Structural and characterization of novel copper(II) azodye complexes

Article abstract of DOI:10.1016/j.saa.2011.08.070

The synthetic methods of novel Cu(II) and adduct complexes, with selective azodyes containing nitrogen and oxygen donor ligands have been developed, characterized and presented. The prepared complexes fall into the stoichiometric formulae of [Cu(L_n

Full text of DOI:10.1016/j.saa.2011.08.070

Spectrochimica Acta Part A 83 (2011) 490–498
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Structural and characterization of novel copper(II) azodye complexes
A.Z. El-Sonbati∗, M.A. Diab, A.A. El-Bindary, S.G. Nozha1
Chemistry Department, Faculty of Science (Demiatta), Mansoura University, Demiatta, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 June 2011
Received in revised form 25 August 2011
Accepted 29 August 2011
The synthetic methods of novel Cu(II) and adduct complexes, with selective azodyes containing nitrogen
and oxygen donor ligands have been developed, characterized and presented. The prepared complexes
fall into the stoichiometric formulae of [Cu(Ln)2](A) and [Cu(Ln)2(Py)2](B), where two types of complexes
were expected and described. In type [(A) (1:2)] the chelate rings are six-membered/four coordinate,
whereas in type [(B) (1:2:2)] they are six-membered/six coordinate. The important bands in the IR spectra
and main 1H NMR signals are tentatively assigned and discussed in relation to the predicted assembly of
the molecular structure. The IR data of the azodye ligands suggested the existing of a bidentate binding
involving azodye nitrogen and C–O oxygen atom of enolic group. They also showed the presence of Py
coordinating with the metal ion. The coordination geometries and electronic structures are determined
from the framework of the proposed modeling of the formed novel complexes. The complexes (1–5) exist
in trans-isomeric [N,O] solid form, while adduct complexes (6–10) exist in trans isomeric (Py) form. The
square planar/octahedral coordination geometry of Cu(II)/adduct is made up of an N-atom of azodye, the
deprotonated enolic O-atom and two Py. The azo group was involved in chelation for all the prepared
complexes. ESR spectra show the simultaneous presence of a planar trans and a nearly planar cis isomers in
the 1:2 ratio for all N,O complexes [Cu(Ln)2]. The ligands in the dimmer are stacked over one another. In the
solid state of azo-rhodanine, the dimmers have inter- and intramolecular hydrogen bonds. Interactions
between the ligands and Cu(II) are also discussed.
Keywords:
Structural and characterization
Cu(II) and mixed ligand azo complexes
Hydrogen-bonding
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
class of substances which have furnished many useful drugs and
other substances of value in selectively used in medicine for their
Interest in the study of azodye has been growing because of their
antimicrobial, anti-tuberculosis, and anti-tumor activities [1–4].
Azodyes play also an important role in inorganic chemistry, as they
easily form stable complexes with most transition metal ions. The
behaviour of azodye complexes has attracted the attention of the
bioinorganic chemists since a number of these complexes are rec-
ognized to serve as models for biologically important species [5–7].
Azo sulphadrug is a subject of current and growing interest and that
may have numerous applications, e.g., anticancer [8], antibacterial
[9], antiviral [10], antifungal [11] and other biological properties
[12,13]. Azo sulphadrug containing moieties are of great interest
because of their great versatility as ligands [14], due to presence of
several potential donor atoms, their flexibility and ability to coor-
dinate in either neutral or deprotonated form. They also contain
antibacterial properties. The combined antibacterial activity of sul-
phanamides and antimicrobial activity of heavy metal with a view
to established the relationship and importance of metal–drug inter-
actions have investigated [16]. The metal chelates of sulphadrugs
have been found to be more bacteriostatic than the drugs them-
selves [17].
In continuation of our studies on the ligating properties of azo
sulphadrug, we report herein the preparation and characterization
of copper(II) complexes with 5-(4ꢀ-derivatives phenylazo)-3-
(4-methoxyphenyl)-2-thioxothiazolidinone (HLn) and pyridine
adduct of copper(II) complexes of HLn.
2. Experimental
C
N–NH structure unit, which form a strong chelate ring giving
The standard chemical rhodanine, aniline and 4-alkyl-anilines
(alkyl: OCH3, CH3, Cl and NO2; Aldrich Chemical Co.) were used
without any further purification.
possible electron delocalization associated with extended conju-
gation that may affect the nature of the complex formed. They can
yield complexes some of which are biologically relevant [15]. Metal
binding substances, many of which function by chelation, form a
2.1. Preparation of 3-(4-methoxyphenyl)-2-thioxo-
4-thiazolidinone
∗
Corresponding author. Tel.: +20 60081581; fax: +20 502254000.
E-mail address: elsonbatisch@yahoo.com (A.Z. El-Sonbati).
Abstracted from her M.Sc..
3-(4-Methoxyphenyl)-2-thioxo-4-thiazolidinone was prepared
by adding equimolar amounts of 4-methoxyaniline to a solution of
1
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.08.070

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 83 (2011) 490–498
491
trithiocarbodiglycolic acid [18] in bidistilled water with constant
stirring on a steam bath. The white precipitate was filtered off,
washed with hot bidistilled water, and recrystallized from abso-
lute ethanol, empirical formula C10H9NO2S2 (molecular weight:
239.30). Its purity was checked by elemental analysis (found: C
50.05, H 3.78, N 5.80%; calcd.: C 50.19, H 3.79, N 5.85%).
The reaction mixtures were maintained under reflux tempera-
ture for 1.5 h to ensure complete reaction. Polycrystalline solid
complexes were immediately formed. The solid complexes were
filtered off while hot, washed several times with water and a small;
quantity of methanol, followed by Et2O, and finally dried in a vac-
uum over at P2O5.
2.2. Synthesis of 5-(4ꢀ-derivatives
2.4. Preparation of adduct copper(II) complexes (6–10)
phenylazo)-3-(4-methoxyphenyl)-2-thioxothiazolidinone (HLn)
The metal complexes (1–5) were placed in a conical flask of
50 mL capacity and dissolved in a minimum quantity of pyridine.
After stirring the solution for 45 min, and followed by the addi-
tion of n-hexane (30 mL) slowly, dark colored compounds were
formed on standing for ∼24 h. Adducts thus obtained were collected
by filtration, washed with hot water and hexane and dried under
vacuum over CaCl2.
5-(4ꢀ-Alkylphenylazo)-3-(4-methoxyphenyl)-2-thioxothiazoli-
dinone (HLn) were typically prepared by adding a 25 mL of distilled
water containing hydrochloric acid (12 M, 2.68 mL, 32.19 mmol)
were added to aniline (10.73 mmol) or 4-alkyl anilines. To the
resulting mixture, stirred and cooled to 0 ◦C, a solution of sodium
nitrite (10.73 mmol, in 20 mL of water) was added drop wise.
The so-formed diazonium chloride was consecutively coupled
with an alkaline solution of 3-(4-methoxyphenyl)-2-thioxo-4-
thiazolidinone (10.73 mmol) in 20 mL of ethanol containing 602 mg
(10.73 mmol) of potassium hydroxide. The red precipitates, which
formed immediately were filtered and washed several times with
water. The crude product obtained was purified by crystallization
from hot ethanol (yield ∼55–75%), then dried in vacuum desiccator
over P2O5.
2.5. Measurements
C, H, and N microanalyses were carried out at the Cairo Uni-
versity Analytical Center, Egypt. The complexes were determined
after decomposition by aqua-regia, by complexometric titration
using EDTA using meroxide as indicator at pH ∼ 10 [19]. 1H NMR
spectrum was obtained with a Jeol FX90 Fourier transform spec-
trometer with DMSO-d6 as the solvent and TMS as an internal
reference. Infrared spectra were recorded using Perkin-Elmer 1340
spectrophotometer. Ultraviolet–visible (UV–vis) spectra of the
complexes were recorded in Nuzol solution using a Unicam SP 8800
spectrophotometer. The magnetic moment of the prepared solid
complexes was determined at room temperature using the Gouy
method. Mercury(II) (tetrathiocyanato)cobalt(II) [Hg{Co(SCN)4}],
The resulting formed ligands are: 5-(4ꢀ-methoxyphenylazo)-3-
(4-methoxyphenyl)-2-thioxothiazolidinone (HL1), 5-(4ꢀ-methyl-
phenylazo)-3-(4-methoxyphenyl)-2-thioxothiazolidinone (HL2),
5-(4ꢀ-phenylazo)-3-(4-methoxyphenyl)-2-thioxothiazolidinone
(HL3), 5-(4ꢀ-chlorophenylazo)-3-(4-methoxyphenyl)-2-thioxothi-
azolidinone (HL4), and 5-(4ꢀ-nitrophenylazo)-3-(4-methoxy-
phenyl)-2-thioxothiazolidinone (HL5) were characterized by
microanalyses, IR and 1H NMR spectroscopy.
NaNO2
HCl.H2O
/
-
N+
N
Cl
R
HCl
R
NH2
+
0-5 C
H3CO
H3CO
O
O
N
PH=10-12
-
N
N+
N
Cl
R
+
CH3OH, CH3COONa KOH
/
S
S
:
S
S
N
N
0-5 °C
R
H3CO
H3CO
HO
N
O
N
OH
N
N
=
S
S
S
S
N
N
R
R
N
H
n=1, R = OCH3 (HL1); n=2, CH3 (HL2); n=3, H (HL3); n=4, Cl (HL4); and n=5, NO2 (HL5)
The formation mechanism of azodye ligands (HLn)
was used for the calibration of the Gouy tubes. Diamagnetic correc-
tions were calculated from the values given by Selwood [20] and
Pascal’s constants. Magnetic moments were calculated using the
2.3. Synthesis of copper(II) complexes (1–5)
A hot solution of CuCl2·2H2O (0.01 mol) in CH3OH (30 cm3) was
added to the appropriate ligands (0.022 mol) in CH3OH (30 cm3).
equation, (eff = 2.84 [Tꢀcoor. 1/2. EPR measurements of powdered
]
M

492
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 83 (2011) 490–498
Table 1
Analytical data of azorhodanine derivatives (HLn).
