Teoria do Campo Ligante - Part II

8/18/2019 Teoria do Campo Ligante - Part II

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Electronic spectra of transition metal complexes


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Characteristics of electronic spectra

a) Wavelength Energy of electronic transition

b) Shape. Gaussian Band Shape - coupling of electronic and

vibrational states

c) Intensity. Molar absorptivity, ε (M − 1cm− 1 ) due to probability

of electronic transitions

d) Number of bands !ransitions bet"een States of given d n configuration


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Electronic transitions are controlled by quantum mechanical selection rules hich determine the probability !intensity) of the transition.

"ransition

#max !$−%cm−%)

Spin and Symmetry forbidden &d-d & bands '.'( %

Spin allo"ed and Symmetry forbidden &d-d & bands !*h) % %'

!"d) %' + %',

Spin and Symmetry allo"ed -$C" and $-C" bands %', x %'/

0and intensity in electronic spectra !ε)


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Spin Selection #ule$ !here must be no change in the spin multiplicity ( (S % % )

during the transition

ie the spin of the electron must not change during the transition.

Symmetry (&aporte) Selection #ule$ !here must be a change in parity (g ' u)

during the transition

Since s and d orbitals are g !gerade) and p orbitals are u!ungerade)1 only

s ' p and p ' d transitions are alloed and d 2 d transition are formally

forbidden. 3ie only transitions for hich 4l 5 6 % are alloed7.

d 2 d bands are alloed to the extent that the starting or terminal level ofthe transition is not a pure d orbital. !ie it is a molecular orbital of the

complex ith both metal and ligand character).


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States for d n configurations

8usselSaunders Coupling

• 9ngular momentum of individual electrons couple to give total angular

momentum for d n configuration $- 5 ∑ml

• Spin momentum of individual electron spins couple together to give total

spin1 S 5 ∑s

• Interelectronic repulsions beteen the electrons in the d orbitals give rise to

ground state and excited states for d n configurations.

• States are labeled ith "ern Symbols

• Electonic transitions beteen ground and excited states are summari:ed in*rgel and "anabeSugano diagrams .

• Term Symbols !labels for states) contain information about - and S for state

;undor states of same spin1 ground state has maximum -.


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Triple degeneracy of a d 2 ion’s 3T2gground state due to three possible sites

for hole in t 2g level

Singly degenerate 3T2g ground state.

Only one possible arrangement for

three electrons in t 2g level

Singly degenerate 3T2g ground state.Only one possible arrangement for

six t 2g electrons.

Triple degenerate ground state for d

Three possible sites for hole in t 2g level

eg

t (g

=round State Excited States

eg

t (g

eg

t (g

eg

t (g

d 2

d 3

d 7

d 8

!umber of d"d bands in electronic spectrum

#xcitation from ground state to excited stated of dn configuration


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$abeling of d"d bands in electronic spectrum.

• %onsider states of dn configuration

• &etermine free ion ground state Term Symbol 'labels for

states(

• )ssign splitting of states in ligand field

• Spectroscopic labeling of bands.

• Orgel diagrams 'high"spin(

• Tanabe"Sugano diagrams 'high"spin and lo*"spin(


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Individual electron l = 2, ml = 2, 1, 0,

-1, -2

Maximum ml = l

l = 0, 1, 2, 3,Orbital: s, p, d , f

_______________________________

dn con!uration, " = 0, 1, 2, 3, # $erm %&mbol %, ', (, ), *

M"

= + ml

, maximum M"

= "

%pin Multiplicit& = 2 % 1


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+ree ion ground state Term Symbols for d n configurations

Term Symbols 'labels for states( contain information about $ and S for ground state

,und’s -ules. i( round state has maximum spin/ S

ii( +or states of same spin/ ground state has maximum $2 1 0 -1 -2ml =l =2,SL 2S + 1

2 012 2

3 0 3

3 312

2 2

4 12 5

L = ML(max) ML = ml S = s

Termsymbol

2&

3+

+

&

5S


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Splitting of the *ea6 field d n ground state terms in an

octahedral ligand field

round state determined by inspection of degeneracy of terms for given dn


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∆od % ∆od ( d , ∆od

/

(! (g

( E g

(? />

, (g

,! (g

,! %g

/ (g∆o

/! %g

/! (g

E g

! (g

?,>

/"%g!@)

,@ /@

,"%g!@)

(! (g( E g ,! %g

,! (g

,! %g

,! %g

, (g

,

"%g!@)

Orgel &iagrams

Ti37 827 %r 37 9n

37


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"he d-d bands of the d ion 3A!;(*)B7,


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'a( :!i',24(5;27 'b( :!i'!,3(5;

27


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3+

3<

0S

0&

d2

#'3+( = ) " >?

#'0&( = ) " 3? 7 2%

#'3


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The Tanabe"Sugano diagram for the d 2 ion


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#vidence for covalent bonding in metal"ligand interactions

The !ephelauxetic #ffect '@cloud expansionA(

-eduction in electron"electron repulsion upon complex formation

Racah Parameter, BB electron"elctronic repulsion parameter

Bo is the inter" electronic repulsion in the gaseous 9n7 ion.

B is the inter" electronic repulsion in the complexed 9$xn7 ion.

The smaller values for B in the complex compared to free gaseous ion ista6en as evidence of smaller inter"electronic repulsion in the complex due toa larger @molecular orbitalA on account of overlap

of ligand and metal orbital/ i.e. evidence of covalency 'cloud expansionA(.

!ephelauxetic -atio/ C = B

Bo


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!ephelauxetic #ffect

!ephelauxetic $igand Series

D E ?r E %! E %l E !%S E %2O2" E en E !,3 E ,2O E + Small C $arge C

%ovalent Donic

!ephelauxetic 9etal Series


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#mpirical -acah parameters/ h/ 6

C = 0G :h'ligand( x 6'metal(;

%r'!,3(537 C = 0 Gh6 C = 0 G'0.('4.20(

= 4.45

%r'%!(53" C = 0 Gh6

C = 0 G'2.4('4.20(

= 4.>4

Bo " B = hligands x k metal ion

Bo


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"ypical 4o and D

max values for octahedral !$-

B) d bloc metal complexes

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

F Complex 4

o cm% G D

max !nm) Complex 4

o cm% D

max

!nm)

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

3"i!;(*)

B7, ('1,'' /H, 3>e!;

(*)

B7( H1/'' %'B/

3A!;(*)

B7, ('1,'' /H, 3>e!;

(*)

B7, %,1'' ,'

3A!;(*)

B7( %(1/'' J'B 3>e!CN)

B7, ,1''' (JB

3Cr>B7, %1''' BB 3>e!CN)B7/ ,,1J'' (HB

3Co!;(*)

B7,1 l.s. ('1'' /J, 3>e!C

(*

/)

,7, %/1%'' 'H

3Cr!;(*)

B7( %/1%'' 'H 3Co!CN)

B7, l.s. ,/1J'' (J

3Cr!;(*)

B7, %1/'' 3Co!N;

,)

B7, l.s. ((1H'' /,

3Cr!N;,)

B7, (%1B'' /B, 3Ni!;

(*)

B7( J1'' %%B

3Cr!en),7, (%1H'' / 3Ni!N;

,)

B7( %'1J'' H(B

3Cr!CN)B7, (B1B'' ,B 3Ni!en)

,7( %%1'' J'

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF


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0. )ssign the metal oxidation state in the follo*ing compounds.

a. H2:

Teoria do Campo Ligante - Part II

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