Synthesis and spectroscopic characterization of gallic acid and some of its azo complexes

Article abstract of DOI:10.1016/j.molstruc.2012.01.041

A series of gallic acid and azo gallic acid complexes were prepared and characterized by elemental analysis, IR, electronic spectra and magnetic susceptibility. The complexes were of different geometries: Octahedral, Tetrahedral and Square Planar. ESR was studied for copper complexes. All of the prepared complexes were of isotropic nature. The thermal analyses of the complexes were studied by DTA and DSC techniques. The thermodynamic parameters and the thermal transitions, such as glass transitions, crystallization and melting temperatures for some ligands and their complexes were evaluated and discussed. The entropy change values, ΔS^#, showed that the transition states are more ordered than the reacting complexes. The biological activities of some ligands and their complexes are tested against Gram positive and Gram negative bacteria. The results showed that some complexes have a well considerable activity against different organisms.

Full text of DOI:10.1016/j.molstruc.2012.01.041

Journal of Molecular Structure 1014 (2012) 17–25
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis and spectroscopic characterization of gallic acid and some
of its azo complexes
c
Mamdouh S. Masoud a, Sawsan S. Hagagg a, Alaa E. Ali b, , Nessma M. Nasr
⇑
a Chemistry Department, Faculty of Science, Alexandria University, Alexandria, Egypt
b Chemistry Department, Faculty of Science, Damanhour University, Damanhour, Egypt
c Science Park for Pharmaceuticals, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 October 2011
Received in revised form 25 January 2012
Accepted 25 January 2012
Available online 4 February 2012
A series of gallic acid and azo gallic acid complexes were prepared and characterized by elemental anal-
ysis, IR, electronic spectra and magnetic susceptibility. The complexes were of different geometries: Octa-
hedral, Tetrahedral and Square Planar. ESR was studied for copper complexes. All of the prepared
complexes were of isotropic nature. The thermal analyses of the complexes were studied by DTA and
DSC techniques. The thermodynamic parameters and the thermal transitions, such as glass transitions,
crystallization and melting temperatures for some ligands and their complexes were evaluated and dis-
Keywords:
cussed. The entropy change values,
D
S#, showed that the transition states are more ordered than the
Gallic acid complexes
Azo derivatives
IR
UV spectroscopy
Biological activity
Thermal analysis
reacting complexes. The biological activities of some ligands and their complexes are tested against Gram
positive and Gram negative bacteria. The results showed that some complexes have a well considerable
activity against different organisms.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
acid [9]. Gallic acid molecule is essentially planar and has two
intramolecular hydrogen bonds between hydroxyl groups, the
Gallic acid, an organic acid, known as 3,4,5-trihydroxybenzoic
acid (C6H2(OH)3COOH), is found widely throughout the plant king-
dom. High gallic acid contents can be found in gallnuts, grapes,
sumac, witch hazel, tea leaves, hops, and oak bark. Gallic acid ex-
ists in two forms as the free molecule and as part of tannins. Pure
gallic acid is a colorless crystalline organic powder, salts and esters
of gallic acid are termed gallates [1]. It has many applications in
chemical research and industry such as being used as a standard
for determining the phenol content of various analytes by the
Folin–Ciocalteau assay [2] and also used for making dyes and inks
[3].
Gallic acid is commonly used in the pharmaceutical industry
because many in vivo and in vitro studies in humans, animals,
and cell culture have provided evidence for the following actions
of gallic acid. It shows cytotoxicity against cancer cells, without
harming healthy cells [4] and it can be used to treat albuminuria
and diabetes [5], also it seems to have antifungal and antiviral
properties [6], which is used as an antioxidant and helps to protect
human cells against oxidative damage [7]. It can be used as a re-
mote astringent in cases of internal hemorrhage [8] and can also
used to treat psoriasis and external hemorrhoids containing gallic
hydrogen atoms of the three hydroxyl groups are oriented in the
same direction around the ring and form intra-and intermolecular
hydrogen bonds. The crystal structure is stabilized by all available
intermolecular hydrogen bonds [10]. The two adjacent hydroxyl
groups are engaged in a complex [11] and the remaining hydroxyl
group is suggested to form hydrogen bonding with COOꢀ of the
other legend presented on the same molecule forming a ring like
structure.