Ligandsa
Formula/color
Exp. (Calcd.)%
C
H
N
HL1
HL2
HL3
HL4
HL5
C17H15N3O3S2
Orange
C17H15N3O2S2
Brown
C16H13N3O2S2
Dark yellow
C16H12N3O2S2Cl
Brown
54.67 (54.69)
4.05 (4.02)
11.25 (11.26)
57.12 (57.14)
55.96 (55.98)
50.86 (50.86)
49.77 (49.49)
4.23 (4.20)
3.81 (3.79)
3.20 (3.18)
3.12 (3.09)
11.76 (11.77)
12.24 (12.24)
11.12 (11.13)
14.43 (14.43)
C16
H12N4O4S2
Brown
a
HL1–HL5, air stable, colored, insoluble in water, but soluble in hot ethanol and soluble in coordinating solvent.
samples were recorded at room temperature (Tanta University,
Egypt) using an X-band spectrometer utilizing a 100 kHz magnetic
field modulation with diphenylpicrylhydrazyle (DPPH) as a refer-
ence material. The conductance measurement was achieved using
Sargent Welch scientific Co., Skokie, IL, USA.
positions of an geometrical structure. In all complexes, lig-
and/mixture ligand acts as a bidentate/monobasic chelating agent.
The formation of the complexes may be represented by the fol-
lowing reactions.
CuCl2·2H2O reacts with the HLn (n = 1–5) in 1:2 in methanol and
1:2:2 in n-hexane (mole ratios), giving partially soluble products.
3. Results and discussion
CuCl2·2H2O + 2HLn → [Cu(Ln)2] (1 : 2) (A)
The structure of the ligand was elucidated by elemental analy-
ses, IR, electronic and 1H NMR spectra. The results of the elemental
analysis (Table 1) are in good agreement with the proposed for-
mula. The HLn ligand was allowed to react with Cu(II) ion in the
molar ratio 1:2 (M:L). Also, the ligand was allowed to react with
these metal ion in the presence of secondary ligand (Py) in the
molar ratio 1:2:2 (M:L:Py). The obtained complexes were charac-
terized by elemental analyses, IR, electronic, ESR spectra as well as
conductivity and magnetic measurements.
CuCl2·2H2O + 2HLn + 2Py → [Cu(Ln)2(Py)2] (1 : 2 : 2) (B)
where Ln represents the anion of the corresponding monofunc-
tional bidentate HLn, Py = pyridine.
Py
O
N
O
N
Cu
Cu
N
O
N
3.1. Stoiciometries of the novel copper(II) complexes
O
Py
The stoichiometries of the complexes have been deduced
from their elemental analysis (Table 2), which indicates
that the metal complexes fall into two distinct categories,
namely 1:2 (monomeric) (metal:ligand) (A) and 1:2:2 (adduct)
(metal:ligand:ligand) (B). HLn is mononucleating and hence
requires one metal ion for coordination. All the products were
partially soluble in common organic solvents. Microanalytical data
are in good agreement with stoichiometry proposed for complexes
(Table 2).
(A)
(B)
Structures of [Cu(Ln)2](A) and [Cu(Ln)2(Py)2](B) products obtained
from the reaction of 1:2 and 1:2:2 molar ratios, respectively.
Structures of [Cu(Ln)2] (A) and [Cu(Ln)2(Py)2] (B) products
obtained from the reaction of 1:2 and 1:2:2 molar ratios, respec-
tively.
The elemental analysis correspond to the general formula
[Cu(Ln)2](A), and [Cu(Ln)2(Py)2](B) for all complexes. The princi-
pal ligand HLn undergoes mono deprotonation to form Ln in Cu(II)
complexes and acts as a bidentate ligand thus occupying two
3.2. Molar conductance of the complexes
The molar conductance of 10−3 M of solutions of the complexes
in DMSO is measured at 25 2 ◦C. It is concluded from the results
Table 2
Analytical data of Cu(II) complexes.a
Complexesb
Exp. (Calcd.)%
C
Mol. ratio
H
N
Metal
[Cu(L1)2] (1)
[Cu(L2)2] (2)
[Cu(L3)2] (3)
[Cu(L4)2] (4)
1:2
1:2
1:2
1:2
50.50 (50.40)
51.35 (51.29)
51.34 (51.23)
46.88 (46.91)
45.87 (45.74)
54.74 (54.57)
56.54 (56.44)
55.65 (55.53)
51.54 (51.61)
53.79 (53.99)
3.66 (3.71)
3.88 (3.77)
3.54 (3.47)
3.05 (2.93)
2.95 (2.86)
4.23 (4.13)
4.32 (4.28)
4.10 (3.97)
3.53 (3.48)
3.71 (3.64)
10.65 (10.38)
10.48 (10.56)
11.53 (11.21)
10.48 (10.26)
13.67 (13.34)
11.88 (11.58)
11.67 (11.97)
12.66 (12.34)
11.75 (11.47)
14.78 (15.00)
8.05 (7.85)
8.30 (7.99)
8.84 (8.48)
7.99 (7.76)
7.89 (7.57)
6.97 (6.57)
6.98 (6.79)
7.43 (7.00)
6.79 (6.51)
6.54 (6.81)
[Cu(L5)2] (5)
1:2
[Cu(L1)2(Py)2] (6)
[Cu(L2)2(Py)2] (7)
[Cu(L3)2(Py)2] (8)
[Cu(L4)2(Py)2] (9)
[Cu(L5)2(Py)2](10)
1:2:2
1:2:2
1:2:2
1:2:2
1:2:2
a
Microanalytical data as well as metal estimations are in good agreement with the stoichiometries of the proposed complexes, air stable, non-hydroscopic, high melting
temperature and colored.
b
L1–L5 are the anions of the ligands HL1–HL5.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 83 (2011) 490–498
493
Fig. 1. General formula and proton numbering of the 5-(4ꢀ-derivatives phenylazo)-3-(4-methoxy phenyl)-2-thioxothiazolidinone (HLn).
that Cu(II) chelates with HLn ligands under investigation were
found to have molar conductance values in the range from 1.25 to
8.56 ꢁ−1 mol−1 cm2 indicating their non-electrolytic nature [21].
distances are the same. However, if such a mechanism is taking
place in case of intermolecular hydrogen bond, the OH· · ·O and
OH· · ·N bond distances differ (Fig. 1E and F, respectively).
The broad absorption of a band located at ∼3400 cm−1 is
assigned to ꢂOH. The low frequency bands indicate that the
hydroxyl hydrogen atom is involved in keto ↔ enol (1A ↔ 1B, in
Fig. 1) tautomerism through hydrogen bonding.
3.3. Infrared spectra and nature of coordination
The infrared spectra of HLn (Table 3) give interesting results and
conclusions. The ligands exhibit two bands at ∼3400–3200 cm−1
due to asymmetric and symmetric stretching vibrations of N–H
group and intramolecular hydrogen bonding NH· · ·O systems
(Fig. 1D), respectively. When the OH group is involved in
intramolecular hydrogen bond (Fig. 1C), the OH· · ·N and N· · ·O bond
On the other hand, the OH group (Fig. 1B) exhibits more than one
absorption band. The two bands located at 1330 and 1370 cm−1 are
assigned to in-plane deformation and that at 1130 cm−1 is due to
ꢂC–OH. This observation has been seen previously [22–24], where
the different modes of vibrations of C–H and C–C band are identified

494
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 83 (2011) 490–498
Table 3
Important IR bands and their assignments for 5-(4ꢀ-derivatives phenylazo)-3-(4-methoxyphenyl)-2-thioxothiazolidinone (HLn) and their Cu(II) complexes.
Compounda
ꢂ(N N)
ıOH, ꢂC–OH, ꢃOH
ꢂC–O
M–O
M–N
M–Npy
ꢂPy
HL1
HL2
HL3
HL4
HL5
1
2
3
4
5
1545
1549
1552
1557
1562
1525
1529
1532
1536
1541
1526
1530
1534
1536
1543
1290, 1205, 818
1292, 1202, 819
1294, 1205, 820
1296, 1207, 823
1240
1244
1246
1249
1255
1248
1254
1257
1260
1266
1250
1256
1261
1262
1270
–
–
–
–
–
440
442
443
445
446
441
440
444
446
445
–
–
–
–
–
450
455
460
470
479
480
485
495
505
518
–
–
–
–
–
–
–
–
–
1297, 1209, 825
–
–
–
–
–
–
–
–
–
–
–
6
7
8
9
275
281
276
280
285
1572, 625, 500
1580, 633, 509
1585, 640, 515
1593, 646, 618
1604, 652, 622
10
a
Numbers as given in Table 2.
by the presence of characteristic bands in the low frequency side
of the spectrum in 600–200 cm−1
free ligands. New bands assigned to ꢂ(OH) in the free ligands
is absent, suggesting the cleavage of intramolecular hydrogen
bonding of ꢂOH group and coordination of oxygen to the metal
ion. The positive shift of ꢂ(C–O) by 5–15 cm−1 in all the com-
plexes further confirms the complexation through the oxygen
[27–29]. IR spectra of the Cu(II) complexes indicate the coordi-
nation via deprotonation.
.
The ligands show also a medium broad band located at
∼3460 cm−1 due the stretching vibration of some sort of hydrogen
bonding. El-Sonbati et al. [25,26] have reported detailed studies
for the different types of hydrogen bonding which are favorable to
exist in the investigated molecules. These hydrogen bonding types
are:
3. The bands of ıOH at 1295 cm−1, ꢂC–OH at 1210 and ꢃOH at
823 cm−1 display sharp decreases in their intensities to such an
extent that they nearly vanish. This can be taken as an indication
for the complete removal of OH group by the Cu(II) ion react-
ing with the ligands. Since the ligand reacts with Cu(II) ion, as
gathered from the results of elemental analysis, the Cu(II) ion
therefore, would displace only one proton from the OH group
contained in the ligands molecule. The possible structure of the
Cu(II) complexes could be suggested based on: (i) the absence of
one anion, (ii) the disappearance of C O, (iii) the coordination
of azo group. Under such conditions, the ligand is of bidentate
nature with respect to the evidence above.
