George Mason University
General Chemistry 212
Chapter 23
Transition Elements
Acknowledgements
Course Text: Chemistry: the Molecular Nature of Matter and
Change, 7th edition, 2011, McGraw-Hill
Martin S. Silberberg & Patricia Amateis
The Chemistry 211/212 General Chemistry courses taught at George
Mason are intended for those students enrolled in a science
/engineering oriented curricula, with particular emphasis on
chemistry, biochemistry, and biology The material on these slides is
taken primarily from the course text but the instructor has modified,
condensed, or otherwise reorganized selected material.
Additional material from other sources may also be included.
Interpretation of course material to clarify concepts and solutions to
problems is the sole responsibility of this instructor.
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1
Transition Elements

Properties of the Transition Elements

The Inner Transition Elements

Highlights of Selected Transition Elements

Coordination Compounds

Theoretical Basis for the Bonding and Properties of
Complexes
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2
Transition Elements

Main-Group vs Transition Elements

Most important uses of Main-Group elements involve
the compounds made up of these elements

Transition Elements are highly useful in their elemental
or uncombined form
Main –Group
Transition Elements
Main-group elements change from
metal to non-metal across a period
All transition elements are metals
Most main-group ionic compounds
are colorless and diamagnetic (nonmagnetic)
Many transition metal compounds
are highly colored and paramagnetic
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Transition Elements

Properties of Transition Elements

Recall: The “A” (Main Group) elements make up the
“s” and “p” blocks

Transition Elements make up the

“d” block (B group)

“f” block elements (Inner Transition Elements)

As ions, transition metals (elements) provide
fascinating insights into chemical bonding and
structure

Transition metals play an important role in living
organisms
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Transition Elements
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5
Transition Elements

Electron Configurations of the Transition Metals

In the Periodic Table, the Transition metals,
designated “d-block (B-Group)” elements, are located
in:

40 elements in 4 series within Periods 4 -7

Lie between the last ns-block elements in group
[2A(2)] (Ca – Ra) and the first np-block elements in
group [(3A(13)] (Ga & element 113 (unnamed)

Each series represents the filling of the 5 d orbitals
l = 2  [ml = -2 -1 0 +1 +2]
(5 orbitals per period x 2 electrons per orbital x 4 Periods
= 40 Elements
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6
Transition Elements

Condensed d-block ground-state electron configuration:
[noble gas] ns2(n-1)dx, with n = 4 -7; x= 1-10
(several aufbau build-up exceptions)

Partial (valence shell) electron configuration
ns2(n-1)dx

Recall: Chromium (Cr) and Copper (Cu) are exceptions to the
above aufbau configuration setup
Expected:
Cr [Ar] 4s23d4
Cu [Ar] 4s23d9
Actual:
Cr [Ar] 4s13d5
Cu [Ar] 4s13d10
Reasons: change in relative energies of 4s & 3d
orbitals and the unusual stability of ½ filled and filled
sublevels (level 4 relative to level 3)
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Transition Elements
Note Aufbau build up exceptions for “Cr” & “Cu”
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Transition Elements

The “Inner Transition” elements

Lie between the 1st and 2nd members of the “d-block”
elements in Periods 6 & 7 (n=6 & n=7)

Condensed f-block ground-state electron configuration
(Periods 6 & 7):
[noble gas] ns2 (n-2)f14(n-1)dx, with n = 6 -7

The 28 “f” orbitals are filled as follows:
l = 3  [ml = -3 -2 -1 0 +1 +2 +3]
7 orbitals per period x 2 electrons per orbital x 2 periods
= 28 Elements
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Transition Elements

Transition Metal Ions

Form through the loss of the “ns” electrons
before the (n-1)d electrons
Ex. Ti2+ [Ar] 3d2 4s2 → [Ar] 3d2 + 2e-
(not [Ar] 4s2)
(Ti2+ also called d2 ion)

Ions of different transition metals with the same electron
configuration often have similar properties
Ex.
Mn2+ and Fe3+ are both d5 ions
Mn2+ [Ar] 3d54s2 → [Ar] 3d5 + 2eFe3+ [Ar] 3d64s2 → [Ar] 3d5 + 3eBoth Ions have pale colors in aqueous solutions
Both form complex ions with similar magnetic
properties
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10
Practice Problem
Write condensed electron configurations for the following ions:
Zr
V3+
Vanadium (V)
Mo3+
– Period 4
Zirconium (Zr) & Molybdenum (Mo) – Period 5
General Configuration:
ns2(n-1)dx
a. Zr is 2nd element in the 4d series: [Kr] 5s24d2 (d2 ion)
b. V is the 3rd element in the 3d series: [Ar] 4s23d3
“ns” electrons lost first
In forming V3+, 3 electrons lost – two 4s & one 3d
 V3+ = [Ar] 4s23d3 → [Ar] 3d2 (d2 ion) + 3ec.
Mo lies below Cr in Period 5, Group 6B(6): [kr] 5s1 4d5
Note: Same electron configuration exception as Cr
 Mo3+ = [Kr] 5s1 4d5 → [Kr] 4d3 (d3 ion) + 3 e-
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Transition Elements

Trends of Transition Elements Across a Period

Transition elements exhibit smaller, less regular
changes in

Size

Electronegativity

First Ionization Energy
than the Main Group Elements in the same group
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Transition Elements

Atomic Size
 General overall decrease across a period for both
Main group and Transition group elements
 As the “d” orbitals are filled across a period, the
change in atomic size within the transition elements
evens out because the “d” orbitals are less effective
in shielding the outer electrons from the increased
nuclear charge
Main group
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Transition Metals
Main group
13
Transition Elements

Electronegativity

Electronegativity generally increases across period

Change in electronegativity within a series (period)
is relatively small in keeping with the relatively small
change in size

Small electronegativity change in Transition
Elements is in contrast with the steeper increase
between the Main Group elements across a period

Magnitude of Electronegativity in Transition
elements is similar to the larger main-group metals
Transition Metals
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Transition Elements

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Ionization Energy

Ionization Energy of Period 4 Main-group elements
rise steeply from left to right as the electrons
become more difficult to remove from the poorly
shielded increasing nuclear charge, i.e., no “d”
electrons; thus, electrons held tighter to nucleus

