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1
Ligand Field Theory Crystal-field theory provides
a simple conceptual model and can be used to
interpret spectra and thermochemical data by
appealing to empirical values of ?o.On closer
inspection, however, the CFT is defective
because it treats ligands as point charges or
dipoles and does not take into account the
overlap of ligand and metal orbitals. Ligand-field
theory, which is an application of
molecular orbital theory that concentrates on the
d-orbitals of the central metal atom, provides a
more substantial framework understan- ding ?o.The
valence orbitals on the metal and ligand are used
to form symmetry-adaptod linear
combinations(SALCs),
2
Symmetry-adapted combinations of ligand ?
orbitals in an octahedral complex
3
Metal orbital Symmetry label
Degeneracy s
a1g
1 px,py,pz t1u
3 dxy,dyz,dzx
t2g
3 dx2-y2,dz2 eg
2
Ligand combinations a1g ?1 ?2 ?3 ?4 ?5
?6 t1u ?1- ?3, ?2- ?4, ?5- ?6 eg ?1- ?2 ?3-
?4, 2 ?62 ?5- ?1- ?2- ?3- ?4 These six
combinations accounts for all the ligand
orbitals of ? symmetryThere is no combination of
ligands ? orbi- tals that has the symmetry of the
metal t2g orbitals, so the latter do not
participate in ? bonding.
4
Molecular orbitals energy levels of a typical
octahedral complex
5
Six bonding molecular orbitals of the complex are
mainly ligand-orbital in character in the sense
that c2Lgtc2M.These six bonding orbitals can
accommodate the 12 electrons provi- ded by the
six ligand lone pairs. The numbers of electrons
to accommodate in addition to those supplied by
the ligands depends on the number of d
electrons, n, supplied by the metal atom or
ion.The frontier orbitals of the complex are the
nonbonding entirely metal t2g orbitals and the
antibonding eg orbitals. The octahedral
ligand-field splitting parameter, ?o, in this
approach is the HOMO-LUMO separation(High
Occupation Molecular Orbital- Low Unoccu- pation
Molecular Orbital). In LFT, The molecular
orbitals involved are largely, but
not completely, confined to the metal atom.CFT
exaggerates that confinement by supposing that
the d electrons are strictly confined to the
metal. The qualitative MOT permits us to identify
more deeply the origin and magnitude of the
splitting of the orbitals.
6
Example Using a photoelectron spectrum to obtain
information about a complex The photoelectron
spectrum of gas- phase Mo(CO)6 is shown .Use
the spectrum to infer the energies of the MO of
complex
Answer Twelve electrons are provided by the six
CO ligands they enter the bonding orbitals and
result in the configuration a21gt61ue4g.Ox. No of
Mo, 0, so Mo provides a further six
valence electrons.As CO is a strong-field ligand,
the ground-state electron configuration
a21gt61ue4gt62g. The HOMOs are the three t2g
orbitals that are largely confined to the Mo
atom,and their energy can be identified by
ascribing the peak of lowest ionization energy
(close to 8 eV) to them.The group of ionization
energies around 14 eV are probably due to the
Mo-CO ? bonding.14 eV is close to the
ionization energy of CO itself arising from
bonding orbitals in CO.
7

• Bonding
• If the ligands in a complex have orbitals with
  local ? symmetry
• with respect to the M-L axis(as two of the p
  orbitals of a halide
• ligand have), they may form bonding and
  antibonding ? mole-
• cular orbitals with the metal orbitals.The
  combination have net
• overlap with the metal t2g orbitals, which are
  therefore no longer
• purely nonbonding on the metal atom.Depending on
  relative energies
• of the ligand and metal orbitals, the energies of
  the t2g MOs lie above
• or below the energies they had as nonbonding AO,
  so the
• HOMO-LUMO gap (that is,?o) is decrese or
  increase, respectively.