Gallic acid is a strong chelating agent and forms complexes of
high stability with iron [12,13]. The complex starts from pH = 3
and continues to pH = 9. The degree of chelating increases as the
pH increase. Iron is attached to gallic acid through two adjacent
hydroxyl groups presented on aromatic ring. Neodymium gallates
were reported as a solid in which, metal to legend ratio was 1:2
and phenolic hydroxyl group vibrations were defined at 1282
and 1212 cmꢀ1 [14]. Complexes of lanthanides (III), from (LaALu)
and Y (III) with gallic acid were obtained as solids with general for-
mula Ln (C7H5O5) (C7H4O5)ꢁnH2O (n = 2 for LaAHo and Y:n = 0 for
(ErALu). The infrared spectrum of gallic acid shows a sharp absorp-
tion band of carboxylic group ACOOH at 1664 cmꢀ1 [14], absorp-
tion bands of dOH at 1428 and at 864 cmꢀ1 as well as mCAOH at
1320 cmꢀ1, while, lanthanides gallic acid complexes give mas OCO
ꢀ
at 1544–1528 cmꢀ1 and mas OCO for dihydrated complexes, which
ꢀ
⇑
are shifted to lower frequencies of about 8–12 cmꢀ1 and have
Corresponding author. Tel.: +20 111 5799866.
E-mail address: dralaae@yahoo.com (A.E. Ali).
not changed their position for anhydrous complexes (ErALu).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2012.01.041

18
M.S. Masoud et al. / Journal of Molecular Structure 1014 (2012) 17–25
2.2. Physical measurements
HO
HO
X
COOH
O
The KBr disk infrared spectra were recorded on Perkin–Elmer
1430 spectrophotometer. The electronic spectra were measured
by using Perkin Elmer spectrophotometer, model Lambda 4B, cov-
ering the range 200–900 nm. Molar magnetic susceptibilities, cor-
rected for diamagnetism using Pascal’s constants, were determined
at room temperature (298 °K) using faraday’s method .The appara-
tus was calibrated with Hg [Co (SCN)4]. The ESR spectra of the cop-
per complexes were recorded with a reflection spectrometer
operating at 9.75 GHz (X-Band) in a cylindrical resonance cavity
with 100 kHz modulation. The g-values were determined by com-
parison with DPPH signal (g = 2.0037). Thermal analysis (DAT and
DSC) were carried out in the temperature range 25–500 °C, and
the rate of heating was 10 °C/min.
N
N
HO
OH
HO
OH
OH
Gallic acid (H4L1)
I
X
H4L2 H5L3 H5L4
OH COOH
H
Fig. 1. The structure of gallic acid and its azo derivatives.
2. Experimental
The order of chemical reactions (n) was calculated via the peak
symmetry method by Kissinger [16,38]. The value of the decom-
posed substance fraction, (am), at the moment of maximum devel-
2.1. Synthesis of azo legends and their metal complexes
opment of reaction with T = Tm was determined from the relation
[17,39,18,40].
All the organic compounds (I) were prepared in a similar way
using the usual diazotization process [15]. The following abbrevia-
tions are given for the compounds under investigation: gallic acid
[H4L1], 2-(phenyl azo 3,4,5-trihydroxy benzoic acid) [H4L2], 2-(2-
hydroxy phenyl azo 3,4,5-trihydroxy benzoic acid) [H5L3] and 2-
(2-carboxy phenyl azo 3,4,5-trihydroxy benzoic acid) [H5L4]. The
structures of gallic acid and its azo derivatives are represented in
Fig. 1. Manganese, cobalt, nickel, copper, zinc, cadmium and uranyl
complexes were prepared by mixing 0.01 mol of metal chloride
salt in an ammonia solution. The reaction mixture was refluxed
for 1 h. The resulting solid complexes were removed by filtration,
then washed several times with water–ethanol and dried under
vacuum over CaCl2 .The metal content was determined by atomic
absorption technique, titrimetric with standard EDTA solution
using the appropriate indicator [15]. The elemental analysis data
for the complexes are given in Tables 1 and 2.
1
1ꢀn
ð1 ꢀ amÞ ¼ n
The values of collision factor, Z, are obtained from the following
equation:
!
!
E
E
RT2m
kTm
h
D
S#
R
z ¼
/ exp
¼
exp
RTm
where,
gas constant, / represents rate of heating (K sꢀ1), k represents the
Boltzmann constant and represents the Planck’s constant
[19,41]. The heat of transformation
H#, can be calculated from
the DTA curves [20,42]. In general, the change in enthalpy (
H#)
for any phase of transformation taking place at any peak tempera-
ture Tm can be given by the following equation:
S# H#/Tm.
DS
# represents the entropy of activation, R represents molar
h
D
D
D
= D
Table 1
Elemental analysis data, EAS and room temperature (298°K) magnetic moment values for H4L1 complexes.
Complex
% Calculated/(found)
M
k (nm)
leff
Geometry
C
H
Mn (H2L1)ꢁ4H2O
Co (H2L1)ꢁ2H2O
Ni (H3L1)2ꢁ4H2O
Cu (H2L1)ꢁ4H2O
Zn (H2L1)ꢁ3H2O
Cd (H2L1)ꢁ4H2O
UO2 (H2L1)ꢁ2H2O
18.6 (18.2)
22.4 (22.0)
12.4 (11.9)
22.0 (21.7)
22.7 (22.3)
31.9 (32.6)
50.2 (49.8)
28.4 (28.9)
31.9 (32.1)
35.8 (36.4)
29.2 (29.8)
29.2 (29.7)
23.8 (24.2)
17.7 (18.1)
4.0 (4.4)
3.0 (3.4)
3.8 (4.2)
4.1 (4.5)
4.1 (4.6)
3.4 (3.7)
1.7 (1.6)
300, 390, 450, 510
300, 389, 675
286, 314, 350, 460, 510
400, 485, 510, 565
300, 382, 486, 564
260, 450, 470
5.4
4.6
3.8
1.73
0.00
0.00
0.00
Octahedral
Tetrahedral
Octahedral
Square planar
Tetrahedral
Tetrahedral
Octahedral
300, 400, 500
Table 2
Elemental analysis data, EAS and room temperature (298°K) magnetic moment values for the prepared azo gallic acid complexes.
Complex
% Calculated (found)
k (nm)
leff
Geometry
M
C
H
N
X
Co (H3L2) (H4L2) Clꢁ4H2O
Ni (H3L2) (H4L2) Clꢁ4H2O
Cu (H4L2)Cl2ꢁ6H2O
7.9 (8.0)
8.2 (7.9)
43.9 (44.1)
43.9 (44.1)
30.3 (30.7)
47.9 (48.1)
3.3 (3.3)
3.3 (3.6)
3.8 (4.4)
3.0 (3.5)
7.8 (7.4)
7.8 (8.5)
5.4 (6.1)
8.6 (9.7)
4.9 (5.1)
4.9 5.1)
13.6 (14.1)
–
282, 375, 565
5.20
3.36
1.81
4.60
Octahedral
Octahedral
Square planar
Octahedral
274, 370, 470, 580
300, 370, 485, 545
300, 370, 470, 546
12.3 (12.0)
Cu 6.5 (6.8)
Ni 6.0 (5.3)
11.2 (11.0)
11.1 (11.2)
13.4 (13.3)
13.1 (12.8)
13.1 (13.2)
13.0 (12.7)
24.2 (24.5)
NiCu(H2L2)2 (H4L2)ꢁ2H2O
Co (H5L3)ꢁCl2ꢁ6H2O
Ni (H5L3)Cl2ꢁ6H2O
Cu (H5L3)Cl2ꢁ3H2O
Co (H3L4)ꢁ5H2O
Ni (H3L4)ꢁ4H2O
29.7 (30.8)
29.7 (30.2)
32.8 (33.2)
36.1 (36.6)
37.6 (38.1)
34.4 (34.8)
36.1 (36.5)
3.8 (4.2)
3.8 (4.1)
2.9 (3.5)
3.4 (3.6)
3.5 (3.7)
4.1 (4.4)
2.5 (2.8)
5.3)5.6)
5.3 (5.7)
5.8 (6.1)
6.0 (6.4)
6.2 (6.6)
5.7 (5.9)
6.0 (6.4)
13.3 (13.6)
13.3 (13.7)
14.7 (14.3)
–
–
–
–
350, 540, 600, 630
350, 535, 580, 606
325, 400, 630
306, 390, 556
300, 400, 475
300, 400, 530
300, 450
5.20
3.60
1.75
5.10
3.70
1.78
0.00
Octahedral
Octahedral
Square planar
Tetrahedral
Octahedral
Square planar
Tetrahedral
Cu (H3L4)ꢁ6H2O
Cd (H3L4)ꢁ2H2O

M.S. Masoud et al. / Journal of Molecular Structure 1014 (2012) 17–25
19
Table 3
Fundamental infrared bands (cmꢀ1) of H4L1 and its azo complexes.