In the Transition metals, however, the first
ionization energies increase relatively little because
of the combined effects of less effective shielding by
the inner “d” electrons and the increasing nuclear
charge
Transition Metals
15
Transition Elements

Trends Within (down) a Group (relative to main-group elements)

Vertical trends differ from those of the Main Group elements

Atomic Size
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
Increases, as expected, from Period 4 to 5 where electron
repulsion dominates the increasing nuclear charge

No increase from Period 5 to 6

The Lanthanide Contraction describes the atomic radius
trend that the Lanthanide series exhibit

The Lanthanide Contraction refers to the fact that the 5s
and 5p orbitals penetrate the 4f sub-shell so the 4f orbital
is not shielded from the increasing nuclear change, which
causes the atomic radius of the atom to decrease
16
Transition Elements
n=1
n=2
n=3
l=0
(1s)
ml = 0
l=0
l=1
(2s)
(2p)
0 -1 0 +1
l=0
(3s)
0
l=1
(3p)
-1 0 +1
l=2
(3d)
-2 -1 0 +1 +2
n=4
Note:
n>7&
l>3
Sublevels
not utilized
for any
element in
the current
Period Table
l=0
(4s)
ml = 0
l=1
(4p)
-1 0 +1
l=2
(4d)
-2 -1 0 +1 +2
l=3
(4f)
-3 -2 -1 0 +1 +2 +3
n=5
l=0
(5s)
ml = 0
l=1
(5p)
-1 0 +1
l=2
(5d)
-2 -1 0 +1 +2
l=3
(5f)
-3 -2 -1 0 +1 +2 +3
n=6,7
l=0
(6s,7s)
ml = 0
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l=1
(6p,7p)
-1 0 +1
l=2
(6d)
-2 -1 0 +1 +2
l=3
(6f)
-3 -2 -1 0 +1 +2 +3
17
Transition Elements
Main Group Non-metals
Main Group Metals
Transition Metals
Inner Transition Metals
Order of Sublevel Orbital Filling
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Transition Elements

Trends Within a Group (relative to main-group elements)

Electronegativity (EN) – Relative ability of an atom in a covalent
bond to attract shared electrons

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EN of Main-group elements decreases down group

greater size means less attraction by nucleus

Greater Reactivity

EN in Transition elements is opposite the trend in Main-group
elements because of less effective shielding of “d” orbitals

EN increases from period 4 to period 5

No change from period 5 to period 6, since the change in
volume is small and Zeff increases ( weak shielding from
f orbital electrons)

Transition metals exhibit more covalent bonding and attract
electrons more strongly than main-group metals

The EN values in the heavy metals exceed those of most
metalloids, forming salt-like compounds, such as CsAu and
the Au- ion
19
Transition Elements

Trends Within a Group (relative to Main-group elements)

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Ionization Energy – Energy required to remove an
electron from a gaseous atom or ion

Main-group elements increase in size down a group,
decreasing the Zeff , making it relatively easier to
remove the outer electrons

The relatively small increase in the size of transition
metals because of ineffective shielding from the
increasing nuclear charge (Zeff) by “d” orbital
electrons makes it more difficult to remove a
valence electron, resulting in a general increase in
the first ionization energy down a group
20
Transition Elements

Trends Within a Group (relative to Main-group elements)

Density

Atomic size (volume) is inversely related to density
(As size increases density decreases)

Transition element density across a period initially
increases, then levels off, finally dips at end of series

From Period 5 to Period 6 the density increases
dramatically because atomic volumes change little
while nuclear mass increases significantly

Period 6 series contains some of the densest
elements known:
Tungsten, Rhenium, Osmium, Iridium, Platinum, Gold
(Density 20 times greater than water,
2 times more dense than lead)
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Transition Elements
Trends are unlike those for the Main-group elements in several ways
 2nd & 3rd members of a transition group are nearly same size
 Electronegativity increases down a transition group
 1st ionization energies are highest at the bottom of transition group
 Densities increase down a transition group (mass increases faster than
density
3/15/2016
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22
Transition Elements

Chemical Properties of the Transition Elements

Atomic & physical properties of Transitions elements
are similar to Main group elements

Chemical properties of transition elements are very
different from main group elements

Oxidation States

Main-group elements display one, or at most two,
oxidation states

The ns & (n-1)d electrons in transition elements
are very close in energy
All or most can be used as valence electrons in
bonding – Transition metals can have multiple
oxidation states
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Transition Elements
Oxidation State (Number)
Magnitude of charge an
atom in a covalent
compound would have if its
shared electrons were held
completely by the atom that
attracts them more strongly
Oxidation State
Manganese (Mn)
dx
Electronic
Configuration
0
d5
[Ar] 4s2 3d5
+1
d5
[Ar] 4s1 3d5
+2
d5
[Ar] 3d5
+3
d4
[Ar] 3d4
+4
d3
[Ar] 3d3
+5
d2
[Ar] 3d2
+6
d1
[Ar] 3d1
+7
d0
[Ar]
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4s
3d
4p
Note: All 3 d5
Ex. MnO2 ; O.N. Mn +4
Ex. MnO4- ; O.N. Mn +7
24
Transition Elements

Metallic Behavior

Atomic size and oxidation state have a major effect on
the nature of bonding in transition metal compounds

Transition elements in their lower oxidation states
behave more like metals – Oxides more basic

Transition elements in their higher oxidation states
exhibit more covalent bonding – Oxides more acidic
Ex. TiCl2 (Ti2+) is an ionic solid
TiCl4 (Ti4+) is a molecular liquid
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Transition Elements

Metallic Behavior
 In the higher oxidation states:
 The atoms have fewer electrons
 The nuclear charge pulls remaining electrons closer,
decreasing the volume and increasing the density
 The charge density (ratio of the ion’s charge to its
volume) increases
 The increase in charge density leads to more polarization
of the electron clouds in non-metals
 The bonding becomes more covalent
 The stronger the covalent bond, the less metallic
 The oxides, therefore, become less basic
Ex. TiO (Ti2+) is weakly basic in water
TiO2 (Ti4+) is amphoteric, reacting with both acid and
base
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Transition Elements

Electronegativity, Oxidation State, Acidity/Basicity

Why does oxide acidity increase with oxidation state?