8
?-donor ligand is a ligand that, before any
bonding is conside- red, has filled orbitals of ?
symmetry around the M-L axis. The energies of
these full ? orbitals are usually close to,
but somewhat lower than, those of the metal d
orbitals.We need consider only the full orbitals
when considering the effects of ? bonding in the
complex.Such ligands include Cl-, Br- and H2O.The
net effect is that nonbonding metal-ion
t2g orbitals become antibonding and hence are
raised closer in energy to the mainly metal
antibonding eg orbital. It follows that strong ?
donor ligands decrease ?o.
The ? overlap that may occur between a ligand p
orbital perpendi- cular to the M-L axis and a
metal dxy
9

• Overlap Metal t2g ? orbital b) Overlap Metal
  t2g Metal t2g
• c) Overlap Metal t2g ? orbital

10
The effect of ? bonding on the ligand-field splitt
ing parameter. Ligands that act as ? donors
decrease ?o.
M?L
11
A ?-acceptor ligand is a ligand that has filled ?
orbitals at lower energies than metal t2g
orbitals, it also has empty ? orbitals that are
available for occupation.The ? acceptor orbitals
are vacant antibonding orbitals on the ligand,
as in CO and N2, and these orbitals lie above the
metal d orbitals in energy.The ?-donor character
of CO is very low and in most d-metal carbonyl
comp- lexes CO is a net ? acceptor. Because the
?-acceptor orbitals on most ligands are higher
energy than the metal d orbitals.They form MO
orbitals in which the bonding t2g combinations
are largely of metal d orbitals character. The
net result is that ?o is increased by the
?-acceptor interaction.
12
Ligands that act as ? acceptors increses ?o
M?L
13
The overall order of the spectrochemical series
may be inter- preted in broad terms as dominated
by ? effect, and in general the series can be
interpreted as follows -increasing ?o ? ?
donorltweak ? donor ltno ? effects lt ?
acceptor Representative ligands that match these
classesare I- lt Br- lt Cl- lt F- lt H2O lt
NH3 lt PR3 lt CO ? donorltweak ? donor ltno ? effects
lt ? acceptor ?- donor ligands decrease ?o and ?
-acceptor ligands increse ?o the
spectrochemical series is largely a consequence
of the effects of ? bonding when such bonding is
feasible.
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15
Reactions of Complexes The reactions of d-metal
complexes are usually studied in solution.the
formation of complex with another ligand is a
substitution reaction, a rection in which an
incoming group displaces a ligand already
present. The incoming group is called the
entering group and the displaced ligand is the
leaving group.We normally denote the leaving
group as X and the entering group as Y.Then a
substitution reaction is the Lewis displacement
reaction MX Y ? MY X
16
Coordination Equilibria A spesific example of a
coordination equilibrium is the reaction of
Fe(III) with SCN- to give Fe(NCS)(OH2)52, a
red complex used to detect either iron(III) or
the thiocyanate ion. Fe(OH2)63(aq) NCS-(aq)
Fe(NCS)(OH2)52, aq) H2O(l)
Fe(NCS)(OH2)52 Kf Fe(OH2)63
NCS- The equilibrium constant, Kf, is the
formation constant of the complex.A ligand for
which Kf is large is one that binds more tightly
than H2O. A ligand for which Kf is small may not
be a weak ligand in an absolute sense, but merely
weaker than H2O.
17
Formation Constants The stepwise formation
constants are M L ML K1
ML/ML ML L ML2 K2
ML2/MLL MLn-1 L MLn K3
Ml/MLn-1L When we want to calculate the
concentration of the final productthe complex
MLn) we use the overall formation constant, ?
?n MLn/MLn ?n K1K2K3.....Kn
18

• Rates and Mechanism of Ligand Subsitution
• Rate of reaction are as important as equilibria
  in coordination
• chemistry. What determines whether one complex
  will survive
• for long periods while another will undergo rapid
  reaction?
• Lability and Inertness
• Complex that are thermodynamically unstable but
  survive for
• long periods(at least a minute) are called inert.