1. Intramolecular hydrogen bond between the nitrogen atom of the
–N N– system and hydrogen atom of the hydroxyl hydrogen
atom (Fig. 1C). This is evident by the presence of a broad band
centered at 3460 cm−1
.
2. Hydrogen bonding of the OH· · ·N type between the hydroxyl
hydrogen atom and the N–Ph group (Fig. 1C).
3. Intermolecular hydrogen bonding is possible to form a cyclic
dimer through OH· · ·OH (E) or OH· · ·N N (F) or NH· · ·O C (G)
(Fig. 1).
4. The bands observed in the region 450–520 cm−1 has been
assigned to the ꢂ(Cu–N) vibrations on the foot note of the
earlier observations [30]. Two bands due to ꢂ(Cu–N) in these
complexes suggest that the ligands occupy trans position. The
medium intensity bands around 440 5 cm−1 in the complexes
are attributed to the ꢂ(Cu–O) vibration.
In general, hydrogen bonding involving both NH and OH groups
are proton donors and both –N and –O atoms are proton accep-
tors. It is of interest since such multiplicity of proton donor and
acceptor sites are prevalent in biological systems. Both intra and
intermolecular OH–N and NH–O may form a number of structures
in simultaneous equilibrium.
5. All complexes exhibit ꢂ(C C) in the 1595–1610 cm−1 region;
while the phenyl ring vibration appears at 1480–1510 cm−1. The
presence of a p-substituted benzene ring in the ligands as well as
in the complexes is indicated by strong and sharp bands around
630–650 cm−1. The defined band at ∼2960 cm−1 in the com-
plexes is assigned to ꢂ(C–H) vibration of the aromatic system.
6. The observation of new bands which do not appear in the parent
complexes (1–5) in the 1575–1608 and 275–285 cm−1 regions
are assigned to ꢂ(C N) (Py ring) and ꢂ(M–N) (Py ring) vibration
modes, indicating the presence of pyridine in complexes (6–10).
Again; the three bands of ıOH at 1380, 1340 and 1310 cm−1
and the two bands of ꢂC–O at ∼1240 cm−1 are together strong
indications to keto ↔ enol equilibria.
By comparing the infrared spectra of the free ligands to that of
the prepared complexes the following points are observed.
1. In the IR spectra of all ligands the band at ∼1545 cm−1 due to
the ꢂ(–N N–) mode is observed. In the metal chelates, this fre-
quency is lowered by 10–25 cm−1 indicating the bonding of the
azo nitrogen to the copper atom. The ꢂ(C–N) vibration appear-
ing at ∼1480 cm−1 in the ligands suffers a downward shift of
∼10 cm−1, thereby supporting the assumption that the copper
ion is coordinated to one of the azo nitrogen atoms.
2. The absence of any peak attributed to the C–OH moiety, in the
3440 and 3180 cm−1 region, implies that the ligands exist pre-
dominantly in solution as the form shown in Fig. 1A. However,
in solution and in the presence of copper ion these compounds
exist in a tautomeric equilibrium 1B ↔ 1C. The main change is
observed in the carbonyl stretching vibration, thus suggesting
that the form shown in Fig. 1C is prevailed. This tautomeric
form losses enolic proton when complexed with copper ion as
mononegative chelating agents produces the CO/OH mode of the
The HLn ligand takes its usual anionic (Ln) to chelate Cu(II)
through N– of azo group and oxygen atom of enol group as potential
binding sites. The observed shifts in the vibrational modes of C–C,
C
C, C–N and C–H after complexation indicate that the aromaticity
of the complex differ from one complex to another.
3.4. 1H NMR spectra
The 1H NMR spectroscopy was used to differentiate stereoiso-
mers. El-Sonbati and coworkers [22–26] investigated the 1H NMR
spectra of azo rhodanine and its derivatives with various transition

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 83 (2011) 490–498
495
Fig. 2. 1H NMR chemical shift (DMSO-d6) (ppm vs. TMS); (a) HL2; (b) HL2 with D2O.
2
2
2
2
metal salts. The 1H NMR spectra of HL2 shown in Fig. 2 are in
agreement with the proposed structures. Fig. 2a exhibits signal for
CH (∼4.42 ppm), favoring formation of an intramolecular hydrogen
bond with the N N (azodye) group. Electron-withdrawing sub-
stituents reduce the intramolecular hydrogen bond as indicated
by the marked shift of the hydroxyl signal to higher field in
the p-NO2 and p-Cl compounds. Electron-donating substituents
give the opposite effect, arising from the increasing basicity of
the azo-nitrogen. The broad signals assigned to the OH protons
at ∼11.2–11.68 ppm are not affected by dilution. The previous
two protons disappear in the presence of D2O as seen in Fig. 2b.
