Tetra- and hexadentate Schiff base ligands and their Ni(II), Cu(II) and Zn(II) complexes. Synthesis, spectral, magnetic and thermal studies

Article abstract of DOI:10.1016/j.saa.2011.10.037

Tetradentate N₂O₂, N₄ Schiff bases, 1,2-bis(4-oxopent-2-ylideneamino) benzene (BOAB), 1-(4-oxopent-2-ylideneamino-2- [(2-hydroxyphenyl)ethylideneamino] benzene (OAHAB), 7,16-bis(4- chlorobenzylidene)-6,8,15,17-tetra-methyl-7,16-dihydro -5,9,14,18-tetraza- dibenzo[a,h] cyclo tetradecene (BCBDCT), 7,16-bis(2-hydroxy-benzylidene)-6,8,15, 17-tetramethyl-7,16-dihydro-5,9,14,18-tetraza-dibenzo [a,h] cyclo tetradecene (BHBDCT) and hexadentate N₄O₂ Schiff bases, 2,4-bis {2-[1-(2-hydroxyphenyl) ethylideneamino] phenylimino}-3-(2-hydroxybenzylidene) pentane (BHAPHP), 2,4-bis {2-[1-(2-hydroxyphenyl) ethylideneamino] phenylimino}-3-(4-chlorobenzylidene) pentane (BHAPCP) were prepared and characterized by elemental analysis, IR, UV-Vis, ¹H NMR and mass spectra. The solid complexes of the prepared Schiff base ligands with Ni(II), Cu(II) and Zn(II) ions were isolated and characterized by elemental and thermal analyses, IR, electronic and ESR spectra as well as conductance and magnetic susceptibility measurements. The results showed that most complexes have octahedral geometry but few can attain the tetrahedral arrangement. The TG analyses suggest high stability for most complexes followed by thermal decomposition in different steps. The kinetic and thermodynamic parameters for decomposition steps in Cu(II) complexes thermograms have been calculated.

Full text of DOI:10.1016/j.saa.2011.10.037

Spectrochimica Acta Part A 86 (2012) 276–288
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Tetra- and hexadentate Schiff base ligands and their Ni(II), Cu(II) and Zn(II)
complexes. Synthesis, spectral, magnetic and thermal studies
Tarek M.A. Ismail∗, Akila A. Saleh, Mosad A. El Ghamry
Department of Chemistry, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 June 2011
Received in revised form 10 October 2011
Accepted 14 October 2011
Tetradentate N2O2, N4 Schiff bases, 1,2-bis(4-oxopent-2-ylideneamino) benzene (BOAB), 1-(4-oxopent-
2-ylideneamino-2-[(2-hydroxyphenyl)ethylideneamino] benzene (OAHAB), 7,16-bis(4-chlorobenz-
ylidene)-6,8,15,17-tetra-methyl-7,16-dihydro -5,9,14,18-tetraza-dibenzo[a,h] cyclo tetradecene (BCB-
DCT), 7,16-bis(2-hydroxy-benzylidene)-6,8,15,17-tetramethyl-7,16-dihydro-5,9,14,18-tetraza-dibenzo
[a,h] cyclo tetradecene (BHBDCT) and hexadentate N4O2 Schiff bases, 2,4-bis {2-[1-(2-hydroxyphenyl)
ethylideneamino] phenylimino}-3-(2-hydroxybenzylidene) pentane (BHAPHP), 2,4-bis {2-[1-(2-
hydroxyphenyl) ethylideneamino] phenylimino}-3-(4-chlorobenzylidene) pentane (BHAPCP) were
prepared and characterized by elemental analysis, IR, UV–Vis, 1H NMR and mass spectra. The solid com-
plexes of the prepared Schiff base ligands with Ni(II), Cu(II) and Zn(II) ions were isolated and characterized
by elemental and thermal analyses, IR, electronic and ESR spectra as well as conductance and magnetic
susceptibility measurements. The results showed that most complexes have octahedral geometry but
few can attain the tetrahedral arrangement. The TG analyses suggest high stability for most complexes
followed by thermal decomposition in different steps. The kinetic and thermodynamic parameters for
decomposition steps in Cu(II) complexes thermograms have been calculated.
Keywords:
Schiff base derivatives
Schiff base complexes
Spectral
Magnetic
Thermal properties
© 2011 Elsevier B.V. All rights reserved.
elemental analysis, IR, UV–Vis, 1H NMR and mass spectra. Then,
their Ni(II), Cu(II) and Zn(II) complexes were prepared and the
1. Introduction
Metal complexes of Schiff bases occupy a central role in the
development of coordination chemistry [1–6], the interest in the
chemistry of Schiff base complexes lies in their importance in
some biological processes such as the biological functions of
bacteriorhodopsin [7], they can be used as biological models in
understanding the structure of biomolecules [8–11] or metallopro-
tein models [12–14]. This is due to their resemblance to natural
systems [15,16], also these compounds have received much atten-
tion as active parts of metalloenzymes [17,18]. Transition metal
complexes of Schiff base compounds are used as growth inhibiting
agents for most of bacteria and fungi [19–23] also they are widely
used as potential therapeutics [24], they are useful in health and
skin care [25]. The complexes of this type are also used as catalysis
[26–33] for various chemical reactions. The Schiff base complexes
of transition metal ions can be applied, particularly in the develop-
ment of agrochemical and pharmaceutical industries [34].
spectral, magnetic and thermal properties of these complexes were
studied in detail. Also, the kinetic and thermodynamic parameters
for decomposition steps in thermograms of Cu(II) complexes were
calculated.
2. Experimental
2.1. Materials
Most of the chemicals used in the present investigation
were BDH. Materials which are not generally provided into the
analar grade were of highest available purity. They included
o-phenylenediamine, acetylacetone, p-chlorobenzaldehyde, salicy-
laldehyde, o-hydroxyacetophenone, NiCl2·6H2O, CuSO4·5H2O and
ZnSO4·7H2O. The solvents used were methanol, ethanol, dioxan
and dimethylformamide (DMF), these solvents were either spec-
troscopically pure or purified by the recommended methods [35].
In the present work, we have prepared new Schiff base com-
pounds, (BOAB), (OAHAB), (BHAPHP), (BHAPCP), (BCBDCT) and
(BHBDCT). The structures of these compounds were studied by
2.2. The apparatus and physical measurements
The elemental microanalyses of the prepared compounds for
carbon, hydrogen, nitrogen, sulphur and chlorine were performed
in the microanalytical center, Cairo University. The infrared spectra
∗
Corresponding author. Tel.: +20 1525659182.
E-mail address: tarek.ismail70@yahoo.com (T.M.A. Ismail).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.10.037

