Coordination Chemistry

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Coordination Chemistry

• A basic introduction with a critical application!

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Coordination Compound

• Complex ion a transition metal with associated
  ligands
• Counter ions cations or anions needed to
  produce a neutral charge on the complex ion.

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Coordination Number

• Number of ligands attached to the metal

Zumdahl, 5th ed.
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Ligand

• A neutral molecule or ion having a lone e- pair
  that can be used to forma a bond to a metal ion
• Coordinate covalent bond metal-ligand bond
• Unidentate (monodentate) ligand a ligand that
  can form only one bond to a metal ion
• Bidentate a ligand that can form two bonds to a
  metal ion
• Chelate a ligand that can form more than one
  bond to a metal ion.

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Isomers
Zumdahl, 5th ed.
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Crystal Field Model

• Approximations
• ligands are negative point charges
• metal ligand bonding is 100 ionic.
• The overlap of orbitals ___________ energy.

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Octahedral
Zumdahl, 5th ed.
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Tetrahedral
Zumdahl, 5th ed.
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Degree of Overlap

• Can you group the d orbitals in an octahedral
  complex based on their degree of overlap with the
  ligands?
• How about in a tetrahedral complex?

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Splitting patterns

• Octahedral 2 over 3
• Tetrahedral 3 over 2

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?E tet vs. ?Eoct

• Is there a relationship between ?Etet vs. ?Eoct?
• If so, what is it? Justify your answer.

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Strong vs. Weak Field

• Strong field (high ?E) low spin
• Weak field (low ?E) high spin
• Spectrochemical Series
• CN1- gt NO21- gt en gt NH3 gt H2O gt OH1- gt F- gt Cl- gt
  Br- gt I-

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Light Absorption Color

• Can you remember the formula we use to calculate
  the wavelength of light something absorbs?
• What variables does it involve?
• Is there more than one formula?
• If so which one would be appropriate here?
• How does the wavelength of light absorbed by
  something generally relate to its color?

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?E ? color

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Why are coordination compounds important?

• Two very good examples are hemoglobin and
  chlorophyll!
• Can you propose from these structures and from
  what you have learned so far about coordination
  compounds what might make these compounds
  significant?

http//www.wheatgrass.com/book/chapter3.php
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Lets focus of hemoglobin!

• Hemoglobin is a protein which serves the function
  of binding O2 in your blood so that it can be
  carried to your tissues, etc.

http//www.chemistry.wustl.edu/edudev/LabTutorial
s/Hemoglobin/MetalComplexinBlood.html
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Two key components

• Heme group Fe2 coordinated to a molecule known
  as a porphyrin.
• Histidine residue

http//www.chemistry.wustl.edu/edudev/LabTutorial
s/Hemoglobin/MetalComplexinBlood.html
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Heme

• Fe2 complexed with the porphyrin molecule.
• How would you describe the porphyrin molecule?
• How many ligands does it represent?
• What type of geometry and splitting pattern would
  you expect this to take on?

http//www.chemistry.wustl.edu/edudev/LabTutorial
s/Hemoglobin/MetalComplexinBlood.html
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Heme Histadine Hemoglobin

• What do you expect this to do to the shape?
• What type of splitting to you expect it to
  undergo now?

http//www.chemistry.wustl.edu/edudev/LabTutorial
s/Hemoglobin/MetalComplexinBlood.html
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Return to the function of Hemoglobin

• What did we say the function of hemoglobin is?
• Now that you can see the structure of hemoglobin
  can you predict how its structure and function
  relate?

http//www.chemistry.wustl.edu/edudev/LabTutorial
s/Hemoglobin/MetalComplexinBlood.html
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Lets watch a little movie clip
Click diagram to play movie!
http//www.chemistry.wustl.edu/edudev/LabTutorial
s/Hemoglobin/MetalComplexinBlood.html
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Some more pics of the oxy and deoxy hemoglobin
conformations!
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A little bit of anatomy!

• Where is your blood oxygenated?
• Where is it not oxygenated (deoxygenated)?
• What color is your blood when you have it drawn
  for a test or when you give blood?
• Where is blood drawn from when you have one of
  these tests?
• What color are your veins?

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Blue vs. Red Blood

• Can we come up with a complex ion explanation for
  the blue vs. the red color of blood?
• What questions should we ask?
• Lets define our essential question
• Why is our blood red sometimes and blue others?

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Key Questions

• Why does something appear a particular color?
• How do color absorbed and color reflected relate?
• What color is the red blood absorbing?
• What color is the blue blood absorbing?
• Draw plots of the absorption spectrum you would
  expect for oxyhemoglobin and deoxyhemoglobin.

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Oxy- and Deoxyhemoglobin Absorption Plots
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Color and Coordination

• We know hemoglobin is a coordination compound and
  we are investigating its color.
• How do coordination compounds and color relate?
• Can you define the relationship we need to use in
  order to relate them?

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Re-visit Plots
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Energy and Color

• How does the color of light absorbed relate to
  the energy of the complex?
• Using grammatically correct English sentences
  compare the energy of deoxyhemoglobin to that of
  oxyhemoglobin base on their respective colors.

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Splitting Patterns and Color

• What does the difference in color tell us about
  the splitting patterns in deoxy- and
  oxyhemoglobin respectively?
• Do you expect them to have different splitting
  patterns all together? Justify your answer.

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HOMEWORK

• Write a one page explanation of the difference in
  color between oxy- and deoxyhemoglobin on the
  basis of coordination complexes.
• Be sure your explanation is understandable to any
  of your classmates who have taken chemistry at
  ANY level.

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References

• Zumdahl, Chemistry, 5th ed.
• http//www.chemistry.wustl.edu/edudev/LabTutorial
  s/Hemoglobin/MetalComplexinBlood.html