Metal with a higher oxidation state is more positively
charged

Attraction of electrons is increased, i.e., electronegativity
increases
Effective Electronegativity = Valence State Electronegativity

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EN Cr
– 1.6
Cr3+ – 1.7
Cr6+ – 2.3
Al – 1.5 (basic oxide)
P – 2.1 (acidic oxides)
27
Transition Elements

Metallic Behavior
 Reduction Strength (Redox)
 Standard Electrode Potential, Eo ,
generally decreases across a period
 As the value of Eo becomes more
negative, i.e., at the beginning of
the series, the ability of the species
to act as a reducing agent increases
Standard Electrode Potentials
of Period 4 M2+ Ions
Thus, Ti2+, Eo = -01.63V, is a
stronger reducing agent than Ni2+,
Eo = -0.25V



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All species with a negative value of Eo can reduce H+
2H+(aq) + 2e-  H2(g) Eo = 0.0V)
Note: Cu2+ (Eo = +0.34 V) cannot reduce H+
The magnitude of the Eo values between two species, and
the relative degree of surface oxidation, determines the
level of reactivity of the oxidation/reduction reaction in
water, steam, or acid solution
28
Transition Elements

Color in Transition Elements


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Most Main-Group Ionic Compounds are colorless

Metal ions have a filled outer shell

With only much higher energy orbitals available to
receive an “excited” electron, the ion does not
absorb visible light
The partially filled “d” orbitals of the transition metals
can absorb visible wavelengths and move to slightly
higher energy “d” levels
29
Transition Elements

Magnetism in Transition Elements

Magnetic properties are related to electron sublevel
occupancy

A “Paramagnetic” substance has atoms or ions with
“unpaired” electrons

A “Diamagnetic” substance has atoms or ions with only
“paired” electrons

Most Main-Group metal ions are diamagnetic (filled
outer shells)

Many Transition metal compounds are paramagnetic
because of unpaired electron in the “d” subshells
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Transition Elements

Chemical Behavior Within a Group

Main_Group


The decrease in Ionization Energy (IE) going down a
group results in “increased reactivity”
Transition metals

Ionization Energy increases down group
Some Properties of Group 6B(6) Elements

The Standard Electrode Potential (Eo) also increases
(becomes more positive)
Chromium is stronger reducing agent
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31
Transition Elements

The Inner Transition Elements

Lanthanides (Rare Earth Elements)
(Cerium (Ce); Z = 58 – Lutetium (Lu); Z = 71)

Silvery, high melting point (800 – 1600oC) metals

Small variations in chemical properties makes them
difficult to separate

Occur naturally in the +3 oxidation state as M3+ ions of
very similar radii

Most lanthanides have the ground-state electron
configuration filling the “f” subshell level
[Xe] 6s2 4fx 5d0

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x varies across series (Period)
Exceptions – Ce, Gd, Lu have single e- in 5d orbital
32
Sample Problem
Finding the Number of Unpaired Electrons
The alloy SmCo5 forms a permanent magnet because both
Samarium and Cobalt have unpaired electrons
How many unpaired electrons are in the Sm atom (Z=62)?
Ans:
Samarium is the eighth element after Xe (Noble Shell)
[Xe] 6s2 4f6
Two (2) electrons go in the 6s sublevel
In general, the 4f sublevel fills before the 5d sublevel (slide 17)
Recall previous slide - only Ce, Gd, Lu have 5d electrons
 Remaining 6 electrons go into the 4f orbitals
6s
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4f
Six unpaired electrons
5d
6p
33
Transition Elements

The Actinides:
(Thorium (Th); Z=90 - Lawrencium; Z=103)

All Actinides are Radioactive (Alpha (4He2) Decay

Only Thorium & Uranium occur in nature

Share very similar chemical & physical properties

Silvery and chemically reactive

Principal oxidation state is +3, similar to lanthanides
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Transition Elements

Highlights of Selected Transition Metals
 Period 4 – Chromium & Manganese
 Chromium
 Silvery, shiny metal with many colorful compounds
 Cr2O3 acts as protective coating on easily corroded
(oxidized) metals, such as iron
 “Stainless” steels contain as much as 18 % Cr, making
them highly resistant to corrosion
 Electron Configuration ([Ar] 4s1 3d5) with 6 valence
electrons occurs in all possible positive oxidation states
 Important ions Cr2+, Cr3+, Cr6+
 Non-metallic character and oxide acidity increase with
metal oxidation state
 Cr2+ potential reducing agent (Cr loses additional
electrons)
 Cr6+ potential oxidizing agent (Cr gains electrons)
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Transition Elements

Highlights of Selected Transition Metals
 Chromium
 Chromium (II) – Cr2+
 CrO is basic and largely ionic
 Forms insoluble hydroxide in neutral or basic
solution
 Dissolves in acid to yield Cr2+ ion and water
CrO(s) + 2H+ → Cr2+ (aq) + H2O(l)
 Chromium(III) – Cr3+
 Cr2O3 is amphoteric, similar properties as Aluminum
 Dissolves in acid to yield violet Cr3+ ion
Cr2O3(s) + 6H+(aq) → 2Cr3+(aq) + 3H2O(l)
 Reacts with base to form the green Cr(OH)4- ion
Cr2O3(s) + 3H2O + OH- → 2Cr(OH)4-(aq)
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Transition Elements

Highlights of Selected Transition Metals

Chromium (con’t)

Chromium (VI) - Cr6+ (Deep Red)

CrO3 is covalent and acidic

Dissolves in water to form Chromic Acid (H2CrO4)
CrO3(s) + H2O(l) → H2CrO4(aq)

H2CrO4 yields yellow Chromate ion (CrO42-) in base
H2CrO4(aq) + 2OH-(l) → CrO42-(aq) + 2H2O(l)

Chromate ion forms orange dichromate (Cr2O72-) ion
in acid
2CrO42-(aq) + 2H+(aq) ⇆ Cr2O72-(aq) H2O(l)
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37
Transition Elements

Highlights of Selected Transition Metals

Manganese

Hard and Shiny

Like Vanadium & Chromium used to make steel alloys

Chemistry of Manganese is similar to Chromium

Metal reduces H+ from acids to form Mn2+ ion
Mn(s) + 2H+(aq) → Mn2+(aq) + H2(g)