T.M.A. Ismail et al. / Spectrochimica Acta Part A 86 (2012) 276–288
277
(1)
(1)
CH3
(2)
(3)
(2)
O
CH3
O
H3C
C
N
N
C
CH3
H2
H2
.
-CH3
(m/e = 273)
.
+
(3)
(2)
(M+1)
(1)
+
+
O
O
N
CH3
CH3
N
N
CH3
CH3
O
H3C
C
N
N
C
+
H2
H2
CH2
CH3
+
+
(m/e = 257)
(m/e = 57)
-CO
(m/e = 157)
-COCH3
CH3
CH3
CH3
.
(m/e =77)
N
-MeCN
+H
CH3
CH3
+
-MeCN
-C2H2
N
C
H
CH3
H3C
+
+
C4H3
N
(m/e =51)
(m/e =119)
(m/e = 132)
Scheme 1. Mass fragmentation pattern of (BOAB) compound.
were recorded using Bruker IR spectrometer in the microanalyt-
ical center of Azhar university within the range 4000–400 cm−1
and Perkin elmer 1430 IR spectrophotometer in the microanalyt-
2.3. Preparation of the Schiff base compounds
2.3.1. Preparation of the compound (BOAB)
Acetylacetone (2.00 g, 0.02 mol) was added dropwise to o-
phenylenediamine (1.08 g, 0.01 mol) in absolute ethanol (50 ml).
The reaction mixture was refluxed on a hot plate for 6 h. The product
was allowed to cool till room temperature, filtered off and recrys-
tallized from ethanol then dried under vaccum to give dark brown
crystals, yield 90%, m.p. 150 ◦C.
ical center of Tanta university within the range 4000–200 cm−1
.
IR spectra of the ligands and their solid complexes were obtained
in the solid state using KBr disc technique. Nuclear magnetic reso-
nance spectra were recorded by EM-3909, MHz NMR spectrometer,
in the microanalytical center of Cairo University using d6-DMSO,
which was obtained from Alderich chemical company. The ultra-
violet and visible spectra were recorded at room temperature over
the wave length 200–850 nm by Jasco, V-550, UV–Vis. spectropho-
tometer using 1.0 cm matched silica cells. The molar conductance
measurements were recorded using conductometer corning model
441. All measurements were performed at room temperature using
DMF as solvent. The magnetic moment of the prepared metal com-
plexes were determined at room temperature applying the Gouy’s
method using the magnetic susceptibility balance (CTM/Johnson
Matthey Alfa products). Molecular susceptibilities were correct for
diamagnetism of the component atoms applying the Pascal’s con-
stants [36]. Thermal analyses (TGA and DTA) of the solid complexes
were performed at national drug research center using TGA-50
thermogravimetric analyzer (Shimadzu) from ambient temper-
ature up to 800 ◦C with heating rate 10 ◦C/min using nitrogen
atmosphere. Mass spectra were recorded by the aid of the Ms-5988
spectrometer, in the microanalytical center of Cairo university.
The X-band ESR spectra of the powder complexes were recorded
using Joel spectrometer model JES-FE2XG equipped with an E101
microwave bridge in the microanalytical center of Tanta University.
The magnetic field was calibrated with 2,2-dipicryl hydrazyl. Metal
contents of complexes were determined complexometrically using
standard EDTA titration.
2.3.2. Preparation of 2-[(2-hydroxyphenyl)
ethylideneamino]-phenylamine
A
mixture of o-phenylenediamine (1.08 g, 0.01 mol) and
o-hydroxyacetophenone (1.36 g, 0.01 mol) in absolute ethanol
(50 ml) was refluxed for 8 h. The reaction mixture was concentrated
to 20 ml then cooled to room temperature, filtered off, recrystal-
lized from ethanol and dried under vaccum to give yellow crystals,
yield 78%, m.p. 95 ◦C.
2.3.3. Preparation of the compound (OAHAB)
A
mixture
of
2-[(2-hydroxyphenyl)ethylideneamino]-
phenylamine (2.26 g, 0.01 mol) and acetylacetone (1.00 g, 0.01 mol)
in absolute ethanol (50 ml) was refluxed for 8 h. The reaction
mixture was concentrated to 20 ml and then cooled to room
temperature, filtered off, recrystallized from ethanol and dried
under vacuum to give orange crystals, yield 85%, m.p. 192 ◦C.
2.3.4. Preparation of 2-hydroxy (or
4-chloro)-3-arylidene-2,4-pentanedione
A mixture of 2-hydroxybenzaldehyde (1.22 g, 0.01 mol) or 4-
chlorobenzaldehyde (1.40 g, 0.01 mol) and acetylacetone (1.00 g,

