General Chemistry CHM113M
Dr. Ritika Gautam Singh (Inorganic) - E-mail: rgautam@iitk.ac.in
CHM113M GENERAL CHEMISTRY: INORGANIC & ORGANIC CHEMISTRY
Units: 3 – 1 – 0 – 0 = 4 (Modular Course, second half)
Inorganic: Structure of Coordination Complexes, Crystal Field Theory, Organometallic Chemistry, Oxidative Addition,
Reductive Elimination, Insertion Reactions, Monsanto Acetic Acid Process, Hydrogenation, Hydroformylation, Ziegler-Natta
Polymerization, and Metalloenzymes.
Lectures Hall: L-19
The Inorganic Section will commence on 3rd March 2025 followed by Organic Section in April
Grading policy: Relative grading
Attendance policy: A minimum of 75% attendance (including tutorial classes) is required.
Notes:
1. Students must attend all lectures and tutorials.
2. Lecture notes, assignments/solutions will be provided through HelloIITK portal.
3. Final Examination is compulsory to complete the course requirement and 75% attendance is required.
4. A make-up final examination may be arranged exclusively for students who have obtained approval for their leave from
SUGC. There won't be any opportunities for make-up quizzes.
Reference book
Inorganic
1.
Shriver and Atkins' Inorganic Chemistry (5th Edition).
2. James E. Huheey, Ellen A. Keiter, Richard L. Keiter and Okhil K. Medhi, Inorganic Chemistry: Principles of
Structure and Reactivity (4th Edition).
Inorganic: Lectures and tutorial details
The class will Commence on 3rd March 2025 (With Inorganic Chemistry lectures).
The quiz is scheduled on: 8th April 2025 (Tuesday) 7:10 to 7:40 PM
Inorganic: Lectures and tutorial details
Lectures: L19, Lecture Hall Complex
Sections
Sections C
Section-wise Lecture schedules
March: 3rd, 5th, 17th, 19th, 24th, 26th
Monday & Wednesday: 5:00 - 5:50
Sections D
March: 4th, 6th, 18th, 20th, 25th, 27th
Tuesday & Thursday: 3:00 - 3:50
Inorganic Tutorials:
Sections C/D: 3:00-3:50. Tutorials will take place in L8, L 10, L 11, L 12, L 14 and L 15
Inorganic: Lectures and tutorial details
Inorganic Tutorials:
Sections C/D: 3:00-3:50. Tutorials will take place in L8, L 10, L 11, L 12, L 14 and L 15
Section
Room
Inorganic Faculty Tutors
C1
L 10
Prof. Basker Sundararaju, E-mail: basker@iitk.ac.in
C2
L 11
Prof. Sabuj K. Kundu, E-mail: sabuj@iitk.ac.in
C3
L 12
Prof. Anantharaj Sengeni, E-mail: ananths@iitk.ac.in
D1
L 13
Dr. Raja Angamuthu, E-mail: raja@iitk.ac.in
D2
L 14
Dr. G. Ananthraman , E-mail: garaman@iitk.ac.in
D3
L 15
Dr. Ritika Gautam Singh, E-mail: rgautam@iitk.ac.in
Bonding theory in Coordination Compounds
❑ Valence Bond Theory (VBT)
❑ Proposed by Linus Pauling (Nobel Prize 1954) for the nature of chemical bonds and elucidation of the structure
of complex systems.
❑ The model utilizes hybridization of metal valence orbitals to account for the observed structures.
❑ (n-1)d, ns and np undergo hybridization to give hybridized orbitals.
❑ An empty hybrid orbital on the metal center can accept a pair of electrons from a ligand to form a σ-bond.
Linus Pauling
Nobel Prize in 1954
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Valence Bond Theory: Limitations
❑ Limitations of Valence Bond Theory
❑ Electronic and spectroscopic properties (color) of coordination complexes can’t be explained.
❑ Dipole moment can’t be predicted exactly, as the shape of the compound can’t be predicted exactly.
❑ It can’t exactly predict the geometry of the complex having coordination number four (CN =4) (if SP
or Td?)
