Transcript Chapter 22s - Valdosta State University

Chapter 22
Transition Elements
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Transition Elements – d- and f-block
• Used in construction and manufacturing (iron), coins (nickel,
copper, zinc), ornamental (gold, silver, platinum).
• Densest elements (osmium d=22.49 g/cm3, iridium d=22.41g/cm3).
• Highest melting point (tungsten, mp=3410oC) and lowest melting
point (mercury, mp=-38.9oC).
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Metal Chemistry
• Radioactive elements with atomic number less
than 83 (technetium 43; promethium 61).
• All elements are solids, but mercury.
• Have metallic sheen, conduct electricity and
heat.
• Are oxidized and form ionic compounds.
• Some are essential to living organisms: Cobalt
(vitamin B12), iron (hemoglobin and myoglobin),
molybdenium and iron (nitrogenase).
• Compounds are highly colored and used as
pigments: Fe4[Fe(CN)6)3 14 H2O (prussian blue),
TiO2 (white).
• Ions give color to gemstons: Iron(II) ions give
yellow color in citrine and chromium(III) ions
produce the red color of a ruby.
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Electron Configurations
• General:
[noble gas core] nsa (n-1) db
• Valance electrons for
transition elements reside in
the ns and (n-1) d subshells.
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Reactions
• All metals undergo oxidation with oxygen, halogens, aqueous acids.
• First the outermost electron is removed, followed by one or more d
electrons.
• Some generate cations with unpaired electrons = paramagnetism.
• Are colored.
• For first transition series common oxidation numbers are +2 and +3.
Fe: [Ar]3d64s2
Fe + Cl2
Fe + O2
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Fe + HCl
Fe + O2
Fe2O3
Fe3+
[Ar]3d5
Fe + Cl2
FeCl3
Fe3+
[Ar]3d5
Fe + HCl
FeCl2 + H2
Fe2+
[Ar]3d6
Trends: Oxidation number
Most common
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Trends: Atom Radius
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Trends: Density
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Trends: Melting Point
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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 ---> 2 Fe + 3 CO
Fe2O3 + 3 CO ---> 2 Fe + 3 CO2
• Lime added to remove impurities,
chiefly SiO2
SiO2 + CaO ---> CaSiO3
• Product is impure cast iron or pig
iron
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Hydrometallurgy
• Use aqueous solutions (flotation). Some use bacteria.
• Add CuCl2(aq) to ore such as CuFeS2 (chalcopyrite)
CuFeS2(s) + 3 CuCl2(aq) --> 4 CuCl(s) + FeCl2(aq) + 2 S(s)
• Dissolve CuCl with xs NaCl
CuCl(s) + Cl-(aq) --> [CuCl2]• Cu(I) disproportionates to Cu metal
2 [CuCl2]- --> Cu(s) + CuCl2 (aq) + 2 Cl-
Azurite, 2CuCO3•Cu(OH)2
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Native copper
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.
••
H N H
H
••
H O H
••
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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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Myoglobin / Hemoglobin
p.1084
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Coordination Chemistry
Vitamin B12
A naturally occurring
cobalt-based compound
Co atom
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Coordination Chemistry
• 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 Chemistry
Nickel ion:
coordination compounds
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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.
Ligand: monodentate
Coordinate to the metal via a
single Lewis base atom.
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Inner coordination sphere
Nomenclature
+
Ligand: polydentate
also chelating ligands
Coordinate with more
than one donor atom.
(Bidentate)
Co3+ + 2 Cl- + 2 neutral ethylenediamine molecules
Cis-dichlorobis(ethylenediamine)cobalt(II) chloride
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Cl-
Bidentate Ligands
Acetylacetone (acac)
Ethylenediamine (en)
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Bipyridine (bipy)
Oxalate (ox)
Bidentate Ligands
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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Give the formula of a coordination
compound
A Co3+ ion bound to one Cl- ion, one ammonia
molecule, and two ethylenediamine (en) molecules.
1.
2.
Determine the net charge (sum the charges of the
various components).
Place the formula in brackets and the net charge
attached.
[Co(H2NCH2CH2NH2)2(NH3)Cl]2+
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Determine the metal’s oxidation
number and coordination number
Pt(NH3)2(C2O4)
Oxalate: (C2O4)2Ammonia: NH3
Pt must be 2+ (oxidation number = +2)
Coordination number = 4 (two from oxalate and each ammonia filling one).
[Co(NH3)5Cl]SO4
Chloride: ClSulfate: SO42Overall complex must be 2+
Co must be 3+ (oxidation number = +3)
Coordination number = 6 (sulfate is not coordinated to the metal).
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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 in roman
numerals.
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Nomenclature
Co(H2O)62+
Hexaaquacobalt(II)
H2O as a ligand is aqua
Pt(NH3)2Cl2
Cu(NH3)42+
Tetraamminecopper(II)
diamminedichloroplatinum(II)
NH3 as a ligand is ammine
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Nomenclature
Tris(ethylenediamine)nickel(II)
[Ni(NH2C2H4NH2)3]2+
IrCl(CO)(PPh3)2
Vaska’s compound
Carbonylchlorobis(triphenylphosphine)iridium(I)
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Geometry of Coordination Compounds
Defined by the arrangement of donor atoms
of ligands around the central metal ion.
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Isomerim of Coordination Compounds
• 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.
Geometric and Optical
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Constitutional Isomers
O
Aldehydes & ketones
CH3-CH2-CH
O
H3C C CH3
3C, 1O, 6H
- Coordination isomerism: it is possible to exchange a
ligand and the uncoordinated counterion.
Example: [Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br
(violet)
(red)
- Linkage isomerism: it is possible to attach a ligand to the
metal through different atoms.
Usually: SCN- and NO2Valdosta State University
Constitutional Isomers
NH3 2+
H3N
NO2
sunlight
Co
H3N
NH3
NH3
2+
NH3
H 3N
ONO
Co
H3N
NH3
NH3
Such a transformation could be used as an energy
storage device.
Pentaamminenitritocobalt(III)
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Pentaamminenitrocobalt(III)
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 Isomers
Cis and trans-dichlorobis(ethylenediamine)cobalt(II)
chloride
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Geometric Isomers
For octahedral complexes (MX3Y3):
fac isomer has three identical ligands lying at the corners of a
triangular face of octahedron (fac=facial).
mer isomer ligands follow a meridian (mer=meridional).
fac isomer
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mer isomer
Stereoisomers
• 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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Enantiomers
[Co(NH2C2H4NH2)3]2+
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Stereoisomers
[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
N
Cl
have a plane of
Co
N
OH2
symmetry. Not chiral.
NH3
NH3 2+
N
NH3
Co
N
OH2
Cl
These two are
asymmetric. Have
non-superimposable
mirror images.
Stereoisomers
[Co(en)(NH3)2(H2O)Cl]2+
These are non-superimposable mirror images:
enantiomers
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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 ---> ligand field theory
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Bonding
• 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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Ligand Field Theory
[Ar]
4s
All electrons have the
same energy in the free ion
    