278
T.M.A. Ismail et al. / Spectrochimica Acta Part A 86 (2012) 276–288
0.01 mol) in absolute ethanol (50 ml) in the presence of two drops of
piperidine was refluxed for 4 h. The reaction mixture was concen-
trated to 20 ml and then cooled to room temperature, filtered off,
recrystallized from ethanol and dried under vaccum to give white or
yellow crystals, m.p. 90 ◦C, 75 ◦C, yields 73% and 76%, respectively.
2.3.5. Preparation of the compounds (BHAPHP) and (BHAPCP)
A mixture of 2-[(2-hydroxyphenyl)ethylideneamino]-phenyl-
amine (4.52 g, 0.02 mol) and 2-hydroxy-3-arylidene-2,4-penta-
nedione (2.04 g, 0.01 mol) or 4-chloro-3-arylidene-2,4-penta-
nedione (2.22 g, 0.01 mol) in absolute ethanol (50 ml) was refluxed
for 8 h. The reaction mixture was concentrated to 20 ml and
then cooled to room temperature, filtered off, recrystallized from
ethanol and dried under vacuum to give brown crystals, m.p. 179 ◦C
(BHAPHP) and 164 ◦C (BHAPCP), yields 75% and 78%, respectively.
2.3.6. Preparation of the compounds (BHBDCT) and (BCBDCT)
A
mixture of o-phenylenediamine (2.16 g, 0.02 mol) and
2-hydroxy -3-arylidene-2,4-pentanedione (4.08 g, 0.02 mol) or 4-
chloro-3-arylidene-2,4-pentanedione (4.45 g, 0.02 mol) in absolute
ethanol (50 ml) was refluxed for 6 h. The reaction mixture was con-
centrated to 20 ml then cooled to room temperature, filtered off,
recrystallized from ethanol and dried under vacuum to give brown
crystals, m.p. 129 ◦C (BHBDCT) and 138 ◦C (BCBDCT), yields 79% and
82%, respectively.
The purity of the prepared Schiff base compounds was exam-
ined by elemental analysis, IR, 1H NMR, UV–Vis and mass spectra.
Anal. Calcd (BOAB): C, 70.59; H, 7.35; N, 10.29. Found: C, 70.19;
H, 7.13; N, 9.92, Calcd (OAHAB): C, 74.03; H, 6.49; N, 9.09. Found:
C, 73.51; H, 6.42; N, 8.61, Calcd (BHAPCP): C, 75.18; H, 5.48; N,
8.77; Cl, 5.56. Found: C, 74.91; H, 5.64; N, 8.61 Cl; 5.78, Calcd
(BHAPHP)·2H2O: C, 73.20; H, 6.10; N, 8.54. Found: C, 72.93; H,
5.91; N, 8.31, Calcd (BCBDCT): C, 73.34; H, 5.09; N, 9.51; Cl, 12.05.
Found: C, 73.82; H, 5.05; N, 9.20; Cl, 11.95, Calcd (BHBDCT)·3/2
H2O: C, 74.61; H, 6.05; N, 9.67. Found: C, 74.32; H, 6.11; N, 9.92.
The color of the compound (OAHAB) was yellow while the another
compounds were brown. IR (cm−1), ꢀOH of lattice H2O molecules
3490–3528 for (BHAPHP) and (BHBDCT) compounds, ꢀOH phenolic
3350–3462 for (OAHAB), (BHAPCP), (BHAPHP) and (BHBDCT) com-
pounds, ꢀOH enolic 3048–3070, ꢀC 1704–1708, ꢀC 1620–1640
Fig. 1. Mass spectrum of (BOAB) compound.
O
N
for (BOAB) and (OAHAB) compounds, ꢀC N 1636–1645, 1590–1614
for (BHAPCP), (BHAPHP), (BCBDCT) and (BHBDCT) compounds. 1
H
H3C
H3C
H3C
CH3
NMR, ı(ppm), ıOH phenolic 9.60–12.30 for (OAHAB), (BHAPCP),
(BHAPHP) and (BHBDCT) compounds, ␦CH aromatic 6.70–8.20,
ı = CH 5.70–6.60, ıOH enolic 5.20–5.60 for (BOAB) and (OAHAB)
compounds, ıCH aliphatic 2.00–2.60. The broad diffuse signals
at 9.5–14.7 may be attributed to the presence of intramolecular
hydrogen bonds between the phenolic OH or the enolic OH groups
with the azomethine groups. UV–Vis spectra, ꢁmax(nm), the band
located at (239–289) range is due to the low energy ꢂ–ꢂ* tran-
sition of the aromatic system, C C (Lb–LA) [37], the band within
the (312–408) range can be assigned to ꢂ–ꢂ* transition within the
N
N
OH
O
N
N
O
O
CH3
H3C
CH3
(OAHAB)
(BOAB)
C
N groups and the band within the (430–485) range is due to
X
an intramolecular charge transfer within the whole molecule (CT).
In case of (BOAB) and (OAHAB) compounds, there is another band
within (273–342) range, due to ꢂ–ꢂ* transition of C O groups. The
mass spectrum of the Schiff base (BOAB) as an example for the
fragmentation of the Schiff bases under investigation is shown in
Fig. 1, The fragmentation mode of (BOAB) [the molecular ion peak
(M + 1)+• (m/e) = 273, I = 2.33)] occurs through three main pathways,
Scheme 1. The Schiff base compounds have the following structural
formulae:
CH3
CH
C
CH3
C
C
N
N
N
N
C
C
HO
OH
CH3
CH3
X = p-Cl (BHAPCP)
X = o-OH (BHAPHP)

