1
Chapter 7-1Chemistry 481, Spring 2017, LA Tech
Instructor: Dr. Upali Siriwardane
e-mail: [email protected]: 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 4 , 2017: Test 1 (Chapters 1, 2, 3, 4)
April 27, 2017: Test 2 (Chapters (6 & 7)
May 16, 2016: Test 3 (Chapters. 19 & 20)
May 17, Make Up: Comprehensive covering all Chapters
Chemistry 481(01) Spring 2017
Chapter 7-2Chemistry 481, Spring 2017, LA Tech
Chapter 7. An introduction to coordination compounds
The language of coordination chemistry 7.1 Representative ligands
7.2 Nomenclature
Constitution and geometry7.3 Low coordination numbers
7.4 Intermediate coordination numbers
7.53Higher coordination numbers
7.6 Polymetallic complexes
Isomerism and chirality7.7 Square-planar complexes
7.8 Tetrahedral complexes
7.9 Trigonal-bipyrmidal and square-pyramidal complexes
7.10 Octahedral complexes
7.11 Ligand chirality
Chapter 7-3Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-4Chemistry 481, Spring 2017, LA Tech
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.
Chapter 7-5Chemistry 481, Spring 2017, LA Tech
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.
Chapter 7-6Chemistry 481, Spring 2017, LA Tech
1) What is a coordination compound?
2
Chapter 7-7Chemistry 481, Spring 2017, LA Tech Chapter 7-8Chemistry 481, Spring 2017, LA Tech
Coordination sphere
• Coordination sphere - the sphere around the
central ion made up of the ligands directly
attached to it. Primary and secondary coordination
sphere.
Chapter 7-9Chemistry 481, Spring 2017, LA Tech
Preparation of Complexes
• 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- .
[Fe(H2O)6]2+ + 6 CN- [Fe(CN)6]
4- + 6 H2O
Chapter 7-10Chemistry 481, Spring 2017, LA Tech
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.
Chapter 7-11Chemistry 481, Spring 2017, LA Tech Chapter 7-12Chemistry 481, Spring 2017, LA Tech
3
Chapter 7-13Chemistry 481, Spring 2017, LA Tech
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+.)
Chapter 7-14Chemistry 481, Spring 2017, LA Tech
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).
Chapter 7-15Chemistry 481, Spring 2017, LA Tech
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.
Chapter 7-16Chemistry 481, Spring 2017, LA Tech
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+.
Chapter 7-17Chemistry 481, Spring 2017, LA Tech Chapter 7-18Chemistry 481, Spring 2017, LA Tech
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.
4
Chapter 7-19Chemistry 481, Spring 2017, LA Tech
Porphyrins and phthalocyanins
Chapter 7-20Chemistry 481, Spring 2017, LA Tech
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.
Chapter 7-21Chemistry 481, Spring 2017, LA Tech
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)
Chapter 7-22Chemistry 481, Spring 2017, LA Tech
Some Common Ligand Names
Chapter 7-23Chemistry 481, Spring 2017, LA Tech
Names of Ligands (continued)
Chapter 7-24Chemistry 481, Spring 2017, LA Tech
Coordination Sphere Nomenclature
• Cationic coordination sphere
• -ium ending
Anionic coordination sphere
• -ate ending
5
Chapter 7-25Chemistry 481, Spring 2017, LA Tech
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)
Chapter 7-26Chemistry 481, Spring 2017, LA Tech
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)
Chapter 7-27Chemistry 481, Spring 2017, LA Tech
Naming
• [Cu(NH3)4]SO4
tetraaminecopper(II) sulfate
• [Ti(H2O)6][CoCl6]
hexaaquatitanium(III)
hexachlorocobaltate(III)
K3[Fe(CN)6]
• potassium hexacyanoferrate(III)
Chapter 7-28Chemistry 481, Spring 2017, LA Tech
2) Give the formula of following coordination
compounds
a)Dichlorobis(ethylenediammine)nickle
b) Potasium trichloro(ethylene)platinate(1-)
Chapter 7-29Chemistry 481, Spring 2017, LA Tech
c) Tetrakis(pyridine)platinum(2+)
tetrachloroplatinate(2-)
d) Tetraamminebis(ethylenediamine)
--hydroxo- -amidodicobalt(4+) chloride
Chapter 7-30Chemistry 481, Spring 2017, LA Tech
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
6
Chapter 7-31Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-32Chemistry 481, Spring 2017, LA Tech
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.
Chapter 7-33Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-34Chemistry 481, Spring 2017, LA Tech
5) Draw the formula and find the BITE of following
ligands.
a) 2,2'-bipyridine (bipy) ;
b) terpy;
c) cyclam;
d) edta;
Chapter 7-35Chemistry 481, Spring 2017, LA Tech Chapter 7-36Chemistry 481, Spring 2017, LA Tech
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 Br-
as an accompanying anion (not a ligand) and
[CoBr(NH3)5]SO4 has Br - as a ligand and SO42-as
accompanying anion.
7
Chapter 7-37Chemistry 481, Spring 2017, LA Tech
Ionization IsomersThe 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.