  Complex that
• undergo more rapid equilibration are called
  labile
• There are a number of generalizations that help
  us to anticipate
• the lability of the complex we are likely to meet.

19
1 All comp. Of s-block ions except the
smallest(Be2 and Mg2) are very labile. 2
Across the first d series, complex of d-block
M(II) ions are mode- rately labile,with
distorted Cu(II) complexes among the most
labile. However, d6 complexes with high field
ligands are an exception for example,
Fe(CN)64- and Fe(phen)32. Complexes of
M(III) ions are distinctly less labile. 3
Complexes of low oxidation number d10 ions (Zn2,
Cd2, and Hg2 )are highly labile. 4
Srong-field d3 and d6 octahedral complexes of the
first series are generally labile. 5 In the
first d series, the least labile M(II) and
M(III) ions are those with greatest LFSE. 6
Inertness is quite commong among the complexes of
the second and third d series, which reflects
the high LFSE and strength of the metal- ligand
bonding. 7 The M(III) ions of the f-block are
very labile.
20
Characteristic lifetimes for exchange of water
molecules in aqua complexes
21
(b) Trends in successive formation constants The
magnitude of the formation constant is a direct
reflection of the sign and magnitude of the Gibbs
energy of formation (because ?G0 -RTlnKf). It
is commonly observed that stepwise formation
constants lie in the order K1 ? K2 ? K3....... ?
Kn. This general trend can be explained quite
simply by considering the decrease in the number
of the ligand H2O molecules available for
replacement in the formation step, as
in M(OH2)5L L ? M(OH2)4L2 H2O compared
with M(OH2)4L2 L ? M(OH2)3L3
H2O Physically, the decrease in the stepwise
formation constants reflects the unfavorable
entropy change as free ligands are progressively
immobilized by coordination to the metal
22
A reversal of the relation Kn?Kn1 is usually an
indication of major change in the electronic
structure of the complex as more ligand are
added. An example is that the tris(bipyridine)
comp. of Fe(II), Fe(bipy)32, strikingly stable
compared with the Fe(bipy)2(OH2)22.This
observation can be correlated with the change
from a weak field t42ge2g in the bis complex to
a srong field t62g conf. in the tris comp.
K3/K2 1/7 for the Halogeno comps of
Hg(II) Because of forming four- coordination
23
Example Interpreting irregular successive
formation constants The formation of cadmium
comps. with Br- exhibit the successive equilibrium
constants logK1 1.56, log K2 0.54, log K3
0.06 log K4 0.37. Suggest an explanation of why
K4 is larger than K3. Answer the anomaly
suggest a sructural change. Aqua comps are
usually six-coordinate Wherease halo comps. of
M2 ions are commonly tetrahedral. The reaction
of the comp. with three Br- groups to add the
fourth is CdBr3(OH2)3-(aq) Br- (aq) ?
CdBr42- (aq) 3H2O(l) This step is favored by
the release of three molecules of water from the
relatively restricted coordination sphere
environment. The reesult is an increase in K
24
The chelate effect The chelate effect is the
greater stability of a comp. containing a
coordinated polydentate ligand compared with a
complex containing the equivalent number of
analogous monodentate ligands. When K1 for a
bidentate chelate ligand, such as
ethlenediamine, is compared with the value of ?
for the corresponding bisammine comp, it is found
that the former is generally larger Cu(OH2)6
en ? Cu(en)(OH2)42 2H2O log
K1 10.06 ?H0 -54 kJmol-1 ?S0
23JK-1 Cu(OH2)6 2NH3
Cu(NH3)2(OH2)42 2H2O log K1 7.7 ?H0
-46 kJmol-1 ?S0 -8.4JK-1
25
Steric effect and electron delocalization Steric
effect have an important influence on formation
constant. The stability of chelates involving
diimine ligands ( such as bipyridine,
phenanthroline) is a result of the chelate effect
in conjuction with the ability of the ligands to
act as ? acceptors as well as ? donors.An example
is the copm. Ru(bipy)32. The small bite angle
imposed by these ligands distorts the comp. from
octahedral symmetry.