T.M.A. Ismail et al. / Spectrochimica Acta Part A 86 (2012) 276–288
279
X
CH3
H3C
H3C
N
N
N
N
CH3
X
X = p-Cl (BCBDCT)
X = o-OH (BHBDCT)
2.4. Preparation of the solid complexes
The complexes ML were prepared by the reaction of Schiff
base ligands with the metal sulphate or chloride in a (1:1) (L:M)
molar ratio. 5 mmol of the metal salt, NiCl2.6H2O, CuSO4.5H2O or
ZnSO4.7H2O dissolved in ethanol (10 cm3) was added to 5 mmol
of the ligand dissolved in ethanol (20 cm3), the resulting solu-
tions were stirred for about 1 hour, then refluxed on a hot plate
from 6 to 8 hours. The solid complexes which separated out on hot
were filtered off after cooling to room temperature, washed with
small amounts of bidistilled water, ethanol and ether. The com-
plexes were dried in vacuo, then subjected to elemental analysis,
the results of microanalysis of the prepared complexes are collected
in Tables 1 and 2.
3. Results and discussion
On the basis of elemental analysis, the transition metal ion
complexes of Schiff base ligands were assigned to posses the com-
positions and molecular formulae listed in Tables 1 and 2. The
results reveal that the ligands (BOAB), (OAHAB), (BCBDCT) and
(BHBDCT) behave as neutral or dianionic tetradentate, while the
ligands (BHAPCP) and (BHAPHP) behave as neutral or dianionic
hexadentate towards the metal ions (Ni2+, Cu2+ and Zn2+).
The molar conductance of the metal complexes under investi-
gation are measured for 10−3 M solution in DMF, Tables 1 and 2.
Complexes (1, 3, 4, 5, 9, 10 and 13) have ˝m values in the range
8.0–13.0 ohm−1 cm2 mol−1 which fall within the range of nonelec-
and Cl−ions are involved
2−
trolytes [38]. This indicates that SO4
in the coordination sphere. Complexes (11), (12), (14), (15), (16)
and (17) have ˝m values in the range 72.6–87.1 ohm−1 cm2 mol−1
which fall within the range of 1:1 electrolytes [38]. This indicates
that SO4 and Cl− ions are existing partially or completely in the
2−
outer sphere. The complexes (2, 6, 7, 8 and 18) have ˝m values
in the range 136.2–147.0 ohm−1 cm2 mol−1 which fall within the
and Cl−
2−
range of 1:2 electrolytes [38]. This indicates that SO4
ions are in the outer sphere.
3.1. Thermal analyses (TGA and DTA), kinetic and
thermo-dynamic parameters studies of Cu(II) complexes
The results of thermal analyses (TGA and DTA) of Cu(II) com-
plexes were recorded in Tables 3 and 4. The TGA curves of Cu(II)
complexes show loss in weight within the temperature range
50–99 ◦C, which is due to removal of the lattice water molecules.
Also, the Cu(II) complexes show mass loss within the tempera-
ture range 102–180 ◦C, which is due to removal of the coordinated