Compound
H4L1
mOH
mC@O
mC@C and m CAC
mCAOH and dOH
dCAOH
dC@O
cOAH
cCO
H. bonding OH in COOH
733
3494
3279
2669
1666
1612
1540
1426
1318
1384
1266
1098
634
865
794
558
Mn (H2L1)ꢁ4H2O
3429
3287
–
1639
1593
–
–
–
–
–
–
–
793
–
–
1388
Co (H2L1)ꢁH2O
Ni (H3L1)2ꢁ4H2O
Cu (H2L1)ꢁ4H2O
Zn (H2L1)ꢁ3H2O
3417
3295
–
–
–
–
1606
1574
–
651
668
680
–
–
797
–
–
–
–
–
1383
3446
3263
–
–
–
–
–
–
1588
1383
1115
3449
2664
1597
–
1393
–
–
760
–
3460
–
2664
–
–
–
–
792
1563
–
1384
1116
Cd (H2L1)ꢁ4H2O
UO2 (H2L1)ꢁ2H2O
3665
3340
–
–
–
1595
1554
–
–
–
636
672
–
791
–
–
–
3398
–
2705
1615
1514
1431
1344
–
1260
1097
–
767
Co (H2L1).2H2O, Td
Mn (H2L1). 4H2O, Oh
Ni (H3L1) 2 .4H2O, Oh
UO2 (H2L1).2 H2O, Oh
M = Cd, Zn
Cu (H2L1). 4H2O, SP
Zn (H2L1). 3H2O, Td n = 1
Cd (H2L1).4H2O Td, n = 2
Fig. 2. The structures of the prepared gallic acid complexes.

20
M.S. Masoud et al. / Journal of Molecular Structure 1014 (2012) 17–25
phenolic hydroxyl with the formation of quinone structure [23].
3. Results and discussion
These bands are affected on coordination with metal ions, to pin-
point that the oxygen atom is a center for coordination with the
metal ions, also dC@O is a strong indicative that oxygen atom inter-
act with metal ions. The different modes of vibrations of CAC, C@C
and CAH are affected the complex, probably due to the aromaticity
of the formed chelate is different from the legend [23]. he uranyl
complex exhibits two bands at 942 and 825 cmꢀ1, which are as-
signed to the asymmetric stretching frequency m3 and symmetric
3.1. Infrared, electronic spectra and magnetic susceptibility of gallic
acid and its complexes
Table 3 collects the infrared spectra of gallic acid and its com-
plexes. Three bands were detected at 3494, 3279 and 2669 cmꢀ1
,
which are assigned to mOH. In case of manganese, cobalt, nickel, zinc
and cadmium complexes, the first two peaks shifted from their
positions and the third disappeared, whereas phenolic hydroxyl
groups participated in forming the complexes [21]. The mC@O of
the free legend is identified at 1666 cmꢀ1. This band is absent in
case of cobalt, nickel, copper, zinc, cadmium and uranyl complexes.
In case of manganese complex, the mC@O is shifted to lower fre-
quency of about 27 cmꢀ1. Such data are in favor of suggesting that
the carbonyl group is strongly affected on coordination with tran-
stretching frequency (m1), respectively, of the dioxouranium ion
[24]. The m3 value is used for the calculation of the force constant
(F) [25] for the bonding sites of the O@U@O as follows:
(m
3)2 = (1307)2 ꢂ (FUAO)/14.103,
value is found to be
)
FUAO
7.3 m dyne Aꢀ1 and RUAO = 1.08 (FUAO
ꢀ1/3 + 1.17. Also, the UAO
bond distance, RUAO is calculated [26] and equals to 1.72 Å. The
EAS of the black manganese-complex, [Mn (H2L1)ꢁ4H2O], gave four
bands. The first two peaks were at 300 and 350 nm, which are as-
sition [22]. H4L1 gave dOH
, cOH and mCAO modes of vibrations. Such
data favored the carboxylate radical as possible oxidation of the
signed to 6 1g ? 4A1g, while the third at 450 nm and that is due to
A
Table 4
Fundamental infrared bands (cmꢀ1) of H4L2, and its complexes.
Compound
H4L2
mOH
mC@O
mC@C and mCAC
m N@N
dC@O and cCO
cOAH
H. bonding OH in COOH
750
mMAO
MAN
3452
3218
3033
1670
1595
1445
1493
690
835
–
–
Co (H3L2) (H4L2) Clꢁ4H2O
Ni (H3L2) (H4L2) Clꢁ4H2O
Cu (H4L2)Cl2ꢁ6H2O
3340
3060
–
–
–
1591
–
1506
1504
1498
692
694
696
833
–
744
746
750
513
511
507
609
613
–
3352
3060
1587
–
3433
3344
3058
1589
–
839
Ni Cu (H2L2)2 (H4L2)ꢁ2H2O
3367
3056
–
1589
–
1498
694
–
756
478
621
Table 5
Fundamental infrared bands (cmꢀ1) of H5L3 and its complexes.
