Crystal Field Model Octahedral

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Crystal Field Model - Octahedral

• Ligands are on axes

• Orientation of metal d orbitals affects energy

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Orbital Energy Splitting
E
Free metal ion 3d orbitals
3
Ex Fe2
six electrons
Low-spin case
High-spin case
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Effect of Ligands on ?

• Make a list of ligands in order of ability to
  produce
• d-splitting (spectrochemical series)

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Effect of Ligands on ?

• For ligands in middle of series, ? increases with
  charge of metal
• Example
• NH3 is weak field for Co2 and strong field for
  Co3

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Example

• If the compound Co(H2O)6Cl3 has 4 unpaired
  electrons, does the H2O ligand produce a weak or
  strong field?
• Co3 6 electrons
• Two Possibilities

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• Predict the number of unpaired electrons in the
  complex ion of Co(en)3Cl3

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Other Geometries

• Tetrahedral

Always small ?, high spin
t2g slightly closer to ligands than eg
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Other Geometries

• Square Planar

Linear
Fig 19.29 pg 964
Well only do problems on octahedral and
tetrahedral geometries
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Example

• Draw the crystal field diagram for the complex
  ion MnCl42-   How many unpaired electrons does
  this ion have?
• What about Mn(CN)42-?

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• Colors!

• Electrons in the split d orbitals can absorb
  energy and be promoted to the higher energy levels

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• Colors!

• Electrons in the split d orbitals can absorb
  energy and be promoted to the higher energy levels

Speed of Light
?E h ? h c ?
Wavelength
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• Colors!

• The wavelength corresponding to ? is in the
  visible region of the electromagnetic spectrum

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Colors

• The observed color is what is left over after the
  complex absorbs a certain color
• Ex Ti(H2O)63 absorbs yellow-green light

Fig 19.25 pg 962
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Colors

• The observed color is across the color wheel from
  the absorbed color

Color Wheel
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Colors

• Changing ligands will increase or decrease ?
  according to the spectrochemical series

Increasing ? decreases wavelength absorbed
?E h ? h c ?
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violet blue green
yellow orange red ?
(nm) 400 500 600
700
Increasing Wavelength Absorbed
Increasing ?
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• Ni(H2O)62 appears green, absorbs red.
• What colors could Ni(NH3)62 be?

Changing to NH3 gives a larger ?, lower ? absorbed
Ni(H2O)62 could appear blue
Ni(H2O)62 (aq) 6 NH3 (aq) ? Ni(NH3)62
(aq) 6 H2O (l)
violet blue green yellow
orange red ? (nm) 400 500
600 700
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Ni(NH3)62 appears blue Change to Ni(en)32
Changing to en gives larger ?, lower ? absorbed
Ni(NH3)62 (aq) 3 en (aq) ? Ni(en)32 (aq)
6 NH3 (aq)
violet blue green yellow
orange red ? (nm) 400 500
600 700
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• Another Example
• Which complex absorbs light of the shortest
  wavelength?
• Ca2CoF6
• Co(H2O)5ClCl
• Co(NO2)4(en)

violet blue green yellow
orange red ? (nm) 400 500
600 700