Table 2
Elemental analysis and some physical properties of the ligands (BHAPHP), (BCBDCT), (BHBDCT) and their metal complexes.
Complex
M:L
Color
M.P. (◦C)
M. Wt. (gm)
Analysis (Calc. %) Found %
˝
(ohm−1 cm2 mol−1
)
m
% C
% H
% N
% S
% Cl
% M
(10)
(11)
(12)
(13)
(14)
(15)
(16)
(17)
(18)
[Ni3(BHAPHP)(H2O)4Cl3(OH)]·2H2O
[Cu2(BHAPHP)(H2O)6]SO4·2H2O
[Zn2((BHAPHP)(H2O)2]SO4·2H2O
[Ni2(BCBDCT)(H2O)2Cl4]·H2O
[Cu(BCBDCT)(H2O)2]SO4·2H2O
[Zn(BCBDCT)]SO4·5H2O
3:1 Brown
>300
>300
>300
>300
>300
>300
210
1025.6
985.0
916.6
902.4
820.54
840.3
699.6
711.54
928.6
(46.80) 46.04
(48.73) 48.29
(52.37) 51.83
(47.87) 47.19
(52.65) 51.97
(51.41) 50.96
(61.75) 61.30
(60.71) 60.83
(46.52) 46.44
(4.58) 4.21
(5.08) 4.15
(4.58) 4.49
(3.99) 4.27
(4.63) 4.13
(4.76) 4.77
(4.86) 5.83
(4.50) 5.33
(4.09) 4.80
(5.46) 6.14
(5.69) 6.25
(6.11) 6.11
(6.21) 6.24
(6.82) 7.27
(6.66) 7.88
(8.00) 8.99
(7.87) 7.51
(6.03) 6.27
–
–
–
–
–
–
–
–
(10.38) 10.22
–
–
(23.60) 23.80
–
–
(10.15) 10.19
–
–
(17.17) 16.90
(12.89) 12.69
(14.25) 13.92
(13.01) 12.80
(7.74) 8.20
(7.77) 7.34
(8.39) 8.10
(8.93) 8.50
(14.06) 13.81
11.1
78.0
72.6
11.0
78.4
86.8
87.1
74.9
136.2
2:1 Dark brown
2:1 Pale brown
2:1 Brown
1:1 Black
1:1 Brown
1:1 Yellowish green
1:1 Dark brown
2:1 Yellowish brown
[Ni(BHBDCT)Cl(H2O)]Cl
[Cu(BHBDCT)]SO4
[Zn2(BHBDCT)(H2O)2](SO4)2·H2O
>300
180
(6.89) 7.27
Table 3
Results of thermal analyses (TGA) and (DTA) of Cu(II) complexes of the ligands (BOAB), (OAHAB) and (BHAPCP).
Complex
Formula and structure of compound (M.wt)
Temperature range (◦C)
DTA peaks (◦C)
% loss in weight Found (Calc.)
Decomposed product lost
50–99
72 (exo)
140.17 (exo)
170 (exo)
5.46 (4.90)
3.86 (4.90)
9.84 (9.80)
Loss of two lattic H2O molecules
Loss of two coordinated H2O molecules
Loss of four coordinated H2O molecules
The anhydrous complex is thermostable up to 360 ◦
Loss of two H2SO4 molecules
Loss of C8H14O2
Loss of C6H4N2
Residue, [Cu2(O)2(CO)2]
(2)
[Cu2(BOAB)(H2O)6](SO4)2·2H2O
104–150
155–180
185–360
365–420
425–705
710–800
(735)
Thermal stability
25.61 (26.12)
20.15 (19.32)
14.03 (14.15)
21.05 (20.81)
8.75 (8.88)
Thermal stability
41.61 (42.66)
Thermal stability
9.35 (10.11)
40.29 (38.35)
4.67 (3.62)
Thermal stability
19.51 (19.33)
18.42 (19.17)
57.40 (57.88)
C
C
C
392(exo)
590 (exo)
738 (exo)
110–160
165–210
215–570
575–720
725–800
65.56 (exo)
456.97 (exo)
776 (endo)
62.61 (exo)
Loss of two coordinated H2O molecules
The anhydrous complex is thermostable up to 210 ◦
Loss of C11H11NO
(5)
(8)
[Cu(OAHAB)(H2O)2]
(405.5)
Loss of CH3CONH2 molecule
Residue, [Cu(C2O4H)2(C2O4H2)]
Loss of two coordinated H2O molecules
The anhydrous complex is thermostable up to 205 ◦
Loss of two H2SO4 molecules
Loss of C12H11Cl
Residue, [Cu2(OH)2(C14H13N2O)2]
105–140
145–205
210–395
400–800
[Cu2(BHAPCP)(H2O)2](SO4)2
(993.5)
311.39 (exo)
553.46 (exo)

T.M.A. Ismail et al. / Spectrochimica Acta Part A 86 (2012) 276–288
281
water molecules. The dehydrated complexes (2), (5), (8), (11)
and (14) are thermally stable up to 360 ◦C, 210 ◦C, 205 ◦C, 250 ◦C
and 195 ◦C, respectively, then the Cu(II) complexes show mass
loss within the temperature range 190–425 ◦C, which is due to
2−
removal of the SO4 ions. Finally the complexes undergo decom-
position of the organic ligands within the temperature range
up to 800 ◦C, leading to the formation of the final products
[Cu2(O)2(CO)2], [Cu(C2O4H)2(C2O4H2)], [Cu2(OH)2(C14H13N2O)2],
[Cu(C2O4)], [Cu(C2O4H)2 (C2O4H2)] and [Cu(C2O4)] for complexes
(2), (5), (8), (11), (14) and (17), respectively.
The DTA curves of the Cu(II) complexes show endothermic or
exothermic peaks in the temperature range 50–99 ◦C which are
due to removal of the lattic water molecules from the outer sphere,
also Cu(II) complexes show exothermic peaks in the temperature
range 102–180 ◦C which are due to removal of the coordinated
water molecules from the inner sphere. The DTA curves of Cu(II)
complexes also exhibit exothermic peaks within the temperature
range 190–425 ◦C which are due to removal of the SO42− ions exist-
ing outside the coordination sphere, after that the exothermic or
endothermic peaks within the temperature range up to 800 ◦C may
be due to lattice rearrangement, phase transformation or decom-
position of the organic ligands leading to the formation of the final
products [39].
The order, n and activation energy, E* of the decomposition steps
for Cu(II) complexes were determined from TGA results using the
Coats–Redfern equation [40]:
ꢀ
ꢁ
ꢂ
ꢃ
{1 − (1 − ˛)1−n
(1 − n)T2
}
M
T
ln
ln
=
+ B for n =/ 1
(1)
(2)
ꢄ
ꢅ
ꢂ
ꢃ
{− ln(1 − ˛)}
M
=
+ B for n = 1
T2
T
where M = −E*/R and B = ln(AR/˚E*); E*, R, A and ˚ are the activa-
tion energy, gas constant, pre-exponential factor and heating rate,
respectively, n = 0, 0.33, 0.5, 0.66, 1.
The other thermo kinetic parameters (ꢃH*, ꢃS*, ꢃG*) were cal-
culated using the relationships:
ꢃH∗ = E∗ − RT
ꢄ
ꢂ
ꢃ
ꢅ
Ah
KT
ꢃS∗ = R ln
− 1
ꢃG∗ = ꢃH∗ − TꢃS∗
where K is the Boltzmann constant and h is Plankꢀ s constant. The
order (n) and thermo kinetic parameters of the decomposition steps
for the chosen complexes are listed in Table 5. From the obtained
data, the following remarks can be pointed out:
(1) The ꢃS* values for complexes were found to be negative. This
indicates that the activated complex is more ordered than the
reactants and/or the reactions are slow [41].
(2) The values of ꢃG* increase significantly for the subsequently
decomposition stages due to increasing the values of TꢃS* from
one step to another which override the values of ꢃH*. This
increase reflects that the rate of removal of the subsequent
ligand will be lower than that of the precedent ligand [42].
This may be attributed to the structural rigidity of the remain-
ing complex after the explusion of one and more ligands, as
compared with the precedent complex, which requires more
energy for its rearrangement before undergoing any composi-
tional change.
(3) The positive values of ꢃH* means that the decomposition pro-
cesses are endothermic.

