John C. Kotz
Paul M. Treichel
John Townsend http://academic.cengage.com/kotz
Chapter 22
The Chemistry of the Transition Elements
John C. Kotz • State University of New York, College at Oneonta

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5
Citrine and amethyst are quartz (SiO
2
) with a trace of cationic iron that gives rise to the color.
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Rhodochrosite, MnCO
3

7
Fe + Cl
2
Fe + HCl
Fe + O
2
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Most common
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• Involves high temperature, such as Fe
• C and CO used as reducing agents in a blast furnace
•
• Fe
2
O
3
Fe
2
O
3
+ 3 C f 2 Fe + 3 CO
+ 3 CO f 2 Fe + 3 CO
2
• Lime added to remove impurities, chiefly
SiO
2
SiO
2
+ CaO f CaSiO
3
• Product is impure cast iron or pig iron
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See Active Figure 22.8

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Molten iron is poured from a basic oxygen furnace.

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Azurite, 2CuCO
3
·Cu(OH)
2
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Native copper

• Uses aqueous solutions
• Add CuCl
2
(aq) to ore such as CuFeS
2
(chalcopyrite)
CuFeS
2
(s) + 3 CuCl
2
(aq) f 4 CuCl(s) + FeCl
2
(aq) + 2 S(s)
• Dissolve CuCl with xs NaCl
CuCl(s) + Cl (aq) f [CuCl
2
] -
• Cu(I) disproportionates to Cu metal
2 [CuCl
2
] f Cu(s) + CuCl
2
(aq) + 2 Cl -
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SeeFigure 22.11
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• Coordination compounds
– combination of two or more atoms, ions, or molecules where a bond is formed by sharing a pair of electrons originally associated with only one of the compounds.
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CH
2
Cl
CH
2
Pt
Cl
Cl
-
19

Pt(NH
3
)
2
Cl
2
20
Co(H
2
O)
6
2+
“Cisplatin” - a cancer chemotherapy agent
Cu(NH
3
)
4
2+
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An iron-porphyrin, the basic unit of hemoglobin
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A naturally occurring cobalt-based compound
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Co atom

• Biological nitrogen fixation contributes about half of total nitrogen input to global agriculture, remainder from Haber process.
• To produce the H
2 for the Haber process consumes about 1% of the world’s total energy.
• A similar process requiring only atmospheric T and P is carried out by N-fixing bacteria, many of which live in symbiotic association with legumes.
• N-fixing bacteria use the enzyme nitrogenase — transforms N
2
NH
3
.
into
• Nitrogenase consists of 2 metalloproteins: one with Fe and the other with Fe and Mo.
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Coordination
Compounds of Ni 2+
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Nomenclature
Ni(NH
3
)
6
] 2+
A Ni 2+ ion surrounded by 6, neutral NH
3 ligands
Gives coordination complex ion with 2+ charge.
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Nomenclature
Inner coordination sphere
Ligand: monodentate
+
Cl -
Ligand: bidentate
Co 3+ + 2 Cl + 2 neutral ethylenediamine molecules
Cis-dichlorobis(ethylenediamine)cobalt(II) chloride
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Common Bidentate Ligands
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Acetylacetone (acac)
Ethylenediamine (en)
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Bipyridine (bipy)
Oxalate (ox)

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Acetylacetonate
Complexes
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Commonly called the “acac” ligand. Forms complexes with all transition elements.

EDTA 4- ethylenediaminetetraacetate ion
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Multidentate ligands are sometimes called
CHELATING ligands

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Co 2+ complex of EDTA 4-

Nomenclature
Cis-dichlorobis(ethylenediamine)cobalt(III) chloride
1. Positive ions named first
2. Ligand names arranged alphabetically
3. Prefixes -- di, tri, tetra for simple ligands bis, tris, tetrakis for complex ligands
4. If M is in cation, name of metal is used
5. If M is in anion, then use suffix -ate
[CuCl
4
] 2= tetrachlorocuprate
6. Oxidation no. of metal ion indicated
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[Co(H
2
O)
6
] 2+
Hexaaquacobalt(II)
H
2
O as a ligand is aqua [Cu(NH
3
)
4
] 2+
Tetraamminecopper(II)
Pt(NH
3
)
2
Cl
2 diamminedichloroplatinum(II)
NH
3 as a ligand is ammine
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Pt(
Tris(ethylenediamine)nickel(II)
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[Ni(NH
2
C
2
H
4
NH
2
)
3
] 2+
IrCl(CO)(PPh
3
)
2
Vaska’s compound
Carbonylchlorobis(triphenylphosphine)iridium(I)
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• Two forms of isomerism
– Constitutional
– Stereoisomerism
• Constitutional
– Same empirical formula but different atomto-atom connections
• Stereoisomerism
– Same atom-to-atom connections but different arrangement in space.
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O
Aldehydes & ketones
CH
3
-CH
2
-CH H
3
C
O
C CH
3
H
2
O
H
2
O
OH
Cr
2
Cl
OH
2
Cl green
Cl
H
2
O
H
2
O
OH
2
Cr
OH
2
OH
2
OH
2 violet
Cl
3
Peyrone’s chloride: Pt(NH
3
)
2
Magnus’s green salt: [Pt(NH
3
)
Cl
2
4
][PtCl
4
]
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H
H
3
3
N
N
NH
3
Co
2+
NO
2
NH
3
NH
3 sunlight
H
H
3
3
N
N
NH
Co
3
NH
3
ONO
NH
3
2+
Such a transformation could be used as an energy storage device.
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• One form is commonly called geometric isomerism or cis-trans isomerism . Occurs often with square planar complexes .
38 cis trans
Note: there are VERY few tetrahedral complexes. Would not have geometric isomers.
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Cis and trans-dichlorobis(ethylenediamine)cobalt(II) chloride
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Fac isomer
Mer isomer

