Stereochemistry of new nitrogen containing heterocyclic aldehyde. VII. Potentiometric, conductometric and thermodynamic studies of novel quinoline azodyes and their metal complexes with some transition metals

Article abstract of DOI:10.1248/cpb.49.1308

A novel series of quinoline azodyes (5-(4′-derivatives phenyldiazo)-8-hydroxy-7-quinolinecarboxaldehyde) (HL₁-HL₅) has been prepared and characterized by elemental analyses, ¹H-NMR and IR spectra. The IR spectral data indicate that the compounds can exist in two resonance structures. Proton-ligand dissociation constants of quinoline azodyes and their subsituted derivatives, and metal-ligand stability constants of their complexes with bivalent (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺) metal ions have been determined potentiometrically in 0.1 M KCl and 40% (v/v) dimethylformamide (DMF)-water mixture. The influence of substituents on the dissociation and stability constants was examined on the basis of the electron repelling property of the substituent. The order of the stability constants of the formed complexes was found to be Mn²⁺2+2+2+. The effect of temperature was studied and the corresponding thermodynamic parameters (ΔG, ΔH, ΔS) were derived and discussed. The stoichiometries of these complexes were determined conductometrically and indicated the formation of 1:1 and 1:2 (metal:ligand) complexes was indicated.

Full text of DOI:10.1248/cpb.49.1308

1308
Chem. Pharm. Bull. 49(10) 1308—1313 (2001)
Vol. 49, No. 10
Stereochemistry of New Nitrogen Containing Heterocyclic Aldehyde. VII.
Potentiometric, Conductometric and Thermodynamic Studies of Novel
Quinoline Azodyes and Their Metal Complexes with Some Transition
Metals
Adel Zaki EL-SONBATI,* Ashraf Abdel-Aziz EL-BINDARY, Abdel-Ghany Farag SHOAIR, and
Rehan Mohamed YOUNES
Chemistry Department, Faculty of Science (Demiatta), Mansoura University, Demiatta, Egypt.
Received May 23, 2001; accepted July 4, 2001
A novel series of quinoline azodyes (5-(4؅-derivatives phenyldiazo)-8-hydroxy-7-quinolinecarboxaldehyde))
(HL1—HL5) has been prepared and characterized by elemental analyses, 1H-NMR and IR spectra. The IR spec-
tral data indicate that the compounds can exist in two resonance structures. Proton–ligand dissociation constants
of quinoline azodyes and their subsituted derivatives, and metal–ligand stability constants of their complexes
with bivalent (Mn2؉, Co2؉, Ni2؉, Cu2؉) metal ions have been determined potentiometrically in 0.1 M KCl and
40% (v/v) dimethylformamide (DMF)–water mixture. The influence of substituents on the dissociation and sta-
bility constants was examined on the basis of the electron repelling property of the substituent. The order of the
stability constants of the formed complexes was found to be Mn2؉ϽCo2؉ϽNi2؉ϽCu2؉. The effect of temperature
was studied and the corresponding thermodynamic parameters (DG, DH, DS) were derived and discussed. The
stoichiometries of these complexes were determined conductometrically and indicated the formation of 1 : 1 and
1 : 2 (metal : ligand) complexes was indicated.