Manganese can use all its valence electrons (several
oxidation states) to form compounds


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Eo = 1.18 V
Mn2+ Mn4+ Mn7+ most important
As oxidation state rises from +2 to +7, the valence state
electronegativity increases and the oxides of Mn change
from basic to acidic

Mn(II)O
(basic)
Mn(III)2O3
(amphoteric)

Mn(IV)O2 (insoluble) Mn(VII)2O7 (acidic)
38
Transition Elements

All Manganese species with oxidation states greater than +2
act as oxidizing agents (gaining the electrons lost by the
atoms being oxidized)
Mn7+O4-(aq) + 4H+ + 3e- → Mn4+O2(s) + 2H2O(l) Eo = 1.68
Mn7+O4-(aq) + 2H2O + 3e- → Mn4+O2(s) + 4OH-
Eo = 0.59
(Mn7+O4- is a much stronger oxidizing agent in acid solution
than in basic solution – note difference in Eo values)
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Oxidation
State
Manganese
(Mn)
dx
Electronic
Configuratio
n
0
d5
[Ar] 4s2 3d5
+1
d5
[Ar] 4s1 3d5
+2
d5
[Ar] 3d5
+3
d4
[Ar] 3d4
+4
d3
[Ar] 3d3
+5
d2
[Ar] 3d2
+6
d1
[Ar] 3d1
+7
d0
[Ar]
4s
3d
4p
39
Transition Elements

Manganese

1/19/2015
Unlike Cr2+ & Fe2+, the Mn2+ (3d5) ion resists
oxidation in air

Recall: half-filled (-1/2 spin electrons missing) &
filled sublevels are more stable than partially filled
sublevels

Cr2+ is a d4 species and readily loses a 3d electron
to form the d3 ion Cr3+, which is more stable

Fe2+ is a d6 species and removing a 3d electron
yields the stable, half-filled d5 configuration of Fe3+

Removing an electron from Mn2+ disrupts the more
stable d5 configuration
40
Transition Elements & Their
Coordination Compounds

Coordination Compounds (Complexes)
 Most distinctive aspect of transition metal chemistry




1/19/2015
Complex – Substances that contain at least one
complex ion
Complex ion – Species consisting of a “central metal
cation” (either a main-group or transition metal) that is
bonded to molecules and/or anions called “Ligands”
The Complex ion is typically associated with other
(counter) ions to maintain neutrality
A coordination compound behaves like an electrolyte in
water
 Complex ion and counter ion separate
 Complex ion behaves like a polyatomic ion – the
ligands and central atom remain attached
41
Transition Elements & Their
Coordination Compounds

Components of Coordination Compound
 When solid complex dissolves in water, the complex ion and
the counter ions separate, but ligands remain bound to
central atom
[Co(NH ) ]Cl (s)
3 6
3
Octahedral
Geometry
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Central
Atom
Ligands
Counter
Ions
42
Transition Elements & Their
Coordination Compounds

Complex ions
 A complex ion is described by the metal ion and
the number and types of ligands attached to it
 The bonding between metal and ligand generally
involves formal donation of one or more of the
ligand's electron pairs
 The metal-ligand bonding can range from
covalent to more ionic
 Furthermore, the metal-ligand bond order can
range from one to three (single, double, triple
bonds)
 Ligands are viewed as Lewis Bases (donate
electron pairs), although rare cases are known
involving Lewis acidic ligands
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43
Transition Elements & Their
Coordination Compounds

Complex ions
 The complex ion structure is related to three
characteristics:
 Coordination Numbers
 The number of ligand atoms that are
bonded directly to the central metal ion
 Coordination number is specific for a given
metal ion in a particular oxidation state
and compound
 Coordination number in [Co(NH3)6]3+ is 6
 The most common coordination number in
complex ions is 6, but 2 and 4 are
common, with a few higher
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44
Transition Elements & Their
Coordination Compounds

Complex ions
 Geometry – Depends on Coordination No. & Nature of Metal Ion
Metal
ion
C
N
Shape
dx
Cu+
2
Linear
d10
Ag+
2
Linear
d10
Au+
2
Linear
d10
Ni2+
4
Octahedral Sq Planar
d8
Pd2+
4
Octahedral Sq Planar
d8
Pt2+
4
Octahedral Sq Planar
d8
Cu2+
4
Octahedral Sq Planar
d9
Cu3+
4
Tetrahedral
d8
Zn2+
4
Tetrahedral
d10
Cd2+
4
Tetrahedral
d10
Mn2+
4
Tetrahedral
d5
Ti3+
6
Octahedral
d1
V2+
6
Octahedral
d3
Cr3+
6
Octahedral
d3
Mn2+
6
Octahedral
d5
Fe3+
6
Octahedral
d5
Octahedral
d6
Co3+
6
Coordination Numbers and Shapes of Some Complex Ions
d1
d8
d3
d9
d5
d10
d6
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45
Transition Elements & Their
Coordination Compounds

Complex Ions

1/19/2015
Donor Atoms per Ligand

The Ligands of complex ions are “molecules”
or “anions” with one or more donor atoms
that each donate a lone pair of electrons to
the metal ion to form a covalent bond

Atoms with lone pairs of electrons often
come from Groups 5A, 6A, or 7A (maingroup elements)
46
Transition Elements & Their
Coordination Compounds

Complex Ions

1/19/2015
Ligands are classified in terms of the number of
donor atoms (teeth) that each uses to bond to
the central metal ion

Monodentate Ligands use a “single” donor
atom

Bidentate Ligands have two donor atoms

Polydentate Ligands have more than two
donor atoms
47
Transition Elements & Their
Coordination Compounds
Some Common Ligands in Coordination Compounds
Donor Atom
The Ligands contains one or more Donor atoms that
have electron pairs to donate to the Central Atom
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48
Transition Elements & Their
Coordination Compounds

Complex Ions
 Chelates (Greek “chela” – crab’s claw)
 Bidentate and Polydentate ligands give rise to “rings” in the
complex ion
 Ex: Ethylene Diamine (abbreviated (en) in formulas)
(:N – C – C – N:)
forms a 5-member ring, with the two electron donating
N atoms bonding to the metal atom
Such ligands seem to grab the metal ion like claws
Ethylenediaminetetraacetate (EDTA)
1/19/2015
Used in treating heavy-metal poisoning, by acting as a scavenger of lead and
other heavy-metal ions, removing them from blood and other body fluids
49
Transition Elements & Their
Coordination Compounds