Compound
H5L3
mOH
mC@O
mC@C and mCAC
mN@N
dC@O and cCO
cOAH
H. bonding OH in COOH
753
mMAO
MAN
3312
1681
1606
1518
1604
–
1597
1568
–
1452
–
1451
663
818
–
–
Co (H5L3)ꢁCl2ꢁ6H2O
Ni(H3L4)ꢁ4H2O
3344
3340
3342
1654
–
668
–
756
761
764
592
445
446
640
541
534
1383
1383
1114
1117
680
696
Cu (H3L4)ꢁ6H2O
1599
1446
Table 6
Fundamental infrared bands (cmꢀ1) of H5L4 and its complexes.
Compound
H5L4
mOH
mC@C and m CAC
mN@N
mCAOH and dOH
dC@O and cCO
cOAH
H. bonding OH in COOH
758
mMAO
mMAN
3367
3203
3072
1710
1601
1452
1491
688
879
–
–
Co (H3L4)ꢁ5H2O
3321
3224
3217
–
1575
–
–
687
–
759
445
503
Ni (H3L4)ꢁ4H2O
Cu (H3L4)ꢁ6H2O
Cd (H3L4)ꢁ2H2O
3340
1597
1568
–
–
–
–
680
696
684
–
761
764
759
445
446
437
541
534
511
1383
3342
–
1599
1446
–
1383
839
–
3406
–
1579
–
1388

M.S. Masoud et al. / Journal of Molecular Structure 1014 (2012) 17–25
21
6A1g ? 4T2g transition, and the last band was at 510 nm, which is
assigned to 6A1g ? 4T1g transition [27,28]. Their room temperature
leff value of 5.4 B.M typified the existence of Octahedral configura-
tion. The black cobalt-complex, [Co (H2L1)ꢁ2H2O] gave three bands
COOH
N
N
.
6 H O
2
Cu
O
H
Cl
HO
Cl
OH
M = Ni, Co
Co (H3L2) (H4L2) Cl.4H2O, Oh
Cu (H4L2)Cl2. 6H2O, SP
Ni (H3L2) (H4L2) Cl.4H2O, Oh
COOH
COOH
HO
COOH
N
N
N
O
N
OH
N
HO
Ni
OH
N
O
O
.
3 H O
H
2
O
OH
2
Cu
Cu
HO
O
Cl
HO
O
OH
2
N
H
Cl
OH
N
COOH
Cu (H5L3)Cl2. 3H2O, Td
Ni Cu(H2L2)2 (H4L2)2H2O, Oh
COOH
HOOC
COOH
N
N
H
.
H O
4
2
N
O
OH HO
.
2
H O
N
2
O
HO
Cl
M
OH
O
2
OH
HO
2
i
N
Cl
H
O
OH
M= Co, Ni
2
OH
Co (H5L3) .Cl2.6H2O, Oh
Ni (H5L3)Cl2.6H2O, Oh
2
Ni (H3L4).4H2O, Oh
M= Cu , Cd
Co (H3L4). 5H2O
Cu (H3L4). 6H2O, SP n=5
Cd (H3L4). 2H2O, Td n= 1
Fig. 3. The structures of the prepared azo gallic acid complexes.

22
M.S. Masoud et al. / Journal of Molecular Structure 1014 (2012) 17–25
at 300, 389 and 675 nm (broad in nature), 4A2 ? 4T1 (P) transition
of Td structure [29]. Their room temperature leff value of 4.6 B.M
verified such geometry. The black nickel-complex, [Ni (H2L1)
(H4L1) .4H2O] gave five bands at 286, 314, 320, 460 and 510 nm
and their leff value, which equals 3.8 B.M of Octahedral structure
[30]. The black copper-complex, [Cu (H2L1)ꢁ4H2O] gave four bands
at 400, 485, 510 and 565 nm, typified the presence of Square Planar
stereochemistry mainly of 2B1g ? 2B2g electronic transition in D4h
symmetry [31]. The room temperature magnetic moment value,
3.3. ESR of copper complexes
The room temperature polycrystalline X-band ESR spectra of
[Cu (H2L1)ꢁ4H2O], [Cu (H4L2) Cl2ꢁ6H2O], [Cu (H5L3) Cl2ꢁ3H2O] and
[Cu (H3L4)ꢁ6H2O] complexes gave similar spectral patterns, Fig. 4.
