Transcript Coordination Chemistry: History, Introduction to Structure, and Nomenclature Chapter 7 and 19

Coordination Chemistry:
History, Introduction to Structure, and Nomenclature
Chapter 7 and 19
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1. Coordination Compounds
Composed of:
 Metal atoms or ions
 One or more ligands (atoms, ions, or molecules) that donate e- to the metal
 Chemistry of the metal d-orbitals
Consist of the formation of coordinate covalent bonds:
M
+
L
M-L
 Lewis Acid-Base Adduct
Metal is the Lewis Acid
Ligand is the Lewis Base
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2. History
A. A tale as old as time (Prehistoric)
B. Formally introduced by Alfred Werner (late 19th Century)
 Introduced new bonding concepts
 The famous Werner Cobalt Compounds
Compound
A
B
C
D
Elemental Formula
CoN6H18Cl3
CoN5H15Cl3
CoN4H12Cl3
CoN3H9Cl3
Color
Yellow
Red
Green or Purple
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2. History: Werner Compounds
Compound
A
B
C
D
Elemental Formula
CoN6H18Cl3
CoN5H15Cl3
CoN4H12Cl3
CoN3H9Cl3
Color
Yellow
Red
Green or Purple
 Early bonding theories allowed only three atoms to be attached to cobalt
because of its valence of 3 (Co3+) for charge balance.
 Jørgensen proposed that for the above compounds
• N could form chains because of its valence of 5
• Chloride (Cl-) could be bound to N or to Co3+
 Werner proposed something very radical for the time
• As many as 6 N (as NH3) could bond directly to Co3+
• Cl- could bond to Co3+ or associate loosely; two kinds of Cl
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2. History: The Werner Titrations
n AgCl + Complexn+
Complex + AgNO3
Compound
Jørgensen
AgCl mols
A
3
B
2
Warning: Isomer?
C
1
Warning: 0 Cl?
D
0
Werner
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2. History: Werner’s Theory
A. Primary Bonding (3Cl-)


The positive charge of the metal ion is balanced by negative ions.
Does not have to involve direct bonding to the metal ion.
A. Secondary Bonding (6NH3)




Ligands (molecules or ions) directly attached to the metal ion.
This interaction constitutes the coordination sphere; the complex ion.
• Today we refer to it as the primary coordination sphere.
Defines the coordination number.
Defines a specific geometry; “directed in space”.
Remember these are older theories
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2. History: Werner’s Theory
Which one would give us the isomer that we need for complex C?
=
a
b
c
d
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2. History: Werner’s Theory
Which are the possible isomers?
cis mirror images (violet)
trans (green)
or
Co
Co
or
Co
Ethylenediamone (en)
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3. Nomenclature Rules
A. For charged molecules, the cation comes first followed by the anion.
The following rules apply to both neutral and charged molecules:
B. The elemental formulation has the inner coordination sphere in brackets.
[Pt(NH3)4]Cl2
 When writing the name, the ligands within the coordination sphere are written before the
metal and are listed in alphabetical order.
tetraammineplatinum(II) chloride
C. Ligand names (handout page 1).
 Monodentate: Ligands with one point of attachment
 Chelates (Bidentate…multidentate): Ligands with two or more points of attachment
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3. Nomenclature Rules
C. The number of ligands of each kind is indicated by prefixes using the following table.
A
B

Use prefixes in column A for simple cases.

Use prefixes in column B for ligands with names that already
use prefixes from column A.
[Co(en)2Cl2]+
Dichlorobis(ethylenediamine)cobalt(III)
 Always use prefixes in column B when the name of a ligand
begins with a vowel.
[Rh(en)3]3+
Tris(ethylenediamine)rhodium(III)
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3. Nomenclature Rules
D. Ligands are written in alphabetical order-according to the ligand name, not the prefix.
E. Special:
 Anionic ligands are given an o suffix.
 Neutral ligands retain their usual name
 Coordinated water is called aqua
 Coordinated ammonia is called ammine
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3. Nomenclature Rules
F. Designate the metal oxidation state after the metal.
[PtClBr(NH3)(H2O)]
Ammine
Ammineaquabromochloroplatinum(II)
aqua
bromo
chloro
platinum(II)
[Pt(NH3)4]2+
Tetraammineplatinum(II)
If the molecule is negatively charged, the suffix –ate is added to the name
[Pt(NH3)Cl3]Amminetrichloroplatinate(II)
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3. Nomenclature Rules
Special names for metals when in a negatively charged molecule:
Copper (Cu): Cuprate
Iron (Fe): ferrate
Silver (Ag): argentate
Lead (Pb): Plumbate
Tin(Sn): Stannate
Gold(Au): Aurate
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3. Nomenclature Rules
G. Prefixes designate adjacent (cis-) and opposite (trans-) geometric locations
 cis-diamminedichloroplatinum(II) is an anticancer agent.
 The trans isomer is not.
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3. Nomenclature Rules
H. Bridging ligands between two metal ions have the prefix μ
μ-amido-μ-hydroxobis(tetraaminecobalt)(IV)
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