Formulas and Names of Coordination Compounds

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Important rules for writing formulas of
coordinate compounds

The cation is written before the anion

The charge of the cation(s) is balanced by
the charge of the anions

In the complex ion, neutral ligands are
written before anionic ligands

The entire ion is placed in brackets, i.e., [ ]
50
Transition Elements & Their
Coordination Compounds

Formulas and Names of Coordination Compounds

Coordination Compound Formulas

Example # 1
K 2 [Co(NH3 )2 Cl 4 ]
Two compound cations (K+)
Ion Central Metal Cation (Co2+)
Neutral Ligands (2 NH3)
Counter Ions (4 Cl-)
Net Charge on Complex Ion
+
2+
–
–
–
–
–
Total Charge +2
Total Charge +2
Total Charge 0
Total Charge -4
- 2 [Co(NH3)2Cl4]-2
-
-2
K 2 [Co (NH 3 )2 Cl 4 ]
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51
Transition Elements & Their
Coordination Compounds

Formulas and Names of Coordination Compounds

Coordination Compound Formulas

Example # 2 – Complex Ion and Counter Ion
[Co(NH3)4Cl2]Cl
 Counter Ion (Cl-) (not part of complex ion) – Total charge -1
 Complex Ion - Neutral Ligands (4 NH3)
– Total Charge 0
 Complex Ion - Anion Ligands (2 Cl-)
– Total Charge -2
 Complex Ion - [Co(NH3)4Cl2]+
– Total Charge +1
 Complex Ion - Central Metal Atom (Co)
– Total Charge +3
[Co3+(NH3)4Cl-2]+Cl1/19/2015
52
Transition Elements & Their
Coordination Compounds

Formulas and Names of Coordination Compounds
 Example #3 – Complex Cation and Complex Anion
[Co(NH3)5Br]2[Fe(CN)6]
 Complex Cation - [Co(NH3)5Br]2+
 Complex Cation Central Atom (Co+3)
– Total charge +3
 Complex Cation Neutral Ligands (5 NH3) – Total Charge 0
 Complex Cation Anionic Ligand (Br-)
– Total Charge -1
 Complex Anion ([Fe(CN)6]4-)
– Total Charge -4
 Complex Anion Central Cation (Fe2+)
– Total Charge +2
 Complex Anion Ligand (6 CN-1)
– Total Charge -6
[Co3+(NH ) Br-] [Fe2+(CN-) ]
3 5
2 x (3 - 1) = 4
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2
6
2 - 6 = -4
53
Transition Elements & Their
Coordination Compounds

Formulas and Names of Coordination Compounds
 Naming Coordination Compounds
 Rules
 The Cation is named before the Anion
 Within the Complex Ion, the Ligands are named, in
alphabetical order, before the metal ion
 Neutral Ligands generally have the molecule name, with
exceptions Ex NH3 (ammine), H2O (aqua), C=O
(carbonyl)
 Anionic Ligands drop the –ide and add –o after the root
name Ex. Cl- becomes “chloro”
 A numerical prefix indicates the number of ligands of a
particular type Ex di (2), tri (3), tetra (4)
[Co(NH3)4Cl2]Cl
Tetra ammine di chloro cobalt(III)chloride
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54
Transition Elements & Their
Coordination Compounds

Formulas and Names of Coordination Compounds
Names of Some Neutral
and Anionic Ligands
Symbol
Fe
Cu
Pb
Ag
Au
Sn
Names of Some Metals Ions
in Complex Anions
Numerical Prefixes used
In Complex Anions
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Di
Bis
II
Tri
Tris
III
Tetra
Tetrakis
IV
Penta
pentakis
V
Hexa
Hexakis
VI
Septa
Septakis
VII
55
Transition Elements & Their
Coordination Compounds

Formulas and Names of Coordination Compounds
 Naming Coordination Compounds
 Rules
 Some ligand names already contain a
numerical prefix
Ethylenediamine
In these cases the number of ligands is
indicated by such terms as:
bis (2)
tris(3)
tetrakis(4)
A compound with two ethylene ligands would contain
the following ligand name
bis(ethylenediamine)
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56
Transition Elements & Their
Coordination Compounds

Formulas and Names of Coordination Compounds
 Naming Coordination Compounds
 Rules
 The oxidation state of the central metal ion is given by
a Roman numeral (in parentheses) only if the metal
ion can have more than one state, as in the compound
[Co(NH3)4Cl2]Cl
[Co3+(NH3)4Cl-2]ClTetra ammine di chloro cobalt(III)chloride
 If the complex ion is an anion, drop the ending of the
Central metal name and add “–ate”
K[Pt(NH3)Cl5]
K+[Pt4+(NH3)Cl-5]Potassium ammine penta chloro platinate(IV)
Na4[FeBr6]
Na+4[Fe2+Br-6]
Sodium hexa bromo ferrate(II)
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57
Practice Problem
What is the systematic name of Na3[AlF6]?
Ans: Complex ion – [AlF6]3Ligands 6 (hexa) F- ions (Fluoro)
Complex ion is an “anion”
(net charge -3)
End of metal ion Aluminum must be changed to –ate
Complex ion name – hexafluoroaluminate
Aluminum has only the +3 oxidation state so Roman
numerals are not required
Na3+ is the positive counter ion; it is separated from
the complex anion by a space
Na3[AlF6] Sodium Hexfluoroaluminate
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58
Practice Problem
What is the systematic name of [Co(en)2Cl2]NO3?
Ans: Listed alphabetically, there are two Cl- (dichloro) and
two “en” [bis(ethylenediamine)] ligands
Note: Alphabetically refers to the root chemical names:
Chloro &
Ethylenediamine
The “Complex ion” is a “Cation,” with a charge of +1
[Co3+(en)2Cl-2]+
The metal name in a complex ion is unchanged - Cobalt
Because Cobalt can have several oxidation states,
its charge must be specified - Cobalt (III)
One Nitrate ion (NO-3) balances the +1 complex cation
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Dichloro bis (ethylene diamine)cobalt(III) nitrate
59
Practice Problem
What is the formula of:
Tetra ammine bromo chlroro platinum(IV) chloride
Ans: The central atom of the complex cation is written first
Platinate(IV) Pt4+
The ligands follow in alphabetical order of root chemical name
Tetraammine (NH3) Bromo (Br-) Chloro (Cl-)
Complex ion formula - [Pt(NH3)4BrCl]2+ [Pt4+(NH3)4Br-Cl-]2+
To balance the +2 charge of the complex cation,
2 Cl- counter ions are required
[Pt(NH3)4BrCl]Cl2
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60
Practice Problem
What is the formula of
Hexa ammine cobalt(III) tetra chloro ferrate(III)
Ans: Compound consists of two complex ions
Complex Cation – Six hexammine (NH3) & cobalt(III) (Co3+)
Complex Cation – [Co(NH3)6]3+
[Co3+(NH3)6]3+
Complex Anion – tetrachloro - 4 ClComplex Anion – ferrate(III) - Fe3+
Complex Anion – [FeCl-4]Complex cation – balanced by 3 complex anions
Coordinate Compound – [Co(NH3)6][FeCl4]-3
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61
Transition Elements & Their
Coordination Compounds