26
(e) The Irving-Williams series Fig is obtained
when log Kf is plotted for comps. of the M2
ions of the first series. This variation is
summarized by the Irving- Williams series for the
order of formation constants. For M2 Ba2 lt
Sr2 lt Ca2 lt Mg2 lt Mn2 lt Fe2 lt Co2 lt Ni2 lt
Cu2 lt Zn2 The order is relatively insensitive
to the choise of ligands
The series reflects electrostatic
effects. However, beyond Mn2 there is a
sharp increase in the value of Kf for Fe(II), d6,
Co(II), d7, Ni(II) d8,and Cu(II) d9. These ions
experince an additional stabilization
proportional to the LFSE. Tetragoanally distorted
Cu(II) enhances the stabilization of comp.
27
The Electronic Spectra of Complexes The aim of
this chapter is to demonstrate how to interpret
the origins of the electronic spectra of
coordination comps and to correlate these spectra
with bonding.
The spectrum of the d3 complex Cr(NH3)6 in
aqueous solution
28
The band at lowest energy is very weak that is an
example of a spin- fordidden transition.The two
bands with intermediate intensities, which will
turn out to be spin allowed transitions between
the t2g and eg orbitals of the comp (t22ge1g ?
t32g), which are derived from the metal d
orbitals. The third feature in the spectrum is
the intense band at short wavelenth labeled CT
which is related with charge-transfer. This
splitting of a single transition into two bands
is in fact an outcome of the electron-electron
repulsions that will be one focus of this
chapter.
29
The electronic spectra of atoms The different
ways in which can occupy the orbitals
specified in the configuration are called the
microstates of the configura tion. For example,
one microstate of a 2p2 configuration is (1,
1-) this notation signifies that both electrons
occupy an orbital with ml 1 but do so opposite
spins, the superscript indicating ms 1/2
and indicating ms -1/2. Another microstate of
the same configuration is (-1, 0). In this
microstate, both electrons have ms 1/2 but
one occupies the 2p orbital with ml -1 and the
other occupies the orbital with ml 0
30
Spectroscopic Term If we group together the
microstates that have same energy when electron
repulsion are taken into account, we obtain the
spectros- copically distinguishable energy levels
called terms. The most important property of a
microstate for helping us to decide its energy is
the relative orientation of the spins of the
electrons. Next in important is the relative
orientation of the orbital angular momenta of the
electrons. It follows that we can identify the
terms of ligth atoms and put them in order of
energy by sorting the microstate to their total
spin quantum number S and then according to their
total orbital angular momentum quantum number L.
31
By analogy with the notation s,p,d,..... For
orbitals l 0,1,2,..... the orbital angular
momentum of an atomic term is denoted by the
equivalent upper case letter, L 0
1 2 3 4 ......
S P D F G
then alphabetical ML ml1 ml2 MS
ms1ms2 The total spin is normally reported as
the value of 2S1, which is called the
multiplicity of the term S 0
½ 1 3/2 2
............ 2S1 1 2
3 4 5 ............ The
multiplicity is written as a left superscript on
the letter representing the value of L, and the
entire label of a term is called a term
symbol.Thus, the term symbol 3P denotes a term
(a collection of degenerate state) with L 1 and
S 1 and is called triplet term.
32

• Example Give the term symbols for an atom with
  the configurations
• s1, (b) p1, and (c ) s1p1.
• Answer (a) The single s electron has l 0 and s
  ½. Because there
• is only one electron, L 0 (an S term), S ½, and
  2S1 2(a doublet
• Term).The term symbol is therefore 2S. (b) For a
  single p electron,
• l 1 so L 1 and the term is 2P.(c) With one s
  and p electron, L011,
• a P term. The electrons may be paired (S0) or
  (S1). Hence both
• 1P and 3P terms are possible.
