Chemistry 481(01) Spring 2015
Instructor: Dr. Upali Siriwardane
e-mail: upali@latech.edu
Office: CTH 311 Phone 257-4941
Office Hours:
M,W 8:00-9:00 & 11:00-12:00 am;
Tu,Th, F 9:30 - 11:30 a.m.
April 7 , 2015: Test 1 (Chapters 1, 2, 3)
April 30, 2015: Test 2 (Chapters 6 & 7)
May 19, 2015: Test 3 (Chapters. 19 & 20)
May 19, Make Up: Comprehensive covering all Chapters
Chemistry 481, Spring 2015, LA Tech
Chapter 7-1
Chapter 7. An introduction to coordination
compounds
The language of coordination chemistry
7.1 Representative ligands
7.2 Nomenclature
Constitution and geometry
7.3 Low coordination numbers
7.4 Intermediate coordination numbers
7.53Higher coordination numbers
7.6 Polymetallic complexes
Isomerism and chirality
7.7 Square-planar complexes
7.8 Tetrahedral complexes
7.9 Trigonal-bipyrmidal and square-pyramidal complexes
7.10 Octahedral complexes
7.11 Ligand chirality
Chemistry 481, Spring 2015, LA Tech
Chapter 7-2
Chapter 7. An introduction to
coordination compounds
Thermodynamics of complex formation
7.12 Formation constants
7.13 Trends in successive formation constants
7.14 Chelate and macrocyclic effects
7.15 Steric effects and electron delocalization
Chemistry 481, Spring 2015, LA Tech
Chapter 7-3
Coordination compound
A compound formed from a Lewis acid and Lewis
base.
A metal or metal ion acting Lewis acid (being an
electron pair acceptor) and a atom or group of
atoms with lone electron pairs Lewis base electron
pair donor forms an adduct with dative or
coordinative covalent bonds.
Ni(ClO4)2 (aq)+ 6NH3 → [Ni(NH3)6](ClO4)2 (aq)
The Lewis bases attached to the metal ion in such
compounds are called ligands.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-4
The coordination number (CN)
CN of a metal ion in a complex is defined as the
number of ligand donor atoms to which the metal
is directly bonded.
[Co(NH3)5Cl]2+
CN is 6, 1 chloride and 5 ammonia ligands each
donating an electron pair.
For organometallic compounds. An alternative
definition of CN would be the number of electron
pairs arising from the ligand donor atoms to which
the metal is directly bonded.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-5
1) What is a coordination compound?
Chemistry 481, Spring 2015, LA Tech
Chapter 7-6
Chemistry 481, Spring 2015, LA Tech
Chapter 7-7
Coordination sphere
• Coordination sphere - the sphere around the
central ion made up of the ligands directly
attached to it. Primary and secondary coordination
sphere.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-8
Preparation of Complexes
[Fe(H2O)6]2+ + 6 CN-
[Fe(CN)6]4- + 6 H2O
• The figure at left shows cyanide ions (in the
form of KCN), being added to an aq. solution
of FeSO4.
• Since water is a Lewis base, the Fe2+ ions were
originally in the complex [Fe(H2O)6]2+
• The CN- ions are driving out the H2O
molecules in this substitution reaction that
form the hexacyanoferrate(II) ion, [Fe(CN)6]4- .
Chemistry 481, Spring 2015, LA Tech
Chapter 7-9
Various Colors of d-Metal Complexes
The color of the complex depends
on the identity of the ligands as
well as of the metal..
Impressive changes of color often
accompany substitution reactions.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-10
Chemistry 481, Spring 2015, LA Tech
Chapter 7-11
Chemistry 481, Spring 2015, LA Tech
Chapter 7-12
Structures and symmetries
• Six-coordinate complexes are almost all
octahedral (a).
• Four-coordinate complexes can be tetrahedral (b)
or square planar (c).
• (Square planar usually occurs with d8 electron
configurations, such as in Pt2+ and Au3+.)
Chemistry 481, Spring 2015, LA Tech
Chapter 7-13
Representing Octahedral Shapes
• Instead of a perspective drawing (a), we can
represent octahedral complexes by a simplified
drawing that emphasizes the geometry of the
bonds (b).