Key words quinoline azodye; potentiometry; conductometry; complexation; thermodynamic
ical aniline and 4-alkyl-anilines (alkyl: CH3, OCH3, Cl, NO2; Aldrich Chem-
El-Sonbati and El-Bindary focussed their research on the
ical Co.) were used without any further purification. The experimental tech-
insertion reaction involving monomeric and polymeric model
nique has been described previously.1,2,11)
complexes of quinoline azodyes.1,2)
The novel 5-(4Ј-derivatives phenyldiazo)-8-hydroxy-7-quinolinecarbox-
aldehyde) (HLn) were prepared from aniline or its p-substituted derivatives
As part of our studies on simple inorganic models of inter-
est for the development of the bioinorganic chemistry of ura- (10 mmol) was dissolved in hydrochloric acid (20 mmol/25 ml distilled
nium,2) we have started investigation on a dioxouranium(VI)
complex with 8-hydroxyquinoline azodye derivatives which
appear to be suitable models due to the pretence of dioxoura-
H2O). The hydrochloric compound was diazotized below Ϫ5 °C with a solu-
tion of sodium nitrite (0.8 g, 10 mmol, 30 ml distilled H2O). The diazonium
chloride was coupled with an alkaline solution of oxine (1.7 g, 10 mmol) in
20 ml of ethanol. The crude dye was collected by filtration and was crystal-
nium(VI) for oxygen donors in biological systems. The
chemistry of quinoline and its derivatives has attracted spe-
cial interest due to their therapeatic properties.3) Quinoline
sulphonamides have been used in treatment of cancer,4)
turberculosis,5) and malaria.6)
lized from DMF, then dried in a vacuum dessicator over P2O5.
Reagents and Materials Metal ion solutions (0.0001 M) were prepared
from Analar metal chlorides in bidistilled water and standardized with
EDTA.12) The ligand solutions (0.001 M) were prepared by dissolving the ac-
curate weight of the solid in DMF (Analar). Solutions of 0.001 M HCl and
1 M KCl were also prepared in bidistilled water. A carbonate-free sodium hy-
droxide solution in 40% (v/v) DMF–water mixture was used as titrant and
standardized against oxalic acid (Analar).
Potentiometric Measurements The apparatus, general conditions and
methods of calculation were the same as in the previous work.9,10) The fol-
lowing mixtures were prepared and titrated potentiometrically at 298 K
against standard 0.004 M NaOH in 40% (v/v) DMF–water mixture:
i) 5 ml 0.001 M HClϩ5 ml 1 M KClϩ20 ml DMF;
ii) 5 ml 0.001 M HClϩ5 ml 1 M KClϩ15 ml DMFϩ5 ml 0.001 M ligand;
iii) 5 ml 0.001 M HClϩ5 ml 1 M KClϩ15 ml DMFϩ5 ml 0.001 M
ligandϩ5 ml 0.0001 M metal chloride.
For each mixture, the volume was made up to 50 ml with bidistilled water
before the titration. These titrations were repeated for temperatures of 308
Azo compounds based on quinoline play a central role as
chelating agents for a large number of metal ions, as they
form a stable six-membered ring after complexation with the
metal ion and can also be used as analytical reagents.7) Di-
methylformamide (DMF) or DMF/water mixtures as solvent
can be used due to: i) hydrolytic reactions of highly charged
metal ions; ii) insolubility of the ligand or of one or more of
the complexes to be formed. DMF is an aprotic solvent
which readily dissolves many water-soluble salts as well as
other sparingly soluble substances.8)
In continuation of our earlier work,9,10) we report herein and 318 K. A constant temperature was maintained at Ϯ0.05 K by using an
ultrathermostat (Neslab 2 RTE 220). The pH-meter readings in 40% (v/v)
the synthesis of quinoline azodyes (Chart 1) and the stability
constants of Mn2ϩ, Co2ϩ, Ni2ϩ and Cu2ϩ complexes with
DMF–water mixture are corrected according to the Van Uitert and Hass re-
lation.13)
quinoline azodyes at different temperatures. Ionization po-
tential and substituent effects on the dissociation and stability
constants are also investigated. Furthermore, the correspond-
ing thermodynamic functions of complexation are evaluated
Conductometric Measurements Solutions of 10Ϫ4 M of metal chloride
were titrated with 10Ϫ3 M of ligands. These titrations were performed using
YSI model 32 conductance-meter and carried out at 298 K.
and discussed. Moreover, the stoichiometries of these com- Results and Discussion
plexes are determined conductometrically at 298 K.
Characterization of the Azo Compounds Analytical
data (Table 1) are in agreement with the proposed formulae.