❑ Weak and strong ligands or high-spin and low-spin complexes can’t be distinguished.
❑ The thermodynamic and kinetic stabilities of complexes are not quantitatively interpreted.
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Crystal Field Theory (CFT)
❑ Assumptions/Features of CFT
❑ The interaction between the metal ion and the ligand is assumed to be purely electrostatic (ionic) in nature.
❑ The theory was initially used to explain the crystalline materials and hence named “crystal field theory”.
❑ The ligands are treated as point charges (ions/dipoles).
❑ Examines the energetics (splitting) of d-orbitals in certain geometries.
❑ Nature of Interaction between Metal and Ligand
❑ The approaching ligands which are negatively charged (as they are electron-rich) are
repelled by the electrons present in a d-orbitals of metal.
❑ Therefore, the energy of d orbitals on a metal in a complex would not remain
degenerate (as compared to free metal ion).
John Van Vleck
Nobel Prize in Physics, 1977
❑ Those that point toward ligands would be higher in energy than those that do not.
❑ In ideal CFT, no covalent interaction between the metal and ligands is considered.
To overcome the limitations of VB theory, the crystal field theory was proposed
by Hans Bethe (1929) and van Vleck (1935)
Hans Bethe
Nobel Prize in Physics, 1967
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Shape (Spatial arrangements) of the d-Orbitals
These three atomic orbitals
point in between the axes
These two atomic orbitals point along
the axes, so large repulsion occurs when
ligands point directly at them
The phase of the wave function for the different d-orbitals
dz2 orbital is the linear combination of dz2-x2, and dz2-y2 , thus it is actually d2z2-x2-y2
It creates a torus of electron density in the xy-plane.
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Splitting of d-orbitals in an Oh field
❖ In free metal, five d-orbitals remain degenerate but when ligands approach the metal ion, some of the d-orbitals
experience more repulsion than others based on the geometric structure of the compounds.
❖ Since ligands approach from different directions, not all d-orbitals interact directly. These interactions cause the
splitting of d-orbital energy, called crystal field splitting.
The -ve
sign
indicates
ligand
Spherical
crystal field
Free metal ion
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0
Ligands-metal d orbitals interactions an octahedral field
Six ligands approach differently in the
octahedral complex. Two on the xaxis, two on the y-axis, and two on
the z-axis.
The orbitals that are oriented along the axis will be repelled more by the ligands and hence will be higher in energy
than that of the orbitals that are oriented in between the axis
MIT opencourse
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1
Crystal field splitting in an octahedral field
The energy separation between the two levels is denoted
by Δo or 10 Dq.
The higher energy set of orbitals (dz2 and dx2-y2) are labeled
as eg and the lower energy set is labeled as t2g.
dx2-y2 , dz2
10Dq
To maintain the average energy, the eg orbitals need to be
destabilized by +0.6 Δo (6 Dq) and the t2g orbitals to be
stabilized to the extent of -0.4 Δo (4 Dq)
‘t’ denotes a triply degenerate orbital,
‘e’ denotes a doubly degenerate orbital.
dxy, dxz, dyz
The symbols ‘g’ and ‘u’ refer to the behavior of an orbital under operation of inversion
g = gerade (symmetric); u = ungerade (anti-symmetric)
p-orbitals: signs of the lobe changes on inversion in Oh field; hence they are ungerade.
There is a center of inversion in the d-orbital and hence it is gerade.
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2
Crystal field splitting in tetrahedral field
t2 orbitals
Spherical
field
Important note: Due to less splitting of the e, and t2
levels, tetrahedral complexes are generally high-spin
http://faculty.uml.edu/ndeluca/84.334/topics/topic6.htm
e orbitals
• No orbitals directly pointing towards the
ligands.
• The “e” orbitals point between the two
t2
ligands present at the opposite corners of
the cube and hence it is less affected than
” orbitals.
the
“t
2
e
• The “t2”orbitals lie half an edge of the cube
from the ligand and point more directly
towards
ligands
and
hence
more
destabilized than “e” orbitals.