• Self-test What terms arise from a p1d1
  configuration?

33
The classification of microstates We start the
analysis by setting up a table of microstates of
the d2 configurationhave been only the
microstates allowed by the pauli principle have
been included.The largest value of ML, which for
a d2 configuration is 4. This state must belong
to a term with L4 (a G term). We can concluded
that the terms of a 3d2 configuration are 1G, 3F,
1D, 3P, and 1S. These terms account for all 45
permitted states Term Number
of state 1G 9x1 9 3F
7x3 21 1D
5x1 5 3P
3x3 9 1S 1x1
1 Total 45
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35
The energies of the term It is possible to
identify the term of lowest energy by using
Hunds rule 1. For a given configuration, the
term with the greatest multiplicity lies lowest
in energy. For the d2 configuration, this rule
predicts that the ground state will be either 3F
or 3P. 2. For a term of given multiplicity, the
greater value of L, the lower the energy. In this
case, the 3F term is lower in energy than 3P
term.The ground term of a d2 species such as
Ti2 is expected to be 3F. Thus, for d2 the rules
predict the order 3F? 3P ? 1G ? 1D ? 1S but the
order observed for Ti2 from spectroscopy is 3F
? 1D ? 3P ? 1G ? 1S
36
The procedure may then be summarized as
follows 1. Identify the microstate that has the
highest value of Ms 2. Identify the highest value
of ML for that multiplicity Example What is
the ground term for the configurations a) 3d5 of
Mn2 and b) 3d3 of Cr3? Answer a) The d5
configuration permits occupation of each d
orbital singly, the maximum value of S is 5/2 and
the maximum multiplicity is 2x5/21 6, a
sextet term, L 0 and the term 6S. B) For the
configuration d3, the maximum multiplicity
corresponds to all three electrons having the
same spin quantum number,so S 3/2. The
multiplicity is 2 x3/2 1 4, quartet. ML
210 3, an F term. The ground term of d3 is 4F.
37
Selection rule The relative intensities of
absorption bands are governed by a series of
selection rules which are based on the symmetry
and spin multip- licity of ground and exited
electronic state 1. Transitions between states of
the same parity (symmetry with res- respect to a
center of inversion) are forbidden.This means
that tran- sitions between d orbitals are
forbidden (g ? g) transitions(d orbitals are
symmetric to inversion),but transition between d
and p orbitals are allowed(g ? u)p orbitals
antisymmetric to inversion. This is known as the
Laporte selection rule. 2. Transition between
states of different spin multiplicities are
forbidden. For example, transition between 4A2
and 4T1 are spin-allowed,but between 4A2 and 2A2
are spin-forbidden. These rules would seem to
rule out most electronic transition for
tran- sition metal complexes by various mechanism
in which these rules can be relaxed.
38
Some of the most important of these
mechanism 1. The bonds in transition metal
complexes are not rigid but undergo vibrations
that may temporarily change the symmetry which
provides a way to relax the first selection
rule.As a consequence, d-d transitions having
molar absorptivities in the range of
approximately 10 to 50 L mol-1 cm-1 commomly
occur. 2. Tetrahedral complexes often absorb more
srongly than octahedral complexes of the same
metal in the same oxidation state.The mixing of p
orbital character (of u symmetry) with d orbital
character provides a second way of relaxing the
first selection rule. 3. Spin-orbital coupling in
some cases provides a mechanism of relaxa- tion
of the second selection rule. Such absoption
bands are usually very weak, with typical molar
absorptivities less than 1 L mol-1 cm-1.
39
Our first example will be a metal complex having
a d2 configuration and octahedral geometry
V(H2O)3. In discussing spectra, it will be
particularly useful to be able to relate the
electronic spectra of transition metal complexes
to the ligand- field splitting, ?o for octahedral
complexes.To do this, it will be necas- cary to
introduce two special types of diagrams,
correlation diagram and Tanabe-Sugano
diagrams. Correlation Diagrams These diagrams
make use of two extremes 1 Free ions (no ligand
field) d2 configuration has 3F,3P,1G,1D, and
1S terms, with the 3F term being of lowest
energy.These term describe the eneryg levels of
a free d2 ion in the absence of any interaction
with ligands.These free ion terms will be shown
on the far left.
40
2 Srong Field Ligand There are three possible
configurations for two d electrons in an
octa- hedral ligand field.
In correlation diagrams, we will show these
states on the far righ, as the srong field
limit In actual coordination comp, the situation
is intermediate between these extremes.For d2,
the five terms 3F,3P,1G,1D, and 1S these terms
will represent five different atomic states
having different energies.The ef- fect of ligands
tend to push the energy levels toward t22g,
t12ge1g, and e2g configurations.In constructing a
diagram to correlate the free ion and srong field
limits, we will seek a way to deal with the
in-between case in which both factors are
important.
41
In an octahedral ligand field the free ion terms
will be split into states corresponding to the
irreducible representations as shown Below.
Splitting of free ion terms in octahedral symmetry
Although representations based on atomic orbitals
may have either g or u symmetry, the terms given
here are d orbitals and as a result have only g
symmetry.
42
Correlation diagram for a free ion and the
srong- field terms of a d2 confg.
43
From the information of The cystal-field
theory E(t22g, T1g) 2(-2/5?o) -0.8 ?o
E(t12ge1g, T2g) (-2/5 -3/5) ?o 0.2 ?o
E(e2g, A2g) 2(3/5) ?o 1.2 ?o Therefore,
relative to the energy of the lowest term, their
energy are E(t22g, T1g) 0 E(t12ge1g, T2g)
?o E(e2g, A2g) 2 ?o In summary, For a
given metal ion, the energy of the individual
terms respond differently to ligands of incresing
field strength and the correlation between free
atom terms of a complex can be displayed on an
Orgel diagram.
44
Tanabe-Sugano diagrams These diagrams are special
correlation diagrams that are particularly
useful in the interpretation of electronic
spectra of coordination comps.The lowest energy
state is plotted along the horizontal
axis,thus the vertical distance above this axis
is a measure of the energy above the ground
state.
This diagrams depict the energy of
electronic states of comp. As a function of the
the srength of the ligand field.
the horizontal axis ?o/B B Racah parameter, a
measure of repulsion between terms of the same
multiplicity. For d2, the energy difference
between 3F and 3P is 15B. Vertical axis E/B
where E is the energy abo- ve the ground state.
Tanabe-Sugano diagram for d2 confg.
45
Absorption spectrum of V(H2O)63
Two bands are readily observed at 17800 and 25000
cm-1, a third band ,at approximately 38000cm-1 ,
is obs- cured in solution by charge
transfer bands nearby.
Spin-allowed transitions for d2 confg.
46
Electronic spectrum of Cr(H2O)63
?1 4A2g(F) ? 4T2g ?2 4A2g(F) ? 4T1g(F) ?1 4A2g(F)
? 4T1g(P)
47
Electronic spectrum of Cr(H2O)62
?1 5Eg(D) ? 5T2g
48
Electronic spectrum of Mn(H2O)62
Why is absorption by Mn(H2O)62 so
weak? 6A1?Excited states is no spin-allo- wed
absoption, may be very weak forbidden transitions
to excited state of spin multiplicity other than 6
49
Electronic spectrum of Fe(H2O)62
?1 5T2g(D) ? 5Eg
50
Electronic spectrum of Co(H2O)62
?1 4T1g(F) ? 4T2g ?2 4T1g(F) ? 4A2g ?1 4T1g(F) ?
4T1g (P)
51
Electronic spectrum of Ni(H2O)62
?1 3A2g(F) ? 3T2g ?2 3A2g(F) ? 3T1g ?1 3A2g(F) ?
3T1g (P)
52
B1g? Eg
B1g? B2g
When degenerate orbitals are asymmet rically
occupied, J-T distortions are likely
Free ion term Oh
D4h
53
Eg ? A1g Eg ? B1g
54
Applications of Tanabe-Sugano Diagrams Determinin
g ?o from spectra ?o can be determined depend on
the d electron configuration of the Metal d1,
d4(high spin), d6(high spin), d9
d1 d4(high spin) d6 (high
spin) d9
Determining ?o for d1, d4(h.s.), d6 (h.s.), and
d9 confg.
55
d2 (or d7 confg.)
d3(or d8 confg.)
56
?1 3T1g(F) ? 3T2g ?2 3T1g(F) ? 3T1g(P) ?3 3T1g(F)
? 3A2g
?o the energy difference between 3A2g And
3T2g ?o Energy of transition 3T1g ?3A2g
Energy of transition 3T1g ? 3T2g
57
Example V(H2O)63 has absorption at 17800 and
25700 cm-1. Using Tanabe-Sugano diagram for d2,
estimate values of ?o and B for this
complex. From the Tanabe-Sugano diagram there
are three possible spin- allowed transitios ?1
3T1g(F) ? 3T2g (lowest energy) ?2 3T1g(F) ?
3T1g(P) ?1 3T1g(F) ? 3A2g The ratio of energies
of the absorption bands, 25700/17800 1.44 The
ratio of energy of the higher energy
transition(?2 or ?3) to the lowest energy
transition (?) must be approximately 1.44.
FromT-S diagrams, we can see that the ratio of ?3
to ?1 is approximately 2,regardless of
the srength of ligand field thereby eliminating
?3 . This means that the 25700 band must be ?2
for ?2 3T1g(F) ? 3T1g(P).
58
1.44 ?2/ ?1 The ratio varies as a function of
the strength of the ligand field.By taking values
from Fig. And plotting the ratio ?2/ ?1 versus
?o/B We find that ?2/ ?1 1.44 approximately
?o/B 31 ?2 E/B 42(approximately) B E/42
25700cm-1/42 610 cm-1 ?1. E/B 29
(approximately) B E/29 17800 cm-1/29 610
cm-1 Since ?o/B 31, ?o 31xB 31x 610 cm-1
19000cm-1
59

• The nephelauxetic series
• In the same example, we found that B 610 cm-1
  for V(H2O)63.
• This value is smaller than that of a free ion in
  the gas phase(B 861 cm-1),
• which indicates that electron repulsions are
  weaker than in the free
• ion. This weakening occurs because the occupied
  moleculer orbitals
• are delocalized over the ligands and away from
  the metal.
• The reduction of B from its free ion values is
  normally reported in
• terms of the nephelauxetic parameter,?
• B(comp)/ B(free ion)
• The values of ? depend on the metal ion and the
  ligand. They vary
• along the nephelauxetic series
• Br-? Cl- ? CN- ? NH3 ? H2O ? F-
• A small value of ? indicates a large measure of
  d-electron delocalization
• on to the ligands and hence a significant
  character in the complex.The
• softer ligand, the smaller the nephelauxetic
  parameter.

60
Each spectrum has three bands as expected d8
octa- hedral comp. Ni(en)32 bands are at
higher frequen- cies than corresponding Ni(H2O)6
2bands, in accord with the spectrochemical Series
. On the basis of the Orgel and Tanabe- Sugano
diagrams,One would assign the lowest
frquency band to 3A2g?3T1g(F) tran- sition,the
intermediate- frequency band to 3A2g? 3T2g(F) and
highest one to 3A2g?3T1g(P).The plusi- bility can
be verified by using the d8 T-S diagrams
Ni(en)32(purple)
Ni(H2O)62(green)
25000cm-1
14000cm-1
9000cm-1
Absorption spectra of Ni(H2O)62 (solid line,)
and Ni(en)32(dashed line).The colors of the
visible region of the spectrum are indicated
above.
?o for Ni(H2O)62 is 9000 cm-1 Which is the
lowest transition Energy.