All complexes are isotropic in nature with gs values at 2.14, 2.48,
2.09 and 2.11 and (A) values at 280, 200, 210 and 300, respectively.
The spectra show broad signals, which might be due to the poly-
meric nature of these complexes. These data resulted due to isotro-
pic spectral feature [41,42].
leff, is 1.73 B.M. The black zinc and cadmium complexes, [Zn
(H2L1)ꢁ3H2O], [Cd (H2L1)ꢁ4H2O], respectively, gave four bands at
300, 382, 486 and 564 nm for zinc complex and three bands at
260, 450 and 470 nm for cadmium complex. Both complexes are
diamagnetic. The EAS of the brown uranyl-complex, [UO2
(H2L1)ꢁ2H2O] gave three bands, the first two peaks were at 300
and 400 of charge transfer, probably ligand ? OdbndU@O, while
theþ last band at 500 nm can be definitely assigned to the
3.4. Thermal analysis
The (DTA) for H4L1, H4L2, H5L3 and H5L4 compounds and their
complexes are presented in Table 7. The change of entropy,
D
S#,
values for all complexes, are nearly of the same magnitude and
lie within the range of (ꢀ0.27 to ꢀ0.32) kJ Kꢀ1 moleꢀ1. So, the tran-
sition states are more ordered, the fraction appeared in the calcu-
lated order of the thermal reaction, n, confirmed the reactions
proceeded in the complicated mechanisms. The calculated values
of the collision parameters, Z, showed a direct relation to Ea [43].
The values of the decomposed substance fraction (am), at maxi-
mum development of the reaction were calculated. It is nearly with
the same magnitude and lies within the range 0.5–0.8. Based on
P
1
!
2p4 transition [32].
g
From the analytical data, and the foregoing spectral and mag-
netic moment results, gallic acid is of bidentate attachment
through two oxygen atoms in the hydroxyl group on the reaction
with transition metal salts of Mn (II), Co (II), Ni (II), Cu (II), Zn
(II), Cd (II), UO2 (II) and so the structures are suggested as in
Fig. 2.
least square calculations, the lnDT versus 1000/T plots for all com-
plexes gave straight lines from which, the activation energies were
calculated [44].
DSC is a technique used to study the thermal transitions of a
compound, such as glass transitions, crystallization and melting.
3.2. Infrared, electronic spectra and magnetic studies of azo gallic acid
complexes
The fundamental bands of azo gallic acid compounds and their
complexes are given in Tables 4–6. By comparing the infrared
spectra of the complexes with that of the free legend, it should
be possible to determine the binding sites. The vibration frequen-
cies of coordinated functional groups (e.g.
mOH, mC@O, dOAH,
N@N,. . .) were affected with different degrees. In case of H4L2
and H5L4, three bands appeared at 3452, 3218, 3033 cmꢀ1 and
3367, 3203, 3072 cmꢀ1, respectively. While H5L3 legend gave a
broad band at 3312 cmꢀ1, which is assigned to
mOH, [33–35] (Ta-
bles 4 and 5). Some changes occurred on the complex, the data in
such region are related either to the AOH group which affected
the coordination or to the existence of water molecule. Hydrogen
bonded structures were expected due to intra-molecular H-bond-
ing between the azo group and the o-carboxy H-bonding of the
type OAHꢁ ꢁ ꢁN between the AOH or ACOOH substituent and the
N@N group [36–39]. The mC@O of H4L2, H5L3 and H5L4 legends
are at 1670, 1681 and 1710 cmꢀ1, respectively [22]. This peak
was absent in all complexes, suggesting that the carbonyl group
is strongly affect the coordination with transition metal ions
either by direct interaction between the lone pair of electrons
of the carbonyl group with metal ion or through tautomerization.
Also, dC@O vibration band led to the same conclusion. H4L2, H5L3
and H5L4 compounds gave bands at 1493, 1452 and 1491 cmꢀ1
,
respectively, which identified the azo vibration [36–38]. The shift
of this band in all complexes indicated that the azo group is in-
volved in coordination. The presence of cC@O, mC@O modes of
vibrations in the metal complexes, suggests that the oxygen atom
is also a center of coordination [23]. New bands appeared in all
azo gallic acid complexes in the frequency ranges 437–
592 cmꢀ1 and 503–640 cmꢀ1, which are attributed to mMAN and
mMAO, respectively. Table 1 illustrates the spectral, electronic
transitions and magnetic properties of the complexes. The data
indicated the existence of most complexes in Octahedral and Tet-
rahedral geometries [29,31,40], except the copper complexes
which is Square Planar. From the analytical data, electronic spec-
tra and magnetic moment results, the structures are suggested as
in Fig. 3.
