C h a pt e r
20
Transition Elements and
Coordination Chemistry
Chemistry 4th Edition
McMurry /Fay
Dr. Paul Charlesworth
Michigan Technological University
Transition Metal Properties
Prentice Hall ©2004
Chapter20
Transition Metal Properties
02
Slide 2
03
••Lanthanide
Atomic
RelativeRadii
melting
Contraction:
of Transition
Lanthanides:
points
Elements:
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Chapter20
Slide 3
1
Transition Metal Properties
Relative Densities:
•
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Chapter20
Transition Metal Properties
•
04
Slide 4
04
Oxidation States:
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Chapter20
Transition Metal Properties
Slide 5
05
Oxidation States: With the exception of Cu, first
row solid transition metals are more easily oxidized
than hydrogen.
•
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Chapter20
Slide 6
2
Transition Metal Properties
•
Oxidation States: Most
transition metal oxidation
states are brightly colored.
•
Manganese is shown left to
right:
• Mn2+
• Mn3+
• Mn4+
• Mn6+
• Mn7+
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06
Chapter20
Slide 7
Coordination Compounds
•
Coordination compounds are species in which a
central metal ion (or atom) is attached to a group of
surrounding molecules or ions by coordinate
covalent bonds.
•
•
•
•
01
Surrounding groups are called Ligands .
Central metal is a Lewis acid.
Ligand is a Lewis base.
The number of ligand donor atoms surrounding the
central metal is called the coordination number.
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Chapter20
Slide 8
Coordination Compounds
•
Coordinate bond:
H
H
Ag +(aq) + 2
H
H
H
+
H
H Ag H
H
H
•
02
H
H
Coordination Sphere:is the central metal and
surrounding ligands. The square brackets separate
the complex from counter ions such as SO42–.
[Ag(NH3)2]2 SO4
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Chapter20
Slide 9
3
Coordination Compounds
•
03
Charge of a complex is the sum of the charges on
central metal and ligands.
[Cu(NH 3 ) 4 ] 2+
+2
+
4 (0) = +2
1)
What is the oxidation number for [Co(NH 3)5Cl](NO3)2?
2)
A complex ion contains a Cr3+ bound to four H 2O
molecules and two Cl– ions. Write its formula.
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Chapter20
Coordination Compounds
•
Slide 10
04
Geometries:
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Chapter20
Ligands
Slide 11
01
•
Monodentate ligands bond using the electron
pairs of a single atom.
•
Bidentate ligands bond using the electron pairs of
two atoms.
•
Polydentate ligands bond using the electron pairs
of many atoms. This group includes bidentate.
•
Polydentate ligands are also known as chelating
agents.
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Chapter20
Slide 12
4
Ligands
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02
Chapter20
Ligands
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03
Chapter20
Ligands
Slide 14
04
•
EDTA4– is commonly added
to food products such as
commercial salad dressings.
•
EDTA4– is often used to treat
heavy metal poisoning such
as Hg2+, Pb2+, and Cd2+.
•
EDTA4– bonds to Pb2+, which
is excreted by the kidneys as
[Pb(EDTA)]2–.
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Slide 13
Chapter20
Slide 15
5
Ligands
05
(a) and (b) represent bidentate ligands bound to cobalt.
(c) and (d) represent a hexadentate ligand bound to cobalt.
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Chapter20
Nomenclature
•
01
Systematic naming specifies the type and number
of ligands, the metal, and its oxidation state.
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Chapter20
Nomenclature
•
Slide 16
Slide 17
02
Systematic naming follows IUPAC rules:
•
If compound is a salt, name cation first and then the
anion, just as in naming simple salts.
•
In naming a complex ion or neutral complex, name
ligands first and then the metal.
•
If the complex contains more than one ligand of a
particular type, indicate the number with the appropriate
Greek prefix: di–, tri–, tetra–, penta–, hexa–.
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Chapter20
Slide 18
6
Nomenclature
•
03
If the name of a ligand itself contains a Greek prefix, put
the ligand name in parentheses and use: bis (2), tris (3),
or tetrakis (4).
•
Use a Roman numeral in parentheses, immediately
following the name of the metal, to indicate the metal’s
oxidation state.
