C21J Tutorial Papers

Aspects of Crystal Field Theory

• 1) Give the electronic configuration for the following metal ions in:
  i) Octahedral (high spin)
  ii) Tetrahedral crystal fields
  
  Ti(III), Cu(II), Ni(II), Fe(III), Co(III), Cr(III), V(II), Mn(III), Fe(II), Co(II).

• 2) Calculate the crystal field stabilisation energies associated with the following metal ions in both octahedral and tetrahedral crystal fields. Cu(II), Fe(III), Co(II), Co(III), Cr(III), Mn(III).

• 3) Draw a graph of the Octahedral Site Preference Energies for high spin d⁵-d¹⁰ electron configurations.
• 4) Write the electronic configuration of Cu(I), Cr(II), Ti(III), Mn(II), Ni(III) and Co(II).
• 5) What is the Irving-Williams series and how can it be rationalised in terms of Crystal Field Theory.
• 6) What is the Jahn-Teller theorem and what are Jahn-Teller distortions?
• 7) Write the electronic configurations for those ions expected to show Jahn-Teller distortions.
• 8) Briefly explain why Fe₃O₄ adopts the inverse spinel structure, while Mn₃O₄ is normal.
  What structures would you expect for FeCr₂O₄ and Co₃O₄ ?

Russell-Saunders and Spectroscopy and Magnetism

• 1) What are the ground state terms of the following ions? a) Ti(II) b) Cr(V) c) Mn(II) d) Fe(II) e) Co(II)
• 2) Determine the ground state terms for the following configurations d³, d⁶, d⁵
• 3) Calculate the energy gap between two bands observed at:
  i) 600nm and 500nm
  ii) 500nm and 400nm.
• 4) The absorbance of a 0.1 M aqueous solution of [Ti(H₂O)₆]³⁺ was found to be 0.56 when measured in a 1 cm cuvette. A distorted absorption band was centered at 20,300 cm^-1. Account for the spectrum and calculate the molar absorbance (ε). What would be the absorbance of the same solution in a 2 cm cuvette?
• 5) The electronic absorption spectrum of [Ni(H₂O)₆]²⁺ shows three bands at 8,500, 13,800 and 25,300 cm^-1. Account for these bands using an Orgel diagram.
• 6) Assign the frequencies given below to appropriate d-d transitions. Calculate Δ (10Dq) for each case.

      Ion           ν1        ν2        ν3
    [Cr(H2O)6]2+    14,000
    [V(H2O)6]3+     17,800      25,700
    [V(H2O)6]2+     12,350      18,500      27,900 cm-1
  

• 7) Comment on the observation that MnSO₄. 7H₂O is of a very pale pink colour.
• 8) To what does the Racah parameter B refer and what factors determine its magnitude?
• 9) Give the relevant selection rules for electronic transitions in high spin first row transition metal complexes. What factors can lead to their violation?
• 10) What is the difference between the spectrochemical series and the nephelauxetic series? How were these series established and how do they suggest that there are deficiencies in Crystal Field Theory?
• 11) How does spin orbit coupling affect: i) the magnetic moments of complexes with A or E ground states. ii) the magnetic moments of complexes with T ground states?
• 12) Interpret the following room temperature (300K) magnetic moments. Predict the values at 80K.

    i) Fe(acac)3 5.92 BM     ii) Mn(acac)3  4.86 BM iii)  BaMnF6  3.80 BM
    iv) Cs2CoCl4 4.71BM v) K2Cu(SO4)2.6H2O 1.91 BM vi) [Cr(en)3]I3.H2O  3.93 BM 
    vii) VCl4  1.69 BM   viii) [V(bipy)3]Cl2 3.67 BM
    ix) [Ni(NH3)6]Cl2  3.11 BM x)  [Cu(NH3)4](NO3)2  1.89 BM
  

Descriptive Chemistry of the First Row TM ions and complexes

• 1) Arrange the first row transition metal elements in order of increasing abundance in the Earth's crust.
• 2) Describe the extraction of Ti, Fe, Ni and Cu.
• 3) Discuss the structure of VF₅ in the solid, liquid and gas phases.
• 4) Give the structure and method of preparation of basic manganese(III) acetate.
• 5) How is cobalt(III) fluoride prepared? Account for the lack of all other Co(III) halides.
• 6) Why is it difficult to obtain Cu(I) species in aqueous solution?
• 7) What happens when:
  a) solid potassium manganate(VII) is added to conc. HCl?
  b) potassium manganate(VII) is used as an oxidant under strongly alkaline conditions?
• 8) Many compounds of the type MX₂ (where X=F,Cl,Br,I) adopt structures that can be described as: rutile, CdCl₂ or CdI₂. Describe these three structures, giving examples of first row transition metal halides that adopt them.

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