1
3
Comparison of Octahedral and Tetrahedral Field
• The splitting of the energies of d orbitals in a
tetrahedral complex (Δt) is much smaller
than that for an octahedral complex (Δo),
however, for two reasons:
OCTAHEDRON
• The d orbitals interact less strongly with the
ligands in a tetrahedral arrangement.
• There are only four negatively-charged
regions rather than six, which decreases the
electrostatic interactions by one-third if all
other factors are equal.
TETRAHEDRON
OCTAHEDRON
5
• The crystal field splitting in the tetrahedral
field is intrinsically smaller than in the
octahedral field. For most purposes, the
relationship may be represented as
Δt = 4/9 Δo
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Determination
ofof
△Δ
Determination
Crystal field splitting parameter (Δ) is measured by electronic absorption spectroscopy
Determination of Δ
Ground State
Excited State
[Ti(H2O)6]3+
[TiIII(H2O)6]3+
[Ti(H2O)6]3+
Determination of Δ
Δ is Relatable to Colour
q Complementary colour wheel.
Absorb Orange See Blue
The maximum absorption peak of [TiIII(H2O)6]3+ appears at 493 nm
(Δo = 20,300 cm-1 = 243 kJ/mol). The value can be calculated using
ΔE = hν = hc/λ equation.
Absorb Red See Green
This is the simplest possible example where the observed spectral
transition reflects the actual energy difference between t2g and eg
levels.
3+
1
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Factors affecting the magnitude of ∆
1. Oxidation state of metal ions: Higher ionic charge on the metal ion, pulls the ligands closer towards it, and higher
electrostatic repulsion results in larger splitting of d-orbitals
Δ =10,200 cm-1 for [CoII(NH3)6]2+ and 22,870 cm-1 for [CoIII(NH3) 6]3+ [FeII(CN)6]4- Δ = 32,200 cm-1 [FeIII(CN)6]3- Δ = 35,000 cm-1
2. Nature of metal ion: On going down the group 3d to 4d to 5d, the larger size of 4d and 5d orbitals results in
stronger interactions with the ligands, thus the splitting of the d-orbitals will be more
e.g., hexaammine complexes [MIII(NH3)6]3+: Δo = 22,870 cm-1 (Co) < 34,100 cm-1 (Rh) < 41,200 cm-1 (Ir)
3. Nature of ligands: Some ligands cause more splitting of d-orbitals called strong field ligands and some ligands
cause lesser splitting called weak field ligands, the series is called “spectrochemical series” The spectrochemical
series ranks ligands according to the ability to cause crystal field splitting.
I− < Br− < S2− < SCN− (S–bonded) < Cl− < NO3– < N3− < F− < OH− < C2O42− < H2O < NCS− (N–bonded) < CH3CN < py
(pyridine) < NH3 < en (ethylenediamine) < bipy (2,2'-bipyridine) < phen (1,10-phenanthroline) < NO2− (N–bonded) <
PPh3 (Triphenylphosphine) < CN− < CO (The stronger the ligand, the higher the Δ value)
4. Geometry of the metal-complex: Tetrahedral complexes have generally lesser splitting than octahedral
complexes
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Factors Influencing the Δ
17
Factors that influence the △
Nature of ligands: weak-field vs. strong-field ligand
Effect of Ligands onEffect
the Magnitude
of the
Δ Magnitude of Δ
of Ligands on
fect of Ligands on the Magnitude of Δ
q Example nickel complexes
ckel complexes
q Example nickel complexes
[NiII(H2O)6]2+
romium complexes
[NiII(NH3)6]2+
[NiII(en)2]2+
[FeIII(H2O)6]3+
[FeIII(CN)6]3+
q Example chromium complexes
q Example chromium complexes
The stronger the ligand, the higher the Δ value
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Analysis of Spectrochemical Series through CFT
All aspects of spectrochemical series can’t be explained by the Crystal Field Theory.
How do you rationalize the strength of anionic ligands weaker than the neutral ligands?
Anionic ligands are expected to interact electrostatically more strongly than neutral ligands.
However, many anionic ligands (Br–, Cl–, F– etc.) are relatively weak than neutral CO, Phen etc.
e.g., H2O vs OH- ; The former is a stronger ligand than the latter.