Chemistry 481, Spring 2015, LA Tech
Chapter 7-14
Ligands
The Brønsted bases or Lewis base attached to the
metal ion in such compounds are called ligands.
These may be
Simple ions such as Cl–, CN–
Small molecules such as H2O or NH3,
Larger molecules such as H2NCH2CH2NH2
N(CH2CH2NH2)3
Macromolecules, EDTA and biological molecules
such as proteins.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-15
Representative Ligands and Nomenclature
Bidentate Ligands
Polydentate Ligands
• Some ligands can simultaneously occupy more
than one binding site.
• Ethylenediamine (above) has a nitrogen lone pair
at each end, making it bidentate. It is widely used
and abbreviated “en”, as in [Co(en)3]3+.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-16
Chemistry 481, Spring 2015, LA Tech
Chapter 7-17
Ethylenediaminetetraacetate Ion (EDTA)
• EDTA4- is another example of a
chelating agent. It is
hexadentate.
• This ligand forms complexes
with many metal ions, including
Pb2+, and is used to treat lead
poisoning.
• Unfortunately, it also removes
Ca2+ and Fe2+ along with the
lead.
• Chelating agents are common
in nature.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-18
Porphyrins and phthalocyanins
Chemistry 481, Spring 2015, LA Tech
Chapter 7-19
Chelates
• The metal ion in [Co(en)3]3+ lies
at the center of the three
ligands as though pinched by
three molecular claws. It is an
example of a chelate,
• A complex containing one or
more ligands that form a ring
of atoms that includes the
central metal atom.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-20
Naming Transition Metal Complexes
• Cation name first then anion name.
• List first the ligands, then the central atom
• The ligand names are made to end in -O if negative
• Anion part of the complex ends in -ate
Eg. Cu(CN)64- is called the hexacyanocuprate(II) ion
• The ligands are named in alphabetic order
• Number of each kind of ligand by Greek prefix
• The oxidation state of the central metal atom
shown in parenthesis after metal name
• Briding is shown with  ( -oxo)
Chemistry 481, Spring 2015, LA Tech
Chapter 7-21
Some Common Ligand Names
Chemistry 481, Spring 2015, LA Tech
Chapter 7-22
Names of Ligands (continued)
Chemistry 481, Spring 2015, LA Tech
Chapter 7-23
Coordination Sphere Nomenclature
• Cationic coordination sphere
• -ium ending
Anionic coordination sphere
• -ate ending
Chemistry 481, Spring 2015, LA Tech
Chapter 7-24
Examples
• [Co(NH3)4Cl2]Cl:
• dichlorotetramminecobalt(III) chloride
• [Pt(NH3)3Cl]2[PtCl4]:
di(monochlorotriammineplatinum(II))
tetrachloroplatinate(II).
• K3[Fe(ox)(ONO)4] :
• potassium tetranitritooxalatoferrate(III)
Chemistry 481, Spring 2015, LA Tech
Chapter 7-25
Use bis and tris for di and tri
for chelating ligands
• [Co(en)3](NO3)2 :
• tris(ethylenediamine)cobalt(II) nitrate
• [Ir(H2O)2(en)2]Cl3
• bis(ethylenediamine)diaquairidium(III)
chloride
• [Ni(en)3]3[MnO4] :
• Tris(ethylenediamine)nickel(II)
tetraoxomanganate(II)
Chemistry 481, Spring 2015, LA Tech
Chapter 7-26
Naming
• [Cu(NH3)4]SO4
tetraaminecopper(II) sulfate
• [Ti(H2O)6][CoCl6]
hexaaquatitanium(III)
hexachlorocobaltate(III)
K3[Fe(CN)6]
• potassium hexacyanoferrate(III)
Chemistry 481, Spring 2015, LA Tech
Chapter 7-27
2) Give the formula of following coordination
compounds
a)Dichlorobis(ethylenediammine)nickle
b) Potasium trichloro(ethylene)platinate(1-)
Chemistry 481, Spring 2015, LA Tech
Chapter 7-28
c) Tetrakis(pyridine)platinum(2+)
tetrachloroplatinate(2-)
d) Tetraamminebis(ethylenediamine)
--hydroxo- -amidodicobalt(4+) chloride
Chemistry 481, Spring 2015, LA Tech
Chapter 7-29
3) Give the names of following coordination
compounds
a)
[Co(NH3)6]Cl3;
b)
trans-[Cr(NH3)4(NO2)2]+ ;
c)
K[Cu(CN)2] ;
d)
cis-[PtCl2(NH3)2] ;
e)
fac-[Co(NO2)3(NH3)3]Cl3
Chemistry 481, Spring 2015, LA Tech
Chapter 7-30
The Eta(h) System of Nomenclature
• For for p bonded ligands number of
atoms attached to the metal atom is
shown by hn
(h5 -cyclopentadienyl) tricarbonyl manganese
tetracarbonyl (h3-allyl) manganese, Mn(C3H5)(CO)4
Chemistry 481, Spring 2015, LA Tech
Chapter 7-31
Isomers
• Both structural and stereoisomers are found.
