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Transition Elements & Their
Coordination Compounds
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
6/14/2010 1
Transition Elements & Their
Coordination Compounds
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
Transition Elements make up the “d” block (B group)
and the “f” block elements in the periodic chart
As ions, transition metals (elements) provide
fascinating insights into chemical bonding and
structure
Transition metals play an important role in living
organisms
6/14/2010 2
Transition Elements & Their
Coordination Compounds
Properties of Transition Elements
Main –Group Transition Elements
Main-group elements change from All transition elements are metals
metal to non-metal across a period
Most main-group ionic compounds Many transition metal compounds
are colorless and diamagnetic (non- are highly colored and paramagnetic
magnetic)
6/14/2010 3
Transition Elements & Their
Coordination Compounds
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
for each period [ml = -2 -1 0 +1 +2] (total of 10
electrons, 2 in each orbital) or 10 x 4 = 40 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), where the 28 “f” orbitals
are filled [ml= -3 -2 -1 0 +1 +2 +3] (7 orbitals
per period x 2 electrons per orbital x 2 periods = 28
6/14/2010 4
Transition Elements & Their
Coordination Compounds
6/14/2010 5
Transition Elements & Their
Coordination Compounds
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)
Condensed f-block ground-state electron configuration
(Periods 6 & 7):
[noble gas] ns2 (n-2)f14(n-1)dx, with n = 6 -7
6/14/2010 6
Transition Elements & Their
Coordination Compounds
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
Both Ions have pale colors in aqueous solutions
Both form complex ions with similar magnetic properties
6/14/2010 7
Transition Elements & Their
Coordination Compounds
Note Aufbau build up exceptions for “Cr” & “Cu”
6/14/2010 8
Practice Problem
Write condensed electron configurations for the following ions:
Zr V3+ Mo3+
Vanadium – 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
b. Va 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) + 3e-
c. 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-
6/14/2010 9
Transition Elements & Their
Coordination Compounds
Trends of Transition Elements Across a Period
Transition elements exhibit smaller, less regular changes in size,
electronegativity, and first ionization energy
Atomic Size
General overall decrease across a period
As the “d” orbitals are filled across a period, the change in
atomic size within the transition elements evens out because
the increased nuclear charge shields the outer electrons
preventing them from spreading out
Transition Metals
6/14/2010 10
Transition Elements & Their
Coordination Compounds
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
6/14/2010 11
Transition Elements & Their
Coordination Compounds
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
In the transition metals, however, the first
ionization energies increase relatively little because
of the effective shielding by the inner “d” electrons
reducing the effect of the increased nuclear charge
Transition Metals
6/14/2010 12
Transition Elements & Their
Coordination Compounds
Trends Within (down) a Group (relative to main-group
elements)
Vertical trends differ from those of the main-group
elements
Atomic Size
Increases, as expected, from Period 4 to 5
No increase from Period 5 to 6
Lanthanides with buried “4f” sublevel orbitals appear
between the 4d (period 5) and 5d (period 6) series
An element in Period 6 is separated from the one
above it in Period 5 by 32 electrons
(ten 4d, six 5p, two 6s, and fourteen 4f)
The extra shrinking that results from the increased
nuclear charge due to the addition of the fourteen 4f
electrons is called the:
“Lanthanide Contraction”
6/14/2010 13
Transition Elements & Their
Coordination Compounds
n=1 n=2 n=3
l=0 l=0 l=1 l=0 l=1 l=2
(1s) (2s) (2p) (3s) (3p) (3d)
ml = 0 0 -1 0 +1 0 -1 0 +1 -2 -1 0 +1 +2
n=4
l=0 l=1 l=2 l=3
Note: (4s) (4p) (4d) (4f)
n>7&l>3 -1 0 +1
ml = 0 -2 -1 0 +1 +2 -3 -2 -1 0 +1 +2 +3
Sublevels not
utilized for n=5
any element
in the current l=0 l=1 l=2 l=3
Period Table (5s) (5p) (5d) (5f)
ml = 0 -1 0 +1 -2 -1 0 +1 +2 -3 -2 -1 0 +1 +2 +3
n=6,7
l=0 l=1 l=2 l=3
(6s,7s) (6p,7p) (6d) (6f)
ml = 0 -1 0 +1 -2 -1 0 +1 +2 -3 -2 -1 0 +1 +2 +3
6/14/2010 14
Transition Elements & Their
Coordination Compounds
Main Group Metals Main Group Non-metals
Transition Metals
Inner Transition Metals
Order of Sublevel Orbital Filling
6/14/2010 15
Transition Elements & Their
Coordination Compounds
Trends Within a Group (relative to main-group elements)
Electronegativity (EN) – Relative ability of an atom in a covalent
bond to attract shared electrons
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
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 (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
6/14/2010 16
Transition Elements & Their
Coordination Compounds
Trends Within a Group (relative to main-group elements)
Ionization Energy
Main-group elements increase in size down a
group, decreasing the 1st ionization energy, making
it relatively easier to remove the outer electrons
The relatively small increase in size of transition
metals, combined with the relatively large increase
in nuclear charge (Zeff), results in a general increase
in the first ionization energy down a group
6/14/2010 17
Transition Elements & Their
Coordination Compounds
Trends Within a Group (relative to main-group elements)
Density
Atomic size (volume) is inversely related to density
Across a period densities increase
In transition metals the density down a group
increases dramatically because atomic volumes
change little from Period 5 to Period 6 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)
6/14/2010 18
Transition Elements & Their
Coordination Compounds
Vertical (down group) trends in key properties within the
transition elements.
6/14/2010 19
Transition Elements & Their
Coordination Compounds
Chemical Properties of the Transition Elements
Similar to atomic & physical properties, the 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 in bonding leading to
multiple oxidation states
6/14/2010 20
Transition Elements & Their
Coordination Compounds
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 Electronic
dx 4s 3d 4p
Manganese (Mn) Configuration
0 d5 [Ar] 4s2 3d5
+1 d5 [Ar] 4s1 3d5 Note: All 3 d5
+2 d5 [Ar] 3d5
+3 d4 [Ar] 3d4
+4 d3 [Ar] 3d3 Ex. MnO2 ; O.N. Mn +4
+5 d2 [Ar] 3d2
+6 d1 [Ar] 3d1
+7 d0 [Ar] Ex. MnO4- ; O.N. Mn +7
6/14/2010 21
Transition Elements & Their
Coordination Compounds
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
6/14/2010 22
Transition Elements & Their
Coordination Compounds
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
6/14/2010 23
Transition Elements & Their
Coordination Compounds
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
EN Cr – 1.6 Al – 1.5 (basic oxide)
Cr3+ – 1.7
Cr6+ – 2.3 P – 2.1 (acidic oxides)
6/14/2010 24
Transition Elements & Their
Coordination Compounds
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.
Thus, Ti2+, Eo = -01.63V, is a stronger
reducing agent than Ni2+, Eo = -0.25V
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
6/14/2010 25
Transition Elements & Their
Coordination Compounds
Color in Transition Elements
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
6/14/2010 26
Transition Elements & Their
Coordination Compounds
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
6/14/2010 27
Transition Elements & Their
Coordination Compounds
Chemical Behavior Within a Group
Main_Group
The decrease in Ionization Energy (IE) going down a
group results in “increased reactivtiy”
Transition metals
Ionization Energy increases down group
The Standard Electrode also increases (becomes more
positive)
Chromium is stronger reducing agent
6/14/2010 28
Transition Elements & Their
Coordination Compounds
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 x varies across series (Period)
Exceptions – Ce, Gd, Lu have single e- in 5d orbital
6/14/2010 29
Sample Problem
Finding the Number of Unpaired Electrons
The alloy SmCo5 forms a permanent magnet because both
Samarium and Cobalt and 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 15)
Recall previous slide - only Ce, Gd, Lu have 5d electrons
Remaining 6 electrons go into the 4f orbitals
6s 4f 5d 6p
Six unpaired electrons
6/14/2010 30
Transition Elements & Their
Coordination Compounds
The Actinides (Thorium (Th); Z=90 - Lawrencium; Z=103)
All Actinides are Radioactive
Only Thorium & Uranium occur in nature
Share very similar chemical & physical properties
Silvery and chemically reactive
Principal oxidation state is +3, similar to lanthanides
6/14/2010 31
Transition Elements & Their
Coordination Compounds
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
Chromium – ([Ar] 4s2 3d5) with 6 valence electrons occurs in all
possible positive oxidation states
Cr2+, Cr3+, Cr6+ are most important