Orbital interactions need to be considered to rationalize the order of ligands. Thus, covalency is
incorporated into CFT resulting in the Ligand Field Theory.
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Analysis of Spectrochemical Series through CFT
I− < Br− < Cl− < F− (Ligand field strength).
Among the halides, the F− is the smallest and its charge density is the highest
Explanation of Spectrochemical Series using CFT
It can approach much closer to the metal ion, thereby increasing the electronic
- (Ligand Field strength) : Fluoride ion can
I
Br
Cl
F
repulsion which creates higher Δ
approach much closer to the metal ion thereby increase the
electronic repulsion which leads to higher Δ.
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Analysis of Spectrochemical
Series
through
CFT
q Ligands which have filled p orbitals may act as donors by intera
Observation: F- OH- O2- H2O (Ligand Field strength)
• To understand the difference in the ligand strength, let’s look at the bonding modes between the
suitable metal orbitals.
ligand and the metal.
Interaction between dxy of metal and py of halide:
• All ligands are
“σ donors”. Other than the σ donation, some ligands
(NOT
all)charge
can have
additional
Reduces
positive
on metal
ectrochemical
Series
Reduces Δ
orbitals that can interact with the d orbitals of metal.
Field strength)
Analysis of the Spectrochemical Series
Ligand
Field
Theory
k •at the
bonding modes
between
the
er simplified
diagrams for clarity.
phenomenon.
(LFT) and Molecular- Orbital
Theory (MOT) can properly explain this
2Observation: F
OH O
H2O (Ligand Field strength)
q Ligands which have filled p orbitals may act as
donors by interacting with
s having a hybrid orbital or a p orbital
suitable metal
• F–, OH–, O2– can donate a pair of electrons
fromorbitals.
their filled p-orbitals to symmetrically suitable dσ bonds.
Interaction between dxy of metal and py of halide:
orbitals
the metal.
m the ligand
to the of
metal.
Reduces positive
charge
on2–
metal
–< OH
–< O
H2O
F
xy
Reduces Δ
Interaction between d of metal
and py of halide
Reduces
positive charge
metal
q on
Water
acts only as a sigma-donor ligand.
Reduces Δ
π-bond
q Water acts only as a sigma-donor ligand.
σ-bond
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M etAnalysis
al Carbonyl
Underst ood wSeries
it h M OT
of Spectrochemical
through CFT
St ructstrong
ure Field
andLigands?
Bonding
Why are PPh3, CN– and CO considered
CN– and CO
PPh3
• Donates its sigma (nonbonding) electrons to the
metal (σ bond), while accepting electron density
from the metal through overlap of a metal t2g orbital
and a ligand π* orbital, while latter is called backbonding.
• Such type of ligand that donates σ-electron density Although, all the ligands are σ donors;
to the metal and accepts π-electron density to the in general: π donor < weak π donor < σ only < π
ligand from the metal is called σ-donor and a π- acceptor
acceptor.
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Pairing Energy
2 22 ,2 d 2
dd
x x-y
-y , z
dz2
dxy, dxz, dyz
d4 system
Low Spin
High Spin
PT = Pc + Pe interactions
PT = 357.4 (Fe3+), 285 (Mn2+) kJ/mol
• Pairing energy (P) is needed to force an electron to fill
an orbital that is already occupied with an electron. The
electrons can also fill higher energy orbitals and avoid
the pairing energy. The electron-pairing energy is
composed of two factors.
1. Electrostatic Repulsion: Coulombic repulsion energy
(Pc) is caused by having two electrons in the same
orbital. The destabilizing energy contribution of Pc for
each doubly occupied orbital. As we go down from 3d to
4d to 5d, the Coulombic repulsion decreases. 5d orbitals
are mode diffuse, thus can readily accommodate two
negative charges in the same orbital.
2. Loss of exchange energy: parallel spins ( ) are forced to
become antiparallel ( ): exchange energy is the driving
force of Hund’s rule of maximum spin multiplicity. With
the pairing of electrons, the number of electrons with a
particular spin is decreased. This will lead to the loss of
exchange energy. The exchange energy would be more
for an unpaired d5 electronic system.