282
T.M.A. Ismail et al. / Spectrochimica Acta Part A 86 (2012) 276–288
Table 5
The order (n), temperature of decomposition and activation parameters (E*, ꢃH*, ꢃS* and ꢃG*) for decomposition of the Cu(II) complexes.
Complex
Step
Order (n)
T (K)
E* (KJ mol−1
)
ꢃH* (KJ mol−1
)
ꢃS* (KJ mol−1 K−1
)
ꢃG* (KJ mol−1
)
1st
0.66
0.00
0.33
0.66
0.33
0.00
0.00
0.66
0.00
0.66
0.00
0.00
0.00
0.00
0.50
0.33
0.66
0.50
0.66
0.00
0.33
0.33
0.00
0.66
0.66
72.0
160.2
228.0
532.5
590.0
738.0
65.6
457.0
776.0
62.6
311.4
553.5
79.8
169.7
345.0
520.0
700.0
75.0
3.138
3.921
4.494
7.667
7.669
8.722
3.003
7.947
9.153
2.972
5.328
8.296
3.121
4.012
5.519
7.335
8.573
3.100
3.549
4.416
6.076
9.132
3.721
6.454
7.889
2.540
2.590
2.599
3.242
2.766
2.589
2.729
4.149
2.704
2.452
2.740
3.696
2.458
2.602
2.652
3.014
2.756
2.477
2.552
2.829
2.752
3.182
2.873
2.997
2.695
−0.1703
−0.1799
−0.1779
−0.1744
−0.1802
−0.1817
−0.1810
−0.1794
−0.1810
−0.1697
−0.1842
−0.1875
−0.1813
−0.1799
−0.1756
−0.1818
−0.1721
−0.1737
−0.1704
−0.1821
−0.1805
−0.1820
−0.1826
−0.1750
−0.1726
14.802
31.410
43.160
96.110
109.084
136.684
14.603
86.135
143.160
13.075
60.100
107.477
16.926
33.131
63.234
97.55
123.226
15.505
23.000
37.610
74.952
133.494
21.498
75.797
110.570
(2)
2nd
3rd
4th
5th
6th
1st
2nd
3rd
1st
2nd
3rd
1st
2nd
3rd
4th
5th
1st
(5)
(8)
(11)
(14)
(17)
2nd
3rd
4th
5th
1st
120.0
191.0
400.0
716.0
102.0
416.0
625.0
2nd
3rd
3.2. Spectral measurements
The electronic absorption spectra of the metal complexes under
investigation were recorded within the range 12,500–25,000 cm−1
applying the nujol mull technique and in DMF solution. The data
obtained from these spectra are recorded in Table 8. The elec-
tronic spectra of Ni(II) complexes (4), (7), (10), (13) and (16)
exhibit two bands with no obvious difference on going from nujol
The main bands of IR spectra of the metal complexes and their
tentative assignments are listed in Tables 6 and 7. All solid com-
plexes (except complexes 7 and 17) exhibit broad bands around
3330–3480 cm−1 which are attributed to (OH of water and/or EtOH
molecules associated with the complexes. The disappearance of
mull to DMF solution at (13,793–14,084, 15,015–15,384), cm−1
.
These bands are assigned to 3A2g → T1g (F) and 3A2g → T1g (P)
transitions which may indicate octahedral geometry around Ni(II)
ions [53–55]. The electronic spectrum of Ni(II) complex (1) dis-
plays band at 13,698 cm−1 in DMF solution and at 14,706 cm−1
3
3
(
OH
enolic and/or (OH phenolic bands from the IR spectra of all
complexes (except 2, 6, 7 and 8), support the proton displacement
from the OH groups through the metal ions. In case of complexes
2, 6, 7 and 8, (OH enolic and/or (OH phenolic bands are shifted
to lower wavenumbers by 33–90 and 30–130 cm−1, respectively,
which indicates the participation of OH groups in coordination
to the metal ions through the lone pair of electrons on the oxy-
gen [43]. This is confirmed by the existence of new bands at
510–592 cm−1, which could be assigned to (M–O bands. The (C
in nujol mull which can be assigned to 3T1 → T1(P) transition
3
indicating tetrahedral geometry around Ni(II) ion. The electronic
spectra of Cu(II) complexes (8) and (17) in nujol mull show bands
at 15,384 and 15,151 cm−1, respectively, which can be assigned
to 2T2g → Eg transition within a tetrahedral structure. The posi-
2
bands are shifted to lower wavenumbers by 12–48 and 10–35 cm−1N
,
tions of the bands of Cu(II) complexes in nujol mull spectra exhibit
some shifts to lower wavelength in DMF solution to 16,129 and
15,873 cm−1, respectively, indicating the facile formation of six
coordinate species in DMF which is a coordinating solvent and
tetrahedral geometry in the solid state. In case of Cu(II) complexes
(2), (5), (11) and (14) the electronic spectra in DMF solution exhibit
bands at (13,986–14,124, 15,974–16,207) cm−1 and in nujol mull
at (13,888–14,084, 16,207–16,528) cm−1, which can be assigned to
indicating the coordination of the imino nitrogen atoms to the
metal ions. This can be supported by the existence of new bands at
452–496 cm−1 which could be assigned to (M–N bands [44]. Com-
plexes 1, 10 and 13 show new bands at 325–348 cm−1 which can
be assigned to (M–Cl. The appearance of tow bands at 312,310 and
290,295 for complexes 10 and 13 suggest that tow of Cl ions are
involved in bridging coordination [43]. The binuclear complexes 1,
3 and 6 show new bands at 600–680 cm−1, which can be assigned
2
2
2B1g → Eg and 2B1g → B2g transitions within octahedral struc-
to ␮-oxo, M–O–M [45–49]. The Cu(II) complex (2) shows a new
tures [56].
M
H O
δ
2
3.3. Magnetic properties of the metal complexes
weak band at 890 cm−1, which can be assigned to
out of
M
plane deformation of a water molecule acting as bridge between
two metal ions [50]. For the complexes 2, 6, 8, 11, 12, 14, 15,
17 and 18, the (S–O are situated at 1106–1160, 970–1110 and
The effective magnetic moments of the prepared metal com-
plexes were determined, the data obtained are listed in Table 8.
The observed magnetic moment values of Ni(II) complexes were
found to be in the range 2.50–2.74 B.M. These values indicate the
presence of two unpaired electrons in the d-orbital, therefore, the
complexes formed have either tetrahedral geometry as in complex
(1) or an octahedral geometry as in complexes (4), (7), (10), (13) and
(16). The values show the presence of some spin–spin interaction
606–640 cm−1 which supports the non coordinated nature of the
2−
SO4
(
ions [44]. For complexes 3 and 9, IR spectra show splitted
bands at 1164–1166, 1110–1112 and 1016–1018 cm−1 indi-
S–O
2−
cating the coordinated nature of SO4
ions [51,52].
around the central metal