• The two ions shown below differ only in the
positions of the Cl- ligand, but they are distinct
species, with different physical and chemical
properties.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-32
4)
What is the geometry and coordination
number of compounds in the problem above?
a)
[Co(NH3)6]Cl3;
b)
trans-[Cr(NH3)4(NO2)2]+ ;
c)
K[Cu(CN)2] ;
d)
cis-[PtCl2(NH3)2] ;
e)
fac-[Co(NO2)3(NH3)3]Cl3
Chemistry 481, Spring 2015, LA Tech
Chapter 7-33
5) Draw the formula and find the BITE of following
ligands.
a)
2,2'-bipyridine (bipy) ;
b)
terpy;
c)
cyclam;
d)
edta;
Chemistry 481, Spring 2015, LA Tech
Chapter 7-34
Chemistry 481, Spring 2015, LA Tech
Chapter 7-35
Ionization Isomers
• These differ by the exchange of a ligand with an
anion (or neutral molecule) outside the
coordination sphere. [CoSO4(NH3)5]Br has the Bras an accompanying anion (not a ligand) and
[CoBr(NH3)5]SO4 has Br - as a ligand and SO42-as
accompanying anion.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-36
Ionization Isomers
The red-violet solution of
[Co(NH3)5Br]SO4 (left) has
no rxn w/ Ag+ ions, but
forms a ppt. when Ba2+ ions
are added.
The dark red solution of
[CoSO4(NH3)5]Br (right)
forms a ppt. w/ Ag+ ions,
but does not react w/ Ba2+
ions.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-37
Hydrate Isomers
• These differ by an ex-change
•
•
•
•
•
Chemistry 481, Spring 2015, LA Tech
between an H2O molecule and
another ligand in the
coordination sphere.
The solid, CrCl3. 6H2O, may be
any of three compounds.
[Cr(H2O)6]Cl3 (violet)
CrCl(H2O)5]Cl2.H2O (blue-green)
CrCl2 (H2O)4Cl.2H2O (green)
Primary and secondary
coordination spheres
Chapter 7-38
Linkage Isomers
The triatomic ligand
is the
isothiocyanato, NCS. In (b) it is the
thiocyanato, SCN-.
Other ligands
capable or forming
linkage isomers are
(a) NSC ligand (the N is closest to the
NO2- vs. ONO center); (b) SCN- ligand (S is closest the
center)
CN - vs. NC - .
Chemistry 481, Spring 2015, LA Tech
Chapter 7-39
Coordination Isomers
• These occur when one or more ligands are
exchanged between a cationic complex and an
anionic complex.
• An example is the pair [Cr(NH3)6][Fe(CN)6]
and[Fe(NH3)6][Cr(CN)6].
Chemistry 481, Spring 2015, LA Tech
Chapter 7-40
Stereoisomers
• Ionization, hydrate, linkage, and coordination
isomers are all structural isomers.
• In stereoisomers, the formulas are the same. The
atoms have the same partners in the coordination
sphere, but the arrangement of the ligands in
space differs.
