An Introduction to the Chemistry of Chromium

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An Introduction to the Chemistry of Chromium

• Ethan Englund
• Augustana College
• 05.10.02

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Chromium Chemistry

• Chromium - Comes form the Greek word chroma
  meaning colored.
• First Identified in the PbCrO4
• Multiple Oxidation States

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Cr(Acac)3

• Full Name is Chromium Acetylacetonate
• Octahedral Complex of Cr III
• Optically Active

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Chromium Acac Synthesis

• Acetylacetone is added to a solution containing
  Cr (III) ions and urea.
• The solution is heated thoroughly for around 1
  2 hours.
• Yields a deep red solution with dark red
  precipitate.

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The Ultra Violet Spectrum of Cr(Acac)3
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Chromium d Orbital Split

• Cr (III) - Typical d3 octahedral metal ion.
• Ligand Field Strength Unimportant

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Visible Spectrum

• Obvious Color
• D ? D Transitions
• From this, the LFSE (?o) and B can be
  determined.

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Interpreting Spectrum Data Tunabe - Sugano
Diagram

• From this, one can determine the Racah parameter.
• Also can give the Octahedral Splitting Energy

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Symmetry and Optical Activity

• D3 Symmetry
• Optical activity possible because of the
  enantiomers.
• Right Hand Screw Vs. Left Hand Screw Formation

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Cr(Acac)3 Enatiomers
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The Joys of Computational Chem

• Above The Elctrostatic Potential Graphed on the
  Electron Density via ZINDO on CAChe

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Singly and Doubly Occupied Orbitals

• Prediction based on Jaguar B88 LYP
• Some Oddities in the Predictions

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T2g Vs. eg Orbitals

• Seem to show dx2-y2 orbitals
• Along with dz2 indicate eg

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Chromium Acetate

• Bidentate Acetate Ligands
• Metal-Metal Bond
• Computational methods and approaches

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The Formation of a Delta Bond in a Cr(II) Complex

• Commonly referred to as a quadruple bond.
• Has 8 available valence electrons
• Bond Order of 4

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Orbital View of the Quadruple Bond

• The d orbitals of the delta bond
• dx2-y2 orbitals occupied M-L bonds

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Conclusion

• Transition Metal Computational Work Continues to
  Gain Interest
• The Chromium Chemistry described shows a lot of
  generalities in transition metal chemistry

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Bibliography

• Atkins, Shriver. Inorganic Chemistry Third
  Edition. Freeman and Company N.Y. 1999
• Gray, Swanson, Crawford. Project ACAC An
  Experimental Investigation In Synthesis and
  Structure. Bogden and Quigley Inc. Belmont, Ca.
  1972

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Appreciation goes out to

• Dr. Viste for his invaluable Quantum/Computational
  advise
• Dr. Lindbeck for her guidance in advanced
  inorganic chemistry
• Augustana College