Table 6
Important IR spectral data (cm−1) and their assignment for ligands (BOAB), (OAHAB), (BHAPCP) and their metal complexes.
Compound or complex
ꢀH2O and/or EtOH
ꢀOH phenolic
ꢀOH enolic
ꢀC
ꢀC
ꢀ(M–O–M)
ꢀM–O
ꢀM–N
␯
ꢀCl–M–Cl
Other bands
O
N
M–Cl
(BOAB)
–
3348
3480
3444
–
3430
3404
3420
–
–
–
–
3048
–
3015
–
3070
–
–
2980
1708
1640
1594
1612
1592
1620
1596
1595
1580
1645, 1610
1624, 1590
1618, 1575
1630, 1590
–
680
–
652
–
–
–
600
–
–
–
548
552
592
–
544
550
545
–
–
485
488
452
–
496
470
490
–
–
348
–
–
–
–
–
–
–
–
–
(1)
(2)
(3)
[Ni2(BOAB)Cl2]·2H2O
[Cu2(BOAB)(H2O)6](SO4)2·2H2O
[Zn2(BOAB)(SO4)]·1/2H2O
(OAHAB)
[Ni(OAHAB)(H2O)2]
[Cu(OAHAB)(H2O)2]
[Zn2(OAHAB)(H2O)(EtOH)](SO4)2
(BHAPCP)
–
–
–
ꢀS–O 1108, 970, 616
␯
2−
–
SO4 1166, 1112, 1018
3350
–
1704
–
–
–
(4)
(5)
(6)
–
–
–
–
–
–
–
–
3320
3456
3408
3326
–
ꢀS–O 1148,1110, 616
–
–
–
–
–
–
(7)
(8)
(9)
[Ni(BHAPCP)]Cl2
–
530
540
525
472
490
452
–
–
–
[Cu2(BHAPCP)(H2O)2](SO4)2
[Zn2((BHAPCP)(SO4)]·4H2O
3435
3440
–
–
ꢀS–O 1140, 1104, 628
2−
ꢀSO4 1164, 1110, 1016
Table 7
Important IR spectral data (cm−1) and their assignment for ligands (BHAPHP), (BCBDCT), (BHBDCT) and their metal complexes.
Compound or complex
ꢀH2O and/or EtOH
ꢀOH phenolic
ꢀC
ꢀM–O
ꢀM–N
ꢀM–Cl ꢀCl–M–Cl
Other bands
N
(BHAPHP)·2H2O
3528
3398
3450
3330
–
3438
3470
3444
3490
3350
–
3462
–
–
–
–
–
–
–
1638, 1590
622, 1580
1626, 1580
1616, 1570
1636
1610
1592
1595
1614
–
520
510
560
530
–
–
–
–
–
472
475
490
472
485
460
476
–
–
–
–
(10)
(11)
(12)
[Ni3(BHAPHP)(H2O)4Cl3(OH)]·2H2O
[Cu2(BHAPHP)(H2O)6]SO4·2H2O
[Zn2((BHAPHP)(H2O)2]SO4·2H2O
(BCBDCT)
325 310, 290
–
–
–
ꢀS–O 1160,1108, 640
ꢀS–O 1140,1102, 628
–
–
ꢀS–O 1112, 1016, 616
ꢀS–O 1106, 1030, 606
–
(13)
(14)
(15)
[Ni2(BCBDCT)(H2O)2Cl4]·H2O
[Cu(BCBDCT)(H2O)2]SO4·2H2O
[Zn(BCBDCT)]SO4·5H2O
(BHBDCT)·3/2H2O
331 312, 295
–
–
–
–
–
–
3363
(16)
(17)
(18)
[Ni(BHBDCT)Cl(H2O)]Cl
[Cu(BHBDCT)]SO4
–
–
–
1598
1590
1592
530
540
520
474
452
485
–
ꢀS–O 1110,1014, 620
ꢀS–O 1112,1016, 614
[Zn2(BHBDCT)(H2O)2](SO4)2·H2O
3430

