Download Metal Complex Isomers

Activity 4: Isomers in Transition Metal Complexes
Introduction
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. See Figure 3.1 of Rodgers for definitions of optical isomers
(enantiomers), geometric isomers, coordination isomers, ionization isomers and linkage
isomers. Many useful coordination compounds have been produced, including metallopharmaceuticals, 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.
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.
Criteria for Success
 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.
Resources
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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 0-12592060-1).
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: Isomers of Metal Complexes.
problems 3.38 and 3.42.
Rodgers
Post-assignment for Activity 4: Rodgers problems 3.26 and 3.44.
Activity for Fundamental Inorganic Chemistry contributed by Susan C. Jackels, Seattle University.
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.
Activity for Fundamental Inorganic Chemistry contributed by Susan C. Jackels, Seattle University.
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]
8. [Ru(acac)3]-
(dien is diethylenetriamine)
(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)
Activity for Fundamental Inorganic Chemistry contributed by Susan C. Jackels, Seattle University.