The H-NMR spectra show that the ligands exist as a
broad signal due to C8-OH. This favours formation of an in-
Experimental
1
Preparation of the Ligands 8-Hydroxy-7-quinolinecarboxaldehyde
was prepared according to El-Sonbati and El-Bindary.11) The standard chem-
To whom correspondence should be addressed. e-mail: abdelkhedr@yahoo.com
© 2001 Pharmaceutical Society of Japan

October 2001
1309
26310—24390 cmϪ1, can be is assigned to p–p* transition
within the CϭN group. The band D within 24390—
23800 cmϪ1 assigned to the p–p* transition of the azo-form.
The band F located at 21740—20400 cmϪ1. These latter
bands can be assigned to intramolecular charge transfer inter-
actions within the whole molecule (CT).
By tracing the IR spectra of the azo compounds, no nNH2
stretching vibrations are apparent. This supports the forma-
tion of azodye ligands. The mode of bonding of the HLn to
the metal ions was elucidated by investigating the IR spectra
of the complexes on the basis of a comparative analysis of
the results with respect to literature data of related systems.
The positions of the most relevent and characteristic bands
are due to: i) carbonyl oxygen atom, ii) azo nitrogen, iii) OH
group and iv) CNPy group.
tramolecular hydrogen bond with the CO group. Electron-
withdrawing substituents reduce considerably the intramolec-
ular hydrogen bond as indicated by the marked shift of the
hydroxyl signal to a higher field in the p-NO2 and p-Cl com-
pounds. Electron-donating substituents give the opposite ef-
fect, arising from the increasing basicity of the azo-nitrogen.
The electronic absorption spectra of the ligands exhibit
mainly five bands (A—D, F). The band A located at 41666—
35710 cmϪ1 could be assigned to the low energy p–p* tran-
sition corresponding to the aromatic system. The band B
within 32260—29410 cmϪ1; can be assigned to the p–p*
transition of the CO group. The band C appearing within
Table 1. Analytical Data of Quinoline Azodyesa)
Exp. (Calcd) %
Compoundb)
The spectra exhibit a medium to strong band in the region
1400—1500 cmϪ1 which could be assigned to nNϭN stretch-
ing vibration.1,2) The nCϭC stretching vibrations of the phenyl
ring are traced at 1500—1600 cmϪ1 which are due to the
symmetric and assymetric vibrations, respectively. The inves-
tigation of Rossmey and Mecke14) on deuterated phenolic de-
rivatives showed that the higher frequency band would be re-
lated to d OH, whereas the band within 1100 cmϪ1 can be
due to nC–OH. The higher value of the d OH may account for
the existence of hydrogen bonding. Califan and Luttke15)
found that the –OH in hydroxy compounds suffered a blue
shift when the OH group is involved in a hydrogen bond.
Much has been written about the –OH stretching fre-
quency and intensity of phenol derivatives depending on
many factors (e.g. substituent, medium, . . . etc.). The study of
IR frequencies is especially useful in the analysis of the
properties of hydrogen bonds.
C
H
N
HL1
HL2
HL3
HL4
HL5
66.6
(66.5)
4.2
(4.2)
13.5
(13.7)
70.0
(70.1)
4.6
(4.5)
14.6
(14.4)
69.4
(69.3)
3.9
(4.0)
15.0
(15.2)
61.5
(61.6)
3.2
(3.2)
13.3
(13.5)
59.7
(59.6)
3.0
(3.1)
17.5
(17.4)
a) Further studies with title ligands, using different metal ions, are in progress and
will be published in due coarse. b) The analytical data agree satisfactory with the ex-
pected formulae represented as given in Chart 1 (see Experimental). HL1—HL5 are the
ligand as given in Chart 1. Air-stable, high melting temperature, coloured. Insoluble in
water, but partially soluble in hot ethanol, and soluble in coordinating solvent. Decom-
position near 275 °C. Around 350 °C the decomposition showed for a short period and
became rapid again at about 430 °C. The ligands were completely decomposed at
590 °C.
