Crystal field theory(CFT) ~ NEET chemistry

Given by Bathe and Blank/Vlank

According to CFT, there is a electrostatic force of attraction in between central atom and donar atom of the ligand. ( ionic bond form)
According to CFT, there is no intermixing of orbitals of central atom and donar atom of the ligand. ( no covalent bond form)
CFT deals with only d-orbitals of central atom.
d-orbitals have 5 degenerate orbitals in form of:--

T2g set
Eg set

(1) T2g set :-- Triply degenerate :---dxy, dyz,

dzx

T2g set orbitals lobes lying in between the axis

(2) Eg set :---Doubly degenerate orbitals:--

dx²-y²,dz²

Eg set orbitals lobes lying along the axis.

CFT of d- orbitals participate in tetrahedral, octahedral,tetragonal and square planar complex.

Energy order of square planar :--

dxz=dyz<dz²<dxy<dx²-y²<

Energy order of tetragonal :---

dxz=dyz<dxy<dz²<dx²-y²

Energy order of different complex:---

delta sp>delta tetragonal >delta octahedral>delta tetrahedral

# Filling of electron in octahedral complex :--

Pairing energy >energy of octahedral

When complex is in high spin

d1 --- t2g1 eg0

d² -----t2g² eg0

d³ ------t2g³ eg0

d4 ------t2g³ eg1

d5 -------t2g³ eg²

d6 --------t2g4 eg²

d7 --------t2g5 eg²

d8 --------t2g6 eg²

d9 --------t2g6 eg³

d10 ------t2g6 eg4

Pairing energy <energy of octahedral

When pairing energy is less than energy of octahedral complex then complex is in low spin

d1 ------t2g1 eg0

d2 ------t2g2 eg0

d3 ------t2g3 eg0

d4 ------t2g4 eg0

d5 -------t2g5 eg0

d6 -------t2g6 eg0

d7 -------t2g6 eg1

d8 -------t2g6 eg2

d9 --------t2g6 eg3

d10 -------t2g6 eg4

# Filling of electron in tetrahedral complex:---

For tetrahedral pairing energy is always greater than energy of tetrahedral and complex is in high spin.

d1 -----e1 t2^ 0

d2 ----- e2 t2^0

d3 ------e2 t2^1

d4 -------e2 t2^2

d5 -------e2 t2^3

d6 -------e3 t2^3

d7 -------e4 t2^3

d8 -------e4 t2^4

d9 -------e4 t2^5

d10 ------e4 t2^6

Note :--- Td Complex always form high spin complex because of pairing energy is greater than energy of tetrahedral
Oh complex may be high spin or low spin
To complex & high spin oh complex follows hunds rule buy low spin oh complex violate hund's rule.
d8 oh complex always form high spin complex whether the ligand is strong field or weak field.

# Factors affecting CFT

(1) Nature of central metal:---

Principle quantum no (n) increases

Splitting increases

3d<4d<5d

(2) Oxidation state of central atom:--

As the oxidation state of central atom increases

Splitting increases

M+²<M+³

(3) No of d -electrons :---

No of d- electrons increases

Splitting increases

(4) Nature of ligand :--From spectrochemical series strong field ligand increase splitting.

In the end of spectrochemical series, have strong ligand.

I-<Br-<S2-<SCN-<Cl-<N3-<(ET) 2O<PS2-<F-<urea<OH-<EtOH<Ox2-<O2-<H2O<NSC-<EDTA<Py= NH3<en<bipy=O-phen<NO2-<CH3-<C6H5-<CN-<CO<NO+

(5) Geometry of complex :--

Deltasp>delta tetragonal>delta oh>delta td

Delta td=4/9 delta oh

Delta to =0.44 delta oh

Delta so = 1.3 delta oh

(6) Crystal field stabilisation energy(CFSE):--

The value of CFSE is either negative or zero but never positive.
CFSE is associated with the thermodynamics stability of the complex.
CFSE increases ,thermodynamic stability increases ,reactivity decreases

Calculation of CFSE in oh complex:---

CFSE = (-0.4*n t2g +0.6*n eg) delta+mP

n = no of electron in t2g and eg orbitals

m = no of psired electron

P = pairing energy

Calculation of CFSE in td complex:---

CFSE = (-0.6*n e+0.4*n t2) delta td+mP

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