Concordia
U n i v e r s i t y

Course: CHEMISTRY Number: 341/2 Section: X
Instructor: P.H. Bird
Examination: Final Date: 11th December, 2001 Time: 14:00-17:00 pm # of pages: 12
Materials Allowed: Data sheets attached to this paper - no other materials are allowed.

Calculators Allowed: Yes

The data sheets attached consisted of:
  • Tables of "f" and "g" factors used to calculate an approximate Do.
  • A table and diagrams showing how atomic terms (states) split in a weak octahedral field.
  • A table of free-ion B values.
  • Tanabe-Sugano diagrams for configurations d2 to d8. A periodic table.
Special Instructions: Please attempt all questions: theyu carry equal marks. Write your answers in the spaces provided on this paper. Be sure to give adequate explanations for your answers. Use the back of the pages for rough work and, if necessary, for extra space. If you continue an answer on the back of a page, please indicate this clearly.

Name: _________________________________________________________

Student Number: _________________________________________________




Please leave blank

1 2 3 4 5 6
           




  1. Fill in the following table.
Name Formula Config* Stucture**
cis-diaquadichloroplatinum(II) cis-[Pt(H2O)2Cl2] d8
diamminetetra(thiocyanato)chromate(III)      





hexaaquoiron(III) nitrate      





trans-dichlorobis(ethylenediamine)cobalt(III)      





m-hydroxobis(pentamminechromium(III)

(m means bridging)
     





* Give the configuration in the form dn. ** Sketch a structural diagram.
  1. Draw the possible isomers of the following, (including optical isomers if appropriate):

    1. [RuCl2(NH3)4]

    2. [IrH(CO)(PPh3)2]

    3. [CoBr3(OH2)]-

    4. [IrCl3(PEt3)3]

    5. [CoCl2(ox)(NH3)2]-
      Do not forget ox2- is a bidentate ligand.
      Show its full structure somewhere in your answer.

    1. Draw labelled diagrams showing th way the orbitals are split in octahedra, tetrahedral and square-planar ligand fields.

      To get full marks:

      • You need to show the energy levels (relative to the barycentre for Oh and Td).
      • You need to label levels with the orbitals names and the symmetry designations.
      • You need to show the stabilization/destabilization in units of D for Oh and Td, and the size of the highest gap in D4h.
    2. Fill in the blanks in the following table:

Complex High Spin, Low Spin
or not applicable
Configuration
e.g. t2gmegn
LFSE
In units of D
[Co(NH3)6]3+ Low spin t2g6(eg0) 6 x -2/5Do = 1.2Do
[Fe(OH2)6]2+      
[Fe(CN)6]3-      
Cr(NH3)6]3+      
[W(CO)6]      
FeCl4]2-      
Ni(CO)4]      
    1. An octahedral Fe(II) complex has a large paramagnetic susceptibility. What is its ground state according to the attached data sheets, and what spin-allowed d - d transitions should be observed in its spectrum?

      Find dn, and use either the table of terms and the associated diagrams, or the appropriate Tanabe-Sugano diagram to get the ground state. Use the Tanabe Sugano diagram to determine which transitions are spin-allowed. The question is not asking you to estimate the frequency of the transitions, but you could do that too with the information you are given. you would need to estimate Do and a B value from the free ion values given.

    2. The near UV - visible spectrum of [Co(NH3)6]3+ has a very weak band in the red, and two moderately intense bands to higher energy. Consult the attached sheets and say to which transitions these bands should be assigned.

      You may need to consider the possible presence of spin forbidden or charge transfer bands to answer this, This time some rough calculations are needed to support your conclusions.

    3. The compound [Cr(OH2)6]Cl3 is fairly pale blue-green, but chromate CrO42- is intensely yellow. Characterize the origins of the colours, and explain the relative intensities.

      Find dn's, and, if appropriate, use either the table of terms and the associated diagrams, or the correct Tanabe-Sugano diagram to get the ground state. Use the Tanabe-Sugano diagram to determine which transitions are spin-allowed. The question is not asking you to estimate the frequency of the transitions.

    1. Giving structural formulae, predict the products of the following reactions:
      You need to know the trans-directing order and order of nucleophilicity for the ligands involved to answer this.

      1. [Pt(PR3)4]2+   +   2Cl-      



      2. [PtCl4]2-   +   2PR3      



      3. cis-[Pt(NH3)2(py)2]2+   +   2Cl-   +   



    2. The pairs of compounds below react by the inner-sphere redox mechanism. For each case, explain briefly why:
      To answer these, you need to consider:

      • Lability/inertness of reactants and products.
      • Occupancy of antibonding eg orbitals, before and after electron transfer, which might require bond length changes.

      1. bridge formation limits the rate for: [CoIII(NH3)5X]2+/[VII(H2O)6]2+.



      2. electron transfer limits the rate for: [CoIII(NH3)5X]2+/[CrII(H2O)6]2+.



      3. bridge breaking limits the rate for: [FeIII(CN)5X]3-/[CoII(CN)5]3-.



    1. What is the valence electron count for the two complexes depicted below?

      1. [Ti(h1-C5H5)2(h5-C5H5)]



      2. [W(h3-C5H5)(h5-C5H5)(CO)3]



    2. Distinguish between a Fischer type carbene and a Shrock type carbene, giving a structural formula for each type.
      You know it or you don't!

    3. How would you do the following conversions?
      Not covered in Fall 2003.

      1. Mn2(CO)10      NaMn(CO)5



      2. NaMn(CO)5      CH3COMn(CO)5



      3. (C5H5)2Fe      C5H5Fe(C5H4COCH3)