Isomerism in Coordination Compounds
 Isomers are compounds with the same chemical formula but
different properties
 Constitutional (Structural) Isomers
 Two compounds with the same formula, but with atoms
connected differently
 Two Types
 Coordination Isomers – Composition of the complex
ion changes but not the compound
Ex. Ligand and counter ion exchange positions
[Pt(NH3)4Cl2](NO2)2
[Pt(NH3)4(NO2)2]Cl2
Ex. Two sets of ligands reversed
[Cr(NH3)6][Co(CN)6]
[Co(NH3)6][Cr(CN)6]
(NH3 is ligand of Cr3+ in one compound and of Co3+ in the other)
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62
Transition Elements & Their
Coordination Compounds

Constitutional (Structural) Isomers
 Linkage Isomers
 Composition of the complex ion remains the same, but the
attachment of the ligand donor atom changes
 Some ligands can bind to the metal ion through either of
two donor atoms
Ex. pentaamminenitrocobalt(III) chloride
[Co(NH3)5(NO2]Cl2
pentaamminenitritocobalt(III) chloride
[Co(NH3)5(ONO]Cl2
Ex. Cyanate ion can attach via lone pair of electrons on
the Oxygen atom (NCO:)
or the Nitrogen atom (isocyanato (OCN:)
Other examples of alternate electron
donor pairs for Linkage IsomerS
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63
Transition Elements & Their
Coordination Compounds

1/19/2015
Constitutional (Structural) Isomers
 Stereo Isomers
 Compounds that have the same atomic connections but
different spatial arrangements of the atoms
 Geometric Isomers (cis-trans isomers [diastereomers])
 Atoms or groups of atoms arranged differently in
space relative to the “Central” metal
64
Transition Elements & Their
Coordination Compounds

Constitutional (Structural) Isomers
 Stereo Isomers
 Optical Isomers (enantiomers)
 Occur when a molecule and its mirror image can not be
superimposed
 Optical isomers have distinct physical properties like
other types of isomers, with one exception – the direction
in which they rotate the plane of polarized light
Optical isomerism in an octahedral complex ion
Rotating structure I
in the cis
compound gives
structure III, which
is not the same as
structure II, its
mirror image,
Image I & Image III
are optical isomers
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Rotating structure I
in the trans
compound gives
structure III,which
is the same as
structure II, its
mirror image,
The trans
compound does not
have any mirror
images
65
Practice Problem
Draw all stereo isomers for the following
[Pt(NH3)2Br2]
Br
NH3
H3 N
Pt
H3 N
Br
Pt
Br
trans
Cr(en)3]3+ (en = H2NCH2CH2NH2)
H3 N
Br
cis
Pt(II) complex is Square Planar Geometry
Two different monodentate ligands
Geometric Isomers
Each isomer is superimposable on the
mirror image – no optical isomerism
Ethylenediamine is a bidentate ligand
The Cr3+ has a coordination number of 6
and an octahedral geometry, similar to Co3+
The three bidendate ions are identical
 No geometric isomerism
This complex ion has a nonsuperimposable
mirror image
 Optical Isomerism does occur
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66
Transition Elements & Their
Coordination Compounds

Theoretical Basis for the Bonding and Properties of
Complexes

1/19/2015
Questions

How do Metal Ligand bonds form

Why certain geometries are preferred

Why are complexes often brightly colored

Why are complexes often paramagnetic – attracted
to a magnetic field as a result of their electron pairs
being unpaired
67
Transition Elements & Their
Coordination Compounds

Theoretical Basis for the Bonding and Properties of
Complexes
 Application of Valence Bond Theory to Complex Ions
 In the formation of a complex ion, the filled ligand
orbital overlaps the empty metal-ion orbital
 The Ligand (Lewis Base) donates the electron pair
and the metal-ion (Lewis Acid) accepts it to form one
of the covalent bonds of the complex ion (Lewis
adduct)
 When one atom in a bond donates both electrons
the bond is referred to as a ”coordinate covalent
bond”
 The number and type of metal-ion hybrid orbitals
occupied by ligand lone pairs determine the
geometry of the complex ion
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68
Transition Elements & Their
Coordination Compounds

Application of Valence Bond Theory to Complex Ions
 Octahedral Complexes (six electron groups about central atom)
 Ex. Hexaamminechromium(III) ion
[CrNH3)6]3+
 Six hybrid orbitals are needed to make the ion
 The six lowest energy orbitals of the Cr3+ ion
Two 3d, one 4s, three 4p
mix and become six equivalent d2sp3 hybrid orbitals that point
to the corners of an octahedron
 The six d2sp3 hybrid orbitals are filled with the six electron pairs
from the six NH3 ligands
Paramagnetic
Unpaired e-
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Note the lowest 6 energy levels for Cr3+ involve
both n=3 & n=4 sublevels
The 3d orbitals are of lower energy than the 4s
and 4p orbitals
The hybrid designation, d2sp3, follows this order
If all the orbitals had the same “n” value, the
order would have been sp3d2
69
Transition Elements & Their
Coordination Compounds

Application of Valence Bond Theory to Complex Ions

Square Planar Complexes (four electron groups about central
atom)

