Transcript Transition Metal Chemistry - Site title

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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Transition Metal Chemistry
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Transition Metal Chemistry
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Gems & Minerals
Citrine and amethyst are quartz (SiO2) with a
trace of cationic iron that gives rise to the color.
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Gems & Minerals
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Rhodochrosite, MnCO3
Reactions: Transition Metals
Fe + Cl2
Fe + O2
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Fe + HCl
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Periodic Trends: Atom Radius
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Periodic Trends: Density
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Periodic Trends: Melting Point
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Periodic Trends:
Oxidation Numbers
Most common
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Metallurgy: Element Sources
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Pyrometallurgy
• Involves high temperature, such as Fe
• C and CO used as reducing agents in a
blast furnace
• Fe2O3 + 3 C f 2 Fe + 3 CO
• Fe2O3 + 3 CO f 2 Fe + 3 CO2
• Lime added to remove impurities, chiefly
SiO2
SiO2 + CaO f CaSiO3
• Product is impure cast iron or pig iron
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Metallurgy:
Blast
Furnace
See Active Figure 22.8
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Metallurgy:
Blast
Furnace
Molten iron is poured from
a basic oxygen furnace.
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Metallurgy: Copper Ores
Azurite, 2CuCO3·Cu(OH)2
Native copper
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Metallurgy: Hydrometallurgy
• Uses aqueous solutions
• Add CuCl2(aq) to ore such as CuFeS2 (chalcopyrite)
CuFeS2 (s) + 3 CuCl2 (aq)
f 4 CuCl(s) + FeCl2 (aq) + 2 S(s)
• Dissolve CuCl with xs NaCl
CuCl(s) + Cl-(aq) f [CuCl2]• Cu(I) disproportionates to Cu metal
2 [CuCl2]- f Cu(s) + CuCl2 (aq) + 2 Cl-
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Electrolytic Refining of Cu
SeeFigure 22.11
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Coordination Chemistry
• 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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CH2
CH2
-
Cl
Pt
Cl
Cl
Coordination Chemistry
Pt(NH3)2Cl2
“Cisplatin” - a cancer
chemotherapy agent
Co(H2O)62+
Cu(NH3)42+
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Coordination Chemistry
An iron-porphyrin, the basic unit of hemoglobin
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Vitamin B12
A naturally occurring
cobalt-based compound
Co atom
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Nitrogenase
• Biological nitrogen fixation contributes about half of total nitrogen
input to global agriculture, remainder from Haber process.
• To produce the H2 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 N2 into
NH3.
• Nitrogenase consists of 2 metalloproteins: one with Fe and the other
with Fe and Mo.
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Coordination
Compounds
of Ni2+
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Nomenclature
Ni(NH3)6]2+
A Ni2+ ion surrounded
by 6, neutral NH3
ligands
Gives coordination
complex ion with 2+
charge.
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Nomenclature
Inner coordination sphere
Ligand: monodentate
+
Cl-
Ligand: bidentate
Co3+ + 2 Cl- + 2 neutral ethylenediamine molecules
Cis-dichlorobis(ethylenediamine)cobalt(II) chloride
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Common Bidentate Ligands
Bipyridine (bipy)
Acetylacetone (acac)
Ethylenediamine (en)
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Oxalate (ox)
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Acetylacetonate
Complexes
Commonly called the “acac”
ligand. Forms complexes with
all transition elements.
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Multidentate Ligands
EDTA4- - ethylenediaminetetraacetate ion
Multidentate ligands are sometimes called
CHELATING ligands
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Multidentate
Ligands
Co2+ complex
of EDTA4-
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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
[CuCl4]2- = tetrachlorocuprate
6. Oxidation no. of metal ion indicated
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Nomenclature
[Co(H2O)6]2+
Hexaaquacobalt(II)
H2O as a ligand is aqua
Pt(NH3)2Cl2
[Cu(NH3)4]2+
Tetraamminecopper(II)
diamminedichloroplatinum(II)
NH3 as a ligand is ammine
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Nomenclature
Pt(
Tris(ethylenediamine)nickel(II)
[Ni(NH2C2H4NH2)3]2+
IrCl(CO)(PPh3)2
Vaska’s compound
Carbonylchlorobis(triphenylphosphine)iridium(I)
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Structures of Coordination
Compounds
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Isomerism
• 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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Constitutional Isomerism
Aldehydes & ketones
OH2
H2O
Cl
Cl
Cr
H2O
Cl
OH2
green
O
CH3-CH2-CH
O
H3C C CH3
OH2
H2O
OH2 Cl3
Cr
H2O
OH2
OH2
violet
Peyrone’s chloride: Pt(NH3) 2Cl2
Magnus’s green salt: [Pt(NH3)4][PtCl4]
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Linkage Isomerism
NH3 2+
H3N
NO2
sunlight
Co
H3N
NH3
NH3
2+
NH3
H3N
ONO
Co
H3N
NH3
NH3
Such a transformation could be used as an energy
storage device.
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Stereoisomerism
• One form is commonly called geometric
isomerism or cis-trans isomerism. Occurs often
with square planar complexes.
cis
trans
Note: there are VERY few tetrahedral
complexes. Would not have geometric isomers.
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Geometric Isomerism
Cis and trans-dichlorobis(ethylenediamine)cobalt(II)
chloride
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Geometric Isomerism
Fac isomer
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Mer isomer
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Stereoisomerism
• 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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An Enantiomeric Pair
[Co(NH2C2H4NH2)3]2+
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Stereoisomerism
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[Co(en)(NH3)2(H2O)Cl]2+
N
N
Cl
Co
2+
NH3
NH3
OH2
NH3 2+
N
NH3
Co
N
Cl
OH2
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NH3 2+ These two isomers have
N
Cl
a plane of symmetry.
Co
N
OH2
Not chiral.
NH3
NH3 2+
N
NH3
Co
N
OH2
Cl
These two are
asymmetric. Have
non-superimposable
mirror images.
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Stereoisomerism
These are non-superimposable mirror images
[Co(en)(NH3)2(H2O)Cl]2+
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Bonding in Coordination Compounds
• 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
• 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 Fe3+ ion
[Ar]
All electrons have
the same energy in
the free ion
    