• The cis- and trans- geometric isomers shown in
next slide differ only in the way the ligands are
arranged in space.
• There can be geometric isomers for octahedral
and square planar complexes, but not for
tetrahedral complexes.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-41
Square Planar Complexes
Geometric Isomers
• Properties of geometric isomers can vary greatly.
• The cis- isomer below is pale orange-yellow, has a
solubility of 0.252 g/100 g water, and is used for
chemotherapy treatment.
• The trans- isomer is dark yellow, has a solu-bility
of 0.037 g/100 g water, and shows no
hemotherapeutic effect.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-42
6) Describe the geometrical isomerism in following
compounds:
a)
[Co(NH3)4Cl2]+ ;
b)
[IrCl3(PPh3)3] ;
c)
[Cr(en)2Cl2] ;
Chemistry 481, Spring 2015, LA Tech
Chapter 7-43
cis and trans-PtCl2(NH3)2
Chemistry 481, Spring 2015, LA Tech
Chapter 7-44
Trans Effect & Influence
Chemistry 481, Spring 2015, LA Tech
Chapter 7-45
Preparation Geometrical Isomers
Chemistry 481, Spring 2015, LA Tech
Chapter 7-46
Optical Isomerism
The two complexes at left are mirror
images. (The gray rectangle represents
a mirror, through which we see
somewhat darkly.)
No matter how the complexes are
rotated, neither can be superimposed
on the other.
Note only four of the six ligands are
different.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-47
Combined Stereoisomerisms
•
Both geometrical and optical isomerism can
occur in the same complex, as below. The transisomer is green.
• The two cis- isomers, which are optical isomers of
each other, are violet.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-48
Chemistry 481, Spring 2015, LA Tech
Chapter 7-49
Identifying Optical Isomerism
If a molecule or ion belong to a point group with a Sn
axis is not optically active
Chemistry 481, Spring 2015, LA Tech
Chapter 7-50
Chemistry 481, Spring 2015, LA Tech
Chapter 7-51
Molecular Polarity and Chirality
Polarity
• Polarity:Only molecules belonging to the point
groups Cn, Cnv and Cs are polar. The dipole
moment lies along the symmetry axis
formolecules belonging to the point groups Cn and
Cnv.
• Any of D groups, T, O and I groups will not be
polar
Chemistry 481, Spring 2015, LA Tech
Chapter 7-52
Chirality
Only molecules
lacking a Sn axis
can be chiral.
This includes mirror
planes
and a center of
inversion as
S2=s , S1=I and Dn
groups.
Not Chiral: Dnh,
Dnd,Td and Oh.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-53
Optical Activity
Chemistry 481, Spring 2015, LA Tech
Chapter 7-54
Reactions of Metal Complexes
Formation constants
– the chelate effect
– Irving William Series
– Lability
Chemistry 481, Spring 2015, LA Tech
Chapter 7-55
7) Pick the chiral compounds among the
following:
a)
[Co(en)3]3+ ;
b)
cis-[Cr(en)2Cl2] ;
c)
c) trans-[Cr(en)2Cl2] ;
Chemistry 481, Spring 2015, LA Tech
Chapter 7-56
Formation of Coordination Complexes
typically coordination compounds are more labile or
fluxional than other molecules X is leaving group
and Y is entering group
MX + Y
MY + X
One example is the competition of a ligand, L for a
coordination site with a solvent molecule such as
H2O
[Co(OH2)6]2+ + Cl-
Chemistry 481, Spring 2015, LA Tech
[Co(OH2)5Cl]+ + H2O
Chapter 7-57
Formation Constants
Consider formation as a series of formation
equilibria:
Summarized as:
Chemistry 481, Spring 2015, LA Tech
Chapter 7-58
Values of Kn
Typically: Kn>Kn+1
Expected statistically, fewer coordination sites
