.1
COMPLEXING PROPERTIES OF
5,7-DIIODO-8-HYDROXY QUINOLINE
A.El-Marghany
Chemistry Department, Faculty of Education Suze, Suze Canal University, Egypt
Abstract
5,7-diiodo-8-hydroxy quinoline (DIHQ) and its Mn (II), Fe (III), Co
(II), Cu (II) and Zn (II) complexes have been synthesized and characterized
by their elemental analysis, IR, electronic spectral studies and magnetic
susceptibility measurements. The dissociation constant of the entitled
ligand was determined by different methods. The electronic spectra of the
ligand and their complexes in the presence of different solvents are
analysed by the multiple regression technique using the equation:
Y = ao + a1x1+ a2x2 + a3x3 +…. The multiple regression coefficient
(MCC) and probability of variation (P) have been calculated by multiple
linear analysis.
Introduction
The quinoline nucleus plays an important rule in many areas of
interest including coordination and analytical chemistry. Quinoline
compounds having the general structure 4-(substituted) 3-hydroxy-2quinoline exhibited antibacterial activity and acts as antibiotics.(1,2) The 5,7disubstituted [Cl, Br, I, NO2] derivatives of quinoline and their uranyl
.2
complexes were prepared and characterized. The data illustrated the
formation of complexes with stoichiometries 1:1, 1:2 and 1:3.(3-8) The
dibromo reagent is a highly selective non-extractive spectrophotometric
method for rapid determination of trace level of vanadium (V) in different
materials, alloys and steels,(9) and for the extraction of some rare earth
elements.(9) The present paper reports of the study of 5,7-diiodo-8-hydroxy
quinoline together with its complexes (Mn, Fe, Co, Cu and Zn) by spectral
measurements (IR, UV-VIS) and magnetic moments in the solid state and
in presence of different solvents.
Experimental
Synthesis of the complexes: (0.01 mole) of a solution of the
transition metal chloride salts of Mn (II), Fe (III), Co (II), Cu (II) and Zn
(II)] were refluxed with (0.02 mole) of 5,7-diiodo-8-hydroxy quinoline
dissolved in distilled water by heating. The reaction mixture was cooled
where a complex was precipitated, then dried by a vacuum desiccator over
unhydrous CaCl2. The compounds were characterized by their elemental
analysis (C, H, N, Cl) given in Table (1).
Metal ion analysis
The complexes were digested and decomposed with aqua-regia. The
free metal contents were determined either by the complexometric
titration(10)
procedure
and
atomic
absorption
spectrophotometric
measurements using a Perkin-Elmer 2380 atomic absorption.
.3
Measurements
The infrared spectra of the ligand and its complexes were recorded
on a Perkin-Elmer spectrometer model 1430 covering the frequency range
200- 4000 cm-1.
Nujol mull electronic spectra were recorded on a Perkin-Elmer
spectrophotometer model Lambda 4B covering the wavelength 190-900 nm,
following the procedure of Griswold et al.(11)
Magnetic susceptibilities were determined by the Faraday methods,
and diamagnetic corrections were calculated from the data given by Figgis
and Lewis.(12)
The solvents used [CCl4, CHCl3, dioxane, acetone, methanol,
acetonitriol, DMF and DMSO] were of spectroquality grade.
Calculations
The solvent effect on the electronic absorption spectra of 5,7-diiodo8-hydrox quinoline, Table 2, and its their complexes have been analysed by
the multiple linear regression technique using the following equation: Y =
ao + a1x1+ a2x2 + a3x3 +…. The constants a1, a2, a3,….are the different
regression coefficients and the constant a 0 is the regression intercept. We
selected the independent variables to be the solvent interaction mechanisms
E, N, M and K.(13) The empirical solvent polarity E is sensitive to solventsolute hydrogen bonding and to dipolar interactions. (13) The parameter N is
.4
a measure of the permanent dipole-permanent dipole interactions given as
follows:
D 1 n 2  1
N=
D  2 n2  2
Where D is the dielectric constant and n is the refractive index. The
parameter M is a measure of the solute permanent dipole-solvent induced
dipole interactions defined as follows:(13)
M=
n 2 1
2n 2  1
The parameter K is the polarity of the solvent given in term of the
dielectric constant and defined as:
K=
D 1
2D  1
The intercept a0 and the coefficients a1, a2, a3,….have been calculated
by multiple linear regression anlysis. The SPSS programs has been used on
a PC computer.