five 3d orbitals
4s
Orbitals split into two groups as the ligands approach.
energy
eg
t2g
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
2

2
d(x -y )

dxy

dxz
dz
2

dyz
²E = ²
o
Value of ∆o
depends on
ligand:
e.g., H2O > 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
t2
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
dxy

dxz

d(x 2-y2)

dyz

dz 2
²E = ²
t
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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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Magnetic Properties/Fe2+

d(x2-y2)
eg

dxy

energy
t2g
• High spin

dz

dxz
2
² E small

dyz
Paramagnetic
d(x2-y2)

dxy

dxz


t2g
eg
dz2

dyz
Diamagnetic
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² E large

energy
• Weak ligand field
strength and/or lower
Mn+ charge
• Higher P possible?
• Low spin
• Stronger ligand field
strength and/or
higher Mn+ charge
• Lower P possible?
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High and Low Spin Octahedral Complexes
See Figure 22.25
High or low spin octahedral complexes only possible
for d4, d5, d6, and d7 configurations.
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Crystal Field Theory
Why are complexes colored?
Fe3+
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Co2+
Ni2+
Cu2+
Zn2+
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Crystal Field Theory
Why are complexes colored?
–
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Note that color observed for
Ni2+ in water is transmitted
light
Crystal Field Theory
• Why are complexes colored?
– Note that color observed is transmitted light
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
– d1, d4, d6, and d9 --> 1 absorption band
– d2, d3, d7, and d8 --> 3 absorption bands
• Spectrochemical series — ligand dependence of light
absorbed.
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Light Absorption by
Octahedral Co3+ Complex
d(x -y )

dxz


dxy
dz2

Ground state
+ energy (= ² o)

dyz

2
(light absorbed)
t2g
eg
d(x2-y2)

dxy

t2g
2
dz2

dxz

eg
energy

energy
Excited state
Usually excited complex returns to ground state by losing
energy, which is observed as heat.
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
dyz
Spectrochemical Series
• d orbital splitting (value of ∆o) is in
the order
I- < Cl- < F- < H2O < NH3 < en <
phen < CN- < CO
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 Fe4+
– When amethyst is heated, it forms
citrine as Fe4+ is reduced to Fe3+
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Prussian blue
contains Fe3+
and Fe2+