available to form MLn+1
eg sequential formation of Ni(NH3)n(OH2)6-n 2+
Chemistry 481, Spring 2015, LA Tech
Chapter 7-59
Breaking the Rules
Order is reversed when some electronic or chemical
change drives formation
Fe(bipy)2(OH2)22+ + bipy
Fe(bipy)32+
jump from a high spin to low spin complex
Fe(bipy)2(OH2)2 t2g4eg2
high spin
Fe(bipy)3
t2g6
low spin
Chemistry 481, Spring 2015, LA Tech
Chapter 7-60
Chemistry 481, Spring 2015, LA Tech
Chapter 7-61
Chemistry 481, Spring 2015, LA Tech
Chapter 7-62
Irving William Series
Values of log Kf for 2+ ions including transition
metal species Lewis acidity (acceptance of e-)
increases across the per. table, thus forming more
and more stable complexes for the same ligand
system
Kf series for transition metals:
Mn2+< Fe2+ < Co2+ < Ni2+ < Cu2+ >Zn2+
Chemistry 481, Spring 2015, LA Tech
Chapter 7-63
Irving William Series
Chemistry 481, Spring 2015, LA Tech
Chapter 7-64
Bonding and electronic structure
Bonding Theories of Transition Metal Complexes
• Valance Bond Theory
• Crystal Field Theory
• Ligand Field Theory or Molecular Orbital Theory
Chemistry 481, Spring 2015, LA Tech
Chapter 7-65
Valance Bond Theory
”Outer orbital" (sp3d2) and ”Inner orbital" (d2sp3)
[CoF6]3- - Co3+ : d6
[Co(NH3)6]3+ - Co3+ : d6
Chemistry 481, Spring 2015, LA Tech
Chapter 7-66
Spectrochemical Series for Ligands
• It is possible to arrange representative ligands in
an order of increasing field strength called the
spectrochemical series:
I¯ < Br¯ < -SCN¯ < Cl¯ < F¯ < OH¯ < C2O42¯ < H2O < NCS¯ < py < NH3 < en < bipy < o-phen < NO2¯ <
CN¯ < CO
Chemistry 481, Spring 2015, LA Tech
Chapter 7-67
8) Use valence bond theory (VBT) to predict the
electron configurations, the type of bonding (Inner
and outer orbital) and number of unpaired electrons
in following compounds:
a)
[Co(CN)6]3- ;
b)
[CoCl6]3-;
c)
[Fe(NH3)6]3+;
Chemistry 481, Spring 2015, LA Tech
Chapter 7-68
Crystal Field Theory
• In the electrical fields created by ligands
• The orbitals are split into two groups: a
set consisting of dxy, dxz, and dyz stabilized
by 2/5Do, known by their symmetry
• classification as the t2g set, and a set
consisting of the dx2-y2 and dz2, known as
the eg set, destabilized by 3/5Do where Do
is the gap between the two sets.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-69
Crystal Field Splitting of d Orbitals
Chemistry 481, Spring 2015, LA Tech
Chapter 7-70
Octahedral Crystal Field Splitting
Chemistry 481, Spring 2015, LA Tech
Chapter 7-71
9) What are the symmetry labels of s,p, and d
orbitals in tetrahedral (NiCO)4) and square-planar
([PtCl4]2-) and octahedral (Cr(CO)6) compounds.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-72
10) Explain the effect of ligands on the d orbitals
in octahedral, tetrahedral, trigonal-bipyramid and
square-planar coordination compounds using
Crystal Field Theory.
Octahedral,
Tetrahedral,
Trigonal-bipyramid
Square-planar
Chemistry 481, Spring 2015, LA Tech
Chapter 7-73
11) [Ti(H2O)6]3+ shows a absorption at 20300 cm-1.
Absorption values for similar coordination
compounds of Ti3+ with different ligands are given
below. Based on their absorption values arrange
the following ligands in a Spectrochemical Series.
Absorption(cm-1)
Ligand H2O
CNPPh3
FNH3
20300 20500 20455 20100 20400
Chemistry 481, Spring 2015, LA Tech
Chapter 7-74
Crystal Field Stabilization Energy
• Crystal Field stabilization parameter Do
Chemistry 481, Spring 2015, LA Tech
Chapter 7-75
Crystal Field Stabilization Energy
d7 case.
