg → 2T2g transition; and hence, 10 Dq for this complex is 12000 cm−1. d2-configuration can be used to estimate the value of crystal field splitting energy for these transition metal complexes.

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Answer:
The energy levels of high spin octahedral and tetrahedral transition metal ions can be shown using orgel diagrams. They ONLY display the transitions that are spin allowed.
Explanation:
Energy can be expressed in wavenumber as follows below:
E = hv
From the above expression, we came to know that energy is directly proportional to the wavenumber. So, as the wavenumber increases, the energy of that transition will also increase.
The Δ₀ or 10Dq is the value of the first transition.
In the given chromium complex, chromium is in the +3 oxidation state, so its electronic configuration is 3d³ 4s⁰. It is a d³ system.
So, its ground state, from where the transition occurs, is ⁴A₂g.
The first transition [CrF₆]³⁻ occurs from ⁴A₂g to ⁴T₂g. The wavenumber for this transition is 14900 cm⁻¹. The energy difference for this transition is the least, so its wave number is also smaller one.
Thus, Δ₀ or 10Dq value and the corresponding transition is 14900 cm⁻¹ and ⁴A₂g → ⁴T₂g.
The correct option is (B) 14900 and ⁴A₂g → ⁴T₂g.
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