It contains information about various theories of chemical bonding, mainly CFT. It discusses the splitting diagrams of octahedral, tetrahedral and square planar fields. Jahn-Teller distortion is also explained here in simple terms.

1. NON BONDING ELECTRONS
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2. Models describing Bonding
• VBT
 A covalent bond is formed when orbitals
of two atoms overlap.
• CFT
• Modified CFT, known as Ligand Field Theory
• MOT
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3. CFT- Assumptions
• Interactions between metal ions and ligands are
purely electrostatic or ionic.
• Ligands: point charges.
 Negatively charged: ion-ion interaction.
 Positively charged: ion-dipole interaction.
• Due to repulsion by ligand electrons, electrons on
metal occupy d-orbitals which are farthest from the
direction of ligand approach.
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4. Symmetric field
• d orbitals are degenerate for an isolated gaseous atom.
• If a spherically symmetric field of negative charges is
placed around the metal, these orbitals remain
degenerate, but are raised in energy due to repulsion
between the negative charges on the ligands and in d
orbitals.
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5. Octahedral field
• If discrete point charges (ligands)
interact with metal, degenercy
of d-orbitals is destroyed.
• Splitting of d-orbitals takes
place.
• All d-orbitals do not interact in a
similar way with the ligands.
• Orbitals lying along the axis
i.e., x2-y2, z2 will be destabilized
more in comparison to orbitals
lying in between the axis.
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6. CFT- Octahedral Complexes
• For Oh , difference between Eg and T2g is Δ₀ (10 Dq).
• The baricentre must be conserved on going from
spherical to octahedral field, so the extent of
destabilization of Eg should be equal to the extent
of stabilization of T2g .
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7.  For more than 1 electron in d-orbital, e‾ ─ e‾ interactions
must be taken into account
 For d1 –d3 systems : Hund’s rule predicts that electrons
will not pair and occupy T2g set.
 For d4-d7 systems :
• Put all electrons in T2g and pair them (Low spin or
Strong field, Δ₀ high)
• Put electrons in Eg set which lies higher in energy
i.e., firstly all the orbitals are singly occupied and then
pairing takes place (High spin or Weak Field, Δ₀ small).
 Two important parameters should be considered:
– Pairing energy (P)
– Eg - T2g Splitting ( Δ₀ , CFSE)
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8. Pairing Energy, P
The pairing energy, P, is made up of two parts.
1) Columbic repulsion energy caused by having two
electrons in same orbital. Destabilizing energy
contribution of Pc for each doubly occupied
orbital.
2) Exchange stabilizing energy for each pair of
electrons having the same spin and same energy.
Stabilizing contribution of Pe for each pair having
same spin and same energy
P = sum of all Pc and Pe interactions
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9. CFSE for an Octahedral Complex
CFSE= -0.4 x n(T2g) + 0.6 x n(Eg) Δ₀
If CFSE> P, Pairing occurs
If CFSE< P, no Pairing
d5 system
Δ₀
Δ₀
LS Complex
High Spin Complex
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10. Δ₀ Depends upon:
1. Nature of ligand
2. Charge on metal ion.
3. Principal Quantam No. of d-orbital (3d,4d,5d)
Δ₀(5d)> Δ₀(4d)> Δ₀(3d)
Spectrochemical series:
I− < Br− < S2− < SCN− < Cl− < N3−, F− < urea, OH− <
ox, O2− <H2O < NCS− < py, NH3 < en < bpy, phen <
NO2− < CH3−, C6H5−< CN− < CO.
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11. Applications of CFT
1. Ionic Radii:For a given oxidation state, ionic radii decreases
steadily on going from left to right in transition
series (dotted line).
Trivalent transition
metal ions show a
similar trend.
Eg, Ti-O bonds are
shorter than Ca-O bonds
due to larger interaction
between Ti+2 and
bonding electrons.
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12. Applications of CFT
2. Lattice energy:Crystal field splitting of d-orbitals results in CFSE and
increased lattice energies of ionic compounds.
Occurrence of CFSE leads to an increased lattice energy.
Lattice energy of fluorides of
first row transition elements.
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13. Jahn-Teller Distortion
• If both the eg orbitals are symmetrically filled - all ligands are
repelled equally. Result: regular octahedron
• If asymmetrically filled – some ligands are repelled more than the
other. Result: Distorted octahedron
• for the case of Cu, d9 configuration. Doubly occupied orbitals will
face stronger repulsions than singly occupied.
Consider eg configuration: (dz2 )1 , ( dx2 − y2 )2
Ligands along x, -x, y, -y will be repelled more and bonds will be
elongated i.e. the octahedron will be compressed along the z axis.
Consider eg configuration: : (dz2 )2 , ( dx2 − y2 )1
Ligands along z, -z will be repelled more and bonds elongated. i.e.
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the octahedron will be elongated along the z axis.

14. The
effect
distortions
of
is
JT
best
documented for Cu(II)
complexes (with 3eˉ
in eg)
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15. Square Planar Coordination
• For understanding square planar complexes, consider their d
energy level diagram in octahedral and distorted octahedral fields.
• d8 configuration, 2 electrons in the eg orbitals
• The effect of distorted octahedron:
– For small elongations along z axis P> energy between two eg
orbitals.
– For large elongations P< energy between two eg orbitals
• Distortion is now sufficiently large.
• It results in a 4-coordinate square planar shape, with the ligands
along the z axis no longer bonded to the metal.
• Square planar complexes are quite common for the d8 metals in
the 4th and 5th periods: Rh(I), IR(I), Pt(II), Pd(II) and Au(III).
• Square planar complexes are rare for the 3rd period metals. Ni(II)
generally forms tetrahedral complexes. With very strong ligands
such as CN- square planar geometry is seen with Ni(II).
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16. 16

17. Tetrahedral field
• Imagine a tetrahedral molecule inside a cube with
ligands occupying alternate corners and metal at the
centre of the cube.
• The two ‘e’ orbitals point towards the axis.
• The three ‘t2’ orbitals point in between the axis, i.e.,
nearer to the direction of approach of ligands and
hence these orbitals are of higher energy.
• Magnitude of splitting is less as none of the d-orbitals
point directly towards the approaching ligands.
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18. Tetrahedral Field
Δt < Δ₀
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19. Tetrahedral Field
• There are only 4 ligands in tetrahedral complex, so
ligand field is roughly 2/3 of octahedral field.
Δt = 4/9 Δ₀
• All tetrahedral complexes are high spin since CFSE is
normally smaller than pairing energy.
• If a very strong field ligand is present, square planar
geometry will be favoured.
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20. General Facts
• Most transition metals prefer octahedral coordination
or distorted octahedral coordination. Large CFSE.
• High spin d5 ions, d0 and d10 have no particular
preference for octahedral or tetrahedral as their CFSE is
zero.
• Ions such as Cr+3, Ni+2, Mn+3 show preference for
octahedral coordination.
• Coordination preferences of ions are shown by the type
of spinel structure they adopt.
– Normal
– Inverse
– Intermediate between normal and inverse
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21. Spinels – Use of CFSE
• Spinel is the name given to mineral MgAl2O4 .
• General formula AB2O4 .
Normal Spinel : Oxygens form ccp array.
 Mg(II) (A type) occupy tetrahedral sites.
 Al(III) (B-type) occupy octahedral sites.
[MII]tet[MIIIMIII]ohO4
Inverse spinel : Half of the trivalent ions swap with divalent ions.
 Mg(II) occupies octahedral sites.
[MIII]tet[MIIMIII]ohO4
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22. Spinels – Use of CFSE
• Several transition metal oxides with the formula
AB2O4 .
• CFSE is highly useful in determining whether a
structure would be normal or inverse.
• If M3+ ion has a higher CFSE in an octahedral field
compared to M2+ ion : Normal spinel.
• If M2+ ion has a higher CFSE in an octahedral field
compared to M3+ ion: Inverse spinel.
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23. Inert Pair Effect
• Heavy post transition elements exhibit this effect.
• Eg. Tl, Sn, Pb,Sb.
• Lower oxidation states are stable for elements as
we go down the group.
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24. THANK YOU
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