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)
6/14/2010 32
Transition Elements & Their
Coordination Compounds
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)
6/14/2010 33
Transition Elements & Their
Coordination Compounds
Highlights of Selected Transition Metals
Chromium (con‟t)
Chromium (VI) - Cr6+ (Deep Red)
CrO3 is covalent and acidic
Dissolves in water to from 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)
6/14/2010 34
Transition Elements & Their
Coordination Compounds
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) Eo = 1.18 V
Manganese can use all its valence electrons (several oxidation
states) to form compounds
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)
6/14/2010 35
Transition Elements & Their
Coordination Compounds
All Manganese species with oxidation states greater than +2 acts
as oxidizing agents (gains electrons causing other atoms to lose
electrons)
MnO4-(aq) + 4H+ + 3e- → MnO2(s) + 2H2O(l) Eo = 1.68
MnO4-(aq) + 2H2O + 3e- → MnO2(s) + 4OH- Eo = 0.59
(MnO4- is a much stronger oxidizing agent in acid solution than in
basic solution – note difference in Eo values)
Oxidation State Electronic
dx 4s 3d 4p
Manganese (Mn) 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]
6/14/2010 36
Transition Elements & Their
Coordination Compounds
Manganese
Unlike Cr2+ & Fe2+, the Mn2+ ion resists oxidation in
air
Recall: half-filled (-1/2 spins 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
6/14/2010 37
Transition Elements & Their
Coordination Compounds
Coordination Compounds (Complexes)
Most distinctive aspect of transition metal chemistry
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
6/14/2010 38
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
Central Ligands Counter
Atom Ions
6/14/2010 39
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.
Ligands are viewed as Lewis Bases, although rare
cases are known involving Lewis acidic ligands
6/14/2010 40
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
6/14/2010 41
Transition Elements & Their
Coordination Compounds
Complex ions
Geometry – Depends on Coordination No. & Nature of Metal Ion
Metal ion CN 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 d1 d8
Mn2+ 6 Octahedral d5 d3 d9
Fe3+ 6 Octahedral d5
d5 d10
Co3+ 6 Octahedral d6
d6
6/14/2010 42
Transition Elements & Their
Coordination Compounds
Complex Ions
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 (main-group elements)
6/14/2010 43
Transition Elements & Their
Coordination Compounds
Complex Ions
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
6/14/2010 44
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)
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
6/14/2010 45
Transition Elements & Their
Coordination Compounds
Formulas and Names of Coordination Compounds
Three 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., [ ]
6/14/2010 46
Transition Elements & Their
Coordination Compounds
Formulas and Names of Coordination Compounds
Coordination Compounds Formulas
Example # 1
K2[Co(NH3)2Cl4]
Two compound cations (K+) – Total Charge +2
Ion Central Metal Cation (Co2+) – Total Charge +2
Neutral Ligands (2 NH3) – Total Charge 0
Charged Ligands (4 Cl-) – Total Charge -4
Net Charge on Complex Ion – - 2 [Co(NH3)2Cl4]-2
Net Cation Charge – +2
K+2[Co2+(NH3)2Cl-4]
6/14/2010 47
Transition Elements & Their
Coordination Compounds
Formulas and Names of Coordination Compounds
Coordination Compounds 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]+Cl-
6/14/2010 48
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 6
6/14/2010
2 x (3 -1) = 4 2 - 6 = -4 49
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), CO (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
Tetraamminedichlorocobalt(III)chloride
6/14/2010 50
Transition Elements & Their
Coordination Compounds
Formulas and Names of Coordination Compounds
Names of Some Neutral
and Anionic Ligands
Symbol
Fe
Cu
Names of Some Metals Ions Pb
in Complex Anions Ag
Au
Sn
Di Bis II
Tri Tris III
Numerical Prefixes used Tetra Tetrakis IV
In Complex Anions Penta pentakis V
Hexa Hexakis VI
Septa Septakis VII
6/14/2010 51
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 the following it its
name
bis(ethylenediamine)
6/14/2010 52
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
Tetraamminedichlorocobalt(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 amminepentachloroplatinate(IV)
Na4[FeBr6] Na+4[Fe2+Br-6]
sodium hexabromoferrate(II)
6/14/2010 53
Practice Problem
What is the systematic name of Na3[AlF6]?