On turning our attention to the IR spectra of hydrogen
Chart 1. General Formula and Proton Numbering Scheme of the HLn

1310
Vol. 49, No. 10
Table 2. Thermodynamic Functions for the Dissociation of Quinoline
Azodyes in 40% (v/v) DMF–Water Mixture and 0.1 M KCl at Different Tem-
peratures
containing azo compounds such as HLn (Chart 1), the nNϭN
showed a series of medium to weak bands at 1430, 1490 and
1520 cmϪ1. These besides the very broad bands centered at
ca. 3500 and ca. 2900 cmϪ1 may exist on a six membered
chelate skeleton. The hydrogen bonding in this compounds
could be classified into types according to the position of the
–OH group, vis. i) intramolecular hydrogen bonding between
the C8-OH and CO and/or CN (Chart 1A) and ii) intermolec-
ular hydrogen bonding resulting from the C8-OH group
through two molecules (Chart 1B) and/or C8-OH with CN
(Chart 1C) or CO (Chart 1D) through two molecules. This
could be confirmed by the appearance of the high frequency
band (ca. 3500 cmϪ1) as a result of intermolecular hydrogen
bonding and that at lower frequency (ca. 2900 cmϪ1) due to
the intramolecular hydrogen bonding.
Free energy Enthalpy
Entropy
change
Dissociation
constant
pKH
Temp.
(K)
change
(kJ molϪ1
DG
change
Compound
)
(kJ molϪ1) (J molϪ1 KϪ1
)
DH
ϪDS
HL1
HL2
HL3
HL4
HL5
298
308
318
9.62
9.45
9.27
54.89
55.72
56.44
132.18
130.58
128.74
15.50
298
308
318
9.45
9.30
9.13
53.92
54.84
55.59
141.10
139.51
137.48
11.87
12.25
10.72
16.27
298
308
318
9.21
9.05
8.89
52.55
53.37
54.12
135.23
133.50
131.66
Coggeshall,16) Diab and El-Sonbati17) found three kinds of
bonded-OH structures on the basis of the frequencies: i) only
the oxygen is in the bridge while the hydrogen is free, ii) a
polymer chain is formed in which both hydrogen and oxygen
atoms participate in the hydrogen bond, iii) dimer associates
are formed.
298
308
318
8.85
8.72
8.55
50.49
51.42
52.05
133.45
132.14
129.96
298
308
318
8.20
8.01
7.83
46.78
47.23
47.87
102.38
100.50
99.37
The IR spectral data of HLn exhibits a weak band at ca.
1655 cmϪ1. This is a criterion for nCϭO of the aldehydic
group. A very strong band at 1585Ϯ10 cmϪ1 is apparent and
assignable to nCϭC of the phenyl ring. The very interesting
region is that in the frequency range 2800—3550 cmϪ1. This
is a characteristic region to the vibrational frequency of the
–OH group where vibrational bands at 2900 cmϪ1 of medium
appearance and a broad at 3400—3550 cmϪ1 are apparent.
This is a powerful finding which indicates two types of hy-
drogen bonding: i) intramolecular one between –OH and
aldehydic group (Chart 1A), ii) intermolecular one between
–OH and aldehydic group through two molecules (Chart
1D).
In our laboratory, El-Sonbati and El-Bindary1,2,17—20) pub-
lished a series of papers to spotlight the chemistry, structural
models and chemical equilibria of azo compounds and their
complexes. The presentations and discussions explored many
important points and still many questions remain.
