coordination complexes chapter 20. copyright © houghton mifflin company. all rights reserved.20 | 2...

Coordination Complexes

Chapter 20

Copyright © Houghton Mifflin Company. All rights reserved. 20 | 2

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.


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


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-

· ·


Complexes

Protein Ferrodoxin Plastocyanin Wilkin’s catalysyst


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.


Ligand Names


Ligands


Chelate


EDTA


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


Coordination Number


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.


CN = 4

Tetrahedral

eg) Zn(NH3)42+, CoCl4

2- cf) VSEPR Model

Square planar

eg) Cu(NH3)42+, Ni(II), Pd(II), Pt(II)


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


20.5 Isomers


Linkage Isomer


Ionization Isomers


Coordination (sphere) isomers


Geometric Isomers - SP

Cisplatin


Geometric Isomers - Oh


Geometric Isomerism


Optical Isomerism


20.6 Formulas


Naming Coordination Compounds


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


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)


• 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]


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.


Color and Coordination Compounds


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


Crystal Field Splitting


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


High and Low Spin


Strong Field Ligand vs. Weak Field Ligand

[Co(H2O)6]2+ [CoCl4]2-


[Co(H2O)6]2+ [CoCl4]2-


Effect of Ligands on the Colors of Coordination Compounds


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 )


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


Strong field Weak field Hund’s Rule strong paramagnetic


Magnetic Properties

Paramagnetism illustrated:


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


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


Electron transfer reaction


Problems

• 4, 26, 34, 38, 40, 60, 64, 72

coordination complexes chapter 20. copyright © houghton mifflin company. all rights reserved.20 | 2...

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coordination compounds

coordination complexeschapter

common coordination

o bond angles

bases ligands

following complexes

polydentate ligands

bidentate ligands