Ans: Complex ion – [AlF6]3-
Ligands 6 (hexa) F- ions (fluoro)
Complex ion is an “anion”
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
6/14/2010 54
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
dichlorobis(ethylenediamine)cobalt(III) nitrate
6/14/2010 55
Practice Problem
What is the formula of:
tetraamminebromochlroroplatinum(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
6/14/2010 56
Practice Problem
What is the formula of
hexaamminecobalt(III) tetrachloroferrate(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 Cl-
Complex Anion – ferrate(III) - Fe3+
Complex Anion – [FeCl-4]-
Complex cation – balanced by 3 complex anions
Coordinate Compound – [Co(NH3)6][FeCl4]-3
6/14/2010 57
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)
6/14/2010 58
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
6/14/2010 59
Transition Elements & Their
Coordination Compounds
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
6/14/2010 60
Transition Elements & Their
Coordination Compounds
Constitutional (Structural) Isomers
Stereo Isomers
Optical Isomers (enantiomers)
Occur when a molecule and its mirror image canot 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 Rotating structure I
in the cis in the trans
compound gives compound gives
structure III, which structure III,which
is not the same as is the same as
structure II, its structure II, its
mirror image, mirror image,
Image I & Image III The trans
are optical isomers compound does not
have any mirror
6/14/2010 images 61
Practice Problem
Draw all stereo isomers for the following
[Pt(NH3)2Br2] Cr(en)3]3+ (en = H2NCH2CH2NH2)
Pt(II) complex is Square Planar Geometry
Br NH3 H3N Br Two different monodentate ligands
Pt Pt Geometric Isomers
H3N Br Each isomer is superimposable on the
H3N Br mirror image – no optical isomerism
tran ci
s s
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
6/14/2010 62
Transition Elements & Their
Coordination Compounds
Theoretical Basis for the Bonding and Properties of
Complexes
Questions
How do Metal Ligands 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
6/14/2010 63
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
6/14/2010 64
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
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
Paramagnetic
Unpaired e- 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
6/14/2010 65
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
Note the filling of the first
4 unhybridized 3d orbitals
Paramagnetic
after one 3d, one 4s and
Unpaired e- two 4p orbitals combine to
form the four dsp2 hybrid
orbitals
6/14/2010 66
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
6/14/2010 67
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
Highlights the “effects” on the d-orbital energies of
the metal ion as the ligands approach
6/14/2010 68
Transition Elements & Their
Coordination Compounds
Crystal Field Theory
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”
6/14/2010 69
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
6/14/2010 70
Transition Elements & Their
Coordination Compounds
Crystal Field Theory
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-
6/14/2010 71
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
6/14/2010 72
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
6/14/2010 73
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/
The substance has a “color” because only certain
wavelengths of the incoming white light are
absorbed
6/14/2010 74
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
6/14/2010 75
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
6/14/2010 76
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
6/14/2010 77
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+ > [Ti(H2O)6]3+
6/14/2010 78
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
6/14/2010 79
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)
6/14/2010 80
Transition Elements & Their
Coordination Compounds
Crystal Field Theory
Explanation of Magnetic Properties
Weak-Field ligands and High-Spin complexes
Ex. [Mn(H2O)6]2+ Mn2+ ([Ar] 3d5)
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
6/14/2010 81
Transition Elements & Their
Coordination Compounds
Crystal Field Theory
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, Fewer
i.e., those with fewer unpaired electrons unpaired electrons
Generally Diamagnetic
6/14/2010 82
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
6/14/2010 83
Transition Elements & Their
Coordination Compounds
Crystal Field Theory
Explaining Magnetic Properties
high spin: low spin: high spin: low spin:
weak-field strong- weak-field strong-
ligand field ligand ligand field ligand
6/14/2010 84
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 CN-
The [Fe(H2O)6]2+ has 4 unpaired electrons (high spin)
The [Fe(CN)6]4- has no unpaired electrons (low spin)
6/14/2010 85
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)
Splitting of d-orbital energies Splitting of d-orbital energies by
6/14/2010 by a tetrahedral field of ligands a square planar field of ligands. 86
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)
6/14/2010 87
Transition Elements & Their
Coordination Compounds
Crystal Field Theory (Splitting)
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”
6/14/2010 88
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