• Enantiomers: stereoisomers that have a nonsuperimposable mirror image
• Diastereoisomers: stereoisomers that do not have a non-superimposable mirror image (cistrans isomers)
• Asymmetric: lacking in symmetry—will have a non-superimposable mirror image
• Chiral: an asymmetric molecule
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[Co(NH
2
C
2
H
4
NH
2
)
3
] 2+

[Co(en)(NH
3
)
2
(H
2
O)Cl] 2+
N
N
Cl
Co
NH
OH
2
NH
2+
3
3
N
N
NH
3
Cl
2+
Co
NH
3
OH
2
These two isomers have a plane of symmetry.
Not chiral.
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N
N
NH
3
NH
2+
3
Co
OH
2
Cl
N
N
NH
Co
3
NH
2+
3
Cl
OH
2
These two are asymmetric. Have non-superimposable mirror images.
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These are non-superimposable mirror images
[Co(en)(NH
3
)
2
(H
2
O)Cl] 2+
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Bonding in Coordination Compounds
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• Model must explain
– Basic bonding between M and ligand
– Color and color changes
– Magnetic behavior
– Structure
• Two models available
– Molecular orbital
– Electrostatic crystal field theory
– Combination of the two f ligand field theory
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Bonding in Coordination Compounds
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• As ligands L approach the metal ion M + ,
– L/M + orbital overlap occurs
– L/M + electron repulsion occurs
• Crystal field theory focuses on the latter, while MO theory takes both into account
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Bonding in Coordination Compounds
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Crystal Field Theory
• Consider what happens as 6 ligands approach an Fe 3+ ion
[Ar]
4s
     five 3d orbitals
All electrons have the same energy in the free ion
Orbitals split into two groups as the ligands approach.
energy e g t
2g
 d xy
  d(x 2 -y 2 ) dz 2
 d xz
 d yz
²E = ² o
Value of ∆ o depends on ligand: e.g., H
2
O > Cl -
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Octahedral Ligand Field
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Tetrahedral & Square Planar
Ligand Field
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Crystal Field Theory
• Tetrahedral ligand field
• Note that ∆ t
= 4/9 ∆ o and so ∆ t is small
• Therefore, tetrahedral complexes tend to blue end of spectrum energy e
 d xy
 d xz
 d yz
²E = ² t t
2
  d(x 2 -y 2 ) dz 2
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Ways to Distribute Electrons
• For 4 to 7 d electrons in octahedral complexes, there are two ways to distribute the electrons.
– High spin — maximum number of unpaired e-
– Low spin — minimum number of unpaired e-
• Depends on size of ∆ o and P, the pairing energy.
• P = energy required to create e- pair.
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2+

 
) ) dz t t
Paramagnetic energy e g d(x
2
-y
2
) dz
2 t
2g
 d xy

 d xz

Diamagnetic
 d yz

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² E small
² E large
• High spin
• Weak ligand field strength and/or lower
M n+ charge
• Higher P possible?
• Low spin
• Stronger ligand field strength and/or higher M n+ charge
• Lower P possible?
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High and Low Spin Octahedral Complexes
See Figure 22.25
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High or low spin octahedral complexes only possible for d 4 , d 5 , d 6 , and d 7 configurations.
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Crystal Field Theory
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Why are complexes colored?
Fe 3+
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Co 2+ Ni 2+ Cu 2+ Zn 2+

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Crystal Field Theory
Why are complexes colored?
– Note that color observed for
Ni 2+ in water is transmitted light
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Crystal Field Theory
• Why are complexes colored?
– Note that color observed is transmitted light
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Absorption band
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Crystal Field Theory
• Why are complexes colored?
– Note that color observed is transmitted light
– Color arises from electron transitions between d orbitals
– Color often not very intense
• Spectra can be complex
– d 1 , d 4 , d 6 , and d 9 --> 1 absorption band
– d 2 , d 3 , d 7 , and d 8 --> 3 absorption bands
• Spectrochemical series — ligand dependence of light absorbed.
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Light Absorption by
Octahedral Co 3+ Complex energy e g d(x
2
-y
2
) dz
2 t
2g
 d xy

 d xz

Ground state
 d yz

+ energy (= ² o)
(light absorbed) energy e g t
2g

 d xy
 d(x
2
-y
2
) dz
2
 d xz

 d yz
Excited state
Usually excited complex returns to ground state by losing energy, which is observed as heat.
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Spectrochemical Series
• d orbital splitting (value of ∆ o the order
) is in
I < Cl < F < H
2
O < NH phen < CN < CO
3
< en <
As ∆ increases, the absorbed light tends to blue, and so the transmitted light tends to red.
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Other Ways to Induce Color
• Intervalent transfer bands (IT) between ion of adjacent oxidation number.
– Aquamarine and kyanite are examples
– Prussian blue
• Color centers
– Amethyst has Fe 4+
– When amethyst is heated, it forms citrine as Fe 4+ is reduced to Fe 3+
Prussian blue contains Fe 3+ and Fe 2+
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