coordination complexes chapter 20. copyright © houghton mifflin company. all rights reserved.20 | 2...
TRANSCRIPT
Coordination Complexes
Chapter 20
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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. Bonding in Coordination Complexes II. Ligands III. Coordination Number IV. Structure V. Isomers VI. 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]3-
· ·
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Complexes
Protein Ferrodoxin Plastocyanin 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
Tetrahedral
eg) Zn(NH3)42+, CoCl4
2- cf) VSEPR Model
Square planar
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)]+
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)
Free metal ion in Spherical field in Oh field small o large o
•
E
oo
Approach of six ligands to transition metal cation splits d orbitals into two sets of different energy: explain color and magnetic properties
d
x2 y2 , dz2
dxy , dyz , dxz
•Cristal field splitting energy o , Cristal Field Stabilization Energy
△o
△o
t2g
eg
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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+ [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
- - - - -2 3 2Cl < F < OH < H O < NH < NO < CN < CO
(small ) (large )
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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 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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3 min. 1 day
[Cr(H2O)6]3+
3 min. 1 day
[CrCl2(H2O)4]+
[CoCl4]- [Co(H2O)6]2+
•Labile complexes: exchange ligands rapidly
•Inert complexes: exchange ligands slowly
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Electron transfer reaction
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Problems
• 4, 26, 34, 38, 40, 60, 64, 72