Chapter 22 The Chemistry of the Transition Elements

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Chapter 22The Chemistry of the Transition
Elements
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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

• Rhodochrosite, MnCO3

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Reactions Transition Metals
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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
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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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MetallurgyBlast Furnace
See Active Figure 22.8
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MetallurgyBlast Furnace
Molten iron is poured from a basic oxygen furnace.
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Metallurgy Copper Ores
Azurite, 2CuCO3Cu(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 NaClCuCl(s) Cl-(aq) f
  CuCl2-
• Cu(I) disproportionates to Cu metal2 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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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
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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 worlds 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)62 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
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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 CuCl42- tetrachlorocuprate 6.
Oxidation no. of metal ion indicated
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Nomenclature
Co(H2O)62
Hexaaquacobalt(II)
Cu(NH3)42
H2O as a ligand is aqua
Tetraamminecopper(II)
Pt(NH3)2Cl2
diamminedichloroplatinum(II)
NH3 as a ligand is ammine
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Nomenclature
Tris(ethylenediamine)nickel(II)
Pt(
Ni(NH2C2H4NH2)32
IrCl(CO)(PPh3)2
Vaskas 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 atom-to-atom
  connections
• Stereoisomerism
• Same atom-to-atom connections but different
  arrangement in space.

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Constitutional Isomerism
Aldehydes ketones
Peyrones chloride Pt(NH3) 2Cl2 Magnuss green
salt Pt(NH3)4PtCl4
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Linkage Isomerism
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.

Note there are VERY few tetrahedral complexes.
Would not have geometric isomers.
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Geometric Isomerism
Cis and trans-dichlorobis(ethylenediamine)cobalt(I
I) chloride
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Geometric Isomerism
Mer isomer
Fac isomer
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Stereoisomerism

• Enantiomers stereoisomers that have a
  non-superimposable mirror image
• Diastereoisomers stereoisomers that do not have
  a non-superimposable mirror image (cis-trans
  isomers)
• Asymmetric lacking in symmetrywill have a
  non-superimposable mirror image
• Chiral an asymmetric molecule

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An Enantiomeric Pair
Co(NH2C2H4NH2)32
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StereoisomerismCo(en)(NH3)2(H2O)Cl2
These two isomers have a plane of symmetry. Not
chiral.
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)Cl2
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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

All electrons have the same energy in the free ion
Orbitals split into two groups as the ligands
approach.
Value of ?o depends on ligand e.g., H2O gt 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

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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

• High spin
• Weak ligand field strength and/or lower Mn
  charge
• Higher P possible?

Paramagnetic

• Low spin
• Stronger ligand field strength and/or higher Mn
  charge
• Lower P possible?

Diamagnetic
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High and Low Spin Octahedral ComplexesSee 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
Co2
Cu2
Ni2
Zn2
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Crystal Field Theory

• Why are complexes colored?
• Note that color observed for Ni2 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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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 --gt 1 absorption band
• d2, d3, d7, and d8 --gt 3 absorption bands
• Spectrochemical series ligand dependence of
  light absorbed.

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Light Absorption by Octahedral Co3 Complex
Ground state
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) is in the
  orderI- lt Cl- lt F- lt H2O lt NH3 lt en lt phen lt CN-
  lt 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

Prussian blue contains Fe3 and Fe2