Download Coordination Complexes

Coordination
Complexes
Chapter 20
What we learn from Chap 20
• We begin the chapter with what is among the
most important coordination complexes of all,
iron in hemoglobin (magnesium in
chlorophyll might be another). In Section
20.1, we introduce the coordinate covalent
bond and reintroduce Lewis acids (central
atom) and bases (ligands) as the bonding
species in coordination complexes. We also
discuss how carbon monoxide can replace
oxygen in hemoglobin.
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CHAPTER OUTLINE
I.
II.
III.
IV.
V.
VI.
Bonding in Coordination Complexes
Ligands
Coordination Number
Structure
Isomers
Formulas and Names
A. Formulas
B. Nomenclature
VII. Color and Coordination Compounds
A. Transition Metals and Color
B. Crystal-Field Theory
C. Orbital Occupancy
D. The Result of d Orbital Splitting
E. Magnetism
VIII. Chemical Reactions
A. Ligand Exchange Reactions
B. Electron Transfer Reactions
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20.1 Coordination Complex
• Central metal atom – transition metal.
• Coordinate covalent bond
• Ligand – anion or neutral compound
··
such as H2O: or :NH3.
[Cu(NH3)]2+
[Fe(CN)6]3Copyright © Houghton Mifflin Company. All rights reserved.
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Complexes
Protein Ferrodoxin
Plastocyanin
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Wilkin’s catalysyst
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20.2 Ligands
• Lewis bases having a lone pair of e- to
donate.
• Bidentate ligands form two bonds to the
metal.
• Chelates are polydentate ligands.
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Ligand Names
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Ligands
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Chelate
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EDTA
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EDTA
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20.3 Coordination Number
• Coordination number (CN) is the number of
donor atoms bonded to central metal atom.
• Common coordination numbers are 4 and 6.
• May be as low as 2 and as high as 8.
• CN determined by
– The nature of metal ions : eg. Size
– Charge on the ligand & metal
– Electron configuration of metal
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Coordination Number
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Coordination Number
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20.4 Structure
• CN = 2
– linear complex, 180o bond angles.
• CN = 4
– tetrahedral complex, 109o bond angles.
– square planar complex (nd8electron
configuration), 90o bond angles.
• CN = 6
– octahedral complex, 90o bond angles.
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CN = 4
Square planar
Tetrahedral
eg)
Zn(NH3)42+,
CoCl4
2-
cf) VSEPR Model
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eg) Cu(NH3)42+, Ni(II), Pd(II), Pt(II)
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Sample Problem
Predict the geometry of the following complexes:
[Ni(NH3)6]2+ [Pt(NH3)2 Cl2]
[Au(CN)]+
[Ni(NH3)6]2+
[Pt(NH3)2Cl2]
[Au(CN)]+
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CN = 6, octahedral
CN = 4, square planar
CN = 2, linear
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20.5 Isomers
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Linkage Isomer
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Ionization Isomers
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Coordination (sphere) isomers
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Geometric Isomers - SP
Cisplatin
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Geometric Isomers - Oh
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Geometric Isomerism
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Optical Isomerism
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20.6 Formulas
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Naming Coordination Compounds
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Sample Problem
Write the formulas for the following:
• Sodium hexafluorocobaltate(III)
• Bisethylenediaminecopper(II) chloride
Sodium hexafluorocobaltate(III) = Na3[CoF6]
Bisethylenediaminecopper(II) chloride=[Cu(en)2]Cl2
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Sample Problem
Name the following coordination compounds:
[Co(H2O)2Cl2]Cl
K3[Fe(CN)6]
[Co(H2O)2Cl2]Cl
diaquodichlorocobalt(III) chloride
K3[Fe(CN)6]
potassium hexacyanoferrate(III)
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•
•
•
•
•
•
•
•
•
•
K2[NiCl4]
[Co(NH3)6]Cl3
[Co(NO2)2(NH3)4]2SO4
Diamminebis(ethylenediamine) chronium(II) sulfate
Ammonium hexacyanoferrate(III)
Potassium tetrachloronikelate(II)
Hexaamminecobalt(III) Chloride
Diamminedinitrocobalt(IV) sulfate
[Cr(NH3)2(en)2]SO4
(NH4)3[Fe(CN)3]
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20.7 Color and Coordination Compounds
• Coordination compounds are usually colored.
• The color is due to partially filled d orbitals
separated by an energy difference.
• A photon causes a lower energy electron to move
to a higher energy level.
• The color is the results of the light, missing the
absorbed photon, being reflected from the metal.
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Color and Coordination Compounds
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Crystal Field Theory
• A free gaseous metal atom or ion does
not show an energy level difference
among the d orbitals.
• In the presence of ligands, the d orbital
of the metal are split by a slight energy
difference, Δo
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Crystal Field Splitting
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결정장모델(Crystal Field Model)
Approach of six ligands to transition metal cation splits d orbitals into two sets of
different
• energy: explain color and magnetic properties
eg
dx 2 y 2 , dz2
E
dxy , dyz , dxz
Free metal ion
in Spherical field
t2g
small Do
Do
3/5△o
Do
2/5△o
in Oh field
large Do
•Cristal field splitting energy Do , Cristal Field Stabilization Energy
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Crystal Field Splitting
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Crystal Field Splitting
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High and Low Spin
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Strong Field Ligand vs. Weak Field
Ligand
[Co(H2O)6]2+
[CoCl4]2-
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[Co(H2O)6]2+
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[CoCl4]2-
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Effect of Ligands on the Colors of Coordination Compounds
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Spectrochemical Series
• The nature of the ligand determines the
magnitude of the crystal field splitting, Δo
Cl- < F- < OH- < H2O < NH3 < NO-2 < CN- < CO
(small D)
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(large D )
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Magnetism
• Ferromagnetism
• Paramagnetism
• Diamagnetism
• Magnetic moment, µ=[n(n+2)]1/2
n: # unpaired electron
[Mn(H2O)6]2+ µ=5.9 vs. [Mn(CN)6]4- µ= 2.2
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Strong field
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Weak field
Hund’s Rule
strong paramagnetic
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Magnetic Properties
Paramagnetism illustrated:
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20.8 Chemical Reactions
• Ligand Exchange
[Cu(H2O)4]2+ + 4NH3  [Cu(NH3)4]2+ +
4H2O
K=4x108
[Ni(NH3)6]2+ + 3en  [Ni(en)3]2+ +6NH3
Chelate effect (entropy) K=5x109
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•Labile complexes:
exchange ligands rapidly
3 min.
[CoCl4]-
3 min.
[Co(H2O)6]2+
1 day
[CrCl2(H2O)4]+
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1 day
•Inert complexes:
exchange ligands
slowly
[Cr(H2O)6]3+
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Electron transfer reaction
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Problems
• 4, 26, 34, 38, 40, 60, 64, 72
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