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Isomers in Transition Metal Complexes (Worksheet)

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    126993
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    Work in groups on these problems. You should try to answer the questions without referring to your textbook. If you get stuck, try asking another group for help.

    Learning Objectives

    • Build a model of a transition metal complex and thus improve your ability to visualize the three-dimensional structure from a two-dimensional picture or a name-description.
    • Given the structure of the complex, identify its possibilities for all types of isomers (optical, geometric, coordination, ionization and linkage isomers).
    • Develop a chemical intuition about which parts of a molecule are stereochemically rigid and therefore give rise to isomer possibilities.
    • Quality of the model built and the analysis of the isomer possibilities.
    • Quality of group discussion (teams and class) and participation of all persons in accomplishing the learning objectives.

    The presence of isomers is dominant in the chemistry of transition metal complexes and was crucial to the discovery of octahedral coordination geometry by Alfred Werner in 1910. For definitions of optical isomers (enantiomers), geometric isomers, coordination isomers, ionization isomers and linkage isomers. Many useful coordination compounds have been produced, including metallo-pharmaceuticals, luminescent materials for TV tubes, photo-diodes, lasers, catalysts, and pigments for paints, to name a few. Resolving and studying the enantiomers has been important in the development of structure-property relationships of transition metal complexes, especially in catalysis and in metallobiological compounds. Current FDA policy requires that when optical isomers of pharmacologically active compounds are possible, they must be separated and tested separately. Enantiomers often have different physiological actions.

    Resources

    • Your assigned complex. One per student.
    • Rodgers, Chapter 3 (Glen E. Rodgers, “Descriptive Inorganic, coordination and Solid-State Chemistry,” Brooks/Cole, Thompson Learning, USA, 2002, ISBN 0-12-592060-1).
    • Model kits in the chemistry library. Please build your model before class and bring it to class.
    • Time between class periods (to complete the plan, write responses to critical thinking questions, and write assessment reports).
    Preliminary assignment for Activity 4

    Rodgers problems 3.38 and 3.42.

    Post-assignment for Activity 4

    Rodgers problems 3.26 and 3.44.

    Plan

    1. Form groups of three. Each member discusses their analysis of their model and arrives at group consensus on the analysis of the model.
    2. Answer the critical thinking questions listed below (giving the group consensus).
    3. Each member writes the group’s responses for their molecule and prepares to present to the class.
    4. Refer back to the criteria for performance success and assess your group’s work.

    Critical Thinking Questions

    1. If your complex has the short name of a ligand in its formulation, what does this name stand for? Draw the chemical structure of the ligand. Does the ligand have enantiomers?
    2. Which atoms of the ligands are bound to the metal? What is the oxidation state of the metal in the complex? What is the d electron configuration of the metal in the complex?
    3. Write a description in words for the structure of the complex. See Rodgers Chapters 2 and 3 for ideas. One sentence is enough.
    4. Can this complex have optical isomers? If so, draw a representation of the pair(s).
    5. Are there other geometrical isomers of this same chemical formula? Draw them and name them.
    6. Are there any other isomer possibilities? If so, name the type of isomer and draw them.

    Complexes to be assigned

    1. [Cr(o-phen)(NH3)2Cl2]+ (ophen is orthophenanthroline)
    2. K[Cr(edta)] (edta is ethylenediaminetetraacetate)
    3. [Pt(bipy)2BrCl]+2 (bipy is bipyridine )
    4. [PtBrCl(1-methylethylenediamine)]0
    5. cis-dithiocyanato-bisethylenediaminecobalt(III)
    6. [Co(NO2)3(NH3)3]
    7. [Co(dien)Cl3] (dien is diethylenetriamine)
    8. [Ru(acac)3]- (acac is acetylacetonate)
    9. [Pd (thiocyanate)2(bipy)]
    10. [PtCl2(NH3)2(py)2]2+
    11. [Co(glycinate)3]
    12. K2[Co(cyanide)2(NTA)] (NTA is nitrilotriacetate)
    13. {Co[Co(OH)2(NH3)4]3}Br6 (see figure 3.13)
    14. K[Co(C2O4)2Cl2] (C2O4 is oxalate)

    Reference

    • Susan Jackels, Seattle University
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