Download Chap 24. Transition Metals and Coordination Compounds

Chap 24. Transition Metals and
Coordination Compounds
Hsu Fu-Yin
Gemstones

Rubies are deep red and emeralds are brilliant
green, yet the color of both gemstones is
caused by the same ion Cr3+ ions.
–
–
Rubies are crystals of aluminum oxide (Al2O3) in which about
1% of the Al 3+ ions are replaced by Cr3+ ions.
Emeralds are crystals of beryllium aluminum silicate
[Be3Al2(SiO3)6] in which a similar percentage of the Al3+ ions
are replaced by Cr3+.
Ruby
Emerald
Transition Metals
24.2 Properties of Transition Metals
- Electron Configurations
Properties and Electron Configuration
of Transition Metals


The properties of the transition metals are similar to
each other.
–
And very different from the properties of the main
group metals
–
High melting points, high densities, moderate to very hard,
and very good electrical conductors
The similarities in properties come from similarities in
valence electron configuration; they generally have
two valence electrons.
TABLE 24.1 First-Row Transition Metal
Orbital Occupancy
EXAMPLE 24.1 Writing Electron
Configurations for Transition Metals
Write the ground state electron configuration
for Zr.
FIGURE 24.1 Trends in Atomic Radius
• The atomic radius of Mo is larger than that of Cr
• Atomic radius of W is the same as that of Mo
Why?
W
Mo
Cr
• 18 electrons are added in progressing from Cr to
Mo, and all of them enter s, p, and d subshells.
• Between Mo and W, however, 32 electrons must be
added, and 14 of them enter the 4f subshell.
In the series of elements in which 4f the subshell is
filled, atomic radii decrease.
EX: This phenomenon occurs in the lanthanide series
( Z=58 to 71) and is called the lanthanide contraction.
24.2 Properties of Transition Metals
- Ionization Energy
•The first Ionization Energy of the
transition metals slowly increases across
a series.
•The first Ionization Energy of the third
transition series is generally higher than
the first and second series
– Indicating the valence electrons are
held more tightly
– Trend opposite to main group
elements
24.2 Properties of Transition Metals
- Electronegativity

The electronegativity of the
transition metals slowly increases
across a series.
–

Except for last element in the series
Electronegativity slightly
increases between first and
second series, but the third
transition series atoms are about
the same as the second.
–
Trend opposite to main group
elements
24.2 Properties of Transition Metals
- Oxidation States



Unlike main group metals,
transition metals often exhibit
multiple oxidation states.
The highest oxidation state
for a transition metal is +7 for
manganese (Mn).
Highest oxidation state is the
same as the group number
for groups 3B to 7B.
24.3 Coordination Compounds



When a monatomic cation combines with multiple
monatomic anions or neutral molecules it makes a
complex ion.
The attached anions or neutral molecules are called
ligands.
The charge on the complex ion can then be positive or
negative, depending on the numbers and types of
ligands attached.
[PtCl4]2-
Co(NH3)63+
Coordination compound

a complex ion combines with one or more
counterions (ions of opposite charge that are
not acting as ligands), the resulting neutral
compound is a coordination compound .
EX:
Coordination compounds

Swiss chemist Alfred Werner studied coordination
compounds. He proposed that the central metal ion
has two types of interactions that he named primary
valence and secondary valence .
– The primary valence is the oxidation state on the
central metal atom
– the secondary valence is the number of
molecules or ions directly bound to the metal
atom, called the coordination number .
• the primary valence is +3
• coordination number is 6
Coordination compounds
CoCl3 • 6H2O = [Co(H2O)6]Cl3
• the primary valence is +3
• coordination number is 6
Complex Ion Formation




Complex ion formation is a type of Lewis
acid–base reaction.
the ligands in coordination complexes is
the ability to donate electron pairs to
central metal atoms or ions. Ligand act as
Lewis bases.
In accepting electron pairs, central metal
atoms or ions act as Lewis acids.
A bond that forms when the pair of
electrons is donated by one atom is called
a coordinate covalent bond.
Ligands



Ligands that donate only one electron pair to the
central metal are monodentate.
Ligands have the ability to donate two pairs of
electrons (from two different atoms) to the metal;
these are bidentate .
Ligands, called polydentate ligands, can donate
even more than two electron pairs (from more than
two atoms) to the metal.
TABLE 24.2 Common Ligands
Chelating agent

A chelate is a complex ion containing a multidentate
ligand.
–
The ligand is called the chelating agent.
Geometries in Complex Ions
• Metal ions with a d8 electron
configuration (such as [PdCl4]2- )
exhibit square planar geometry,
• Metal ions with a d10 electron
configuration (such as [Zn(NH3)4]2+)
exhibit tetrahedral geometry.
Naming Coordination Compounds

Anions as ligands are named by using the
ending –o.
–
normally -ide endings change to -o, -ite to -ito,
and -ate to -ato.
Naming Coordination Compounds

Neutral molecules as ligands generally carry
the unmodified name.
–
–
the name ethylenediamine is used both for the
free molecule and for the molecule as a ligand.
Aqua, ammine, carbonyl, and nitrosyl are
important exceptions
Naming Coordination Compounds

The number of ligands of a given type is denoted by
a prefix.
–
Mono, di, tri, tetra, penta, hexa
Ex: pentaaqua signifies five molecules.
–
If the ligand name is a composite name that itself contains a
numerical prefix, such as ethylenediamine, place
parentheses around the name and precede it with bis, tris,
tetrakis, pentakis
EX: presence of two ethylenediamine ligands,
bis(ethylenediamine)
Names of Common Metals when Found
in Anionic Complex Ions
Naming Coordination Compounds

When we name a complex,
–
–
–
–
ligands are named first, in alphabetical order
followed by the name of the metal center.
The oxidation state of the metal center is denoted
by a Roman numeral
If the complex is an anion, the ending -ate is
attached to the name of the metal
EX:
2
3
1
Tetraaquadichlorochromium (III)
EXAMPLE 24.3 Naming Coordination
Compounds
3
1
2
4
Pentaaquachlorochromium(III) chloride.
Potassium hexacyanoferrate(III)
24.4 Structure and Isomerization


Structural isomers are molecules that have the
same number and type of atoms, but they are
attached in a different order.
Stereoisomers are molecules that have the same
number and type of atoms, and that are attached in
the same order, but the atoms or groups of atoms
point in a different spatial direction.
Types of Isomers
Linkage Isomers

Linkage isomers are structural isomers that have
ligands attached to the central cation through
different ends of the ligand structure.
Ligands Capable of Linkage
Isomerization
Geometric Isomers


Geometric isomers are stereoisomers that differ in
the spatial orientation of ligands.
cis–trans isomerism in square-planar complexes
MA2B2
Geometric Isomers


In cis–trans isomerism, two identical ligands are
either adjacent to each other (cis) or opposite to each
other (trans) in the structure.
cis–trans isomerism in octahedral complexes MA4B2
Geometric Isomers


In fac–mer isomerism three identical ligands in an
octahedral complex either are adjacent to each other
making one face (fac) or form an arc around the center
(mer) in the structure.
fac–mer isomerism in octahedral complexes MA3B3
EXAMPLE 24.5 Identifying and Drawing
Geometric Isomers

Draw the structures and label the type of all
the isomers of
Sol:
The ethylenediamine (en) ligand is bidentate, Cl- is monodentate
∴ The total coordination number is 6, so this must be an
octahedral complex.
MA4B2
Optical Isomers


Optical isomers are stereoisomers that are
nonsuperimposable mirror images of each other.
Superimposable and nonsuperimposable objects—
an open-top box
Superimposable
(可重疊)
nonsuperimposable
(不可重疊)
Optical Isomers

Structures that are
nonsuperimposable mirror
images of each other are called
enantiomers (鏡像異構物)
and are said to be chiral (對掌)

Structures that are
superimposable are achiral.
24.5 Bonding in Coordination
Compounds

Valence Bond Theory
Crystal Field Theory

Crystal Field Theory:
–
–
–
Bonding in a complex ion is considered to be an
electrostatic attraction between the positively
charged nucleus of the central metal ion and
electrons in the ligands.
Repulsions also occur between the ligand
electrons and electrons in the central ion.
Crystal field theory focuses on the repulsions
between ligand electrons and d electrons of the
central ion.
d orbitals
six anions to a metal ion to form a complex ion with octahedral structure

Repulsions between ligand electrons and d-orbital electrons
are strengthened in the direct, head-to-head approach of
ligands to the dz2 orbitals and orbitals dx2-y2

These two orbitals have their energy raised with respect to an
average d-orbital energy for a central metal ion in the field of
the ligands.

dxy , dxz, and dyz orbital energies are lowered with
respect to the average d-orbital energy.

The difference in energy between the two groups of d
orbitals is called crystal field splitting (represented by
the symbol △o)
Splitting of d Orbital Energies Due to
Ligands in an Octahedral Complex
The size of the crystal field splitting energy, D, depends on the kinds of
ligands and their relative positions on the complex ion, as well as the kind
of metal ion and its oxidation state.
The Color of Complex Ions and Crystal
Field Strength

The color of an object is related to the
absorption of light energy by its electrons.
–
–
If a substance absorbs all of the visible
wavelengths, it appears black.
If it transmits (or reflects) all the wavelengths
(absorbs no light), it appears colorless.
Complex Ion Color

The observed color is the complementary color of
the one that is absorbed.
A substance that absorbs green
light (the complement of red)
will appear red.
Complex Ion Color

To measure the energy difference between the d
orbitals in a complex ion is to use spectroscopy to
determine the wavelength of light absorbed when an
electron makes a transition from the lower energy d
orbitals to the higher energy ones.
Consider the [Ti(H2O)6]3+ absorption
spectrum shown in Figure. The
maximum absorbance is at 498 nm.
High spin & Low spin


Whether the fourth electron enters the lowest level and becomes
paired or, instead, enters the upper level with the same spin as the
first three electrons depends on the magnitude of △o
△o is less than the pairing energy, greater stability is obtained by
keeping the electrons unpaired. (high spin)
△o
有電子排斥力(pairing energy)
高能階
Ligands and Crystal Field Strength

Ligands such as H2O and F- produce only a small crystal field splitting,
leading to high-spin complexes; such ligands are said to be weak-field
ligands.

Ligands, such as NH3 and CN- produce large crystal field splitting, leading
to low-spin complexes; such ligands are said to be strong-field ligands.

The size of the energy gap depends on what kind of ligands are attached.

–
Strong field ligands include CN─ > NO2─ > en > NH3
–
Weak field ligands include H2O > OH─ > F─ > Cl─ > Br─ > I─.
The size of the energy gap also depends on the type of cation.
–
Increases as the charge on the metal cation increases
–
Co3+ > Cr3+ > Fe3+ > Fe2+ > Co2+ > Ni2+ > Mn2+
Magnetic Properties and Crystal Field
Strength
consider these two complexes of Co(III):
sp3d2
paramagnetic
(unpaired electrons)
d2sp3
diamagnetic
(paired electrons)
Tetrahedral Complexes

For a tetrahedral complex, the d orbital splitting pattern
is the opposite of the octahedral splitting pattern: three
d orbitals (dxy, dxz, and dyz) are higher in energy, and
two d orbitals (dx2-y2 and dz2) are lower in energy
Square Planar Complexes

A square planar complex gives us the most complex
splitting pattern of the three geometries
Z軸的配位基跑至無窮遠處,形成Square-planar complex
造成有z的d軌域能量變低
EX:

The complex ion [Ni(CN)4]2- is diamagnetic. Use ideas
from the crystal field theory to speculate on its
probable structure.
Sol:
The electron configuration of Ni is [Ar]3d84s2 and that of Ni(II) is
[Ar]3d8. Because the complex ion is diamagnetic, all 3d electrons
must be paired.
(a) if the structure were tetrahedra
(b) if the structure were square-planar.
paramagnetic
diamagnetic
Applications of Coordination
Compounds

Extraction of metals from ores
–
–

Use of chelating agents in heavy metal poisoning
–

Silver and gold as cyanide complexes
Nickel as Ni(CO)4(g)
EDTA for Pb poisoning
Chemical analysis
–
Qualitative analysis for metal ions
 Blue = CoSCN+
 Red = FeSCN2+
 Ni2+ and Pd2+ form insoluble colored precipitates with
dimethylglyoxime.
Biomolecules
Applications of Coordination
Compounds

Commercial coloring agents
–
Prussian blue = mixture of hexacyanoFe(II) and
Fe(III)

Inks, blueprinting, cosmetics, paints
Applications of Coordination
Compounds
Cisplatin: A Cancer-Fighting Drug
Biological Applications: Porphyrins
porphyrin structure
metal–porphin complex is called a porphyrin.
Biological Applications: Cytochrome C
& Hemoglobin