CHEM1902 (C10K) Coordination Chemistry Tutorials

From the May 2004 Exam Paper.
1). (a) Give the Oxidation number, d-orbital occupation, co-ordination number and expected magnetic moment of the central metal ion in the following complexes.
Draw the expected structure.

(i) K3[Co(C2O4)3]
(ii) (NH4)2[CoF4]
(iii) diamagnetic [NiCl2{P(C6H5)3}2]
(iv) cis-[CrCl2(bipy)2]Cl
(v) [Mn(H2O)6]SO4
where C2O42- is the oxalate ion and bipy is 2,2'-bipyridine.

(b) Which of the complexes above can exhibit isomerism? Explain.

(c) Give the IUPAC name for the complex (ii) in part (a).
Answers

2) Write down the systematic name for each of the following complexes and indicate the coordination number, oxidation number, electronic configuration, stereochemistry and magnetic moment of the central ion.
  1. K[Cr(oxal)2(H2O)2].3H2O
  2. CrCl3(py)3
  3. K4[Mn(CN)6]
  4. [CoCl(NH3)5]Cl2
  5. Cs[FeCl4]
  6. [NiCl(NH3)(en)2]Cl
  7. [Cu(NH3)4(H2O)]SO4
Answers

3) The hexaquo manganese(II) ion contains five unpaired electrons, while the hexacyano- ion contains only one unpaired electron. Explain, using Crystal Field Theory.

Answers

4) Indicate the type of isomerism exhibited by the following complexes and draw structures for these isomers.
  1. K[Cr(oxal)2(H2O)2].3H2O
  2. [Co(en)3]Cl3
  3. [CoCl(NO2)(NH3)4](NO3)2
  4. PtCl2(NH3)(H2O)
Answers

5) Give an example of each of the following:
  1. Binuclear Complex
  2. Metal Chelate
  3. Low spin complex
  4. High spin complex
  5. Five coordinate complex.
6) The complex ion [Ni(NH3)4]2+, forms on mixing aqueous solutions of ammonia and a nickel salt.
 a) If a solution contains 1.6 x 10-4 % of the nickel ions in the form of Ni2+ when the concentration of free NH3 (aq) is 0.5M. What is the stability constant of the complex [Ni(NH3)4]2+?
(Assume that this is the only complex present).

 b) The octahedral ammine complex can be prepared by using a solution of ammonia which has been supersaturated with ammonia gas, such that:

log K5 = 0.85
log K6 = 0.42.
Calculate the overall β6 for [Ni(NH3)6]2+.
Write the equations for the equilibria corresponding to K5 and K6.
Answers

7) a) Draw the complex, [Ni(en)3]2+, showing the optical isomers.

     b) If at equilibrium, [Ni(en)3]2+, is 0.08M and [en] is 0.40M, calculate [Ni2+].
        Note that β3 for [Ni(en)3]2+ is 4.07 x 1018.

     c) Write equations for the successive formation equilibria.

     d) The first and second stepwise formation constants are:

                                log K1  =       7.66
                        and     log K2  =       6.40.
                Calculate the third stepwise formation constant.
                Ans     b)      3.07 x 10-19.
                        d)      3.55 x 104.
8) a) Place the following ligands in increasing order in the Spectrochemical series:
CN-, NH3, Cl-,H2O
b) For octahedral first row transition metal complexes with between four and seven d electrons, both high and low spin electron configurations are possible.

Use Crystal Field splitting diagrams to determine the number of unpaired electrons and then calculate the expected spin-only magnetic moments.

return to course outline

Problem Class

1) Calculate the equilibrium concentration of the Cu2+ ion in a solution that is initially 0.10 M Cu2+ and 1.0 M NH3, given that β4 for Cu(NH3)42+= 2.1 x 1013.

This is CALCULATION # ONE from the Chelate Effect Lecture.

2) Calculate the entropy changes for the following reactions at 298K and comment on the results:
Zn2+ + 2NH3 <=> Zn(NH3)22+
ΔH=-28.03 kJ mol-1 log β2= 5.01
Zn2+ + en <=> Zn(en)2+
ΔH=-27.6 kJ mol-1 log β2= 6.15
(NB R=8.314 J K-1 mol-1)

This is CALCULATION # TWO from the Chelate Effect Lecture.

3) The stepwise enthalpies ΔHn and the stability constants K for the system Ni2+ - en in aqueous solution at 298K are as follows:

n log10Kn ΔH° /kJmol-1
1 7.51 -37.7
2 6.35 -38.4
3 4.42 -40.6

Calculate the standard free energy ΔG° and entropy changes ΔS° associated with the addition of each ligand.

4) Calculate the overall complex dissociation equilibrium constant for the Cu(NH3)42+ ion given that β4 for this complex is 2.1 x 1013.

5) Calculate the equilibrium concentration of the Fe3+ ion in a solution that is initially 0.10 M Fe3+ and 1.0 M SCN-, given that β2 for Fe(SCN)2+ = 2.3 x 103.

7) What is the ratio of uncomplexed to complexed Zn2+ in a solution that is 10M in NH3 given that β4 for Zn(NH3)42+ = 3 x 109.

8) Given the following data at 25°C:
ΔG° = -41.4 kJ mol-1 for Ag+(aq) + 2NH3 <=> Ag(NH3)2+(aq)
and ΔG° = -55.6 kJ mol-1 for Ag+(aq) + Cl- <=> AgCl(s)

a) Calculate ΔG° for AgCl(s) + 2NH3 <=> Ag(NH3)2+(aq) + Cl-
b) Calculate the equilibrium constant for this reaction.

Will the reaction proceed from L -> R ??
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