An Introduction to the An Introduction to the Chemistry of ChromiumChemistry of Chromium

Ethan EnglundEthan Englund

Augustana CollegeAugustana College

05.10.0205.10.02

Chromium ChemistryChromium Chemistry

• Chromium - Comes form the Greek Chromium - Comes form the Greek word “chroma” meaning colored.word “chroma” meaning colored.

• First Identified in the PbCrOFirst Identified in the PbCrO4 4

• Multiple Oxidation States Multiple Oxidation States

Cr(Acac)Cr(Acac)33

• Full Name is Full Name is Chromium Chromium AcetylacetonateAcetylacetonate

• Octahedral Octahedral Complex of Cr IIIComplex of Cr III

• Optically ActiveOptically Active

Chromium Acac SynthesisChromium Acac Synthesis

• Acetylacetone is added to a Acetylacetone is added to a solution containing Cr (III) ions and solution containing Cr (III) ions and urea.urea.

• The solution is heated thoroughly The solution is heated thoroughly for around 1 ~ 2 hours.for around 1 ~ 2 hours.

• Yields a deep red solution with dark Yields a deep red solution with dark red precipitate.red precipitate.

The Ultra Violet Spectrum The Ultra Violet Spectrum of Cr(Acac)of Cr(Acac)33

Chromium d Orbital SplitChromium d Orbital Split

• Cr (III) - Typical dCr (III) - Typical d33 octahedral metal octahedral metal ion.ion.

• Ligand Field Ligand Field Strength Strength Unimportant Unimportant

Visible SpectrumVisible Spectrum

• Obvious ColorObvious Color• D D D Transitions D Transitions• From this, the From this, the

LFSE (LFSE (oo) and B ) and B

can be can be determined.determined.

Interpreting Spectrum Data: Interpreting Spectrum Data: Tunabe - Sugano DiagramTunabe - Sugano Diagram

• From this, one can From this, one can determine the Racah determine the Racah parameter.parameter.

• Also can give the Also can give the Octahedral Splitting Octahedral Splitting EnergyEnergy

Symmetry and Optical Symmetry and Optical ActivityActivity

• DD3 3 SymmetrySymmetry

• Optical activity Optical activity possible because possible because of the of the enantiomers.enantiomers.

• Right Hand Screw Right Hand Screw Vs. Left Hand Vs. Left Hand Screw FormationScrew Formation

Cr(Acac)Cr(Acac)3 3 EnatiomersEnatiomers

The Joys of Computational The Joys of Computational ChemChem

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

Singly and Doubly Singly and Doubly Occupied OrbitalsOccupied Orbitals

• Prediction based on Prediction based on Jaguar: B88 LYPJaguar: B88 LYP

• Some Oddities in the Some Oddities in the PredictionsPredictions

TT2g2g Vs. e Vs. egg Orbitals Orbitals

• Seem to show dSeem to show dxx22--

yy22 orbitals orbitals

• Along with dAlong with dzz22

indicate indicate eegg

Chromium Acetate Chromium Acetate

• Bidentate Acetate Bidentate Acetate LigandsLigands

• Metal-Metal BondMetal-Metal Bond• Computational Computational

methods and methods and approaches approaches

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

• Commonly Commonly referred to as a referred to as a quadruple bond.quadruple bond.

• Has 8 available Has 8 available valence electronsvalence electrons

• Bond Order of 4Bond Order of 4

Orbital View of the Orbital View of the Quadruple BondQuadruple Bond

• The d orbitals of the delta bondThe d orbitals of the delta bond

• ddxx22--yy22 orbitals occupied M-L bonds orbitals occupied M-L bonds

Conclusion Conclusion

• Transition Metal Computational Transition Metal Computational Work Continues to Gain InterestWork Continues to Gain Interest

• The Chromium Chemistry The Chromium Chemistry described shows a lot of described shows a lot of generalities in transition metal generalities in transition metal chemistry chemistry

BibliographyBibliography

• Atkins, Shriver. Atkins, Shriver. Inorganic Chemistry: Third EditionInorganic Chemistry: Third Edition. Freeman . Freeman and Company N.Y. 1999and Company N.Y. 1999

• Gray, Swanson, Crawford. Gray, Swanson, Crawford. Project ACAC: An Experimental Project ACAC: An Experimental Investigation In Synthesis and StructureInvestigation In Synthesis and Structure. Bogden and Quigley . Bogden and Quigley Inc. Belmont, Ca. 1972Inc. Belmont, Ca. 1972

Appreciation goes out to…Appreciation goes out to…

• Dr. Viste for his invaluable Dr. Viste for his invaluable Quantum/Computational adviseQuantum/Computational advise

• Dr. Lindbeck for her guidance in advanced Dr. Lindbeck for her guidance in advanced inorganic chemistryinorganic chemistry

• Augustana CollegeAugustana College