five 3d orbitals
• Consider what happens as 6 ligands approach an Fe3+
ion: Orbitals split into two groups as the ligands approach.
energy
t2g
eg
d(x2-y2)
dxy
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dxz
dz2
dyz
D0
Value of ligand field
sppliting: ∆o depends
on L: e.g., CN- > H2O
> Cl-
Octahedral Ligand Field
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Tetrahedral and Square Planar Ligand
Fields
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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
absorb “red wavelengths” and be colored blue.
energy
e
t2
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dxy
dxz
d(x2-y2)
dyz
dz2
Dt
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 size of ∆o and P, the pairing energy.
• P = energy required to create e- pair.
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Magnetic Properties of Fe2+
energy
eg
t2g
• High spin
d(x2-y2)
dxy
dz2
DE small
dxz
dyz
2
2
Paramagnetic
energy
t2g
eg
2
d(x -y )
dxy
dxz
dz
dyz
Diamagnetic
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• Weak ligand field strength
and/or lower Mn+ charge
• D0 is smaller than P
• [Fe(H2O)6]2+
• Low spin
D E large
• Stronger ligand field
strength and/or higher Mn+
charge
• D0 is larger than P
• [Fe(CN)6]4-
High and Low Spin Octahedral
Complexes
High or low spin octahedral complexes only possible
for d4, d5, d6, and d7 configurations.
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Why are complexes colored?
Fe3+
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Co2+
Ni2+
Cu2+
Zn2+
Why are complexes colored?
– Note that color observed is transmitted light.
Red and blue are absorbed
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Why are complexes colored?
– Note that color observed is transmitted light.
– Color arises from electron transitions between d
orbitals (d-to-d transitions).
– 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. The ability to split the d
orbitals is determined by spectroscopy.
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Light absorption by octahedral Co3+
complex
d(x -y )

dxz


dxy
dz2
+ energy (= D0 )

dyz

Ground state

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:
small ∆o
large ∆o
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+