Results and Discussion
The electronic absorption spectra of DIHQ in 1,4 dioxane gave three
characteristic bands at 250, 337 and 432 nm due to -* transition of
phenyl ring and n-* transition characteristic for nitrogen of pyridine,
respectively.(14,15) For the free ligand, the n-* transition at 337 nm is blue
shifted on going from non-polar to polar solvent while -* is red shifted.
In presence of high dielectric constant solvents, the -* transition is red
.5
shifted with increasing dielectric constant of the solvent meanwhile red
shift of the n-* transition occurs. The slight shift of max from methanol to
H2O in the free ligand depicts the presence of an intra-molecular hydrogen
bond affected by interaction with n-electrons blocked by the solvation
leading to an increase localization of the electrons and the localized p
orbital involved in the bond to the solvent to increase aggregation
molecules. The complexes are strongly solvated by methanol with a
considerable red shift variation than dioxane with the presence of
characteristic bands at (280-294nm). These bands are absent in presence of
water except for the n  * transition is assigned in the wavelength (210213.3 nm) i.e., no solute-solvent interaction except for Fe DIHQ. For the
-* transition, max is not detected in presence of CCl4 and acetone
solvents. Mn (II), Fe (III), Co (II) and Cu (II) complexes gave electronic
absorption spectral bands with max 263, 267, 260 and 275 nm, respectively
in dioxane. In presence of high dielectric constant solvents, max is red
shifted for all complexes where solute molecule acts as hydrogen donor
except for Mn (II) complex in methanol with max = 258 nm due to the
presence of solute-solvent interaction through hydrogen bond formation.
For the same complex max of -* transition is blue shifted as the
dielectric constant of polar solvents increases. The n-* transitions are
detected in the wave length range (349-337), (378-335), (353) and (353346 nm) for Mn (II), Fe (III), Co (II) and Cu (II) complexes, respectively.
For Mn and Fe complexes, the red shift increases as the dielectric constant
.6
of the solvent increases due to stabilization solvation of excited state more
than ground state.(14-16) The results of calculation for 5,7-diiodo-8-hydroxy
quinoline and their complexes are collected in Tables (3-7). The multiple
regression (MCC) and the probability of variation (P), which are calculated
from the SPSS program, have been considered as a measure of goodness of
the fit.
Based on one-parameter equation, the parameters (E) and (M) plays
the important role for determining the spectral shifts for Fe-complex that
give high correlation (0.795 and 0.707) respectively. This indicates that the
* transition is affected by both solvent solute hydrogen bond and
dipolar interaction. The parameter M (dispersion and orientation, solute
permanent dipole-solvent induced dipole) is moderate correlation (0.583),
for Co-complex. The M parameter points to its effectiveness than the other
parameters. The data based on two parameters equation indicated that the
(M,N) and (K,M) gave higher correlation from their (MCC) values for 5,7diiodo-8-hydroxy quinoline. The (E,N) combination for the Mn-complex,
(K,M), (E,M) and (M,N) for iron (III) complex, (K,N) and (M,N) for cobalt
(II) complex, (E,K) and (E,N) for copper (II) complex are more effective
parameters. For the three parameters correlation the combinations of
(K,M,E), (E,M,N) and (K,M,N) gave good fit to the observed spectral
shifts for the organic compound, Table (3). For the Mn (II) complex the
(K,N,E) and (K,M,N), for the iron (III) complex (E,M,N), (K,M,E) and
(K,M,N) gave good fit to the observed spectral shifts. For the cobalt (II)
complex, the parameters (K,N,E) and (K,M,N) are good effective and the
.7
parameters (K,N,E), (E,M,N) and (K,M,E) for copper (II) complex are
more effective. The data based on the combination of all parameters
(K,M,N and E) gave good fit to the observed spectral shifts for all
compounds, Tables (3-7).
The dissociation constant of 5,7-diiodo-8-hydroxy quinoline is
determined in aqueous medium by different spectrophotometric methods:
half height,(17) modified limiting absorption(18) and Colleter methods
(19)
.The data pK values 9.8, 9.82 and 9.99, respectively.