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High Spin vs Low Spin Complexes
A complex can be of either high spin or low spin is determined by the crystal field splitting
parameter (Δ) and Pairing Energy (P)
For low spin (P<Δ): If the energy cost of placing
an electron into an already singly occupied
orbital must be less than the cost of placing
the additional electron into an eg orbital at an
energy cost of Δ.
P < Δo
P > Δo
For high spin (P > Δ): If the energy required to
pair two electrons is greater than the energy
cost of placing an electron in an eg, Δ, high
spin splitting occurs.
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Spin-Cross Over complexes
What happens when Δo is close to P (pairing energy)?
When Δo ~ P , interconversion between high-spin and low-spin states is a possibility.
Temperature, pressure or light can assist such interconversion
(SCO)
Spin-Cross Over
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Key observations: A trick to remember important aspects
• A complex will show low-spin if Δo>P, and high-spin if Δo<P, Δo ~ P spin-cross over
• 4d & 5d metals generally have a larger value of ∆o than for 3d metals. As a result, those
complexes are typically low-spin.
• 3d complexes are high-spin with weak field ligands and low-spin with strong field ligands.
• High valent 3d complexes (e.g., Co3+ complexes) tend to be low-spin, except [CoF6]3which shows high-spin.
• For 3d metals, tetrahedral splitting is rarely large enough to result in the pairing of the
electrons. As a result, low-spin tetrahedral complexes are not common.
• High and low spin states occur only for 3d metal complexes with between 4 and 7 d
electrons.
• Complexes with 1 to 3 d electrons can accommodate all electrons in individual orbitals in
the t2g set, thus High-spin.
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Question Time !!
Why is the splitting in a tetrahedral field less as compared to an
octahedral field?
1. The number of ligands in the tetrahedral field is less as compared to in the
Oh field
2. Poor orbital overlap between the metal/metal ions and the ligand as none
of the d-orbitals is directly pointed towards the ligands.
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CrystalCrystal
Field Field
Stabilization
Energy
Stabilization
Energy(CFSE)
(CFSE)
CFSE is the additional stability that results from placing a transition metal ion in the crystal
CFSE is the additional stability which results from placing a transition metal
field generated by a set of ligands through the splitting of the d-orbitals.
ion in the crystal field generated by a set of ligands through the splitting of
the d-orbitals.
CFSE = ΔE = Eligand field − Eisotropic field
CFSE = ΔE = Eligand field − Eisotropic field
In this calculation, additional pairing compared to the pre-splitting condition should be
In this calculation, additional pairing compare to the pre-splitting condition
included.
should be included.
CSFE
dependfactors
on multiple
factors including:
• CSFE will depend
onwill
multiple
including:
✓ Geometry
around the metal
Geometry
✓ NumberNumber
of d-electrons
of d-electrons
✓ Spin Pairing
Energy Energy
Spin Pairing
✓ Ligand character
(strong vs. weak field)
Ligand character
For an octahedral complex, an electron in t2g subset will contribute −2/5 Δo whereas an
For an octahedral complex, an electron in t subset will
electron in the higher energy eg subset contributes to a destabilization2gof +3/5 Δo.
contributes −2/5 Δo whereas an electron in the higher energy eg
subset contributes to a destabilization of +3/5 Δo .