According to El-Sonbati and coworkers [22–26], hydrogen bonding
leads to a large deshielding of the protons. The shifts are in the
sequence: p-NO2 > p-Cl > H > p-OCH3 > p-CH3. In the meantime, the
1H NMR of the HL2 exhibits signals at ı (ppm) 3.9 (s, 3H, OCH3)
and 2.3 (s, 3H, CH3). The aromatic protons have resonance at
7.10–7.45 ppm for the ligands
assignable to the transition B1g → B2g and B1g → Eg, respec-
tively, indicating the possibility of a square planar complexes
[32,33]. The observed trend in the low energy d–d band maximum
shifts to a larger wavelength with increasing of donating group.
Thus, the observed red shifts in d–d band is affected both by the
steric effect group in p-positions in aniline moieties.
In general, most of the azo compounds give spectral
localized bands in the wavelength range 46,620–34,480 and
31,250–270,370 cm−1. The first region is due to the absorption of
the aromatic ring compared to 1Bb and 1Lb of mono substituted
benzene, while the second is due to the conjugation between the
azo group and the aromatic nuclei, with intermolecular charge
transfer resulting from ␲-electron migration to the diazo group
from electron donating substituents. The p-substituents increase
the conjugation with a shift to a longer wavelength as a result of the
Hamett’s constant effect [1,24]. The position of the ␲–␲* transition
of the azo groups remains as one of the most interesting, yet unre-
solved questions of molecular spectroscopy. For azobenzenes, as
the possibilities of the mesomerism became greater, the stabiliza-
tion of the excited state is increased relative to that of the ground
state and a bathochromic shift of the absorption bands follows [24].
Based on MO theory [34] the energy terms of the molecular orbital
became more closely spaced as the size of the conjugated system
increases. Therefore, with every additional conjugated double bond
the energy difference between the highest occupied and the lowest
vacant ␲-electron level became smaller and the wavelength of the
first absorption band corresponds to this transition is increased. The
azo group can act as a proton acceptor in hydrogen bonds [24] and
the role of hydrogen bonding in azo aggregation has been reported
and acknowledge for some time [35].
3.5. Spectral studies of copper(II) complexes
HLn exhibits bands at 26,360–26,180 cm−1 (CS) (n → ␲*),
30,560–30,260 cm−1 (CO) (n → ␲*), 32,980–33,150 cm−1 (H-
bonding and association), 40,250–39,900 cm−1 (phenyl) (Ph–Ph*),
(␲–␲*) [31] and 29,620–29,355 cm−1 transition of phenyl rings
overlapped by composite broad ␲–␲* of azo structure. In the
complexes, the (n → ␲*) transition shifts to lower energy at
28,670 cm−1 and the band due to the H-bonding and association
is absent as expected. The (CO) (n → ␲*) transition disappears
with the simultaneous appearance of new bands, being attributed
to ␲ → ␲* (C C) as a sequences of enolization. The band due to
␲ → ␲* transition moves to lower energy. These shifts or disap-
pearance of the bands are indicative of coordinating of the ligands
to metal.
3.6. Magnetic moment of copper(II) complexes
The spectra of complexes (1–5) show two absorption bands
The room temperature magnetic moments of [Cu(Ln)2] fail in the
range 1.81–1.92 B.M. which are typical for square planar (D4h) and
in the region 14,150–15,700 cm−1 and 20,150–22,500 cm−1

496
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 83 (2011) 490–498
Table 4
ESR spectral assignments of copper(II) complexes.
2
Compounda
g
ꢁ
g
⊥
|g|
G
˛
A
ꢁ × 10−4 ˇ2
fb
1
2
3
4
5
2.224 2.035 2.096
2.235 2.042 2.106
2.244 2.044 2.187
2.250 2.060 2.123
2.270 2.060 2.130
>4
>4
>4
>4
>4
0.80 170
0.81 158
0.86 201
0.65 131
0.67 141
0.66 111
0.73 115
0.78 105
0.55
0.60
87
95
a
Numbers as given in Table 2.
b
For square planar structure, f ratio has typical values 100–135 cm−1 and greater
ones for dominant pseudotetrahedral symmetry.
tetrahedrally distorted (D2h) mononuclear copper(II) complexes
and did not indicate any antiferromagnetic at this temperature.
The relatively higher 1.91 B.M. value observed for [Cu(L2)2], seem to
suggest the relatively high tetrahedral distortion from square pla-
nar geometry for these complexes than others in polycrystalline
state. On the other hand, ꢄeff data for [Cu(L1)2] and [Cu(L3–5)2] fall
in the 1.81–1.89 B.M. range and are well consistent with a square
planar geometry (D4h) around the copper centers. The ꢄeff values
of the mononuclear Cu(II) complexes are normal within the range
reported for one unpaired electron in a square planar or tetrahedral
geometry. However, it is impossible to differentiate between these
two geometries on the basis of electronic spectra. Hence, may be
distinguished on the basis of ESR spectra.
Fig. 3. The relation between g and Aꢁ × 10−4 cm−1
.
