Chemistry
Third Edition
Julia Burdge
Lecture PowerPoints
Chapter 22
Coordination Chemistry
Copyright © 2012, The McGraw-Hill Compaies, Inc. Permission required for reproduction or display.
CHAPTER
22
Coordination Chemistry
22.1 Coordination Compounds
22.2 Structure of Coordination Compounds
22.3 Bonding in Coordination Compounds: Crystal Field
Theory
22.4 Reactions of Coordination Compounds
22.5 Applications of Coordination Compounds
2
22.1
Coordination Compounds
Topics
Properties of Transition Metals
Ligands
Nomenclature of Coordination Compounds
3
22.1
Coordination Compounds
Properties of Transition Metals
Coordination compounds contain coordinate covalent bonds
formed by the reactions of metal ions with groups of anions
or polar molecules.
A coordinate covalent bond is a covalent bond in which one of
the atoms donates both of the electrons that constitute the
bond.
A coordination compound often consists of a complex ion and
one or more counter ions.
4
22.1
Coordination Compounds
Properties of Transition Metals
Use square brackets to separate the complex ion from the
counter ion.
Most of the metals in coordination compounds are transition
metals.
5
22.1
Coordination Compounds
Properties of Transition Metals
Transition metals (green) have incompletely filled d subshells
or form ions with incompletely filled d subshells.
6
22.1
Coordination Compounds
Properties of Transition Metals
The Group 2B metals—Zn, Cd, and Hg — are d-block metals,
but they are not transition metals.
Incompletely filled d subshells give rise to several properties:
• distinctive colors
• formation of paramagnetic compounds
• catalytic activity
• tendency to form complex ions
7
22.1
Coordination Compounds
Properties of Transition Metals
The most common transition metals are Sc through Cu.
8
22.1
Coordination Compounds
Properties of Transition Metals
Transition metals have
• higher densities
• higher melting points and boiling points
• higher heats of fusion and vaporization
than the main group and Group 2B metals
9
22.1
Coordination Compounds
Properties of Transition Metals
Transition metals exhibit variable oxidation states.
All these metals can exhibit
the oxidation state +3 and
nearly all can exhibit the
oxidation state +2.
The highest oxidation state for
a transition metal is +7.
10
22.1
Coordination Compounds
Ligands
The molecules or ions that surround the metal in a complex
ion are called ligands.
To be a ligand, a molecule or ion must have at least one
unshared pair of valence electrons.
Examples include:
11
22.1
Coordination Compounds
Ligands
The ligand acts as a
Lewis base while the
transition metal acts
as a Lewis acid.
12
22.1
Coordination Compounds
Ligands
The atom in a ligand that is bound directly to the metal atom
is known as the donor atom.
Nitrogen is the
donor atom in the
[Cu(NH3)4]2+
complex ion.
13
22.1
Coordination Compounds
Ligands
The coordination number in a coordination compound refers
to the number of donor atoms surrounding the central metal
atom in a complex ion.
The coordination number of Cu2+ in [Cu(NH3)4]2+ is 4.
The most common coordination numbers are 4 and 6.
14
22.1
Coordination Compounds
Ligands
Depending on the number of donor atoms a ligand possesses,
it is classified as
• monodentate (1 donor atom)
• bidentate (2 donor atoms)
• polydentate (> 2 donor atoms)
Ethylenediamine
forms two bonds to
a metal atom
(bidendate).
15
22.1
Coordination Compounds
Ligands
Bidentate and polydentate ligands are also called chelating
agents because of their ability to hold the metal atom like a
claw.
EDTA is a
polydentate ligand ‒
6 donor atoms.
16
22.1
Coordination Compounds
Ligands
The oxidation state of a transition metal in a complex ion is
determined using the known charges of the ligands and the
known overall charge of the complex ion.
In the complex ion [PtCl6]2‒, each chloride ion ligand has an
oxidation number of ‒1.
For the overall charge of the ion to be ‒2, the Pt must have an
oxidation number of +4.
17
SAMPLE PROBLEM
22.1
Determine the oxidation state of the central metal atom in
each of the following compounds:
(a) [Ru(NH3)5(H2O)]Cl2
(b) [Cr(NH3)6](NO3)3
(c) Fe(CO)5
18
SAMPLE PROBLEM
22.1
Setup
a) The complex ion is [Ru(NH3)5(H2O)]2+. Each ligand is
neutral.
b) The complex ion is [Cr(NH3)6]3+. Each ligand is neutral.
c) Fe(CO)5 does not contain a complex ion. The ligands are
CO molecules, which have a zero charge.
19
SAMPLE PROBLEM
22.1
Solution
a) [Ru(NH3)5(H2O)]Cl2
+2
b) [Cr(NH3)6](NO3)3
+3
c) Fe(CO)5
0
20
22.1
Coordination Compounds
Nomenclature of Coordination Compounds
The rules for naming ionic coordination compounds are as
follows:
1. The cation is named before the anion. The rule holds
regardless of whether the complex ion bears a net positive
or a net negative charge.
2. Within a complex ion, the ligands are named first, in
alphabetical order, and the metal ion is named last.
21
22.1
Coordination Compounds
Nomenclature of Coordination Compounds
3. The names of anionic ligands end with the letter o,
whereas neutral ligands are usually called by the names of
the molecules. The exceptions are H2O (aqua), CO
(carbonyl), and NH3 (ammine).
4. When two or more of the same ligand are present, use
Greek prefixes di, tri, tetra, penta, and hexa, to specify
their number.
22
22.1
Coordination Compounds
Nomenclature of Coordination Compounds
5. The oxidation number of the metal is indicated in Roman
numerals immediately following the name of the metal.
6. If the complex is an anion, its name ends in –ate.
23
22.1
Coordination Compounds
Nomenclature of Coordination Compounds
24
22.1
Coordination Compounds
Nomenclature of Coordination Compounds
25
SAMPLE PROBLEM
22.2
Write the names of the following coordination compounds:
(a) [Co(NH3)4Cl2]Cl
(b) K3[Fe(CN)6]
26
SAMPLE PROBLEM
22.2
Setup
a) The cation is a complex ion with a charge of +1. The
counter ion is Cl‒. The oxidation state of cobalt +3.
b) The cation is K+, and the anion is a complex ion with a
charge of ‒3. The oxidation state of iron +3.
Solution
a) [Co(NH3)4Cl2]Cl Tetraamminedichlorocobalt(III) chloride
b) K3[Fe(CN)6]
Potassium hexacyanoferrate(III)
27
SAMPLE PROBLEM
22.3
Write formulas for the following compounds:
(a) pentaamminechlorocobalt(III) chloride
(b) dichlorobis(ethylenediamine)platinum(IV) nitrate
28
SAMPLE PROBLEM
22.3
Setup
a) There are five NH3 molecules and one Cl‒ ion. The overall
charge on the complex ion +2. There are two chloride ions
as counter ions.
b) There are two bidentate ethylenediamines and two Cl‒
ions. The overall charge on the complex ion +2. There are
two nitrate ions as counter ions.
29
SAMPLE PROBLEM
22.3
Solution
a) [Co(NH3)5Cl]Cl2 (pentaamminechlorocobalt(III) chloride)
b) [Pt(en)2Cl2](NO3)2
(dichlorobis(ethylenediamine)platinum(IV) nitrate)
30
22.2
Structure of Coordination Compounds
Topics
Structure of Coordination Compounds
31
22.2
Structure of Coordination Compounds
Structure of Coordination Compounds
32
22.2
Structure of Coordination Compounds
Structure of Coordination Compounds
Compounds in which ligands are arranged differently around
the central atom are known as stereoisomers.
Stereoisomers have distinctly different physical and chemical
properties.
Coordination compounds may exhibit two types of
stereoisomerism: geometric and optical.
33
22.2
Structure of Coordination Compounds
Structure of Coordination Compounds
Geometrical isomers are stereoisomers that cannot be
interconverted without breaking chemical bonds.
Geometric isomers come in pairs: cis and trans.
Cis means that two particular atoms are adjacent to each
other.
Trans means that the atoms are on opposite sides in the
structural formula.
34
22.2
Structure of Coordination Compounds
Structure of Coordination Compounds
The cis and trans isomers generally have different colors,
melting points, dipole moments, and chemical reactivities.
35
22.2
Structure of Coordination Compounds
Structure of Coordination Compounds
36
22.2
Structure of Coordination Compounds
Structure of Coordination Compounds
Optical isomers are nonsuperimposable mirror images.
Optical isomers also come in pairs.
The optical isomers of a compound have identical physical
and chemical properties.
Optical isomers differ from each other in their interactions
with plane-polarized light.
37
22.2
Structure of Coordination Compounds
Structure of Coordination Compounds
The structural
relationship between
two optical isomers is
analogous to the
relationship between
your left and right
hands.
38
22.2
Structure of Coordination Compounds
Structure of Coordination Compounds
The cis and trans isomers of
dichlorobis(ethylenediamine)cobalt(III) ion and the mirror
image of each.
The cis isomer and its mirror image are optical isomers.
39
22.2
Structure of Coordination Compounds
Structure of Coordination Compounds
Optical isomers are described as chiral.
Chiral molecules are nonsuperimposable.
Isomers that are superimposable with their mirror images are
said to be achiral.
40
22.2
Structure of Coordination Compounds
Structure of Coordination Compounds
Chiral molecules are optically active because of their ability to
rotate polarized light as it passes through them.
Unlike ordinary light, which vibrates in all directions, planepolarized light vibrates only in a single plane.
We use a polarimeter to measure the rotation of polarized
light by optical isomers.
41
22.2
Structure of Coordination Compounds
Structure of Coordination Compounds
If the plane of polarization is rotated to the right, the isomer
is dextrorotatory and is labeled d.
If the rotation is to the left, the isomer is levorotatory and is
labeled l.
The d and l isomers of a chiral substance, called enantiomers,
always rotate the plane of polarization by the same amount,
but in opposite directions.
42
22.2
Structure of Coordination Compounds
Structure of Coordination Compounds
In an equimolar mixture of two enantiomers, called a racemic
mixture, the net rotation is zero.
43
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Topics
Crystal Field Splitting in Octahedral Complexes
Color
Magnetic Properties
Tetrahedral and Square Planar Complexes
44
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Crystal Field Splitting in Octahedral Complexes
Crystal field theory accounts for the color and magnetic
properties of many coordination compounds.
In a complex ion, two types of electrostatic interaction come
into play.
1. the attraction between the positive metal ion and the
negatively charged ligand
2. the electrostatic repulsion between the lone pairs on the
ligands and the electrons in the d orbitals of the metals
45
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Crystal Field Splitting in Octahedral Complexes
The d orbitals have different orientations but the same
energy, in the absence of an external disturbance.
In an octahedral complex, a central metal atom is surrounded
by six lone pairs of electrons, so all five d orbitals experience
electrostatic repulsion.
The magnitude of this repulsion depends on the orientation
of the d orbital that is involved.
.
46
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Crystal Field Splitting in Octahedral Complexes
The lobes of the dx2 ‒ y2 orbital point toward the corners of the
octahedron along the x and y axes, where the lone-pair
electrons are positioned.
An electron residing in this orbital would experience a greater
repulsion from the ligands than an electron would in the dxy,
dyz, or dxz orbitals.
The energy of the dx2 ‒ y2 orbital is increased relative to the dxy,
dyz, or dxz orbitals.
47
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Crystal Field Splitting in Octahedral Complexes
The dz2 orbital’s energy is also greater, because its lobes are
pointed at the ligands along the z axis.
48
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Crystal Field Splitting in Octahedral Complexes
The five d orbitals in an octahedral complex are split between
two sets of energy levels.
49
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Crystal Field Splitting in Octahedral Complexes
The crystal field splitting (Δ) is the energy difference between
two sets of d orbitals in a metal atom when ligands are
present.
The magnitude of Δ depends on the metal and the nature of
the ligands.
It has a direct effect on the color and magnetic properties of
complex ions.
50
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Color
White light is a combination of all colors.
A substance appears black if it absorbs all the visible light that
strikes it.
An object appears green if it absorbs all light but reflects the
green component.
51
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Color
An object also looks green if it reflects all colors except red,
the complementary color of green.
The best way to measure
crystal field splitting is to
use spectroscopy to
determine the wavelength
at which light is absorbed.
52
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Color
The [Ti(H2O)6]3+ ion
absorbs light in the
visible region of the
spectrum with a
maximum absorption
at 498 nm.
53
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Color
To calculate the crystal field splitting energy, recall
Therefore,
This is the energy required to excite one [Ti(H2O)6]3+ ion.
54
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Color
To express this energy difference in units of kJ/mol, we write
55
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Color
Chemists have calculated the crystal field splitting for each
ligand and established the following spectrochemical series,
These ligands are arranged in the order of increasing Δ.
CO and CN‒ are called strong-field ligands, because they
cause a large splitting of the d orbital energy levels.
The halide ions and hydroxide ion are weak-field ligands,
because they split the d orbitals to a lesser extent.
56
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Magnetic Properties
The magnitude of the crystal field splitting also determines
the magnetic properties of a complex ion.
The configuration
of Fe3+ is [Ar]3d5,
and there are two
possible ways to
distribute the five
d electrons among
the d orbitals.
57
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Magnetic Properties
The actual arrangement of the electrons is determined by the
amount of stability gained by having maximum parallel spins
versus the investment in energy required to promote
electrons to higher d orbitals.
Because F‒ is a weak-field ligand, the five d electrons enter
five separate d orbitals with parallel spins to create a highspin complex.
58
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Magnetic Properties
The CN‒ is a strong-field ligand, so it is energetically preferable
for all five electrons to be in the lower orbitals, thus forming a
low-spin complex.
High-spin complexes are more paramagnetic than low-spin
complexes
59
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Magnetic Properties
A distinction
between low- and
high-spin complexes
can be made only if
the metal ion
contains > 3 and < 8
d electrons
60
SAMPLE PROBLEM
22.4
Predict the number of unpaired spins in the [Cr(en)3]2+ ion.
61
SAMPLE PROBLEM
22.4
Setup
The electron configuration of Cr2+ is [Ar]3d4; and en is a
strong-field ligand.
Solution
Because en is a strong-field ligand, we expect [Cr(en)3]2+ to be
a low-spin complex.
All four electrons will be placed in the lower-energy d orbitals
and there will be a total of two unpaired spins.
62
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Tetrahedral and Square Planar Complexes
The splitting pattern for a tetrahedral ion is the reverse of that
for octahedral complexes.
Most tetrahedral complexes are high-spin complexes.
63
22.3
Bonding in Coordination Compounds: Crystal
Field Theory
Tetrahedral and Square Planar Complexes
The splitting pattern for square-planar complexes is the most
complicated.
64
22.4
Reactions of Coordination Compounds
Topics
Reactions of Coordination Compounds
65
22.4
Reactions of Coordination Compounds
Reactions of Coordination Compounds
Complex ions undergo ligand exchange (or substitution)
reactions in solution.
It is useful to distinguish between the stability of a complex
ion and its tendency to react, which we call kinetic lability.
Stability in this context is a thermodynamic property, which is
measured in terms of the species’ formation constant Kf .
66
22.4
Reactions of Coordination Compounds
Reactions of Coordination Compounds
For example, the complex ion tetracyanonickelate(II) is stable
because it has a large formation constant (Kf = 1 × 1030):
Complexes like the tetracyanonickelate(II) ion are termed
labile complexes because they undergo rapid ligand exchange
reactions.
Thus, a thermodynamically stable species (i.e., one that has a
large formation constant) is not necessarily unreactive.
67
22.4
Reactions of Coordination Compounds
Reactions of Coordination Compounds
A complex that is thermodynamically unstable in acidic
solution is [Co(NH3)6]3+.
This is an example of an inert complex—a complex ion that
undergoes very slow exchange reactions.
It shows that a thermodynamically unstable species is not
necessarily chemically reactive.
68
22.4
Reactions of Coordination Compounds
Reactions of Coordination Compounds
The rate of reaction is determined by the energy of activation.
Most complex ions containing Co3+, Cr3+, and Pt2+ are
kinetically inert.
69
22.5
Applications of Coordination Compounds
Topics
Applications of Coordination Compounds
70
22.5
Applications of Coordination Compounds
Reactions of Coordination Compounds
Metallurgy
Examples of the use of coordination compounds in
metallurgical processes:
• extraction of silver and gold by the formation of cyanide
complexes
• purification of nickel
71
22.5
Applications of Coordination Compounds
Reactions of Coordination Compounds
Chelation Therapy
Chelation therapy is used in the treatment of lead poisoning.
Arsenic and mercury can also be removed using chelating
agents.
72
22.5
Applications of Coordination Compounds
Reactions of Coordination Compounds
Chemotherapy
Several platinum-containing coordination compounds,
including cisplatin [Pt(NH3)2Cl2] and carboplatin
[Pt(NH3)2(OCO)2C4H6], can effectively inhibit the growth of
cancerous cells.
The mechanism for the action of cisplatin is the chelation of
DNA. This causes a bend in the double-stranded structure
which inhibits replication. The damaged cell is then destroyed
by the body’s immune system.
73
22.5
Applications of Coordination Compounds
Reactions of Coordination Compounds
Chemical Analysis
Dimethylglyoxime forms an insoluble brick-red solid with Ni2+
and an insoluble bright-yellow solid with Pd2+.
These characteristic colors are used in qualitative analysis to
identify nickel and palladium.
The quantities of ions present can be determined by
gravimetric analysis.
74
22.5
Applications of Coordination Compounds
Reactions of Coordination Compounds
Detergents
The cleansing action of soap in hard water is hampered by the
reaction of the Ca2+ ions in the water with the soap molecules
to form insoluble salts or curds.
The detergent industry used tripolyphosphate ion as a
chelating agent to form stable complexes with Ca2+ ions .
However, wastewater containing phosphates discharged into
rivers and lakes causes algae to grow, resulting in oxygen
depletion.
75
22.5
Applications of Coordination Compounds
Reactions of Coordination Compounds
Sequestrants
EDTA is used as a food additive to sequester metal ions.
EDTA sequesters Cu, Fe, and Ni ions that would otherwise
catalyze the oxidation reactions that cause food to spoil.
EDTA is a common preservative in a wide variety of consumer
products.
76