284
T.M.A. Ismail et al. / Spectrochimica Acta Part A 86 (2012) 276–288
Fig. 2. ESR spectra of Cu(II) complexes (5), (11) and (17).
between the Ni(II) ions in the different complexes. The observed
magnetic moment values of Cu(II) complexes were found to be in
the range 1.52–1.67 B.M. this means that only one unpaired elec-
tron is present in the d-orbital [57]. Therefore, these complexes
have either tetrahedral geometry as in complexes (8) and (17) or
octahedral geometry as in complexes (2), (5), (11) and (14). For
complexes (2), (8) and (11) the results indicate some spin-spin
coupling due to antiferromagnetic interaction [58].
3.4. ESR spectra of Cu(II) complexes
ESR spectra of Cu(II) complexes have been recorded at room
temperature as shown in Fig. 2. The geff values are calculated and
recorded in Table 9. The shape of ESR signals and the geff values
which are 2.45, 2.65, 2.65 and 2.64 for Cu(II) complexes (2), (5),
(11) and (14), respectively, indicate octahedral geometries around
Cu(II) ions in these complexes, where three anisotropic signals are
observed. While in case of complexes (8) and (17) only two lines
are observed, the shape of signals and the geff value which are 1.87
and 1.89, respectively, may indicate tetrahedral geometries around
Cu(II) ions in these complexes. From the observed g-values of the
Cu(II) complexes, it is clear that gII > g which indicates that the
⊥
unpaired electron is predominantly in the dx2–y2 orbital [59–61]
giving 2B1g as the ground state. The observed data show that the gII
values are >2.0023 for complexes (2), (5), (11) and (14) and hence
the metal–ligand bonding in these complexes are essentially cova-
lent, while for complexes (8) and (17) the gII values are <2.0023,
hence the metal–ligand bonding in the complexes are of apprecia-
ble ionic character [62].

T.M.A. Ismail et al. / Spectrochimica Acta Part A 86 (2012) 276–288
285
Table 9
ESR data of Cu(II) complexes.
Complex no.
Complex formula
gII
g
⊥
geff.
Geometry
(2)
(5)
(8)
(11)
(14)
(17)
[Cu2(BOAB)(H2O)6](SO4)2·2H2O
[Cu(OAHAB)(H2O)2]
[Cu2(BHAPCP)(H2O)2](SO4)2
[Cu2(BHAPHP)(H2O)6]SO4·2H2O
[Cu(BCBDCT)(H2O)2]SO4·2H2O
[Cu(BHBDCT)]SO4
2.13
2.72
1.90
2.85
2.81
1.90
2.68
2.58
1.83
2.44
2.46
1.87
2.45
2.65
1.87
2.65
2.64
1.89
Octahedral
Octahedral
Tetrahedral
Octahedral
Octahedral
Tetrahedral
4. Conclusion
spectra as well as magnetic moments studies, the geometric struc-
tures of the complexes under investigation can be formulated as
follows:
Based on the above results gained from elemental analyses,
conductance measurements, thermal analyses, IR, UV–Vis, ESR
H3C
H3C
CH3
N
N
CH3
CH3
.2H2O
H
C
Ni
H
C
CH3
O
H3C
CH3
N
N
H2
O
(SO4)2.2H2O
OH
HO
O
Cu
Cu
Ni
O
OH2
H2O
H2
Cl
OH2
OH2
Cl
(2)
(1)

286
T.M.A. Ismail et al. / Spectrochimica Acta Part A 86 (2012) 276–288
(4)
(3)
(6)
(5)
(7)
(8)
(9)
(10)

T.M.A. Ismail et al. / Spectrochimica Acta Part A 86 (2012) 276–288
287
(12)
(11)
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(15)
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