I
I

OH


I
N
+ H+
I
OH
N
-
O
The reported dissociation constant of 8-hydroxy quinoline at 20°C
and 25°C are to 5.02 and 9.81, respectively.(20,21) It seem that Pk1 in the
DIHQ is absent in the oxine compound while the pK2 is nearly the same in
both compounds . This is probably related to the bulkiness of the iodine
atoms compared to the probable ionized proton.
Structure and mode of bonding of 5,7 diiodo-8-hydroxy quinoline and
their complexes
(1) The O-H bands at 3442 and 3065 cm-1 for the free ligand
becomes at 3386, 3422, 3445, 3462 and 3422 cm-1 for Mn (II), Fe (III),
Co (II), Cu (II) and Zn (II) complexes, respectively, and the second band in
.8
the free ligand is absent in all complexes. So the –OH group is involved on
complexation and/or the complexes are strongly associated with water
molecules,(22, 23) (2) the C=N at 1655 and 1611 cm-1 are disappeared for all
complexes indicating strong chelation through nitrogen atom, (3) the -OH
and -OH characteristic modes of vibrations for the –OH group at 1390 and
866 cm-1, respectively, in the free ligand are affected with different degrees
through complexation. The first band is disappeared and the second one is
shifted to a lower frequency for all complexes indicating the participation
of –OH group,(24) (4) the C-O band at 1368 and 1335 cm-1 in the free ligand
gave that the first band is shifted towards lower frequency and the second
one is disappeared to confirm M-O interaction, (5) The appearance of
some new bands in the metal complexes in the regions (652, 460), (646,
451), (653, 423) and (663 and 390 cm-1) are probably due to the formation
of M-O and M-N bands for Mn (II), Fe (III), Co (II), Cu (II) and Zn (II)
complexes , respectively.
Electronic spectral and magnetic properties
The magnetic moment values eff at room temperature and the nujol
mull electronic absorption spectrum are given in Table (1). The buff
MnL2.2H2O complex gave four bands at 35714, 29240, 23809 and 18797
cm-1 and room temperature eff = 5.8 B.M. The first two bands are due to
the effect of the metal ion on the -* electronic transitions of the free
ligands and charge transfer. The third and fourth bands are identified to the
complex itself with d-d electronic transition. The bands at 23809 and 18797
cm-1 are assigned to
6
A1g  4 T2g (D) and
6
A1g  4 T2g (G) transitions,
respectively,(25) suggesting octahedral geometry.(26) The dark brown iron
.9
complex [FeL2Cl2] 2H2O, gave four bands at 35714, 25000, 20202 and
15152 cm-1. The first two bands are due to the effect of the metal ion on the
-* electronic transitions of the free ligands and charge transfer. The broad
bands at 20202 and 15152 cm-1 are typical for octahedral complex with
2
E 2g  5 T2g electronic transition. The eff value of 6.1 B.M. supported such
view with high spin configuration. The dark green colour cobalt, [CoL 3],
gave charge transfer bands at 38462, 33333 and 27027 cm -1, while the
visible d-d electronic spectral bands at 22321 and 18797 cm-1 assigned the
transition
4
T1g (F)  4 T1g (P) of an octahedral cobalt complex.(27) The
measured magnetic moment value (5.4 B.M.) is of typical of octahedral
high spin.(28) The green copper complex, [CuL2], gave three bands at
35714, 27933 and 25000 cm-1 due to the effect of metal ion on the -*
electronic transitions of the free ligand and charge transfer. The other three
bands at 22026, 20921 and 16556 cm-1 could be assigned to 2 B1g  2 A1g ,
2
B1g  2 B1g and
2
B1g  2 E g transitions , respectively.(29) The eff value of
the complex is 1.82 B.M. which corresponds to one unpaired electron. All
the data of the copper complex assigned square planar geometry. From
analytical data, ir spectra of Zn (II) complex, ZnL2.4H2O, assigned
octahedral geometry. The proposed structures of the complexes are given in
the following skeletons:
.10
I
I
OH2
N
O
H
O
I I
O
2H2O
N
N
OH2
N
Fe
Mn
I
Cl
I
O
Cl
I
I
I
I
H
O
I
N
O
N
O
Co
I
Cu
N
I
N
O
N
O
I
I
OH2
N
O
Zn
I
N
O
OH2
I
I
2H2O
.11
.12
.13
.14
.15
.16
.17
.18
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.19
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