Transcript Coordination Complexes

First Ionization Energies of Transition Metals
• The first ionization energy increases gradually from left to
right on the periodic table.
5d
3d
4d
Oxidation States of 3d Transition Metals
Element
group
Sc
3
Ti
4
V
5
Oxidation
state
Mn
7
Fe
8
Co
9
Ni
10
Cu
11
Zn
12
Valance configuration
+1
d4
d5
d6
d7
d8
d9
d 10
+2
d1
d2
d3
d4
d5
d6
d7
d8
d9
+3
d0
d1
d2
d3
d4
d5
d6
d7
d8
d0
d1
d2
d3
d4
d5
d6
d0
d1
d2
d3
d4
d0
d1
d2
+4
+5
+6
d 10
d0
+7
Key
Cr
6
+2
+3
+4
d0
*Table lists the configuration of the ion corresponding to each observed oxidation
state. The most important oxidation states of each element are color screened.
Formation of Coordinate Covalent Bonds
• A ligand donates a lone pair of electrons to form a bond to
a metal.
– Ex. The Ni–N bonds in [Ni(NH3)6]2+ form by overlap of the lone
pair sp3 orbital on the nitrogen atom with an empty valence orbital
on the metal.
Donor
Metal
Two
2+
Ni -Ligand
Complexes
• Both water and ammonia form six covalent bonds with
Ni2+, resulting in octahedral geometry.
Colors of Two Ni2+-Ligand Complexes
[Ni(H 2 O)6 ]2+ + 6 NH 3 ® [Ni(NH 3 )6 ]2+ + 6 H 2O
green
blue
[Ni(H2O)6]2+
[Ni(NH3)6]2+
Coordination Number - Two
• Complexes with coordination number two always adopt
linear geometry about the metal cation.
Coordination Number – Four
Tetrahedral and Square planar
Coordination Number – Six
Octahedral
Bidentate Ligands
Heme
• Oxygen-carrying component of
blood.
• Planar structure.
• Multi-ring structure of C and N
atoms.
• Extensive delocalized π system.
• Binds one Fe2+ cation at its
center.
Iron
Repulsion of Ligand Electrons and Metal Electrons
is Greatest with Overlap
• dx2–y2 points directly toward the ligands.
– Overlap results in increased repulsion.
• dxy points between the ligands.
– Lack of overlap results in less repulsion.
y
y
x
x
dxy orbital
dx2–y2 orbital
The Five d Orbitals Interacting with an
Octahedral Set of Ligands
The Crystal Field Level Diagram for
Octahedral Coordination Complexes
• Electron-cation attraction stabilized all five d orbitals.
• Electron-electron repulsion destabilizes the five d
orbitals by different amounts.
Crystal Field Splitting Energy
• Crystal field splitting energy:
– The difference in energy between the eg and t2g sets.
– Symbolized by the Greek letter, Δ.
dx2–y2
Δ
dxy
dxz
eg
dz2
dyz
t2g
The Spectrochemical Series
• The spectrochemical series lists the common ligands in
order of increasing ability to split the energies of
the t2g and eg subsets of orbitals.
• The ranking of ligands is influenced most strongly by the
donor atom:
– Generally decreases across Row 2 of the periodic table.
– Generally decreases down the halogen column.
– Molecular orbital theory is best used to explain the trend.
Relationships Among Wavelength, Color, and Crystal
Field Splitting Energy (Δ)
Wavelength (nm)
Color absorbed Complementary color
Δ (kJ/mol)
>720
Infrared
Colorless
<165
720
Red
Green
166
680
Red-orange
Blue-green
176
610
Orange
Blue
196
580
Yellow
Indigo
206
560
Yellow-green
Violet
214
530
Green
Purple
226
500
Blue-green
Red
239
480
Blue
Orange
249
430
Indigo
Yellow
279
410
Violet
Lemon-yellow
292
<400
Ultraviolet
Colorless
>299
Colors of Cr3+ Coordination Complexes
380 nm
380 nm
650 nm
570 nm
[Cr(CN)6]3–
Absorbance
Absorbance
• The colors of
Cr3+ coordination
complexes depend on the
magnitude of the crystal
field splitting energy.
570 nm
[CrF6]3–
[Cr(H2O)6]3+
[Cr(CN)6]3–
650 nm
[Cr(H2O)6]3+
[CrF6]3–
– Higher Δ, shorter λ.
300
• The spectrochemical
series indicates the
relative magnitude of Δ.
400
300
500
400
600
500λ
Wavelength,
700
600
700
Wavelength, λ
eg
eg
λ = 380 nm
Energy
Energy
λ = 380 nm
λ = 570 nm
λ = 570 nm
t2g
t2g
[Cr(CN)6]3–
3–
[Cr(CN)
absorbs:
violet 6]
appears: absorbs:
yellow-green
violet
[Cr(H2O)6]3+
λ = 650 nm
λ = 650
[CrF6]3–
3–
[Cr(H2O)6]3+
[CrF
absorbs: yellow-green
absorbs:
red6]
appears:
green re
absorbs:violet
yellow-green appears:
absorbs: