Here are the answers to the examples: [Co(NH3)4Cl2]NO3 - coordination sphere= [Co(NH3)4Cl2]+ - ligands= NH3, Cl- - center of coordination= Co - coordination number= 6 - name = tetraamminechloridocobalt(III) nitrate K3[FeCl6] - coordination sphere= [FeCl6]3- - ligands= Cl- - center of coordination= Fe - coordination number= 6 - name = potassium hexachloroferrate(III) [Co(en)2OCO2]Br - coordination sphere=

1. COORDINATION COMPOUNDS
Unit 10A
•
•
•
•
•
23-1
Bonding
Terminology
Nomenclature
Chapter 20 (McM)
Chapter 23.4-23.5 Silberberg

2. Chapter 23
Transition Elements and Their
Coordination Compounds
23-2

3. The Transition Elements and Their Coordination
Compounds
23.3 Coordination Compounds
23.4 Theoretical Basis for the Bonding and Properties of
Complexes
23-3

4. Figure 23.1
23-4
The transition elements (d block) and inner
transition elements (f block) in the periodic table.

5. Properties of the Transition Metals
All transition metals are metals, whereas main-group
elements in each period change from metal to nonmetal.
Many transition metal compounds are colored and
paramagnetic, whereas most main-group ionic compounds
are colorless and diamagnetic.
The properties of transition metal compounds are
related to the electron configuration of the metal ion.
23-5

6. Figure 23.2
23-6
The Period 4 transition metals.

7. Figure 23.5
+2
Mn2+
Aqueous oxoanions of transition elements.
+6
MnO42−
+7
MnO4−
The highest oxidation state for
Mn equals its group number.
+5
VO43−
Transition metal ions are
often highly colored.
23-7
+6
Cr2O72−
+7
MnO4−

8. Color and Magnetic Behavior
Most main-group ionic compounds are colorless and
diamagnetic because the metal ion has no unpaired
electrons.
Many transition metal ionic compounds are highly
colored and paramagnetic because the metal ion has
one or more unpaired electrons.
Transition metal ions with a d0 or d10 configuration are
also colorless and diamagnetic.
23-8

9. Figure 23.6
Colors of representative compounds of the Period 4
transition metals.
potassium nickel(II) nitrate zinc sulfate
titanium(IV) oxide sodium chromate ferricyanide hexahydrate heptahydrate
scandium oxide vanadyl sulfate manganese(II)
dihydrate
chloride
tetrahydrate
23-9
cobalt(II)
chloride
hexahydrate
copper(II) sulfate
pentahydrate

10. Lanthanides and Actinides
The lanthanides are also called the rare earth elements.
The atomic properties of the lanthanides vary little
across the period, and their chemical properties are
also very similar.
Most lanthanides have the ground-state electron
configuation [Xe]6s24fx5d0.
All actinides are radioactive, and have very similar physical
and chemical properties.
The +3 oxidation state is common for both lanthanides
and actinides.
23-10

11. Coordination Compounds
A coordination compound contains at least one complex
ion, which consists of a central metal cation bonded to
molecules and/or anions called ligands.
The complex ion is associated with counter ions of
opposite charge.
The complex ion [Cr(NH3)6]3+ has a central Cr3+ ion bonded to six
NH3 ligands. The complex ion behaves like a polyatomic ion in
solution.
23-11

12. Ammine Complexes
• The ammine complexes contain NH3
molecules bonded to metal ions by
coordinate covalent bonds as in
[Cu(NH3)4]2+.
• Common metal ions that form soluble
ammine complexes with an excess of
aqueous NH3 include Co2+, Co3+,
Ni2+, Cu2+, Ag+, Zn2+, Cd2+, and Hg2+.
23-12

13. Terminology
• Ligand -- a Lewis base that
coordinates to a central metal atom
or ion.
• Center of Coordination -- the electron
pair acceptor(Lewis acid) -- usually a
metal atom or ion
• Donor atom -- the specific atom of a
ligand that donates a lone pair of
electrons to form a coordinate
covalent bond
23-13

14. Terminology
• Unidentate ligand -- a ligand that can bind through
only one atom(has only one donor atom)
• Polydentate ligand -- a ligand that can bind through
more than one donor atom at a time-2=bidentate,
3=tridentate, etc.
• Coordination number -- the number of donor atoms
coordinated to the center of coordination
23-14

15. Terminology
• Coordination sphere -- includes the
metal atom or ion and the ligands
coordinated to it--does not include
uncoordinated counter ions--usually
enclosed in brackets
23-15

16. Coordination Number
The coordination number is the number of ligand atoms
bonded directly to the central metal ion.
Coordination number is specific for a given metal ion in a
particular oxidation state and compound.
- [Cr(NH3)6]3+ has a coordination number of 6.
The most common coordination number in complex ions is
6, but 2 and 4 are often seen.
23-16

17. Figure 23.7
Components of a coordination compound.
[Co(NH3)6]Cl3 dissolves in water. The six
ligands remain bound to the complex ion.
23-17
[Pt(NH3)4]Br2 has four
NH3 ligands and two Brcounter ions.

18. Table 23.5 Coordination Numbers and Shapes of Some
Complex Ions
Coordination
Number
Shape
Examples
2
Linear
[CuCl2]-, [Ag(NH3)2]+, [AuCl2]-
4
Square planar
[Ni(CN)4]2-, [PdCl4]2-,
[Pt(NH3)4]2+, [Cu(NH3)4]2+
4
Tetrahedral
[Cu(CN)4]3-, [Zn(NH3)4]2+,
[CdCl4]2-. [MnCl4]2-
6
Octahedral
[Ti(H2O)6]3+, [V(CN)6]4-,
[Cr(NH3)4Cl2]+, [Mn((H2O6]2+,
[FeCl6]3-, [Co(en)3]3+
The geometry of a given complex ion depends both on the
coordination number and the metal ion.
23-18
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

19. Ligands
The ligands of a complex ion are molecules or anions
with one or more donor atoms.
Each donor atom donates a lone pair of electrons to
the metal ion to form a covalent bond.
Ligands are classified in terms of their number of donor
atoms, or “teeth”:
- Monodentate ligands bond through a single donor atom.
- Bidentate ligands have two donor atoms, each of which bonds to
the metal ion.
- Polydentate ligands have more than two donor atoms.
23-19

20. Table 23.6 Some Common Ligands in Coordination Compounds
23-20

21. Chelates
Bidentate and polydentate ligands give rise to rings in
the complex ion.
A complex ion containing this type of structure is called a
chelate because the ligand seems to grab the metal ion
like claws.
EDTA has six donor atoms and forms very stable complexes
with metal ions.
23-21

22. Terminology
• For the compound K3[Co(CN)6]
– coordination sphere =
– center of coordination =
– ligands =
– donor atoms =
– coordination number =
– uncoordinated counter ions =
23-22

23. Formulas of Coordination Compounds
• A coordination compound may consist of
– a complex cation with simple anionic counterions,
– a complex anion with simple cationic counterions, or
– a complex cation with complex anion as counterion.
• When writing the formula for a coordination compound
– the cation is written before the anion,
– the charge of the cation(s) is/are balanced by the charge of the
anion(s), and
– neutral ligands are written before anionic ligands, and the
formula of the whole complex ion is placed in square brackets.
23-23

24. Determining the Charge of the Metal Ion
The charge of the cation(s) is/are balanced by the charge
of the anion(s).
K2[Co(NH3)2Cl4] contains a complex anion.
The charge of the anion is balanced by the two K+ counter ions, so
the anion must be [Co(NH3)2Cl4]2-.
There are two neutral NH3 ligands and four Cl- ligands. To have an
overall charge of 2-, the metal ion must have a charge of 2+.
Charge of complex ion = charge of metal ion + total charge of ligands
2= charge of metal ion + [(2 x 0) + (4 x -1)]
Charge of metal ion = (-2) – (-4) = +2 or 2+
The metal ion in this complex anion is Co2+.
23-24

25. [Co(NH3)4Cl2]Cl contains a complex cation.
The charge of the cation is balanced by the Cl- counter ion, so the
cation must be [Co(NH3)4Cl2]+.
There are four neutral NH3 ligands and two Cl- ligands. To have an
overall charge of 1+, the metal ion must have a charge of 3+.
Charge of complex ion = charge of metal ion + total charge of ligands
1+
= charge of metal ion + [(4 x 0) + (2 x 1-)]
Charge of metal ion = (+1) – (2-) = +3 or 3+
The metal ion in this complex cation is Co3+.
23-25

26. Naming Coordination Compounds
• The cation is named before the anion.
• Within the complex ion, the ligands are named in alphabetical order
before the metal ion.
– Anionic ligands drop the –ide and add –o after the root name.
• A numerical prefix is used to indicate the number of ligands of a
particular type.
– Prefixes do not affect the alphabetical order of ligand names.
– Ligands that include a numerical prefix in the name use the
prefixes bis (2), tris (3), or tetrakis (4) to indicate their number.
• A Roman numeral is used to indicate the oxidation state for a metal
that can have more than one state.
• If the complex ion is an anion, we drop the ending of the metal name
and add –ate.
23-26

27. Typical Simple Ligands
• Ion/Molecule
•
NH3
•
CO
•
Cl•
CN•
F•
OH23-27
Name
As Ligand

28. Typical Simple Ligands
• Ion/Molecule Name
•
NO
•
NO2•
ONO•
PH3
•
OH2
• NH2CH2CH2NH2
23-28
As Ligand

29. Typical Simple Ligands

Ion/Molecule
CO3-2

C2O4-2

23-29
Name
As Ligand

30. Table 23.7 Names of Some Neutral and Anionic Ligands
Neutral
Anionic
Name
Name
Formula
Aqua
H 2O
Fluoro
F-
Ammine
NH3
Chloro
Cl-
Carbonyl
CO
Bromo
Br-
Nitrosyl
NO
Iodo
I-
Hydroxo
OH-
Cyano
23-30
Formula
CN-

31. Table 23.8 Names of Some Metal Ions in Complex Anions
Metal
Iron
Ferrate
Copper
Cuprate
Lead
Plumbate
Silver
Argentate
Gold
Aurate
Tin
23-31
Name in Anion
Stannate

32. Sample Problem 23.3
Writing Names and Formulas of
Coordination Compounds
PROBLEM:
(a) What is the systematic name of Na3[AlF6]?
(b) What is the sytematic name of [Co(en)2Cl2]NO3?
(c) What is the formula of tetraamminebromochloroplatinum(IV) chloride?
(d) What is the formula of hexaamminecobalt(III) tetrachloroferrate(III)?
PLAN: We use the rules for writing formulas and names of
coordination compounds.
SOLUTION:
(a) The complex ion is [AlF6]3-. There are six (hexa-) F- ions (fluoro)
as ligands. The complex ion is an anion, so the ending of the
metal name must be changed to –ate. Since Al has only one
oxidation state, no Roman numerals are used.
sodium hexafluoroaluminate
23-32

33. Sample Problem 23.3
(b) There are two ligands, Cl- (chloro) and en (ethylenediamine).
The ethylenediamine ligand already has a numerical prefix in
its name, so we indicate the two en ligands by the prefix bis
instead of di.
The complex ion is a cation, so the metal name is unchanged,
but we need to specify the oxidation state of Co. The counter
ion is NO3-, so the complex ion is [Co(en)2Cl2]+.
Charge of complex ion = charge of metal ion + total charge of ligands
1+
= charge of metal ion + [(2 x 0) + (2 x 1-)]
Charge of metal ion = (+1) – (-2) = +3 or 3+
The ligands must be named in alphabetical order:
dichlorobis(ethylenediamine)cobalt(III) nitrate
23-33

34. Sample Problem 23.3
(c) The central metal ion is written first, followed by the neutral
ligands and then (in alphabetical order) by the negative ligands.
Charge of complex ion = charge of metal ion + total charge of ligands
= (4+) + [(4 x 0) + (1 x 1-) + (1 X 1-)]
= +4 + (-2) = +2 or 2+
We will therefore need two Cl- counter ions to balance the charge on the
complex ion.
[Pt(NH3)4BrCl]Cl2
23-34

35. Sample Problem 23.3
(d) This compound consists of two different complex ions. In the
cation, there are six NH3 ligands and the metal ion is Co3+, so
the cation is [Co(NH3)6]3+.
The anion has four Cl- ligands and the central metal ion is Fe3+,
so the ion is [FeCl4]-.
The charge on the cation must be balanced by the charge on
the anion, so we need three anions for every one cation:
[Co(NH3)6][FeCl4]3
23-35

36. Nomenclature
• A. If the compound is a salt, name
the cation first and then the anion.
• B. In naming a complex ion or a
neutral complex, name the ligands
first, in alphabetical order and then
the center of coordination.
– 1. Anionic ligands end in o
– 2. The complex name is one word
23-36

37. Nomenclature
• C. For more than one ligand of a
single type, use the Greek prefixes to
indicate number.
– 2=di, 3=tri, 4=tetra, 5=penta, 6=hexa,
etc.
• D. If the name of the ligand itself
contains a Greek prefix, put the
ligand name in parentheses and use
an alternate prefix.
23-37
– 2=bis, 3=tris, 4=tetrakis, 5=pentakis,
etc.

38. Nomenclature
• E. Use a Roman numeral in
parentheses immediately following
the name of the metal to indicate the
metal’s oxidation state.
• F. In naming the metal, use the
ending -ate if the metal is in an
anionic complex.
23-38

39. Examples
• Fill in the blanks for each of the
following compounds:
• [Co(NH3)4Cl2]NO3
– coordination sphere=
– ligands=
– center of coordination=
– coorrdination number=
– name =
23-39

40. Examples
• Fill in the blanks for each of the
following compounds:
• K3[FeCl6]
– coordination sphere=
– ligands=
– center of coordination=
– coordination number=
– name =
23-40

41. Examples
• Fill in the blanks for each of the
following compounds:
• [Co(en)2OCO2]Br
– coordination sphere=
– ligands=
– center of coordination=
– coordination number=
– name =
23-41

42. Examples
• Fill in the blanks for each of the
following compounds:
• [Ni(NH3)4(OH2)2](NO3)2
– coordination sphere=
– ligands=
– center of coordination=
– coordination number=
– name =
23-42

43. Examples
• Fill in the blanks for each of the
following compounds:
• potassium tetracyanonickelate(II)
• Formula=
–
–
–
–
23-43
coordination sphere=
ligands=
center of coordination=
coordination number=

44. Examples
– Fill in the blanks for each of the
following compounds:
• tris(ethylenediamine)cobalt(II) nitrate
• Formula=
–
–
–
–
23-44
coordination sphere=
ligands=
center of coordination=
coordination number=

45. 23-45

46. 23-46

47. Stereoisomers of Coordination
Compounds
Stereoisomers are compounds that have the same atomic
connections but different spatial arrangements of their
atoms.
Geometric or cis-trans isomers occur when atoms or
groups can either be arranged on the same side or on
opposite sides of the compound relative to the central
metal ion.
Optical isomers (enantiomers) are non-superimposable
mirror images of each other.
23-47

48. Figure 23.9A
Geometric (cis-trans) isomerism.
The cis and trans isomers of [Pt(NH3)2Cl2].
In the cis isomer, identical ligands are adjacent to each other, while in
the trans isomer they are across from each other.
The cis isomer (cisplatin) is an antitumor agent while the trans
isomer has no antitumor effect.
23-48

49. Figure 23.9B
Geometric (cis-trans) isomerism.
The cis and trans isomers of [Co(NH3)4Cl2]+.
Note the placement of the Cl- ligands (green spheres).
23-49

50. Figure 23.10A Optical isomerism in an octahedral complex ion.
Structure I and its mirror image, structure II, are optical isomers
of cis-[Co(en)2Cl2]+.
23-50

51. Figure 23.10B Optical isomerism in an octahedral complex ion.
The trans isomer of [Co(en)2Cl2]+ does not have optical isomers.
Structure I can be superimposed on its mirror image, structure II.
23-51

52. Bonding in Complex Ions
When a complex ion is formed, each ligand donates an
electron pair to the metal ion.
The ligand acts as a Lewis base, while the metal ion acts as a Lewis
acid.
This type of bond is called a coordinate covalent bond
since both shared e- originate from one atom in the pair.
In terms of valence bond theory, the filled orbital of the
ligand overlaps with an empty orbital of the metal ion.
The VB model proposes that the geometry of the complex
ion depends on the hybridization of the metal ion.
23-52

53. Figure 23.12
23-53
Hybrid orbitals and bonding in the octahedral
[Cr(NH3)6]3+ ion.

54. Figure 23.13
23-54
Hybrid orbitals and bonding in the square planar
[Ni(CN)4]2- ion.

55. Figure 23.14
23-55
Hybrid orbitals and bonding in the tetrahedral
[Zn(OH)4]2- ion.

56. Figure 23.15
An artist’s wheel.
Each color has a complementary
color; the one opposite it on the
artist’s wheel.
The color an object exhibits depends
on the wavelengths of light that it
absorbs.
An object will have a particular color because
• it reflects light of that color, or
• it absorbs light of the complementary color.
23-56

57. Table 23.9 Relation Between Absorbed and Observed Colors
Absorbed Color
λ (nm)
Observed Color
λ (nm)
Violet
400
Green-yellow
560
Blue
450
Yellow
600
Blue-green
490
Red
620
Yellow-green
570
Violet
410
Yellow
580
Dark blue
430
Orange
600
Blue
450
Red
650
Green
520
23-57

58. Crystal Field Theory
Crystal field theory explains color and magnetism in
terms of the effect of the ligands on the energies of the
d-orbitals of the metal ion.
The bonding of the ligands to the metal ion cause the
energies of the metal ion d-orbitals to split.
Although the d-orbitals of the unbonded metal ion are equal in
energy, they have different shapes, and therefore different
interactions with the ligands.
The splitting of the d-orbitals depends on the relative
orientation of the ligands.
23-58

59. Figure 23.16
The five d-orbitals in an octahedral field of ligands.
The ligands approach along the x, y and z axes. Two of the
orbitals point directly at the ligands, while the other three
point between them.
23-59

60. Figure 23.17
Splitting of d-orbital energies in an octahedral
field of ligands.
The d orbitals split into two groups. The difference in energy
between these groups is called the crystal field splitting energy,
symbol Δ.
23-60

61. Figure 23.18
The effect of ligands and splitting energy on
orbital occupancy.
Weak field ligands lead to
a smaller splitting energy.
23-61
Strong field ligands lead to a
larger splitting energy.

62. Figure 23.19
The color of [Ti(H2O)6]3+.
The hydrated Ti3+ ion is purple.
Green and yellow light are absorbed
while other wavelengths are
transmitted. This gives a purple color.
23-62

63. Figure 23.19
The color of [Ti(H2O)6]3+.
When the ion absorbs light, electrons can move from the lower t2g
energy level to the higher eg level. The difference in energy
between the levels (Δ) determines the wavelengths of light
absorbed. The visible color is given by the combination of the
wavelengths transmitted.
23-63

64. The Colors of Transition Metal Complexes
The color of a coordination compound is determined
by the Δ of its complex ion.
For a given ligand, the color depends on the oxidation
state of the metal ion.
For a given metal ion, the color depends on the ligand.
23-64

65. Figure 23.20
[V(H2O)6]2+
Effects of oxidation state and ligand on color.
[V(H2O)6]3+
A change in oxidation state
causes a change in color.
23-65
[Cr(NH3)6]3+
[Cr(NH3)5Cl ]2+
Substitution of an NH3 ligand
with a Cl- ligand affects the
color of the complex ion.

66. Figure 23.21
The spectrochemical series.
I- < Cl- < F- < OH- < H2O < SCN- < NH3 < en < NO2- < CN- < CO
WEAKER FIELD
STRONGER FIELD
SMALLER D
LARGER D
LONGER 
SHORTER 
As Δ increases, shorter wavelengths (higher energies) of light
must be absorbed to excite electrons. For reference H2O is
considered a weak-field ligand.
23-66

67. The Magnetic Properties of Transition
Metal Complexes
Magnetic properties are determined by the number of
unpaired electrons in the d orbitals of the metal ion.
Hund’s rule states that e- occupy orbitals of equal energy
one at a time. When all lower energy orbitals are halffilled:
- The next e- can enter a half-filled orbital and pair up by
overcoming a repulsive pairing energy, (Epairing).
- The next e- can enter an empty, higher, energy orbital by
overcoming Δ.
The number of unpaired e- will depend on the relative
sizes of Epairing and Δ.
23-67

68. Figure 23.22
23-68
High-spin and low-spin octahedral complex
ions of Mn2+.

69. Figure 23.23 Orbital occupancy for high-spin and low-spin
octahedral complexes of d4 through d7 metal ions.
high spin:
weak-field
ligand
23-69
low spin:
strong-field
ligand
high spin:
weak-field
ligand
low spin:
strong-field
ligand

70. Table B23.1 Some Transition Metal Trace Elements in Humans
23-70