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CHM 302N
1. Solutions of the complexes [Co(NH3)6]2+, [Co(OH2)6]2+ (both Oh), and [CoCl4]2- are
coloured. One is pink, another is yellow, and the third is blue. Considering the spectrochemical
series and the relative magnitudes of ΔT and ΔO, assign each colour to one of the complexes.
2. The spectrum of d1 Ti3+(aq) is attributed to a single electronic transition eg ← t2g. The band
shown in Fig. 1 is not symmetrical and suggests that more than one state is involved. Suggest
how to explain this observation using the Jahn-Teller theorem.
Figure 1. The optical absorption spectrum of [Ti(OH2)6]3+.
3. Write the Russell-Saunders term symbols for states with the angular momentum quantum
numbers (L,S): (a) (0, 5/2 ), (b) (3,3/2),(c) (2,1/2), (d) (1,1).
4. The gas-phase ion V3+ has a 3F ground term. The 1D and 3P terms lie, respectively, 10 642
and 12 920 cm-1 above it. The energies of the terms are given in terms of Racah parameters as
E(3F) =A -8B, E(3P) =A+ 7B, E(1D) =A-3B+2C. Calculate the values of B and C for V3+.
5. Using the Tanabe-Sugano diagrams, estimate ΔO and B for (a) [Ni(OH2)6]2+ (absorptions at
8500, 15 400, and 26 000 cm-1) and (b) [Ni(NH3)6]2+ (absorptions at 10 750, 17 500, and 28
200 cm-1).
6. The spectrum of [Co(NH3)6]3+ has a very weak band in the red and two moderate intensity
bands in the visible to near-UV. How should these transitions be assigned?
7. Explain why [FeF6]3- is colourless whereas [CoF6]3- is coloured but exhibits only a single
band in the visible region of the spectrum.
8. The Racah parameter B is 460 cm-1 in [Co(CN)6]3- and 615 cm-1 in [Co(NH3)6]3+. Consider
the nature of bonding with the two ligands and explain the difference in nephelauxetic effect.
9. Solutions of [Cr(OH2)6]3+ ions are pale blue-green but the chromate ion, CrO42-, is an intense
yellow. Characterize the origins of the transitions and explain the relative intensities.
10. Classify the symmetry type of the d orbitals in a tetragonal C4v symmetry complex, such as
[CoCl(NH3)52+, where the Cl lies on the z-axis. (a) Which orbitals will be displaced from their
position in the octahedral molecular orbital diagram by π interactions with the lone pairs of the
Cl- ligand? (b) Which orbital will move because the Cl- ligand is not as strong a σ base as NH3?
(c) Sketch the qualitative molecular orbital diagram for the C4v complex.
Tanabe Sugano Diagram for d8 system