Fig. 1. Correlation of pKH with the Hammett’s Constant sR at 298, 308
and 318 K
derivatives are influenced by the inductive or mesomeric ef-
Potentiometric Studies. Proton–Ligand Stability Con- fect of the substituents. The p-OCH3 and p-CH3 derivatives
stants The average number of protons associated with the (HL1, HL2) have a lower acidic character (higher pKH values)
ligands at different pH values, n¯A, were calculated from the than the p-Cl and p-NO2 derivatives (HL4, HL5). This is quite
titration curves of the acid in the absence and presence of a reasonable because the presence of p-OCH3 and p-CH3
ligand. Thus, the formation curves (n¯A vs. pH) for the proton– groups (i.e. an electron donating effect) will enhance the
ligand systems were constructed and found to extend be- electron density by their high positive inductive or me-
tween 0 and 1 in the n¯A scale. This means that ligands have someric effect, whereby a stronger O–H bond is formed. The
one ionizable proton (the enolized hydrogen ion of the hy- presence of p-Cl and p-NO2 groups (i.e. an electron with-
droxyl group in the quinoline moiety). It can be seen that for drawing effect) will lead to the opposite effect.
the same volume of NaOH added the ligand titration curves
The results are also in accordance with Hammett’s para
had a lower pH value than the acid titration curve. The dis- substituent constant values sR.23) Straight lines are obtained
placement of a ligand titration curve along the volume axis on plotting pKH values at different temperatures versus sR
with respect to the acid titration curve is an indication of pro- (Fig. 1). The para substituents in the quinoline moiety have a
ton dissociation. The proton–ligand stability constants were direct influence on the pKH values of the investigated com-
calculated using the method of Irving and Rossotti.21)
pounds, revealing the coplanarity of the molecule and thus
The phenolic –OH group is known to be weakly acidic, in- affording a maximum resonance via delocalization of its p-
dicating a stronger bonding between the proton and the oxy- system.
gen donor. This means that the proton–ligand stability con-
stant of quinoline azodyes should be high due to the dissoci- for the metal complexes were obtained by plotting the aver-
ation of the –OH group.22)
age number of ligands attached per metal ions (n¯) versus the
Metal–Ligand Stability Constants The formation curves
Substituent Effect on pK An inspection of the results in free ligand exponent (pL), according to Irving and
Table 2 reveals that the pKH values of HL3 and its substituted Rossotti.24) These curves were analyzed and the successive

October 2001
1311
Table 3. Stepwise Stability Constants for the Complexation of Substituted Quinoline Azodyes with Mn2ϩ, Co2ϩ, Ni2ϩ and Cu2ϩ in 40% (v/v) DMF–Water
Mixture and 0.1 M KCl at Different Temperatures
298 K
308 K
318 K
Compound
HL1
Mnϩ
log K1
log K2
log K1
log K2
log K1
log K2
Mn2ϩ
Co2ϩ
Ni2ϩ
Cu2ϩ
7.55
7.70
7.75
7.90
5.65
5.73
5.77
5.99
7.74
7.88
7.93
8.10
5.83
5.90
5.96
6.12
7.95
7.99
8.08
8.25
5.98
6.05
6.12
6.28
HL2
HL3
HL4
HL5
Mn2ϩ
Co2ϩ
Ni2ϩ
Cu2ϩ
Mn2ϩ
Co2ϩ
Ni2ϩ
Cu2ϩ
Mn2ϩ
Co2ϩ
Ni2ϩ
Cu2ϩ
Mn2ϩ
Co2ϩ
Ni2ϩ
Cu2ϩ
7.35
7.51
7.57
7.72
5.47
5.55
5.60
5.81
7.59
7.74
7.79
7.91
5.64
5.72
5.77
5.98
7.80
7.86
7.96
8.16
5.82
5.92
5.97
6.20
7.20
7.34
7.41
7.60
5.33
5.41
5.48
5.70
7.41
7.54
7.52
7.70
5.50
5.57
5.65
5.86
7.63
7.80
7.85
7.99
5.78
5.85
5.94
6.15
6.81
6.95
7.06
7.25
4.95
5.05
5.16
5.34
7.18
7.32
7.35
7.50
5.26
5.37
5.41
5.55
7.42
7.67
7.71
7.87
5.53
5.60
5.65
5.80
6.77
6.85
6.99
7.20
4.89
4.95
5.06
5.20
7.00
7.09
7.25
7.43
5.05
5.10
5.18
5.31
7.20
7.30
7.44
7.63
5.30
5.36
5.45
5.60
stability constants were determined using different computa- quite reasonable because the presence of p-OCH3 and p-CH3
tional methods25,26) which agree within 1% error. Accord- groups (i.e. an electron donating effect) will enhance the
ingly the average values are represented in Table 3. The fol- electron density by their high positive indicative or me-
lowing general remarks can be pointed out:
someric effect, whereby stronger chelation was formed and
i) The maximum value of n¯ was Ϸ2 indicating the for- therefore the stability of the complexes.