ꢁ
3.7. ESR spectra of copper(II) complexes
To obtain further information about the stereochemistry and
the site of the metal ligand bonding and to determine the magnetic
interaction in the metal complexes. ESR spectra of the complexes
were recorded in the solid state. The spin Hamiltonian parameters
of the complexes were calculated and summarized in Table 4. The
analysis of spectra of all copper(II) complexes gives agree well with
the values reported for distorted square planar geometry around
Fig. 4. The relation between |g| and Aꢁ × 10−4 cm−1
.
The ESR parameters obtained from a complex are very close to
our values for one system. By analogy with [Cu(Ln)2] complexes,
which present trans molecules. All the ESR parameters are given
in Table 4. g and |A | values indicate a square planar coordination
Cu(II) ion [36,37]. The spectra shows the relation g > g > ge which
ꢁ
⊥
is typical of axially symmetric d9 Cu(II) having one unpaired elec-
tron in dx orbital [38]. The absence of signal corresponding to
ꢁ
ꢁ
geometry for the CuN2O2 moiety. All the spectra are almost super-
imposible. Whatever the electron-withdrawing or donor power
and the ortho, meta or para-position of the substituent on the aro-
2
2
−y
(ꢅMs = 2) in the half field indicates the absence of any Cu–Cu
interaction thus ruling out possibility of dimeric structure. In axial
matic ring, the consonant variation observed in g value is only
ꢁ
symmetry, the G-parameter defined as G = g − 2/g⊥ − 2, reflects the
ꢁ
of the same magnitude as the experimental error. In fact, the ESR
parameters which relate to electron density in CuN2O2 plan are rel-
atively insensitive to the substitution in these ligand aryl groups.
Moreover the empirical factor f is an indication of the stereochem-
istry of the copper(II) complexes. Addision has suggested that this
ratio may be an empirical indication of the tetrahedral distortion of
a square planar geometry [41]. The lowest values of the empirical
factor for the trans species are indicative of a planar trans arrange-
ment whereas the slightly higher values of the empirical factor for
the cis compounds indicate only a nearly planar cis arrangement.
spin interaction between Cu(II) center in complexes. In the present
work, G value comes out to be 4.0 which again indicates absence
of Cu–Cu interaction, thus supporting proposed monomeric struc-
ture. Kivelson and Neiman have reported that g values less than 2.3
ꢁ
indicates considerable covalent character of M–L bond and greater
than 2.3 indicates ionic character. The present value comes out to
less than 2.3 which indicate considerable covalent character of Cu–L
bond [39].
As a measure of the covalency of the in-plane ␴-bonding, ˛2
indicates complete ionic character, whereas ˛2 = 0.5 denotes 100%
covalent bonding, with the assumption of negligible small values
of the overlap integral [39]. The ˇ2, the larger the covalency of the
bonding. From this analysis, the in-plane bonds of the complexes
correspondent to signals 1, 2, 3, 4 and 5 are largely covalent, with
the covalent character increasing from 2 to 3 to 1 to 4 to 5. The
values of ˛2 indicate that approximately 80% of the spin popula-
tion is in the copper dx
orbital of most of the Cu(II) species
2
2
−y
concerned. The g values obtained from ESR spectra indicate, as has
been pointed out by Kivelson and Neiman [39] and by Faber and
Rogers [40], that covalent bonding reduces the magnitude of the g
factor.
The data given in Table 4 indicate that A × 10−4 cm−1 shifts to
ꢁ
higher with g (Fig. 3); |g| (Fig. 4) and ˛2 with |g| (Fig. 5) give straight
ꢁ
line relationship for each chromophore from electron-withdrawing
to electron-donating substituents
Fig. 5. The relation between |g| and ˛2.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 83 (2011) 490–498
497
Table 5
Electronic spectral data (cm−1) of adducts copper(II) complexes.
Compounda
d–d
␲–␲*
L → M
6
7
8
9
10
11,470
11,525
11,935
12,815
12,280
31,750
31,950
31,650
33,220
31,950
23,200
22,737
22,830
28,830
22,730
a
Numbers as given in Table 2.
Also, for square planar structure, empirical factor has typical values
105–135 cm−1 and greater ones for dominant pseudotetrahedral
symmetry. It is noteworthy that the substitution of the aryl group
by a generates a small distortion around the metallic ion.
Fig. 6. The relation between g , Aꢁ × 10−4 and f.
ꢁ
3.8. Electronic spectra and magnetic moment of adduct copper(II)
complexes
the exchange interaction between copper centers in the solid.
According to Hathaway [47], if the value of G is greater than 4, the
exchange interaction between copper(II) centers in the solid state is
negligible, whereas when it is less than 4, a considerable exchange
interaction exists in the solid complex. The calculated G value for
these complexes indicates that there are no interactions between
the copper centers (see Table 6). The value of in-plane sigma bond-
ing parameter ˛2 which is usually taken as a measure of covalency
was estimated for each species, from the expression,
The electronic spectra of the complexes are presented in Table 5.