Fig. 4. X-Band ESR spectra of copper complexes.

M.S. Masoud et al. / Journal of Molecular Structure 1014 (2012) 17–25
23
Table 7
DTA analysis of gallic acid and its azo complexes:
Compound
H4L1
Type
Tm (K)
D
E (kJ molꢀ1
)
n
am
D
S– (kJ Kꢀ1 molꢀ1
)
D
H– (kJ molꢀ1
)
103 (Z sꢀ1
)
Endo
Endo
Exo
Endo
Exo
Exo
Exo
Endo
Exo
Exo
Endo
Exo
Exo
Exo
Exo
397.5
540.6
721.8
377.3
625
676.3
697
383.4
613
664.1
372.5
645.5
383
833.3
873
109.1
439.8
50.74
55.27
10.3.70
225.5
58.92
37.41
101.6
169.5
18.7
1.441
1.206
0.501
1.491
0.864
1.029
1.676
1.385
0.616
2.02
1.627
1.61
1.496
0.492
2.3
1.465
0.957
0.658
1.353
1.206
1.543
0.949
0.912
1.393
1.373
1.156
1.186
0.55
1.57
1.54
1.69
1.94
0.85
1.7
0.7
1.2
1.6
1.9
0.83
0.86
1.608
1.182
0.891
0.97
0.6
0.6
0.7
0.6
0.7
0.6
0.5
0.6
0.7
0.5
0.5
0.5
0.6
0.8
0.5
0.6
0.6
0.7
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.7
0.5
0.6
0.5
0.5
0.7
0.5
0.7
0.6
0.5
0.5
0.7
0.7
0.5
0.6
0.7
0.6
0.6
0.6
0.7
0.6
ꢀ0.29
ꢀ0.29
ꢀ0.31
ꢀ0.3
ꢀ117.2
ꢀ156
ꢀ225
ꢀ113
ꢀ189
ꢀ201
ꢀ216
ꢀ116.2
ꢀ185.4
ꢀ199
ꢀ115
ꢀ192
ꢀ111
ꢀ270
ꢀ267
ꢀ115
ꢀ209
ꢀ181
ꢀ189
ꢀ212
ꢀ115
ꢀ175
ꢀ204
ꢀ106
ꢀ177
ꢀ186
ꢀ209
ꢀ108
ꢀ180
ꢀ254
ꢀ290
ꢀ110
ꢀ182
117.4
ꢀ184.2
ꢀ202.7
ꢀ161.8
ꢀ114.7
ꢀ216.4
ꢀ253.6
ꢀ116
ꢀ210
ꢀ200.3
ꢀ173.8
166.2
ꢀ124
ꢀ190
ꢀ217
0.033
0.098
0.008
0.018
0.02
0.04
0.01
0.012
0.02
0.031
0.006
0.036
0.064
0.002
0.02
0.006
0.003
0.089
0.168
0.077
0.007
0.096
0.026
0.114
0.017
0.032
0.005
0.063
0.771
0.217
0.003
0.031
0.035
0.008
0.023
0.076
0.039
0.007
0.014
0.054
0.012
0.012
0.01
Co (H2L1)ꢁH2O
ꢀ0.3
ꢀ0.3
ꢀ0.31
ꢀ0.3
Ni (H3L1)2ꢁ4H2O
ꢀ0.3
ꢀ0.3
Cu(H2L1)ꢁ4H2O
ꢀ0.31
ꢀ0.3
193.1
203.9
14.37.00
143
H4L2
ꢀ0.29
ꢀ0.32
ꢀ0.31
ꢀ0.3
Co(H3L2) (H4L2)Clꢁ4H2O
Ni (H3L2) (H4L2) Clꢁ4H2O
Exo
373
18.7
658.7
623.6
663
723
373
605
678
373
583
623
663.2
373
658.9
888
903
373
612.5
383
611.4
693
546.7
373
705
853.7
383
682.2
652.6
555.5
573
404.4
623
1873
459.9
925.3
464.6
20.33
480.9
144
352.8
82.78
166.1
25.73
196
4230
1605
24.71
95.5
179.1
24.4
ꢀ0.31
ꢀ0.29
ꢀ0.29
ꢀ0.29
ꢀ0.31
ꢀ0.29
ꢀ0.3
Exo
Exo
Exo
Exo
Exo
Cu(H4L2)Cl2ꢁ6H2O
Ni Cu(H2L2)2 (H4L2)ꢁ2H2O
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
Exo
ꢀ0.28
ꢀ0.3
ꢀ0.3
ꢀ0.32
ꢀ0.29
ꢀ0.27
ꢀ0.29
ꢀ0.32
ꢀ0.29
ꢀ0.3
H5L3
Co(H5L3) Cl2ꢁ6H2O
Ni (H5L3) Cl2ꢁ6H2O
ꢀ0.3
117.1
436.1
179.1
20.5
ꢀ0.3
ꢀ0.29
ꢀ0.29
ꢀ0.3
Cu(H5L3)Cl2ꢁ3H2O
H5L4
79.2
ꢀ0.3
383.2
39.53
68.23
68.2
23.86
395.5
30.44
76.28
399.9
ꢀ0.29
ꢀ0.3
Co (H3L4)ꢁ5H2O
ꢀ0.31
ꢀ0.3
Ni (H3L4)ꢁ4H2O
Cu (H3L4)ꢁ6H2O
ꢀ0.31
ꢀ0.29
ꢀ0.31
ꢀ0.31
ꢀ0.29
0.005
0.083
0.009
0.015
0.065
1.08
Cd (H3L4)ꢁ2H2O
1.163
0.859
1.136
738.8
DSC curves are obtained for H4L1 and its Ni-complex, Fig. 5, which