mation of 1 : 1 and 1 : 2 (metal : ligand) complexes only.
ii) The low stability of HL5 and HL4 complexes can be
ii) The metal ion solution used in the present study was attributed to the presence of the NO2 and Cl groups in the p-
very dilute (10Ϫ4 M), hence there was no possibility of forma- position relative to the azo group, respectively. This is caused
tion of polynuclear complexes.27)
by the negative indicative effect of the NO2 and Cl groups
iii) The metal titration curves were displaced to the which decreases its ability for chelation and therefore the sta-
right-hand side of the ligand titration curves along the vol- bility of the complexes.
ume axis, indicating proton release upon complex formation
iii) For the ligands with the same metal ion at constant
of the metal ion with the ligand. The large decrease in pH for temperature, the stability of the chelates increases in the
the metal titration curves relative to ligand titration curves order HL1ϾHL2ϾHL3ϾHL4ϾHL5.32)
point to the formation of strong metal complexes.28)
Effect of Temperature The dissociation constants (pKH)
iv) In most cases, the colour of the solution after com- for azoquinoline and its substituted derivatives, as well as the
plex formation was observed to be different from the colour stability constants of their complexes with Mn2ϩ, Co2ϩ, Ni2ϩ
of the ligand at the same pH.
and Cu2ϩ have been evaluated at 298, 308 and 318 K, and are
v) For the same ligand at constant temperature, the sta- given in Tables 2 and 4. The slope of the plot (pKH or log K
bility of the chelates increases in the order Cu2ϩϾNi2ϩϾ vs. 1/T) was utilized to evaluate the enthalpy change (DH)
Co2ϩϾMn2ϩ.9,29) This order largely reflect the changes in the for the dissociation or complexation process, respectively.
heat of complex formation across the series from a combina- From the free energy change (DG) and (DH) values one can
tion of the influence of both the polarizing ability of the deduce the entropy changes (DS) using the well known rela-
metal ion30) and the crystal-field stabilization energies.31) The tionships (1) and (2):
greater stability of Cu2ϩ complexes is produced by the well
known Jahn–Teller effect.