Chapter 7-38Chemistry 481, Spring 2017, LA Tech
Hydrate Isomers• These differ by an ex-change
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 7-39Chemistry 481, Spring 2017, LA Tech
Linkage Isomers
The triatomic ligand is the isothiocyanato, NCS-
. In (b) it is the thiocyanato, SCN-.
Other ligands capable or forming linkage isomers are
NO2- vs. ONO -
CN - vs. NC - .
(a) NSC-
ligand (the N is closest to the center); (b) SCN- ligand (S is closest the
center)
Chapter 7-40Chemistry 481, Spring 2017, LA Tech
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].
Chapter 7-41Chemistry 481, Spring 2017, LA Tech
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.
Chapter 7-42Chemistry 481, Spring 2017, LA Tech
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.
8
Chapter 7-43Chemistry 481, Spring 2017, LA Tech
6) Describe the geometrical isomerism in following
compounds:
a) [Co(NH3)4Cl2]+ ;
b) [IrCl3(PPh3)3] ;
c) [Cr(en)2Cl2] ;
Chapter 7-44Chemistry 481, Spring 2017, LA Tech
cis and trans-PtCl2(NH3)2
Chapter 7-45Chemistry 481, Spring 2017, LA Tech
Trans Effect & Influence
Chapter 7-46Chemistry 481, Spring 2017, LA Tech
Preparation Geometrical Isomers
Chapter 7-47Chemistry 481, Spring 2017, LA Tech
Optical IsomerismThe 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.
Chapter 7-48Chemistry 481, Spring 2017, LA Tech
Combined Stereoisomerisms• Both geometrical and optical isomerism can
occur in the same complex, as below. The trans-
isomer is green.
• The two cis- isomers, which are optical isomers of
each other, are violet.
9
Chapter 7-49Chemistry 481, Spring 2017, LA Tech Chapter 7-50Chemistry 481, Spring 2017, LA Tech
Identifying Optical IsomerismIf a molecule or ion belong to a point group with a Sn
axis is not optically active
Chapter 7-51Chemistry 481, Spring 2017, LA Tech Chapter 7-52Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-53Chemistry 481, Spring 2017, LA Tech
ChiralityOnly 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.
Chapter 7-54Chemistry 481, Spring 2017, LA Tech
Optical Activity
10
Chapter 7-55Chemistry 481, Spring 2017, LA Tech
Reactions of Metal Complexes
Formation constants
– the chelate effect
– Irving William Series
– Lability
Chapter 7-56Chemistry 481, Spring 2017, LA Tech
7) Pick the chiral compounds among the
following:
a) [Co(en)3]3+ ;
b) cis-[Cr(en)2Cl2] ;
c) c) trans-[Cr(en)2Cl2] ;
Chapter 7-57Chemistry 481, Spring 2017, LA Tech
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- [Co(OH2)5Cl]+ + H2O
Chapter 7-58Chemistry 481, Spring 2017, LA Tech
Formation Constants
Consider formation as a series of formation
equilibria:
Summarized as:
Chapter 7-59Chemistry 481, Spring 2017, LA Tech
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+
Values of Kn
Chapter 7-60Chemistry 481, Spring 2017, LA Tech
Breaking the Rules
Order is reversed when some electronic or chemical
change drives formation
Fe(bipy)2(OH2)22+ + bipy Fe(bipy)3
2+
jump from a high spin to low spin complex
Fe(bipy)2(OH2)2 t2g4eg2 high spin
Fe(bipy)3 t2g6 low spin
11
Chapter 7-61Chemistry 481, Spring 2017, LA Tech Chapter 7-62Chemistry 481, Spring 2017, LA Tech
Chapter 7-63Chemistry 481, Spring 2017, LA Tech
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+
Chapter 7-64Chemistry 481, Spring 2017, LA Tech
Irving William Series
Chapter 7-65Chemistry 481, Spring 2017, LA Tech
Bonding and electronic structure
Bonding Theories of Transition Metal Complexes
• Valance Bond Theory
• Crystal Field Theory
• Ligand Field Theory or Molecular Orbital Theory
Chapter 7-66Chemistry 481, Spring 2017, LA Tech
Valance Bond Theory
”Outer orbital" (sp3d2) and ”Inner orbital" (d2sp3)
[CoF6]3- - Co3+ : d6
[Co(NH3)6]3+ - Co3+ : d6
12
Chapter 7-67Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-68Chemistry 481, Spring 2017, LA Tech
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+;
Chapter 7-69Chemistry 481, Spring 2017, LA Tech
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.
Chapter 7-70Chemistry 481, Spring 2017, LA Tech
Crystal Field Splitting of d Orbitals
Chapter 7-71Chemistry 481, Spring 2017, LA Tech
Octahedral Crystal Field Splitting
Chapter 7-72Chemistry 481, Spring 2017, LA Tech
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.