are done under a flow of N2 at heating rate 10 °C/min in the tem-
perature range 25–500 °C. It is clear that there are no glass transi-
tion temperatures (Tg) for both H4L1 and its Ni-complex, where the
crystallization temperatures (Tc) for both systems were at 124,
110.7 °C, respectively. The melting temperatures (Tm) are at 449
and 392.6 °C, respectively. The heat capacity can be determined
by dividing the heat flow by the heating rate. The variation of Cp
versus T can be represented using Debye model as the following
relations [45,46]:
R is the universal gas constant equals 8.3 J/mole/K and hD is Debye
temperature, which defined as the separate temperature between
Cp
T
different temperature. By plotting
as y-axis and T2 as x-axis, a
straight line is obtained with a slope equals a, also the intersection
with y-axis gives the coefficient (c), Table 8.
3.5. Biological activity study
In this study, four microorganisms representing different micro-
bial categories, Gram-positive (Staphylococcus aureus), Gram-
negative (Escherichia coli, Pseudomonas aeruginosa) and one Yeast
CP
Cp
¼
a
T3 þ
cT;
¼
a
T2
þ
c
ð1Þ
T
where (a) is the slope of the line and b is the intersection of the line
Table 8
The slopes and intercept for DSC curves of gallic acid and its Ni-complex.
with y-axis (Cp axis), Cp is the specific heat at constant volume,
constant equals 10ꢀ4 cal/g. mole.
According to Debye model [46]:
rffiffiffiffiffiffiffiffiffiffiffi
c is
¼
a
T2
þ c
CꢀP
Compound
Cp = aT + b
T
a
B
c
A
H4L1
0.01
0.03
ꢀ0.54
ꢀ8.47
ꢀ0.225
ꢀ0.012
2 ꢂ 10ꢀ6
234R
hD3
3
234R
a
a
¼
;
hD
¼
[Ni (H3L1)2ꢁ4H2O]
2 ꢂ 10ꢀ7

24
M.S. Masoud et al. / Journal of Molecular Structure 1014 (2012) 17–25
Fig. 5. DTA and DSC curves for gallic acid and its Ni-complex.
Table 9
Biological activities of some selected ligands and their metal complexes.
Compound
G+ bacteria
Gꢀ bacteria
Yeast
Staphylococcus aureus
Escherichia coli
Pseudomonas aeruginosa
Candida albicans
UO2 (H2L1)ꢁ2 H2O
H4L2
+
+
+
+
+
+
+
+
+
+
ꢀ
ꢀ
ꢀ
ꢀ
+
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Ni Cu(H2L2)2ꢁ(H4L2)ꢁ2H2O
ꢀ
H5L3
+
Co(H5L3) Cl2ꢁ6H2O
Cu (H3L4)ꢁ6H2O
ꢀ
ꢀ
(Candida albicans) were used. The study included six compounds,
ions (Co, Ni Cu mixed metal, Cu and UO2). The minimum inhibition
concentrations (MIC) for the tested compounds were determined
two legends (H4L2 and H5L3) and four complexes of different metal

M.S. Masoud et al. / Journal of Molecular Structure 1014 (2012) 17–25
25
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