Weak field case
The configurations would be written t2g5 eg2
5(-2/5Do) + 2(+3/5Do) = -4/5Do
Strong field case
The configurations would be written t2g6 eg1
6(-2/5Do) + 1(+3/5Do) = -9/5Do
Chemistry 481, Spring 2015, LA Tech
Chapter 7-76
CFSE & Paring Energy
[Fe(H2O)6]2+. Iron has a d6 configuration, the value of
Do is 10,400 cm-1 and the pairing energy is 17600cm1.
(1 kJ mol-1 = 349.76 cm-1.) We must compare the
total of the CFSE and the pairing energy for the two
possible configurations.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-77
high spin (more stable)
CFSE = 4 x -2/5 x 10400 + 2 x 3/5 x 10400 = -4160cm-1
(-11.89 kJ mol-1)
Pairing energy (1 pair) = 1 x 17600 = 17600 cm-1
(50.32 kJ mol-1
Total = +13440 cm-1 (38.43 kJ mol-1)
low spin
CFSE = 6 x -2/5 x 10400= -24960 cm-1 (-71.36 kJ mol1)
Pairing energy (3 pairs) = 3 x 17600 = 52800 (151.0 kJ
mol-1)
Total = +27840 cm-1 (79.60 kJ mole-1)
Chemistry 481, Spring 2015, LA Tech
Chapter 7-78
Tetrahedral complexes
• Splitting order or reversed. eg is now lower energy
and t2g is hgher energy
• Because a tetrahedral complex has fewer ligands,
the magnitude of the splitting is smaller. The
difference between the energies of the t2g and eg
orbitals in a tetrahedral complex (t) is slightly less
than half as large as the splitting in analogous
octahedral complexes (o)
•
Dt = 4/9Do
Chemistry 481, Spring 2015, LA Tech
Chapter 7-79
Tetrahedral Ligand Arrangement
Dt = 4/9Do
Mostly forms high spin complxes
Chemistry 481, Spring 2015, LA Tech
Chapter 7-80
Octahedral Crystal Field Splitting
Chemistry 481, Spring 2015, LA Tech
Chapter 7-81
Square-planar Complexes-D4h
Chemistry 481, Spring 2015, LA Tech
Chapter 7-82
Generalizations about Crystal Field
Splittings
• The actual value of D depends on both the metal
ion and the nature of the ligands:
• The splitting increases with the metal ion
oxidation state. For example, it roughtly doubles
going from II to III.
• The splitting increases by 30 - 50% per period
down a group.
• Tetrahedral splitting would be 4/9 of the
octahedral value if the ligands and metal ion were
the same.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-83
Spectrochemical Series for Ligands
• It is possible to arrange representative ligands in
an order of increasing field strength called the
spectrochemical series:
I¯ < Br¯ < -SCN¯ < Cl¯ < F¯ < OH¯ < C2O42¯ < H2O < NCS¯ < py < NH3 < en < bipy < o-phen < NO2¯ <
CN¯ < CO
Chemistry 481, Spring 2015, LA Tech
Chapter 7-84
Spectrochemical Series for Metals
It is possible to arrange the metals according to a
spectrochemical series as well. The approximate
order is
Mn2+ < Ni2+ < Co2+ < Fe 2+ < V2+ < Fe3+ < Co3+ < Mn3+
< Mo3 + < Rh3 + < Ru3 + < Pd4+ < Ir3+ < Pt 3+
Chemistry 481, Spring 2015, LA Tech
Chapter 7-85
Spectrum of [Ti(H2O)6]3+.
1
1 0
0 1
d : t2g eg –> t2g eg
Chemistry 481, Spring 2015, LA Tech
Chapter 7-86
Hydration Enthalpy.
