CHE204 Intermediate Inorganic Chemistry
Coursework 2
(Due on Thursday, April 28th 10 am)
Note:
1. Group discussion is allowed but plagiarism is strictly forbidden.
2. Your answer should be handwritten, not typed.
Crystal Field Theory
1. The solid state structure of crystalline MF2 is shown in the figure below. The variation in lattice energies for MF2 given in the table below.
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Complexes
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ZnF2
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NiF2
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CoF2
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FeF2
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MnF2
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Lattice
energies
(kJ/mol)
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2985
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3060
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2976
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2926
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2780
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a) Plot the trend of lattice energies for MF2. Label the axes of the plot clearly. (Note:
Microsoft Excel or other data processing software are acceptable for the plot.) (6 marks)
b) Describe and interpret the variation you observed.(5 marks)
2. Based on the experimental magnetic moments, predict the value of n in the following transition metal complexes. Write the d-electron configurations for their transition metal centers, respectively. Show your work.
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Transition metal complexes
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[MnCl4]n─
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[Cr(H2O)6]n+
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[Fe(CN)6]n─
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Magnetic moment µs/µB
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5.92
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3.83
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2.83
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(9 marks)
3. Account for the colors and intensities of the following groups of complexes ions in aqueous solution. Briefly explain your reasoning.
a) [Cr(H2O)6]2+ (blue) vs [Cr(H2O)6]3+ (violet)
b) [CoCl4]2– (blue) vs [Co(H2O)6]2+ (light pink)
c)
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Complexes
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[Mn(H2O)6]2+
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KMnO4
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Molar absorption coefficient, ε / dm3 mol–1 cm–1
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~1
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100~105
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(14 marks)
4. A spinel is a metal oxide with a general formula of AB2O4. The two metal ions occupy one tetrahedral and two octahedral sites. If the octahedral sites are occupied by M(II) ions, it is known as a normal spinel. If one of the octahedral sites is occupied by an M(II) ions, it is known as an inverse spinel.
a) For NiFe2O4, list all possible chemical formulae with oxidation states of Ni and Fe for normal and inverse spinel structures, respectively (5 marks)
b) If the oxidation state ofFe is +3, would you predict that NiFe2O4 would adopt a normal spinel or an inverse spinel structure? Explain your reasoning on the basis of the calculated crystal field stabilization energy (CFSE).
(Assumptions are: Δt = 4/9Δo; (Δo)Fe = (Δo)Ni; (Δo)2+ =(Δo)3+ ; and both iron and nickel oxides are high-spin cases.) (10 marks)
Ligand Substitution Reactions
5. For solvent exchange reaction of metal ions:
[M(H2O)n]Z+ + n H2O* [M(H2O)n]Z+ + n H2O
a) Outline the effects of the charge (Z) and the radius (r) of the metal ion MZ+ and CFSE on the rates ofthe reactions. (6 marks)
b) Arrange the following complexes in increasing order of the substitution rates by H2O. Justify your answer.
[Mn(H2O)6]2+ [Cu(H2O)6]2+ [Co(NH3)6]3+ [Rh(NH3)6]3+ [Ir(NH3)6]3+
(8 marks)
6. For a ligand substitution reaction,
a) What is meant by ΔV‡ and ΔS‡? Explain in general terms how these parameters are measured. (4 marks)
b) The ligand exchange reaction of [Pt(MeCN)4]2+ with free MeCN has been studied. The value of ΔS‡ was –88 J K-1 mol-1 and ΔV‡ was –4 cm3 mol-1. What does this suggest about the mechanism. Explain your reasons in detail. (4 marks)
c) Second order rate constants, k2, for the reaction of trans-[Pt(PEt3)2Ph(MeOH)]+ with pyridine (py) in MeOH to give trans-[Pt(PEt3)2Ph(py)]+ vary with temperature as shown below. Use the data to determine the activation enthalpy and activation entropy for the reaction. (10 marks)
d) Given the reactants PPh3, NH3, and [PtCl4]2- , propose efficient routes to both cis- and trans- [PtCl2(NH3)(PPh3)] (8 marks)
Descriptive Transition Metal Chemistry
7. For the following statements of transition metal chemistry, which is(are) NOT true. Give your reasons.
a) Transition metals have high melting points in their elemental form.
b) Transition metals can have multiple oxidation states.
c) Transition metals are poor conductors of electricity.
d) Transition metals are large in atomic volumes and therefore not very dense. (5 marks)
8. Answer the following questions,
a) Completed separation of tungsten from molybdenum in the ores is much more difficult than the separation of chromium from tungsten. Why?
b) The oxidation state of +8 is very rare but does exist in Ru and Os. Identify the metal complexes with +8 oxidation states and comment on the observation. (6 marks)