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Examples for d7 HS and LS Systems
High-spin d7 octahedral complex
Eisotropic field = 2P
Eligand field = (5 × −2/5Δo) + (2 × 3/5Δo) + 2P
= −4/5 Δo + 2P
Isotropic Field
Ligand Field
CFSE = (−4/5 Δo + 2P) − 2P = −4/5 Δo
Low-spin d7 octahedral complex
Eisotropic field = 2P
Eligand field = (6 × −2/5Δo) + (1 × 3/5Δo) + 3P
= −9/5Δo + 3P
CFSE = (−9/5 Δo + 3P) − 2P = −9/5 Δo + P
Isotropic Field
Ligand Field
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CFSE for Oh Complexes
High Spin
Low Spin
d1
t2g1eg0
-2/5 Δo
t2g1eg0
-2/5 Δo
d2
t2g2eg0
-4/5 Δo
t2g2eg0
-4/5 Δo
d3
t2g3eg0
-6/5 Δo
t2g3eg0
-6/5 Δo
d4
t2g3eg1
-3/5 Δo
t2g4eg0
-8/5 Δo + P
d5
t2g3eg2
0 Δo
t2g5eg0
-10/5 Δo + 2P
d6
t2g4eg2
-2/5 Δo
t2g6eg0
-12/5 Δo + 2P
d7
t2g5eg2
-4/5 Δo
t2g6eg1
-9/5 Δo + P
d8
t2g6eg2
-6/5 Δo
t2g6eg2
-6/5 Δo
d9
t2g6eg3
-3/5 Δo
t2g6eg3
-3/5 Δo
d10
t2g6eg4
0 Δo
t2g6eg4
0 Δo
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CFSE for Td Complexes
Tetrahedral
splitting is seldom
large enough to
result in the pairing
of the electrons. As
a result, High-spin
tetrahedral
complexes are
common.
Configuration
CFSE
d1
e1t20
-0.6 Δt
d2
e2t20
-1.2 Δt
d3
e2t21
-0.8 Δt
d4
e2t22
-0.4 Δt
d5
e2t23
0 Δt
d6
e3t23
-0.6 Δt
d7
e4t23
-1.2 Δt
d8
e4t24
-0.8 Δt
d9
e4t25
-0.4 Δt
d10
e4t26
0 Δt
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Octahedral vs Tetrahedral Complexes
Assuming high-spin configurations. The units are Δo, and Δt = 4/9 Δo. Ignore their signs since
we're looking for the difference between them.
Octahedral
Tetrahedral
Difference
d0, d5, d10
0
0
0
d1, d6
0.4
0.27
0.13
d2, d7
0.8
0.53
0.27
d3, d8
1.2
0.36
0.84
d4, d9
0.6
0.18
0.42
The ordering of favorability of octahedral over tetrahedral is:
d3, d8 > d4, d9> d2, d7 > d1, d6 > d0, d5, d10
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the degree of favorability varies with the electronic configuration.
Octahedral
vs.onlyTetrahedral
For d there's
a small gap betweenComplexes
the oct and tet lines, whereas at
1
3 and d8 there's a big gap.
d
In most cases, CFSE favors octahedral over tetrahedral geometry, but the degree of favorability
varies with the electronic configuration.
0
5
However, for d , d high spin and d10, there is no CFSE difference between
octahedral and tetrahedral.
For d1 and d6 there's only a small gap between the Oh and
3,d8 there's a big gap.
Th lines, whereas at
If dlarge
or highly charged ligands are
present, to avoid ligand-ligand repulsion
they may prefer a lower coordination
However, for d0, d5 high-spin
and
d10, there
number (4
instead
of 6) is no CFSE
difference between octahedral and tetrahedral.
If large or highly charged ligands are present, to avoid ligand-ligand repulsion they may prefer a
lower coordination number 4 (thus Td is favorable) instead of 6 (octahedral).
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Splitting of d-orbitals in square planar geometry
Let’s assume that we remove the two
axial ligands along the ± Z axes from the
octahedral complex. Due to the removal
of ligands, the repulsion will decrease,
hence d-orbitals with z-component will
fall in energy
The dz2 orbital points directly at the two
ligands being removed, its energy will
decrease much more rapidly than the
degenerate energies of the dxz and dyz
Tetragonal distortion
Square planar
The energy of dx2−y2 and the dxy orbitals
will increase. As dx2−y2 orbital points
directly towards the ligands, its energy
increases to a greater extent than the
energy of the dxy orbital.
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CFSE of Square Planar Complexes
Square planar coordination is common with:
4d8, 5d8 complexes with any ligands (PtII(NH3)2Cl2), [PdII(H2O)4]2+, [PdCl4]- and
[AuIIICl4]- )
3d8 complexes with strong field ligands (e.g., [NiII(CN)4]2-)
CFSE for d8 configurations
CFSEtd = - 0.36 ∆o
Tetrahedral
Octahedral
Square Planar
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