The electronic spectra of Cu(II) adduct complexes (6–10) differ
considerably from that of Cu(II) complexes (1–5). In the case of
hexa-coordinated copper(II) complexes with moderate Jahn–Teller
2
distortion the lowest energy transition dz → dx
(2B1g→ B2g
)
2
2
2
−y
occur in the 13,425–11,150 cm−1 region [42,43]. The bands present
in the higher wavelength region commensurate that these com-
plexes have distorted octahedral structure (while the present
complexes have square planar structure). A shoulder which appears
near 22,830 cm−1 (Table 5) is attributed to the ␲-Cu(II) LMCT
transition [44]. The high intensity bands observed in the lower
wavelength region (32,050–28,980 cm−1) are due to ␲–␲* tran-
sitions of ligand-to-metal charge-transfer transitions. The charge
transfer may be from p orbital of coordinated oxygen/or nitrogen
to the vacant d orbitals of copper(II) [45]. The room temperature
magnetic moments are in the range 1.93–2.20 B.M. These magnetic
moment values indicate the presence of one unpaired electron, as
expected for copper(II) complexes.
2
˛
= A /0.035 + (g − 2.0023) + 3/7(g⊥ − 2.0023) + 0.04
ꢁ ꢁ
The parameters g , g , A and A of complexes and the energies
ꢁ
⊥
ꢁ
⊥
of the d–d transitions are used to calculate the orbital reduction
parameters (Kꢁ, K ), the bonding parameter (˛2), the dipolar inter-
⊥
action term (p) and the Fermi contact interaction term (K).
The ˛2 values for the complexes 1, 2 and 4 support the covalent
nature [48] of their bonding. Hathaway [49] pointed out that of
pure ␴-bonding, K ≈ K⊥ ≈ 0.77 and for in-plane ␲-bonding K < K ,
ꢁ
ꢁ
⊥
while for out-of-plane ␲-bonding K < K the following simplified
⊥
ꢁ
expressions were used to calculate K and K :
ꢁ
⊥
ꢀ
ꢂ
ꢁ
ꢃ
(g − 2.0023)
ꢁ
Kꢁ2
=
=
× d–d transition
3.9. ESR spectral of adduct Cu(II) complexes
8ꢆ0
The ESR spectra of compounds (6–10). The spin Hamiltonian,
orbital reduction and bonding parameters of these complexes are
(g⊥ − 2.0023)
2ꢆ0
Kꢁ2
× d–d transition
given in Table 6. The observed g values for all complexes are
ꢁ
less than 2.3 commensurate a significant covalent character of the
metal–ligand bond in agreement with the observation of Kivelson
The observed K > K relation indicates the absence of signifi-
ꢁ
⊥
cant in-plane ␲-bonding. Giordano and Bereman [50] suggest the
identification of bonding groups from the values of dipolar term
p. The reduction of p values (0.0194–0.0227) from the free ion
value (0.036 cm−1) might be attributed to the presence of covalent
bonding.
and Neiman [39]. The trend g > g > ge (2.0023) for these com-
ꢁ
⊥
plexes suggests that the unpaired electron is localized in the dx
2
2
−y
orbital [6] of the copper(II) ion. The g values reflect that the Cu(II)
center has a tetragonal distorted octahedral geometry with dx
2
2
−y
orbital as a ground state [46]. The g values is an important func-
The plot of g and A × 10−4 cm−1 versus of f gives straight
ꢁ
ꢁ
ꢁ
tion for indicating covalent character of M–L; for ionic character,
line with increase the value of f decrease g and increase the
ꢁ
g > 2.3 and for covalent character g < 2.3. In the present complex,
A × 10−4 cm−1, Fig. 6. This can be explained. The electron with-
ꢁ
ꢁ
ꢁ
the g is less than 2.3 indicating appreciable covalent character
drawing p-substituent increase the positive charge on the metal
ꢁ
for the Cu–L bond. In addition, the g values are related to the G-
ion leading to a increase in f and A × 10−4 cm−1 and subsequently
ꢁ
factor by the expression, G = (g − 2)/(g⊥ − 2) = 4, which measures
a decrease in g .
ꢁ
ꢁ
Table 6
Spin Hamiltonian and orbital reduction parameters of adduct copper(II) complexes.
2
c
c
c
Complexa
g
ꢁ
g
⊥
gav
.
Gb
˛
A
ꢁ
A
⊥
Aav
K
ꢁ
K
⊥
K
f
6
7
8
9
2.2503
2.2586
2.2587
2.2997
2.3056
2.0344
2.0225
2.0344
2.0464
2.0494
2.1063
2.1011
2.1090
2.1320
2.1347
7.73
12.70
7.99
6.75
6.44
0.97
0.96
141
147
152
120
122
93
93
53
55
0.656
0.668
0.739
0.542
0.74
0.472
0.377
0.473
0.318
0.58
0.354
0.343
159
154
149
191
189
0.98
93
46
0.368
10
a
Numbers as given in Table 2.
b
c
The higher G values for pyridine adducts as compared to parent complexes indicate that there is a large separation between the copper center in adducts.
Units in cm−1
.

498
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A 83 (2011) 490–498
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4. Conclusion
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