Effect of the Substituent R on the Stability of the Com-
plexes An inspection of the results in Table 3 reveals that
the stability constant values of the complexes of HL3 and its
DGϭϪ2.303RT log K
DSϭ(DHϪDG)/T
(1)
(2)
All thermodynamic parameters of the dissociation process
substituted derivatives are influenced by the inductive or me- of HL3 and its derivatives are recorded in Table 2. From these
someric effect of the substituents. This behaviour correlates results the following conclusions can be made:
with the effect of substitution on the phenyl ring as follows:
i) The pKH values decrease with increasing temperature,
i) The high stability of HL1 and HL2 complexes can be i.e., the acidity of the ligands increases, independent of the
attributed to the presence of the OCH3 and CH3 groups in the nature of the substituent.33)
p-position relative to the azo group, respectively. This is
ii) A positive value of DH indicates that the process is

1312
Vol. 49, No. 10
Table 4. Thermodynamic Functions for the Complexation of Substituted Quinoline Azodyes in 40% (v/v) DMF–Water Mixture at 298 K
Free energy change (kJ molϪ1
)
Enthalpy change (kJ molϪ1
)
Entorpy change (J molϪ1 KϪ1
)
Compound
HL1
Mnϩ
ϪDG1
ϪDG2
DH1
DH2
DS1
DS2
Mn2ϩ
Co2ϩ
Ni2ϩ
Cu2ϩ
43.08
43.90
44.20
45.07
32.20
32.60
32.90
34.17
20.10
13.88
15.80
16.75
15.80
15.32
16.75
13.88
212.01
193.89
201.33
207.46
161.06
160.80
166.62
161.24
HL2
HL3
HL4
HL5
Mn2ϩ
Co2ϩ
Ni2ϩ
Cu2ϩ
Mn2ϩ
Co2ϩ
Ni2ϩ
Cu2ϩ
Mn2ϩ
Co2ϩ
Ni2ϩ
Cu2ϩ
Mn2ϩ
Co2ϩ
Ni2ϩ
Cu2ϩ
41.90
42.85
43.19
44.04
31.20
31.66
31.95
33.15
21.53
16.75
18.67
21.05
16.75
17.70
17.70
18.66
212.85
200.00
207.58
218.43
160.92
165.65
166.62
173.86
41.08
41.80
42.28
43.36
30.40
30.80
31.26
32.50
21.06
21.99
21.06
18.67
21.54
21.03
22.02
21.54
208.52
214.06
212.55
208.15
174.30
173.94
178.79
181.34
38.85
39.65
40.28
41.36
28.20
28.80
29.40
30.46
29.19
35.41
31.10
29.66
27.75
26.32
23.92
22.01
228.31
251.86
239.53
238.34
187.75
184.95
178.93
176.07
38.60
39.08
39.88
41.08
27.90
28.20
28.87
29.67
20.58
21.54
21.54
20.58
19.63
19.63
18.67
19.15
198.60
203.42
206.11
206.92
159.48
160.49
159.52
163.82
endothermic.
lent bond formation with the ligand.
iii) A large positive value of DG indicates that the disso-
ciation process is not spontaneous.
References
1) Shoair A. F., El-Bindary A. A., El-Sonbati A. Z., Younes R. M., Pol-
ish. J. Chem., 74, 1047 (2000).
2) Shoair A. F., El-Bindary A. A., El-Sonbati A. Z., Younes R. M., Spec-
trochim. Acta Part A, 57, 1683 (2001).
iv) The dissociation processes for HL3 and its derivatives
have negative values of DS due to increased order as a result
of the solvation processes.
All the thermodynamic parameters of the stepwise stabil-
ity constants of complexes are recorded in Table 4. It is
known that the divalent metal ions exist in solution as octa-
hedrally hydrated species and the obtained values of DH and
DS can then be considered as the sum of two contributions :
a) release of H2O molecules, and b) metal–ligand bond for-
mation. Examination of these values shows that:
i) The stepwise stability constants (log K1, log K2) for lig-
and complexes increases with increasing temperature, i.e., its
stability constants increase with increasing the temperature.
ii) The negative value of DG for the complexation
process suggests the spontaneous nature of such process.9,23)
iii) The DH values are positive, meaning that these
processes are endothermic and favourable at higher tempera-
ture.
3) Proffit E., Buchmann G., Arznemittal Forsch, 10, 181 (1960).
4) La Roche H., Patent, 416648 (1967).
5) Vaichulis J. A., Patent, 3272352 (1966).
6) Schmidt L. H., Ann. Rev. Microbiol., 427, 23 (1969).
7) El-Bindary A. A., El-Sonbati A. Z., Spectroscopy Lett., 32, 581
(1999).
8) Mollar M., Castro I., Lloret F., Julve M., Faus J., Latorre J., Transition
Met. Chem., 16, 31 (1991).
