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UMass Amherst Biochemistry Teaching Initiative
Chem 241Lecture 13
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Exam Stats High – 99 Avg – 73Low – 32 SD – 20.2
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A+ A A- B+ B B- C+ C C- D+ D F
Exam 1
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Out of 94
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Recap• CFT• MOT for Oh
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Ligand Field Theory Ligands with only valence orbital6 Ligand s-donor orbitals lead to 6 SALCS:
o σ1 + σ2 + σ3 + σ4 + σ5 + σ6 (a1g)o σ1 − σ2 + σ3 − σ4 (eg)
2σ6 + 2σ5 − σ1 − σ2− σ3 − σ4
o σ1 − σ3 (t1u)σ2 − σ4
σ5 − σ6
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Ligand Field Theory MOT for Oh symmetryMetal valence orbitals for a 1st row case:
3d - t2g + eg4s - a1g4p - t1u
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Ligand Field Theory
A good σ-donor should result in a strong metal-ligandoverlap, hence a more strongly anti-bonding eg set and a larger value of Δo.
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AbsorptionUltravoilet-visible spectroscopy is the observation of the abosoption of electromagnetic radiation in the ultraviolet and visible (UV) regions of the spectrocopy.
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Absorption of a Metal Complex
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Absorption
A = log (I0/I)Io = Light InI = Light abs.
A = ε B[C]ε = molar abs.B = Path length[C] = concentration
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Consider π-orbitals
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Consider π-orbitals
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Coordination compoundsWe are now in a position to understand the
spectrochemical series.
• Δo: I- < Br- < S2- < -SCN- < Cl- < -O2N- < N3- < F- < OH-
< ox2- < H2O < -NCS- < CH3CN < py < NH3 < en < bipy< phen< -NO2
- < PPh3 < CN- < CO
Δo: σ + π-donors < σ-donors < σ-donors + π-acceptors
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Charge Transfer
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Solvatochromism
• Negative solvatochromismcorresponds to hypsochromic shift, • Positive solvatochromismcorresponds to bathochromic shiftwith increasing solvent polarity.
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Pottery
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Fluorescence and PhosphorescenceFluorescence – is radiative decay from an excited state of the same multiplicity as the ground state.
Phosphorescence - is radiative decay from an excited state of the different multiplicity as the ground state.
2S + 1
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HomeworkFinish reading chapter 19 – 19.3, 19.4, 19.6 (a lot on p-chem.)
Exercises: 1, 2, 3, 4, 5, 7, 8, 24Problem : 3, 8
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