• M2+(g) + 6 H2O(l) = [M(O2H)6]2+(aq)
Chemistry 481, Spring 2015, LA Tech
Chapter 7-87
Irving-Williams Series
Chemistry 481, Spring 2015, LA Tech
Chapter 7-88
Ligand Field Splitting and Metals
the transition metal also impacts Do increases
with increasing oxidation number
Do increases as you move down a group (i.e.
with increasing principal quantum number n)
Chemistry 481, Spring 2015, LA Tech
Chapter 7-89
MO forML6 diagram Molecules
D0
Chemistry 481, Spring 2015, LA Tech
Chapter 7-90
Ligand Field Stabilization Energies
LFSE is a function
of Do
weighted average
of the splitting
due to the
fact that they are
split into groups
of 3 (t2g)
and 2 (eg)
Chemistry 481, Spring 2015, LA Tech
Chapter 7-91
Weak Field vs. Strong Field
now that d orbitals are not degenerate how do we
know what an electronic ground state for a d metal
complex is? need to determine the relative
energies of pairing vs. Do
Chemistry 481, Spring 2015, LA Tech
Chapter 7-92
Splitting vs. Pairing
when you have more than 3 but fewer than 8 d
electrons you need to think about the relative merits
pairing vs. Do
• high-spin complex – one with maximum number of
unpaired electrons
• low-spin complex – one with fewer unpaired
Chemistry 481, Spring 2015, LA Tech
Chapter 7-93
electrons
Rules of Thumb for Splitting vs Pairing
• depends on both the metal and the ligands
• high-spin complexes occur when o is small Do is
small when:
• n is small (3 rather than 4 or 5)– high spin only
really for 3d metals
• oxidation state is low– i.e. for oxidation state of
zero or 2+
• ligands is low in spectrochemical series– eg
halogens
Chemistry 481, Spring 2015, LA Tech
Chapter 7-94
Four Coordinate Complexes:
Tetrahedral
Same approach but different set of orbitals with
different ligand field
• Arrangement of tetrahedral field of point charges
results in splitting of energy where dxy, dzx, dyz are
repelled more by Td field of negative charges
• So the still have a split of the d orbitals into triply
degenerate (t2) and double degenerate (e) pair but
now e is lower energy and t2 is higher.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-95
Tetrahedral Crystal Field Splitting
Chemistry 481, Spring 2015, LA Tech
Chapter 7-96
Ligand Field Splitting: Dt
describes the separation between
reviouslydegenerate d orbitals
• Same idea as Do but Dt < 0.5 Do for comparable
systems
• So …Almost Exclusively Weak Field
Chemistry 481, Spring 2015, LA Tech
Chapter 7-97
Electron configurations in octahedral fields
Weak field and strong fieled cases
Chemistry 481, Spring 2015, LA Tech
Chapter 7-98
Tetragonal Complexes
Start with octahedral geometry and follow the
energy as you tetragonally distort the octahedron
Tetragonal distortion: extension along z and
compression on x and y
Orbitals with xy components increase in
energy, z components decrease in energy
Results in further breakdown of degeneracy
– t2g set of orbitals into dyz, dxz and dxy
– eg set of orbitals into dz2 and dx2-y2
Chemistry 481, Spring 2015, LA Tech
Chapter 7-99
Tetragonal Complexes
Chemistry 481, Spring 2015, LA Tech
Chapter 7-100
Square Planar Complexes
• extreme form of tetragonal distortion
• Ligand repulsion is completely removed from
• z axis
Common
for
8
8 4d and
5d complexes:
Rh(I), Ir(I)
Pt(II), Pd(II)
Chemistry 481, Spring 2015, LA Tech
Chapter 7-101
Jahn Teller Distortion
geometric distortion may occur in systems
based on their electronic degeneracy
This is called the Jahn Teller Effect:
If the ground electronic configuration of a
nonlinear complex is orbitally degenerate, the
complex will distort to remove the degeneracy
and lower its energy.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-102
Jahn Teller Distortions
Orbital degeneracy: for octahedral geometry
these are:
– t2g3eg1 eg. Cr(II), Mn(III) High spin complexes
– t2g6eg1 eg. Co(II), Ni(II)
– t2g6eg3 eg. Cu(II)
basically, when the electron has a choice between
one of the two degenerate eg orbitals, the
geometry will distort to lower the energy of the
orbital that is occupied.