Metal ions with a d8 configuration usually form square planar
complexes

In the [Ni(CN)4]2- ion, the model proposes
one 3d, one 4s, two 4p for Ni2+
to from four dsp2 hybrid orbitals pointing the corners of a
square accepting one electron pair from each of the four
CN- orbitals
Paramagnetic
Unpaired e-
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Note the filling of the first
4 unhybridized 3d orbitals
after one 3d, one 4s and
two 4p orbitals combine to
form the four dsp2 hybrid
orbitals
70
Transition Elements & Their
Coordination Compounds

Application of Valence Bond Theory to Complex Ions
 Tetrahedral Complexes (four electron groups about central atom)
 Metal ions that have a filled d sublevel, such as Zn+2 [Ar] 3d10
often form Tetrahedral complexes
 In the [Zn(OH)4]2- ion, the model proposes the lowest available
Zn2+ orbitals
one 4s, three 4p
mix to become four sp3 hybrid orbitals that point to the corners
of a tetrahedron, occupied by four lone pairs, one from each of
the four OH- ligands
Diamagnetic
1/19/2015
71
Transition Elements & Their
Coordination Compounds

Crystal Field Theory

Valence Bond Theory pictures and rationalizes bonding
and shape of molecules

VB theory gives little insight into the colors of
coordination compounds and can be ambiguous with
regard to magnetic properites

Crystal Field Theory explains color and magnetism

1/19/2015
Highlights the “effects” on the d-orbital energies of
the metal ion as the ligands approach
72
Transition Elements & Their
Coordination Compounds

Crystal Field Theory

1/19/2015
What is Color?

White light is electromagnetic radiation consisting of
“all” wavelengths () in the “visible” range

Objects appear “colored” in white light because they
absorb certain wavelengths and reflect or transmit
others

Opaque objects reflect light

Clear objects transmit light

If the object absorbs all visible wavelengths, it
appears “black”

If the object reflects all visible wavelengths, it
appears “white”
73
Transition Elements & Their
Coordination Compounds

Crystal Field Theory
 What is Color?


Each color has a “complimentary” color
An object has a particular color for two reasons
 It reflects (or transmits) light of that color or
 It absorbs light of the “complimentary” color
Ex. If an object absorbs only red (compliment of
green), it is interpreted as “green”
Colors with approximate wavelength ranges
Complimentary colors, such as red and green,
lie opposite each other
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74
Transition Elements & Their
Coordination Compounds

Crystal Field Theory
1/19/2015

In CF Theory, the properties of complexes result
from the splitting of d-orbital energies

Split d-orbital energies arise from “electrostatic”
interactions between the positively charged metal
ion cation and the negative charge of the ligands

The negative charge of the ligand is either partial as
in a polar neutral ligand like NH3, or full, as in an
anionic ligand like Cl-
75
Transition Elements & Their
Coordination Compounds

Crystal Field Theory

The ligands approach the metal ion along the mutually perpendicular
x, y, and z axes (octahedral orientation), minimizing the overall
energy of the system

B & C Lobes of the dx2-y2 and dz2 orbitals lie directly in line with the
approaching ligands and have stronger repulsions

D, E, F lobes of the dxy, dxz, and dyz orbitals lie “between” the
approaching ligands, so the repulsion are weaker
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76
Transition Elements & Their
Coordination Compounds

Crystal Field Theory

An energy diagram of the orbitals shows all five d orbitals are higher
in energy in the forming complex than in the free metal ion, because
of the repulsions from the approaching ligands
Crystal Field Splitting Energy
Forming Complex

Crystal Field Splitting Energy - The d orbital energies are
“split” with the two dx2-y2 and dz2 orbitals (eg orbital set) higher in
energy than the dxy, dxz, and dyz orbitals (t2g orbital set)

Strong-field ligands, such as CN- lead to larger splitting energy

Weak-field ligands such as H2O lead to smaller splitting energy
1/19/2015
77
Transition Elements & Their
Coordination Compounds

Crystal Field Theory

Explaining the Colors of Transition Metals

Diversity in colors is determined by the energy
difference () between the t2g and eg orbital sets in
complex ions

When the ions absorbs light in the visible range,
electrons move from the lower energy t2g level to the
higher eg level, i.e., they are “excited” and jump to a
higher energy level
 E electron = Ephoton = hv = hc/

1/19/2015
The substance has a “color” because only certain
wavelengths of the incoming white light are absorbed
78
Transition Elements & Their
Coordination Compounds

Crystal Field Theory
 Example – Consider the [Ti(H2O)6]3+ ion – Purple in aqueous
solution
 Hydrated Ti3+ is a d1 ion, with the d electron in one of the three
lower energy t2g orbitals
 The energy difference (A) between the t2g and eg orbitals
corresponds to the energy of photons spanning the green and
yellow range
 These colors are absorbed and the electron jumps to one of the
eg orbitals
 Red, blue, and violet light are transmitted as purple
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79
Transition Elements & Their
Coordination Compounds

Crystal Field Theory

For a given “ligand”, the color depends on the
oxidation state of the metal ion – the number of “d”
orbital electrons available
A solution of [V(H2O)6]2+ ion is violet
A solution of [V(H2O)6]3+ ion is yellow

For a given “metal”, the color depends on the ligand
[Cr(NH3)6]3+ (yellow-orange)
[Cr(NH3)5]2+ (Purple)
Even a single ligand is enough to change the color
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80
Transition Elements & Their
Coordination Compounds

Crystal Field Theory
 Spectrochemical Series
 The Spectrochemical Series is a ranking of ligands with regard
to their ability to split d-orbital energies
 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
 As the crystal field strength of the ligand increases, the splitting
energy () increases (shorter wavelengths of light must be
absorbed to excite the electrons
1/19/2015
81
Practice Problem
Rank the following ions in terms of the relative value of 
and of the energy of visible light absorbed
[Ti(H2O)6]3+
Ti(NH3)6]3+
Ti(CN)6]3+
Ans:
Oxidation State of Ti is +3 in all formulas
From the spectrochemical series table, the ligand
strength is in the order:
CN- > NH3 > H2O
Relative size of , thus, the energy of light absorbed is
Ti(CN)6]3+ > Ti(NH3)6]3+
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>
[Ti(H2O)6]3+
82
Transition Elements & Their
Coordination Compounds

