Principles of Chemical Science_Transition Metals Crystal Field Theory Part II - Lec29
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Course
Chemistry
Institution
Lecture 29: Transition Metals: Crystal Field Theory Part II
1. Spectrochemical Series: Geometry Makes a Difference
2. Crystal Field Theory: Tetrahedral Case
3. Crystal Field Theory: Square Planar Case
4. Other Geometries and Applications
5.111 Lecture Summary #29 Friday, November 21, 2014
Reading For Today: 16.8-16.11 in 4th and 5th editions
Reading for Lecture #30: 14.1-14.5 in 5th ed and 13.1-13.5 in 4th ed.
Topic: I. Spectroscopic Theory: Both Ligand Type and Geometry Make a Difference
II. Crystal Field Theory: Tetrahedral Case
III. Crystal Field Theory: Square Planar Case
IV. Other Geometries and Applications
I. Spectroscopic Theory: Both Ligand Type and Geometry Make a Difference
Nickel Demonstration
Recall the color of light transmitted is complementary to the color of light that is
absorbed. Red is complementary to green; orange is complementary to blue; yellow is
complementary to violet.
[NiCl6]4- (greenish)
Absorbs λ that is ___________; so !o is ;Cl - is a field ligand
H2O
[Ni(H2O)6]2+ (blue-green)
Absorbs λ that is ________________than above; so !o is than above;
H2O is a fiel d ligand than above
EDTA
Ni-EDTA (blue)
Absorbs λ that is ________________than above; so !o is than above;
EDTA is a field ligand than above
Also [Ni(H2O)6]2+ (blue-green)
dimethylglyoxine (dmgH)
Ni-(dmgH)2 (red)
Absorbs λ that is ________________than above; so ! is ___________________; but the
complex is square planar and not octahedral. Geometry matters. Square planar
geometry must allow for a large splitting of the energy of the d-orbitals.
(We will look at this in a few minutes.)
violet blue green yellow orange red
| | | | | | |
λ 400nm 430nm 490nm 560nm 580nm 620nm 800nm
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, II. Crystal Field Theory: Tetrahedral Case
z axis
Z
L- L- Z
M y axis Y Y
X
L- X
L-
x-axis out of the page dx2-y2 dz2
tetrahedral
z axis
L- L- Z
Z
Z
M y axis Y Y Y
X X
L- L- X
dyz dxy
x-axis out of the page dxz
tetrahedral
• There is ___________repulsion between the ligand negative point charges and the
d-orbitals that are 45° off axis (dyz, dxz, dxy) than there is between the ligand negative
point charges and the d-orbitals that are on axis (dz2 and dx2-y2).
• As a result of the above, there is greater orbital destabilization for dyz, dxz, dxy than
for dx2-y2 and dz2 ( of octahedral).
• dz2 and dx2-y2 have the energy with respect to each other (degenerate).
• dyz, dxz, dxy have the same energy with respect to each other (degenerate).
• The tetrahedral crystal field splitting energy (∆T) is than for
octahedral complexes because the point charges are not directed at any orbital set.
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