COORDINATION COMPLEXES OF COBALT

A. COBALT(III) AMMINES


B. LINKAGE ISOMERISM IN [Co(III)(NH3)5NO2]
2+
C. Synthesis of cis- and trans-Dichlorobis(ethylenediamine)cobalt(III)
Chloride
Written Report: Give a reaction scheme for each synthesis that includes structural representations of the reactants and products (use a structure drawing program such as ChemDraw®.) Report the correct names and amounts of chemicals used, reaction times, observations, physical properties, percent yield and spectral data (A copy of the UV-Vis
spectrum and the IR spectrum must be included for each compound.) Your conclusions and reported results must be well substantiated with experimental data.
This Report Should Include the FollowingTitle

Your Name* and the names of your lab partners

Background and Overview- Give a reaction scheme for each synthesis that includes structural representations of the reactants and products (use a structure drawing program such as ChemDraw®.) Briefly discuss linkage isomers and geometric isomerism and clearly show the isomers synthesized. Discuss any other aspects of the complexes that are interesting to you.

Table of Reactants and Products- Report the correct names and amounts of chemicals used, important observations, percent yield and spectral data.
Also give a table showing the color of the complexes and λmax from the UV-Vis spectrum obtained for the compounds.

Results and Discussion-Discuss the results of your experiment in this section.
Include the following in your discussion:
• What evidence indicates the reaction did or did not give the expected
product.
• Give the key spectral or physical evidence obtained for the product. (This should be presented in a table.)
• Propose a possible reason for any unexpected results and a possible change in the experimental procedure to test your hypothesis.
Include copies of all IR spectra. Identify important absorbencies and those that are characteristic for each complex.

Answers to Questions-The questions are given following this table.

References-Give complete citations for the literature sources used for the procedure or to write the report. Do not list references cited in your handouts unless you consult the original reference.
Inorganic Chemistry Laboratory Page 2

Questions:


(1) Show the structures of the complex ions [Co(NH3)6]
3+, [Co(NH3)5Cl]2+, and both
cis-, and trans-[Co(NH3)4Cl2]
+
. What is the oxidation state of cobalt in these
complexes?
(2) The reduction potential of [Ru(NH3)6]
3+ to give [Ru(NH3)6]
2+ is 0.10 V. The
reduction potential of [Co(NH3)6]
3+ to give [Co(NH3)6]
2+ is 0.058 V. Under
standard conditions, would [Ru(NH3)6]
2+ be oxidized more easily than
[Co(NH3)6]
2+?
(3) How does the color the compound appears relate to the wavelength of visible
light absorbed?
(4) Give the structures of the two linkage isomers, including the dominant
resonance form of the nitrite ligand in each isomer.
(5) Did your IR data give any evidence to indicate how the nitrite ligand binds in each of the two isomers? Include copies of all IR spectra. Identify important absorbances and those that are characteristic for each complex. Label and assign absorbances due to N-H and N-O vibrations for the two linkage isomers.
(6) Did your experimental data indicate which linkage isomer is the kinetic product?
Which is the thermodynamic product?
Bonus: Estimate the potential for oxidation of a) [Ru(NH3)6]
2+ and b) [Co(NH3)6]
2+
by atmospheric oxygen under standard conditions. Use the following reduction half
reactions:
O2(g) + 4H+
(aq) + 4e- → 2H2O(l) E° = + 1.23 V
[Ru(NH3)6]
3+(aq) + 1 e- → [Ru(NH3)6]
2+(aq) E° = + 0.10 V
[Co(NH3)6]
3+(aq) + 1 e- → [Co(NH3)6]
2+(aq) E° = + 0.058 V

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