Explaining the Magnetic Properties of Transition Metal
Complexes
 The splitting of energy levels influence magnetic properties
 Affects the number of unpaired electrons in the
metal ion “d” orbitals
 According to Hund’s rules, electrons occupy orbitals one at a
time as long as orbitals of “equal energy” are available
 When “all” lower energy orbitals are “half-filled (all +½ spin
state)”, the next electron can
 Enter a half-filled orbital and pair up (with a –½ spin
state electron) by overcoming a repulsive pairing energy
(Epairing)
or
 Enter an empty, higher energy orbital by overcoming the
crystal field splitting energy ()
 The relative sizes of Epairing and () determine the
occupancy of the d orbitals
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83
Transition Elements & Their
Coordination Compounds

Crystal Field Theory
 Explanation of Magnetic Properties
 The occupancy of “d” orbitals, in turn, determines the
number of unpaired electrons, thus, the paramagnetic
behavior of the ion
 Ex. Mn2+ ion ([Ar] 3d5) has 5 unpaired electrons in 3d
orbitals of equal energy
 In an octahedral field of ligands, the orbital energies
split
 The orbital occupancy is affected in two ways:
 Weak-Field ligands (low ) and High-Spin complexes
 Strong-Field ligands (high ) and Low-Spin
complexes
(from spectrochemical series)
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84
Transition Elements & Their
Coordination Compounds

Crystal Field Theory

1/19/2015
Explanation of Magnetic Properties

Weak-Field ligands and High-Spin complexes

Ex.

A weak-field ligand, such as H2O, has a “small” crystal field
splitting energy ()

It takes less energy for “d” electrons to move to
the “eg” set (remaining unpaired) rather than
pairing up in the “t2g” set with its higher
repulsive pairing energy (Epairing)

Thus, the number of unpaired electrons in a
weak-field ligand complex is the same as in
the free ion

Weak-Field Ligands create high-spin complexes,
those with a maximum of unpaired electrons

Generally Paramagnetic
[Mn(H2O)6]2+
Mn2+ ([Ar] 3d5)
85
Transition Elements & Their
Coordination Compounds

Crystal Field Theory

1/19/2015
Explanation of Magnetic Properties

Strong-Field Ligands and Low-Spin Complexes

Ex. [Mn(CN)6]4-

Strong-Field Ligands, such CN-, cause large crystal field
splitting of the d-orbital energies, i.e., higher ()

() is larger than (Epairing)

Thus, it takes less energy to pair up in the “t2g“ set than would
be required to move up to the “eg” set

The number of unpaired electrons in a
Strong-Field Ligand complex is less than
in the free ion

Strong-Field ligands create low-spin complexes,
i.e., those with fewer unpaired electrons

Generally Diamagnetic
Fewer
unpaired electrons
86
Transition Elements & Their
Coordination Compounds

Crystal Field Theory

Explaining Magnetic Properties

Orbital diagrams for the d1 through d9 ions in
octahedral complexes show that both high-spin and
low-spin options are possible only for:
d4
d5
d6
d7
ions

With three “lower” energy t2g orbitals available, the
d1, d2, d3 ions always form high-spin (unpaired)
complexes because there is no need to pair up

Similarly, d8 & d9 ions always form high-spin
complexes because the 3 orbital t2g set is filled with
6 electrons (3 pairs)
The two t2g orbitals must have either two d8 or one
d9 unpaired electron
3/15/2016
1/19/2015
8787
Transition Elements & Their
Coordination Compounds

Crystal Field Theory

Explaining Magnetic Properties
high spin:
weak-field
ligand
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low spin:
strongfield ligand
high spin:
weak-field
ligand
low spin:
strongfield ligand
88
Practice Problem
Iron(II) forms an essential complex in hemoglobin
For each of the two octahedral complex ions
[Fe(H2O)6]2+
[Fe(CN)6]4-
Draw an orbital splitting diagram, predict the number of unpaired
electrons, and identify the ion as low-spin or high spin
Ans:
Fe2+ has the [Ar] 3d6 configuration
H2O produces smaller crystal field splitting () than CNThe [Fe(H2O)6]2+ has 4 unpaired electrons (high spin)
The [Fe(CN)6]4- has no unpaired electrons (low spin)
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Transition Elements & Their
Coordination Compounds

Crystal Field Theory
 Four electron groups about the central atom
 Four ligands around a metal ion also cause d-orbital
splitting, but the magnitude and pattern of the splitting
depend on the whether the ligands are in a “tetrahedral”
or “square planar” arrangement
 Tetrahedral – AX4
 Octahedral – AX4E2 (2 ligands along “z” axis removed)
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Splitting of d-orbital energies
by a tetrahedral field of ligands
Splitting of d-orbital energies by
a square planar field of ligands.
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Transition Elements & Their
Coordination Compounds

Crystal Field Theory (Splitting)
 Tetrahedral Complexes
 Ligands approach corners of a tetrahedron
 None of the five metal ion “d” orbitals is directly in the
path of the approaching ligands
 Minimal repulsions arise if ligands approach the dxy, dyz,
and dyz orbitals closer than if they approach the
dx2-y2 and dz2 orbitals (opposite of octahedral case)
 Thus, the dxy, dyz, and dyz orbitals experience more
electron repulsion and become higher energy
 Splitting energy of d-orbital energies is “less” in a
tetrahedral complex than in an octahedral complex
tetrahedral < octahedral
 Only high-spin tetrahedral complexes are known because
the magnitude of () is small (weak)
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Transition Elements & Their
Coordination Compounds

Crystal Field Theory (Splitting)

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Square Planar Complexes

Consider an Ocatahedral geometry with the two z axis
ligands removed, no z-axis interactions take place

Thus, the dz2, dxz an dyz orbital energies decrease

The two ‘d” orbitals in the xy plane (dxy, dx2-y2) interact
most strongly with the approaching ligands

The (dxy, dx2-y2) orbital has its lobes directly on the x,y
axis and thus has a higher energy than the dxy orbital

Square Planar complexes are generally strong field – low
spin and generally diamagnetic

D8 metals ions such as [PdCl4]2- have 4 pairs of the
electrons filling the lowest energy levels and are thus,
“diamagentic”
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