Schedule

1
Schedule

• Today Color review, MO theory, applications of
  complex ions
• Monday Review Session Review questions are
  online
• Wednesday Exam 2
• Chapter 17 (properties of solutions)
• and 19 (coordination chemistry)

2

• 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
3
Colors

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

Color Wheel
4
Colors

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

Increasing ? decreases wavelength absorbed
?E h ? h c ?
5

• Cr(NO2)64 appears yellow.
• What colors could Cr(en)32 be?

Cr(NO2)64 absorbs violet Changing to en gives a
smaller ?, longer ? absorbed
A possible new color to absorb is blue or
green Cr(en)32 could appear orange or
red but not violet, blue, green or yellow
violet blue green yellow
orange red ? (nm) 400 500
600 700
6
Question

• Could Zn2 absorb light?

7
Question

• Which will absorb the longest wavelength of
  light?
• Fe(OH)2(H2O)4
• K4FeCl6
• Fe(en)3SO4
• Ca2Fe(NO2)6

8
Molecular Orbital Theory (19.7)

• Crystal field theory only good for explaining
  colors, magnetic properties
• MO theory gives best view of bonding
• Assume ligands on axes, only include ligand
  orbitals that interact with metal ion
• Two AOs have to overlap in space to form MOs
• AOs that are closer in energy interact more
  strongly than those widely seperated.

9

• Ligands on Axes

10
Same as Fig 19.31, pg 967
Free metal ion orbitals
4p
4s
E
Nonbonding
3d
Ligand Lone Pair Orbitals
11
Take Home Message

• MO model better describes bonding
• MO model reduces to the Crystal Field model
• Electrons in metal ion 3d go into t2g and eg MOs
• Energy of ligand AOs affects ?
• Electronegative ligands hold electrons tighter,
• have lower AO energy, less mixing with 3d, lower
  eg energy

12
Figure 19.32, pg 968
Electronegative F ligand, small ?
Lower EN of NH3 ligand, large ?
13
Coordination Complexes in Real Life

• Biology
• Metalloproteins about ¼ of proteins require
  metals to carry out their functions
• Oxygen transport
• Electron carriers for reductions or oxidations
• Enzymes biological catalysts
• Medicine
• Some drugs have coordinated metals

14
Heme
15
Hemoglobin
16
Oxygen Binding
17
Alcohol Dehydrogenase Converts ethanol to
acetaldehyde
? Zinc Atom
18
Biologically Active Molecules (drugs)

• Cisplatin Crosslinks DNA in rapidly dividing
  (cancerous) cells

19
Biologically Active Molecules
Cobalt ion

• Vitamin B12 Involved in cellular metabolism and
  the brain / nervous system