9) El-Bindary A. A., El-Sonbati A. Z., Kera H. M., Can. J. Chem., 77,
1305 (1999).
10) El-Bindary A. A., El-Sonbati A. Z., Kera H. M., Polish J. Chem., 74,
239 (2000).
11) El-Sonbati A. Z., El-Bindary A. A., Polish J. Chem., 74, 621 (2000).
12) Jeffery G. H., Bassett J., Mendham J., Deney R. C., “Vogel’s Textbook
of Quantitative Chemical Analysis,” 5th Edn., Longman, London,
1989.
13) Van Uitert L. G., Hass C. G., J. Am. Chem. Soc., 75, 451 (1953).
14) Rossmey G., Mecke R., Z. Electrochem., 59, 866 (1956).
15) Califan S., Luttke W., Z. Phys. Chem., 5, 240 (1955).
16) Coggeshall N. D., J. Am. Chem. Soc., 69, 1620 (1947).
17) Diab M. A., El-Sonbati A. Z., Polym. Deg. and Stab., 29, 271 (1990).
18) El-Sonbati A. Z., El-Bindary A. A., Mabrouk E. M., Ahmed R. M.,
Spectrochimica Acta, Part A, 57, 1751 (2001).
19) El-Bindary A. A., El-Sonbati A. Z., El-Mossalamy E. H., El-Santawy
E. M., Spectrochimica Acta, Part A, 57, in press (2001).
20) El-Dissouky A., El-Bindary A. A., El-Sonbati A. Z., Hilali A. S.,
Spectrochimica Acta, Part A, 57, 1163 (2001).
21) Irving H., Rossotti H. S., J. Chem. Soc., 1954, 29.
22) Athawale V. D., Nerkar S. S., Monatsh. Chem., 131, 267 (2000).
23) Hine J., “Structural Effects of Equilibria in Inorganic Chemistry,”
Wiley, New York, 1975, p. 667.
iv) The DS values for the ligand complexes are positive,
confirming that the complex formation is entropically
favourable.
Conductometric Studies. Stoichiometries Stoichio-
metries of the complexes of ligands with Mn2ϩ, Co2ϩ, Ni2ϩ
and Cu2ϩ result from the conductometric measurements.
These studies were carried out to investigate the stoichiome-
tries of the formed complexes which denoting the formation
of 1 : 1 and 1 : 2 (metal : ligand) complexes. The increase in
conductance upon titrating metal ions by ligand is probably
due to the liberation of the hydrogen ions from the OH dur-
ing the complex formation.9) The decrease in the conduc-
tance value occurs due to i) the increase of the volume of the
metal ion chelate formation which is accompanied with de-
crease in the value of the diffusion coefficient of the particle,
ii) the lowering of the charge on the metal ion through cova-
24) Irving H., Rossotti H. S., J. Chem. Soc., 1953, 3397.
25) Rossotti F. I. C., Rossotti H. S., Acta Chem. Scand., 9, 1166 (1955).
26) Beck M. T., Nagybal I., “Chemistry of complex equilibrium,” Wiley,
New York, 1990.
27) Sanyal P., Sengupta G. P., J. Ind. Chem. Soc., 67, 342 (1990).
28) Athawale V. D., Lele V., J. Chem. Eng. Data, 41, 1015 (1996).

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29) Ibanez G. A., Escandar G. M., Polyhedron, 17, 4433 (1998).
30) Harlly F. R., Burgess R. M., Alcock R. M., “Solution Equilibria,” Ellis
Harwood, Chichester, 1980, p. 257.
31) Phillips C. S. G., Williams R. J. P., “Inorganic Chemistry,” Oxford,
Vol. 2, 1966, p. 268.
32) Issa Y. M., Sherif O. E., Abbas S. M., Monatsh. Chem., 129, 985
(1998).
33) Bebot-Bringaud A., Dange C., Fauconnier N., Gerard C., J. Inorg.
Biochem., 75, 71 (1999).