Result is some form of tetragonal distortion
Chemistry 481, Spring 2015, LA Tech
Chapter 7-103
Ligand Field Theory
Crystal field theory: simple ionic model, does not
accurately describe why the orbitals are raised or
lowered in energy upon covalent bonding.
• LFT uses Molecular Orbital Theory to derive the
ordering of orbitals within metal complexes
• Same as previous use of MO theory, build ligand
group orbitals, combine them with metal atomic
orbitals of matching symmetry to form MO’s
Chemistry 481, Spring 2015, LA Tech
Chapter 7-104
LFT for Octahedral Complexes
Consider metal orbitals and ligand group orbitals
Under Oh symmetry, metal atomic orbitals transform
as:
Degeneracy
Mulliken Label
Atomic
Orbital
2
eg
dx2-y2, dz2
3
t2g
dxy, dyz, dzx
3
t1u
px, py, pz
1
a1g
s
Chemistry 481, Spring 2015, LA Tech
Chapter 7-105
Sigma Bonding: Ligand Group
Orbitals
Chemistry 481, Spring 2015, LA Tech
Chapter 7-106
Combinationsof Metal andLigand SALC’s
Chemistry 481, Spring 2015, LA Tech
Chapter 7-107
Molecular Orbital Energy Level Diagram: Oh
Chemistry 481, Spring 2015, LA Tech
Chapter 7-108
PI Bonding
pi interactions alter the
MOELD that results from
sigma bonding
• interactions occur between
frontier metal orbitals and the
pi orbitals of L
• two types depends on the ligand
–pi acid - back bonding accepts e- density from M
–pi base -additional e- density donation to the M
• type of bonding depends on relative energy level
of pi orbitals on the ligand and the metal orbitals
Chemistry 481, Spring 2015, LA Tech
Chapter 7-109
: PI Bases and the MOELD Oh
pi base ligands
contribute more
electron density to
the metal
• t2g is split to form a
bonding and
antibonding pair of
orbitals
Do is decreased
• halogens are good
pi donors
Chemistry
481, Spring 2015, LA Tech
Chapter 7-110
PI Acids and the MOELD: Oh
• pi acids accept electron
density back from the
metal
• t2g is split to form a
bonding and antibonding
pair of orbitals
• the occupied bonding
set of orbitals goes
down in energy so ..
• Do increases
• typical for phosphine
and carbonyl ligands
Chemistry 481, Spring 2015, LA Tech
Chapter 7-111
Magnetic Properties of Atoms
• a) Diamagnetism?
• Repelled by a magnetic field due to paired electrons.
b)Paramagnetism?
• attracted to magnetic field due to un-paired electrons.
c) Ferromagnetism?
• attracted very strongly to magnetic field due to un-paired
electrons.
• d)Anti-ferromagnetic?
• Complete cancelling of unpaired electrons in magnetic
domains
Chemistry 481, Spring 2015, LA Tech
Chapter 7-112
Magnetic Suceptibility Vs Temperature
Chemistry 481, Spring 2015, LA Tech
Chapter 7-113
Types of magnetism
Chemistry 481, Spring 2015, LA Tech
Chapter 7-114
Magnetic Properties
A paramagnetic substance is characterised
experimentally by its (molar) magnetic
susceptibility, cm. This is measured by
suspending a sample of the compound under a
sensitive balance between the poles of a powerful
electro-magnet,
Chemistry 481, Spring 2015, LA Tech
Chapter 7-115
Number of Unparied Electrons
The magnetic moment of the substance is given by
the Curie Law:
 = 2.54(cmT)½ (in units of Bohr magnetons)
The formula used to calculate the spin-only
magnetic moment can be written in two forms
= n(n+2) B.M.
Chemistry 481, Spring 2015, LA Tech
Chapter 7-116
Magnetic Properties of Atoms
• Paramagnetism?
• Ferromagnetism?
• Diamagnetism?
• Gouvy Balance
Chemistry 481, Spring 2015, LA Tech
Chapter 7-117
Octahedral Complexes
Chemistry 481, Spring 2015, LA Tech
Chapter 7-118
Tetrahedral Complexes
Chemistry 481, Spring 2015, LA Tech
Chapter 7-119