Teoria do Campo Ligante - Part II
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Transcript of 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: