The document discusses various factors that affect the stability of metal complexes. It explains that complexes formed with ligands having higher charge and smaller size are generally more stable. It also discusses the Irving-Williams order of stability and the factors of charge to radius ratio, electronegativity, and basicity of ligands. The chelate effect is described as an important ligand effect where multidentate ligands form more stable complexes due to entropy gains. Kinetic and thermodynamic stability are distinguished from reactivity concepts of labile and inert complexes.
Classification Of Mechanisms, Ligand Substitution In Octahedral Complexes Without Breaking Metal-ligand Bond, Substitution Reaction In Square Planar Complexes, Factors Which Affect The Rate Of Substitution, Trans Effect (Labilizing Effect), Theories and applications Of Trans Effect
Classification Of Mechanisms, Ligand Substitution In Octahedral Complexes Without Breaking Metal-ligand Bond, Substitution Reaction In Square Planar Complexes, Factors Which Affect The Rate Of Substitution, Trans Effect (Labilizing Effect), Theories and applications Of Trans Effect
1. What is the steady state approximation
2.Definition of Steady state approximation
3. In Chemical kinetics in steady state state approximation
4. Mechanism involving in steady state approximation
5. rate of formation, using steady state approximation plot
Definition - Mechanism - Effect of dielectric constant on the rate of reactions in solutions - Salt effect - Primary salt effect - Bronsted – Bjerrum equation - Secondary salt effect - Effect of pressure on rate of reaction in solution - Volume of activation - Significance
Crown ethers
NOMENCLATURE
GENERAL SYNTHESIS OF CROWN ETHER
AZA CROWN
CRYPTAND
APPLICATIONS
1. SYNTHETIC APPLICTION
Esterification
Saponification
Anhydride formation
Potassium permanganate oxidation
Aromatic substitution reactions
Elimination reactions
Displacement reaction
Generation of carbenes
Superoxide anion
Alkylations – 1. o-alkylations
2. c-alkylations
3. n-alkylations
2. ANALYTICAL APPLICATION
Determination of gold in geological samples
Super critical fluid extraction of trace metal from solid and liquid materials
Application of ionic liquids in analytical chemistry
Oxidation and determination of aldehydes
Crown ethers are used in the laboratory as phase transfer catalyst
OTHER APPLICATION
It is used in photocynation
Resolution of racemic mixture
Benzoin condensation
Hetrocyclisation
Synthesis of furanones
Acetylation of secondary amines in presence of primary amine
Reference,
https://en.wikipedia.org/wiki/Term_symbol
James E. Huheey, Ellen A. Keiter, Richard L.Keiter and Okhil K. Medhi, Inorganic Chemistry, Principles of Structure and Reactivity. 4th Edn. Pearsons
1. What is the steady state approximation
2.Definition of Steady state approximation
3. In Chemical kinetics in steady state state approximation
4. Mechanism involving in steady state approximation
5. rate of formation, using steady state approximation plot
Definition - Mechanism - Effect of dielectric constant on the rate of reactions in solutions - Salt effect - Primary salt effect - Bronsted – Bjerrum equation - Secondary salt effect - Effect of pressure on rate of reaction in solution - Volume of activation - Significance
Crown ethers
NOMENCLATURE
GENERAL SYNTHESIS OF CROWN ETHER
AZA CROWN
CRYPTAND
APPLICATIONS
1. SYNTHETIC APPLICTION
Esterification
Saponification
Anhydride formation
Potassium permanganate oxidation
Aromatic substitution reactions
Elimination reactions
Displacement reaction
Generation of carbenes
Superoxide anion
Alkylations – 1. o-alkylations
2. c-alkylations
3. n-alkylations
2. ANALYTICAL APPLICATION
Determination of gold in geological samples
Super critical fluid extraction of trace metal from solid and liquid materials
Application of ionic liquids in analytical chemistry
Oxidation and determination of aldehydes
Crown ethers are used in the laboratory as phase transfer catalyst
OTHER APPLICATION
It is used in photocynation
Resolution of racemic mixture
Benzoin condensation
Hetrocyclisation
Synthesis of furanones
Acetylation of secondary amines in presence of primary amine
Reference,
https://en.wikipedia.org/wiki/Term_symbol
James E. Huheey, Ellen A. Keiter, Richard L.Keiter and Okhil K. Medhi, Inorganic Chemistry, Principles of Structure and Reactivity. 4th Edn. Pearsons
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Dear Dr. Kornbluth and Mr. Gorenberg,
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harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
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students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
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Model Attribute Check Company Auto PropertyCeline George
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Honest Reviews of Tim Han LMA Course Program.pptxtimhan337
Personal development courses are widely available today, with each one promising life-changing outcomes. Tim Han’s Life Mastery Achievers (LMA) Course has drawn a lot of interest. In addition to offering my frank assessment of Success Insider’s LMA Course, this piece examines the course’s effects via a variety of Tim Han LMA course reviews and Success Insider comments.
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
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2. DEFINING STABILITY
The statement that a complex is stable is rather loose
and misleading very often.
It means that a complex exists and under suitable and
required conditions it can be stored for a long time.
But this cannot be generalized to all complexes.
One particular complex may be stable towards a
reagent and highly reactive towards another
2santhanam SCSVMV
3. Thermodynamic stability
• As for as complexes in solutions are
concerned there are two kinds of stabilities
• Thermodynamic stability – Measure of the
extent to which the complex will be formed
or will be transformed into another species,
when the system has reached equilibrium
3santhanam SCSVMV
4. Kinetic stability
• Kinetic stability – refers to the speed with
which the transformations leading to
equilibrium will occur.
• Under this , the rates of substitutions,
racemisations and their mechanisms.
• The factors which are affecting the rates of
the reactions are also studied
4santhanam SCSVMV
5. Labile and Inert complexes
• The complexes which rapidly exchange their
ligands with other species are called labile.
• If the ligand exchange reaction rate is slow
then they are called inert complexes.
• But the reactive nature should not be
confused with the stability.
5santhanam SCSVMV
6. Stability constant / Formation constant
• According to Bjerrum formation of a complex in
aqueous solution proceeds through a stepwise
fashion with corresponding equilibrium constants
M + L ML K1 = [ML] / [M] [L]
ML + L ML2 K2 = [ML2] / [ML] [L]
ML2 + L ML3 K3 = [ML2] / [ML2] [L]
…………..……………………………….
………….………………………………..
MLn-1 + L MLn Kn = [MLn] / [MLn-1] [L]
These K1,K2 K3 … Kn are called stepwise formation constants
K1
Kn
K3
K2
6santhanam SCSVMV
7. Overall stability constant
• If the complex formation is considered as a
single step process
M + nL MLn
= [MLn] / [M] [L]ᵝn
7santhanam SCSVMV
10. Statistical effect explanation
• When more ligands are entering into the
coordination sphere the number of aqua
ligand decreases.
• This reduces the probability of substitution of
aqua ligand with the new ligand.
• Reflected as decreasing stepwise formation
constants
10santhanam SCSVMV
11. Relationship between Kn and ᵝn
• Let us consider
ᵝ3 = [ML3] / [M] [L]3
= [ML3] . [ML2] . [ML]
[M] [L]3
. [ML2] . [ML]
= [ML] . [ML2] . [ML3]
[M] [L] [ML] [L] [ML2] [L]
= K1 . K2 . K3
In general
ᵝn = K .K .K . ….. K
11santhanam SCSVMV
12. Kinetic Vs Thermodynamic stability
• The terms labile and inert refer to the
reactivity of a complex only.
• Not to be confused with its stability.
• An inert complex may be stable or unstable.
• Similarly a labile complex may be stable or
unstable
12santhanam SCSVMV
13. Exemplification
• The above said fact is clearly shown by the
complex [Hg(CN)4]2-
.
Hg2+
+ 4CN-
[Hg(CN)4]2-
ᵝ ≈ 10 42
• The over all formation constant is having very
high value which means that equilibrium is
lying far too right.
13santhanam SCSVMV
14. • But when this complex exchanges its CN-
ligands with 14
C labeled CN-
solution very high
rate showing that the complex is labile.
• So the thermodynamic stability is not
connected to the lability or inertness of a
complex.
14santhanam SCSVMV
15. Explanation of lability and inertness according to VBT
• VBT classifies octahedral complexes into two
types.
• Inner orbital complexes – d2
sp3
• Outer orbital complex – sp3
d2
• The two d-orbitals involved in the hybridization
are the egset of orbitals.
15santhanam SCSVMV
16. Outer orbital complexes
• The complexes having sp3
d2
hybridization are
called outer orbital complexes.
• In terms of VBT these bonds are weaker.
• They are generally labile.
• Mn(II), Fe(II),Fe(III),Co(II),Ni(II),Cu(II) and Cr(II)
are labile.
16santhanam SCSVMV
17. Inner orbital complexes
• These complexes generally have d2
sp3
hybridization.
• The hybrid orbitals are filled with the ligand
electrons.
• The t2g orbitals of metal accommodate the d
electrons of the metal.
17santhanam SCSVMV
18. • If the t2g levels are left vacant then the
complex can associate with an incoming
ligand and the complex is labile
• If all the t2g levels are occupied then the
complex becomes inert.
18santhanam SCSVMV
19. Labile and inert complexes on the basis of CFT
• According to CFT the ligand field splits the d-
orbitals.
• This splitting leads to a decrease in energy of
the system whose magnitude depends on the
number of d electrons present.
• if the CFSE value increases by association or
dissociation of a ligand then the complex is
labile.
• On the other hand it is inert when there is a
loss in CFSE value. 19santhanam SCSVMV
20. Factors affecting lability of complexes
• Charge of the central ion: Highly charged ions form
complexes which react slowly i.e. inert
• Radii of the ion: the reactivity decreases with
decreasing ionic radii.
• Charge to radius ratio: if all the factors are similar, the
ion with largest z/r value reacts with the least rate.
• Geometry of the complex: Generally four coordinated
complexes are more labile
20santhanam SCSVMV
22. Properties of the metal ion
• Charge and size
• Natural order (or) Irving –William order of
stability
• Class a and Class b metals
• Electronegativity of the metal ion
22santhanam SCSVMV
23. Charge and size of the ion
• In general metal ions with higher charge and
small size form stable complexes.
• A small cation with high charge attracts the
ligands more closely leading to stable
complexes.
• The following tables explain the facts that if
z/r ratio (polarizing power) of the metal ion is
high then stability of the complex is also high
23santhanam SCSVMV
24. Effect of ionic radius
Complex ion Charge on the
ion
Ionic radii (Aₒ
)
Value of ᵝ stability
[BeII
(OH)] +
+2 0.31 107
[MgII
(OH)] +
+2 0.65 120
[CaII
(OH)] +
+2 0.99 30
[BaII
(OH)] +
+2 1.35 4
24santhanam SCSVMV
25. Effect of charge
Complex ion Charge on the
ion
Ionic radii (Aₒ
)
Value of log ᵝ stability
[FeIII
(CN)6] 3-
+3 31.0
[FeIII
(CN)6] 4-
+2 8.3
CoIII
complex +3 high
CoII
complex +2 low
Almost
same
Almost
same
25santhanam SCSVMV
26. Irving – William order of stability
• Stabilities of the high spin complexes of the 3d
metals from Mn2+
to Zn 2+
with a common ligand
is usually
MnMn2+2+
< Fe< Fe2+2+
< Co< Co2+2+
< Ni< Ni2+2+
< Cu< Cu2+2+
> Zn> Zn 2+2+
• This is attributed to the CFSE values of the
complexes and called natural order of
stability.
• There is a discrepancy with Cu which is due to
Jahn – Teller distortion
26santhanam SCSVMV
27. CFSE as a function of no of d-
electrons
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 1 2 3 4 5 6 7 8 9 10 11
no of d-electrons
CFSEinmultiplesofΔ.
Crystal Field Stabilization Energy (CFSE) of
d0
to d10
M(II) ions:
Ca2+
Mn2+
Zn2+
double-
humped
curve
Ni2+
27santhanam SCSVMV
28. log K1(EDTA) as a function of no of d-
electrons
10
12
14
16
18
20
0 1 2 3 4 5 6 7 8 9 10 11
no of d-electrons
logK1(EDTA).
Log K1(EDTA) of d0
to d10
M(II) ions:
Ca2+
Mn2+
Zn2+
double-
humped
curve
= CFSE
rising baseline
due to ionic
contraction
28santhanam SCSVMV
29. log K1(en) as a function of no of d-
electrons
0
2
4
6
8
10
12
0 1 2 3 4 5 6 7 8 9 10 11
no of d-electrons
logK1(en).
Log K1(en) of d0
to d10
M(II) ions:
double-
humped
curve
Ca2+
Mn2+
Zn2+
rising baseline
due to ionic
contraction
= CFSE
29santhanam SCSVMV
30. log K1(tpen) as a function of no of d-
electrons
0
5
10
15
20
0 1 2 3 4 5 6 7 8 9 10 11
no of d-electrons
logK1(tpen).
Log K1(tpen) of d0
to d10
M(II) ions:
Ca2+
Mn2+
Zn2+
double-
humped
curve
N N NN
N Ntpen
30santhanam SCSVMV
31. Class a and Class b metals
• Chatt and Ahrland classified metals into three
types.
• Class a , Class b and border line.
• Class a : H, alkali and alkaline earth metals, Sc -> Cr,
Al -> Cl, Zn -> Br , In, Sn , Sb , I, lathanides and
actinides
• Class b: Rh ,Pd , Ag , Ir , Pt , Au and Hg
• Border line: Mn -> Cu , Tl -> Po, Mo , Te , Ru , W ,
Re , Os and Cd
31santhanam SCSVMV
32. • Class a metals form more stable complexes with
ligands in which coordination atoms are from
second period. ( N , O , F)
• Class b metals form more stable complexes with
ligands having third period elements as ligating
atoms. (P , S , Cl)
• Class b metals are having capacity to form pi bonds
with the ligand atoms. The expansion is possible only
from the third period donor atoms.
• Border line metals do not show any noticeable trend.
32santhanam SCSVMV
33. Electronegativity of the metal
atom
• The bond between metal and ligand atom is,
to some extent due to the donation of
electron pair to the metal.
• If the metal is having a tendency attract the
electron pair (Higher electronegativity) then
more stable complexes are formed .
33santhanam SCSVMV
34. Properties of ligand
• Size and charge
• Basic character
• Chelate effect
• Size of the chelate ring
• Steric effect
34santhanam SCSVMV
35. Size and charge of the ligand
• To some extent we can say that if the ligand is
smaller in size and bearing higher charge it
will form more stable complexes.
• For example usually F-
forms more stable
complexes that Cl-
• In the case of neutral mono dentate ligands,
high dipole moment and small size favour
more stable complexes.
35santhanam SCSVMV
36. Basic character of ligands
• If the ligand is more basic then it will donate
the electron pair more easily.
• So with increased basic character more stable
complexes can be expected.
• Usually the ligands which bind strongly with H+
form more stable complexes.
• This is observed for IA, IIA, 3d, 4f and 5f
elements
36santhanam SCSVMV
37. The chelate effect or chelation is one of the most important ligand effects inThe chelate effect or chelation is one of the most important ligand effects in
transition metal coordination chemistry.transition metal coordination chemistry.
"The adjective chelate, derived from the great claw or chela (chely - Greek)
of the lobster, is suggested for the groups which function as two units
and fasten to the central atom so as to produce heterocyclic rings."
J. Chem. Soc., 1920, 117, 1456
Ni2+
Chelate
37santhanam SCSVMV
38. What are the implications of the following results?
NiCl2 + 6H2O → [Ni(H2O)6]+2
[Ni(H2O)6]+2
+ 6NH3 → [Ni(NH3)6]2+
+ 6H2O log β = 8.6
[Ni(NH3)6]2+
+ 3 NH2CH2CH2NH2 (en)
[Ni(en)3]2+
+ 6NH3
log β = 9.7
[Ni(H2O)6]+2
+ 3 NH2CH2CH2NH2 (en)
[Ni(en)3]2+
+ 6H2O
log β = 18.3
38santhanam SCSVMV
39. NH3 is a stronger (better) ligand than
H2O
∆O NH3 > ∆O H2O
[Ni(NH3)6]2+
is more stable
∆G = ∆H - T∆S (∆H -ve, ∆S≈ 0)
∆G for the reaction is negative
Complex Formation: Major Factors
[Ni(H2O)6] + 6NH3
→[Ni(NH3)6]2+
+ 6H2O
39santhanam SCSVMV
40. Chelate Formation: Major Factors
en and NH3 have similar N-donor environment
but en is bidentate and chelating ligand
rxn proceeds towards right, ∆G negative
∆G = ∆H - T∆S (∆H -ve, ∆S ++ve)
rxn proceeds due to entropy gain
∆S ++ve is the major factor behind chelate
effect
[Ni(NH3)6]2+
+ 3 NH2CH2CH2NH2 (en)
[Ni(en)3]2+
+ 6NH3
40santhanam SCSVMV
42. Reaction of ammonia and en with Cu2+
[Cu(H2O)6]2+
+ en → [Cu(en)(H2O)4]2+
+ 2 H2O
Log K1 = 10.6 ∆H = -54 kJ/mol ∆S = 23 J/K/mol
[Cu(H2O)6]2+
+ 2NH3 → [Cu(NH3)2(H2O)2]2+
+ 2 H2O
Log β2 = 7.7 ∆H = -46 kJ/mol ∆S = -8.4 J/K/mol
Chelate Formation: Entropy Gain
42santhanam SCSVMV
43. Chelate effect
• The stability of the complex of a metal ion with a
bidentate ligand such as en is invariably significantly
greater than the complex of the same ion with two
monodentate ligands of comparable donor ability,
i.e., for example two ammonia molecule.
• The attainment of extra stability by formation of
ring structures , by bi or poly dentate ligands which
include the metal is termed as chelate effect.
43santhanam SCSVMV
44. Why chelates are more stable?
Suppose we have a metal ion in solution,
and we attach to it a monodentate ligand,
followed by a second monodentate ligand.
These two processes are completely
independent of each other.
44santhanam SCSVMV
45. Why chelates are more stable?
• But suppose we have a metal ion and we attach to it
one end of a chelating ligand
• Attachment of the second end of the chelate is now
no longer an independent process once one end is
attached, the other end, rather than floating around
freely in solution, is anchored by the linking group in
reasonably close proximity to the metal ion.
• Therefore more likely to join onto it than a
comparable monodentate ligand would be.
45santhanam SCSVMV
51. number of chelate rings
Metal
complex
No. of
rings
Values of log ᵝ
Mn (II) Fe (II) Co (II) Ni (II) Cu (II) Zn (II) Cd (II)
M (NH3)4 0 - 23.7 5.31 7.79 12.59 9.06 6.92
M (en)2 2 4.9 7.7 10.9 14.5 20.2 11.2 10.3
M (trien) 3 4.9 7.8 11.0 14.1 20.5 12.1 10.0
M (tren) 3 2.8 8.8 12.8 14.0 18.8 14.6 12.3
M (dien)2 4 7.0 10.4 14.1 18.9 21.3 14.4 13.8
M (penten) 5 9.4 11.2 15.8 19.3 22.4 16.2 16.2
51santhanam SCSVMV
52. Chelate ring size - i
In chelates ertain ring sizes are more
preferable than others.
Here are some data for cadmium complexes
of bidentate amines of the type
H2N(CH2)nNH2, where n = 1-4, i.e ring sizes
4-7.
52santhanam SCSVMV
53. Chelate ring size - ii
• When n = 1, the resulting four-membered ring is too
strained at the sp3
-hybridized carbon which wants to
try to have bond angles of 109°.
• It is worth pointing out, however, that there are lots
of perfectly stable four-membered chelate rings that
contain an sp2
-hybridized carbon in that position,
such as carboxylates (O2CR), dithiocarbamate
(S2CNR2), xanthate (S2COR) and so on
53santhanam SCSVMV
54. Chelate ring size - iii
• When n = 2, the resulting five-membered ring is
obviously the most stable one available, though n = 3
(six-membered ring) isn't bad either.
• When n = 4, the stability of the seven-membered
ring is starting to drop again. This is because in order
to accommodate the longer hydrocarbon chain, the
two nitrogens are being forced too far apart
54santhanam SCSVMV
55. Chelate ring size - iv
• The angle occupied by a chelate ligand, in this case
the N-Cd-N angle, is called the bite angle.
• In an octahedral complex, it's going to be happiest at
90°.
• If we try to force the nitrogens too far apart so that
they have a much bigger bite angle, eventually
something will have to give, and one end of the
ligand will dissociate. Hence the lower stability
constant.
55santhanam SCSVMV
56. Steric factors
• when bulky groups are present near or on the
ligating atom, the steric forces come into play.
• Presence of bulkier groups near coordination
sites reduce the chances of ligand getting
closer to the metal.
• Even when complex is formed, to get relieved
from the steric hindrance the bond may
dissociate. This reduces the stability of
complex
56santhanam SCSVMV
58. Spectrophotometric method
• While formation of a complex a striking colour change
also occurs.
• The absorption obeys Beer – Lambert’s law
– A = ε . C. l
• A can be measured by using a spectrophotometer
• If ε and l are known then C can be calculated.
• Considering the following reaction,
M2+
+ L ML2+
K = [ML2+
] / [M2+
] [L]
58santhanam SCSVMV
59. It is known that ,
CM = [M2+
] + [ML2+
]
CL = [L] + [ML2+
]
A = ε [ML2+]. C[ML2+] . l
C[ML2+] = A / ε [ML2+].l
So
[M2+
] = CM - (A / ε [ML2+].l)
[L] = CL - (A / ε [ML2+].l) 59santhanam SCSVMV
60. • A series of solutions containing varying ratios
of metal and ligand are taken.
• The absorption of the solution at wavelength
maximum is measured.
• From the absorbance and C,l values K is
calculated.
60santhanam SCSVMV
61. Potentiometric method
• Also known as Bjerrum method
• When ligand is a weak base or acid, there is
competition between hydrogen ions and
metal ions for the ligand .
L + H+
HL+
Ka = [HL+
] / [L] [H+
]
L + M+
ML+
KF = [ML+
] / [L] [M+
]
• If CH,CM and CL are the molar concentrations
santhanam SCSVMV 61
62. CH = [H+
] + [HL+
]
CL = [L] + [ML+
] + [HL+
]
CM = [M+
] + [ML+
]
• Solving the equations by using the association
constant of the ligand
[ML+
] = CL-CH+[H+] – CH-[H+
] / Ka [H+
]
[M+
] = CM – [ML+
]
[L] = CH – [H+
] / Ka [H+
]
santhanam SCSVMV 62
63. • Except [H+
] all the other parameters are
known , hence the stability constant can be
calculated after measuring the pH of the
solution by using a pH meter
• In order to get precise results the ligand must
be a moderately weak base or acid.
• KF value should be within 105
times of the
association constant
santhanam SCSVMV 63