•
In naming the metal, use the ending –ate if metal is in an
anionic complex.
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Chapter20
Nomenclature
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04
Chapter20
Isomers
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Slide 19
Slide 20
01
Chapter20
Slide 21
7
Isomers
•
01
Isomers are compounds that have the same formula but a
different atomic arrangement.
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Chapter20
Isomers
•
Slide 22
02
Constitutional Isomers: Have different
connections among their constituent atoms.
•
Ionization Isomers differ in that the anion is bonded to
the metal ion. Compare [Co(NH3)5Br]SO4 (violet
compound with Co–Br bond), and [Co(NH3)5 SO 4]Br (red
compound with Co–SO 4 bond).
•
Linkage Isomers form when a ligand can bond through
two different donor atoms. Consider [Co(NH3)5NO2] 2+
which is yellow with the Co–NO2 bond and red with the
Co–ONO bond.
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Chapter20
Isomers
Slide 23
03
[Co(NH3)5NO2]2+, Linkage isomers.
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Chapter20
Slide 24
8
Isomers
•
04
Diastereoisomers (geometric) have the same
connections among atoms but different spatial
orientations of the metal–ligand bonds.
a) cis isomers have identical ligands in adjacent corners
of a square.
b) trans isomers have identical ligands across the
corners from each other.
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Chapter20
Isomers
•
05
Geometric Isomers of Pt(NH3) 2Cl2: In the cis
isomer, atoms are on the same side. In the trans
isomer, atoms are on opposite sides.
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Chapter20
Isomers
•
Slide 25
Slide 26
06
Geometric Isomers of [Co(NH3) 4Cl2]Cl:
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Chapter20
Slide 27
9
Isomers
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07
Chapter20
Isomers
Slide 28
07
•
Enantiomers are stereoisomers of molecules or
ions that are nonidentical mirror images of each
other.
•
Objects that have “handedness” are said to be
chiral , and objects that lack “handedness” are said
to be achiral .
•
An object or compound is achiral if it has a
symmetry plane cutting through the middle.
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Chapter20
Isomers
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Slide 29
08
Chapter20
Slide 30
10
Isomers
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09
Chapter20
Isomers
Slide 31
09
•
Enantiomers have identical properties except
for their reaction with other chiral substances
and their effect on plane-polarized light.
•
Enantiomers are often called optical isomers;
their effect on plane-polarized light can be
measured with a polarimeter.
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Chapter20
Isomers
Slide 32
10
•
Plane-polarized light is obtained by passing
ordinary light through a polarizing filter.
•
In a polarimeter the plane-polarized light is passed
though a chiral solution and the polarization plane
measured with an analyzing filter.
•
If the plane rotates to the right it is dextrorotatory.
•
If the plane rotates to the left it is levorotatory.
•
Equal amounts of each are racemic.
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Chapter20
Slide 33
11
Bonding in Complexes
•
Bonding Theories attempt to account for the
color and magnetic properties
of transition metal complexes.
2+
Ni
Ni2+
Co2+
2+
Cu
Cu2+
Zn2+
Prentice Hall ©2004
of [Ni(H2O)6] 2+ ,
[Ni(NH 3)6] 2+ , & [Ni(en)3] 2+
•Solutions
Chapter20
Bonding in Complexes
•
01
Slide 34
02
The color of any substance is related to the
wavelength(s) of light absorbed by the substance.
E2
EXCITED STATE
hν
E1
GROUND STATE
λ=
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hc
∆E
Chapter20
Bonding in Complexes
Slide 35
03
•
Valence Bond Theory predicts metal complex
bonding arises from overlap of filled ligand orbitals
and vacant metal orbitals.
•
Resulting bond is a coordinate covalent bond.
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Chapter20
Slide 36
12
Bonding in Complexes
•
Complex geometry can be linked to five main
orbital hybridization processes.
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Chapter20
Bonding in Complexes
•
Slide 37
05
Tetrahedral Geometry: Gives [CoCl4]2 – three
unpaired electrons,which makes it paramagnetic
and attracted by magnets.
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Chapter20
Bonding in Complexes
•
04
Slide 38
06
Square Planar Geometry: Gives [Ni(CN) 4]2– all
paired electrons,which makes it diamagnetic and
weakly repelled by magnets.
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Chapter20
Slide 39
13
Bonding in Complexes
•
Octahedral sp3d2 Geometry: Gives [CoF6]3– four
unpaired electrons,which makes it paramagnetic
and is called a high-spin complex.
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Chapter20
Bonding in Complexes
•
08
Chapter20
Bonding in Complexes
•
Slide 40
Octahedral d2sp3 Geometry: Gives [Co(CN) 6]3 –
paired electrons,which makes it diamagnetic and is
called a low-spin complex .
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•
07
Slide 41
09
The difference between sp3d2 and d2sp3 hybrids
lies in the principal quantum number of the d
orbital.
•
In sp3d2 hybrids , the s, p, and d orbitals have the same
principal quantum number—High Spin.
•
In d2sp3 hybrids , the principal quantum number of the d
orbitals is one less than s and p orbitals—Low Spin.
A complex’s magnetic properties determine which
hybrid is being used.
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Chapter20
Slide 42
14
Bonding in Complexes
10
•
Crystal Field Theory is a model that helps explain
why some complexes are high spin and some are
low spin.
•
Crystal Field Theory views bonding in complexes
as the result of electrostatic interactions and
considers the effect of ligand charges on energies
of metal ion d orbitals.
•
Crystal Field Theory uses no covalent bonds.
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Chapter20
Bonding in Complexes
Slide 43
11
CFT – Octahedral
Complexes
•
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Chapter20
Bonding in Complexes
•
Slide 44
12
d-electron to ligand -electron repulsions affect d-orbital
energy levels.
•
dz 2 and dx 2 – y 2 orbitals
point at the ligands
and have higher
energies than other
d-electrons.
•
This energy gap (?) is called crystal field splitting.
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Chapter20
Slide 45
15
Bonding in Complexes
•
13
The crystal field splitting energy (?) corresponds to light
wavelengths in the visible region of the spectrum.
•
[Ti(H2O) 6]3+ contains a single d-electron in lower energy
orbitals. 500 nm light absorption promotes the d-electron.
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Chapter20
Bonding in Complexes
Slide 46
14
•
Absorption spectra of different complexes indicate the
crystal field splitting energy depends on the ligand’s nature.
•
For Ni2+ complexes ? increases as the ligand changes from
H 2O to NH 3 to ethylenediamine (en).
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Chapter20
Bonding in Complexes
•
Slide 47
15
In general, the crystal field splitting energy
increases as the ligand varies in the following
order.
I – < Br – < Cl – < F
–
< H 2 O < NH 3 < en < CN –
Increasing value of ∆
•
This is known as the spectrochemical series.
•
Ligands which lead to small values of ? are called
weak-field ligands. Those which lead to large
values of ? are called strong-field ligands .
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Chapter20
Slide 48
16
Bonding in Complexes
16
•
Crystal Field Splitting can also account for magnetic
properties in terms of high- and low-spin complexes.
•
Weak-field ligands lead to high-spin paramagnetic systems.
•
Strong-field ligands lead to low-spin diamagnetic systems.
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Chapter20
Bonding in Complexes
Slide 49
17
•
CFT – Tetrahedral Complexes.
•
The splitting pattern in tetrahedral complexes are
opposite to that of octahedral complexes.
•
The dz2 and dx2 – y 2 orbitals have lower energies
than the dxy, dxz, and dyz orbitals.
•
The result is that nearly all tetrahedral complexes
are high-spin.
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Chapter20
Bonding in Complexes
Slide 50
18
•
CFT – Square Planar Complexes.
•
Splitting pattern is similar to that of octahedral
complexes except that the two trans ligands on the
z axis are missing.
•
The dx2 – y2 orbitals have higher energies than the
dz2, dxy, dxz, and dyz orbitals.
•
The result is that d8 metal ion complexes are low spin.
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Chapter20
Slide 51
17
Bonding in Complexes
19
Tetrahedral and Square Planar Splitting Patterns.
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Chapter20
Slide 52
18