13
Chapter 7-73Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-74Chemistry 481, Spring 2017, LA Tech
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 CN- PPh3 F- NH3
20300 20500 20455 20100 20400
Chapter 7-75Chemistry 481, Spring 2017, LA Tech
Crystal Field Stabilization Energy
• Crystal Field stabilization parameter Do
Chapter 7-76Chemistry 481, Spring 2017, LA Tech
Crystal Field Stabilization Energy
d7 case.
Weak field case
The configurations would be written t2g5 eg
2
5(-2/5Do) + 2(+3/5Do) = -4/5Do
Strong field case
The configurations would be written t2g6 eg
1
6(-2/5Do) + 1(+3/5Do) = -9/5Do
Chapter 7-77Chemistry 481, Spring 2017, LA Tech
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 17600cm-
1. (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.
Chapter 7-78Chemistry 481, Spring 2017, LA Tech
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 mol-
1)
Pairing energy (3 pairs) = 3 x 17600 = 52800 (151.0 kJ
mol-1)
Total = +27840 cm-1 (79.60 kJ mole-1)
14
Chapter 7-79Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-80Chemistry 481, Spring 2017, LA Tech
Tetrahedral Ligand Arrangement
Dt = 4/9Do
Mostly forms high spin complxes
Chapter 7-81Chemistry 481, Spring 2017, LA Tech
Octahedral Crystal Field Splitting
Chapter 7-82Chemistry 481, Spring 2017, LA Tech
Square-planar Complexes-D4h
Chapter 7-83Chemistry 481, Spring 2017, LA Tech
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.
Chapter 7-84Chemistry 481, Spring 2017, LA Tech
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
15
Chapter 7-85Chemistry 481, Spring 2017, LA Tech
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+
Chapter 7-86Chemistry 481, Spring 2017, LA Tech
Spectrum of [Ti(H2O)6]3+.
d1
: t2g1
eg0–> t2g
0eg
1
Chapter 7-87Chemistry 481, Spring 2017, LA Tech
Hydration Enthalpy.
• M2+(g) + 6 H2O(l) = [M(O2H)6]2+(aq)
Chapter 7-88Chemistry 481, Spring 2017, LA Tech
Irving-Williams Series
Chapter 7-89Chemistry 481, Spring 2017, LA Tech
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)
Chapter 7-90Chemistry 481, Spring 2017, LA Tech
MO forML6 diagram Molecules
D0
16
Chapter 7-91Chemistry 481, Spring 2017, LA Tech
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)
Chapter 7-92Chemistry 481, Spring 2017, LA Tech
Weak Field vs. Strong Fieldnow 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
Chapter 7-93Chemistry 481, Spring 2017, LA Tech
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
electronsChapter 7-94Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-95Chemistry 481, Spring 2017, LA Tech
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.
Chapter 7-96Chemistry 481, Spring 2017, LA Tech
Tetrahedral Crystal Field Splitting
17
Chapter 7-97Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-98Chemistry 481, Spring 2017, LA Tech
Electron configurations in octahedral fields
Weak field and strong fieled cases
Chapter 7-99Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-100Chemistry 481, Spring 2017, LA Tech
Tetragonal Complexes
Chapter 7-101Chemistry 481, Spring 2017, LA Tech
Square Planar Complexes• extreme form of tetragonal distortion
• Ligand repulsion is completely removed from
• z axis
Common for
4d8
and
5d8
complexes:
Rh(I), Ir(I)
Pt(II), Pd(II)
Chapter 7-102Chemistry 481, Spring 2017, LA Tech
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.
18
Chapter 7-103Chemistry 481, Spring 2017, LA Tech
Jahn Teller Distortions
Orbital degeneracy: for octahedral geometry
these are:
– t2g3eg
1 eg. Cr(II), Mn(III) High spin complexes
– t2g6eg
1 eg. Co(II), Ni(II)
– t2g6eg
3 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
Chapter 7-104Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-105Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-106Chemistry 481, Spring 2017, LA Tech
Sigma Bonding: Ligand Group
Orbitals
Chapter 7-107Chemistry 481, Spring 2017, LA Tech
Combinationsof Metal andLigand SALC’s
Chapter 7-108Chemistry 481, Spring 2017, LA Tech
Molecular Orbital Energy Level Diagram: Oh
19
Chapter 7-109Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-110Chemistry 481, Spring 2017, LA Tech
: 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
Chapter 7-111Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-112Chemistry 481, Spring 2017, LA Tech
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
Chapter 7-113Chemistry 481, Spring 2017, LA Tech
Magnetic Suceptibility Vs Temperature
Chapter 7-114Chemistry 481, Spring 2017, LA Tech
Types of magnetism
20
Chapter 7-115Chemistry 481, Spring 2017, LA Tech
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,
Chapter 7-116Chemistry 481, Spring 2017, LA Tech
Number of Unparied ElectronsThe 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.
Chapter 7-117Chemistry 481, Spring 2017, LA Tech
Magnetic Properties of Atoms
• Paramagnetism?
• Ferromagnetism?
• Diamagnetism?
• Gouvy Balance
Chapter 7-118Chemistry 481, Spring 2017, LA Tech
Octahedral Complexes
Chapter 7-119Chemistry 481, Spring 2017, LA Tech
Tetrahedral Complexes