Spectral and thermal study of the ternary complexes of nickel with sulfasalazine and some amino acids

Article abstract of DOI:10.1016/j.saa.2006.01.035

The ternary complexes of Ni(II) with sulfasalazine (H₃SS) as a primary ligand and alanine (ala), aspartic acid (asp), histidene (hist), methionine (meth) and serine (ser) amino acids as secondary ligands have been synthesized. Characterization of the complexes was based on elemental analyses, IR, UV-vis, mass spectra, magnetic moment and thermal analysis (TG). The isolated complexes were found to have the general formula [M(HSS)(AA)]4H₂O (AA = ala, asp, hist, meth, or ser amino acid) where nickel is tetra-coordinated. The thermal stability of the complexes was studied and the weight losses for the decomposition of the complexes were calculated and correlated with the mass fragmentation pattern. In most cases, the amino acid moiety is removed along with the Schiff base moiety leaving NiO as a metallic residue. The metallic residue was confirmed by powder XRD measurements.

Full text of DOI:10.1016/j.saa.2006.01.035

Spectrochimica Acta Part A 65 (2006) 1180–1185
Spectral and thermal study of the ternary complexes of nickel
with sulfasalazine and some amino acids
Ahmed A. Soliman∗
Department of Chemistry, Faculty of Science, Cairo University, Giza, Egypt
Received 30 November 2005; received in revised form 23 January 2006; accepted 25 January 2006
Abstract
The ternary complexes of Ni(II) with sulfasalazine (H3SS) as a primary ligand and alanine (ala), aspartic acid (asp), histidene (hist), methionine
(meth) and serine (ser) amino acids as secondary ligands have been synthesized. Characterization of the complexes was based on elemental
analyses, IR, UV–vis, mass spectra, magnetic moment and thermal analysis (TG). The isolated complexes were found to have the general formula
[M(HSS)(AA)]4H2O (AA = ala, asp, hist, meth, or ser amino acid) where nickel is tetra-coordinated. The thermal stability of the complexes was
studied and the weight losses for the decomposition of the complexes were calculated and correlated with the mass fragmentation pattern. In most
cases, the amino acid moiety is removed along with the Schiff base moiety leaving NiO as a metallic residue. The metallic residue was confirmed
by powder XRD measurements.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Nickel; Schiff base; Amino acids; Ternary complexes; Thermal study
1. Introduction
more insight on chelation behavior of sulfasalazine (H3SS)
(Scheme 1), through the synthesis and characterization of the
nickel(II) ternary system with some amino acids.
Sulfa drugs have attracted special attention for their thera-
peutic importance as they were used against a wide spectrum
of bacterial ailments [1–8]. Also, some sulfa drugs were used
in the treatment of cancer, malaria, leprosy and tuberculosis
[4]. Although the complexes of some sulfa drugs have been
investigated in the solid state, no much data is reported
about their mixed-ligand complexes [8,9]. The formation
and characterization of binary and mixed-ligand complexes,
involving iminodiacetic acid and sulfa drugs as sulfadiazine
and sulfadiamidine, were investigated [8–10].
Binary and ternary complexes of transition metals are com-
monly found in biological media and might play important roles
in process as diverse as the catalytic interaction of viruses with
bacterialcellwalls, thetransportandstorageofoxygen, etc. [10].
Continuing my pervious studies on the binary complexes of
sulfasalazine with Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II),
Ce(IV), Th(IV) and UO2(IV) [11,12], the present work throws
2. Experimental
All chemicals used were of the highest purity grade. They
included: sulfasalazine (Sigma), nickel nitrate hexahydrate
(BDH), amino acids (Merk) and ammonium hydroxide (Merck).
Sulfasalazine has four ionization constants [10]: 0.62, 2.9,
8.7 and 11.1 corresponding to the deprotonation of the pro-
tonated pyridine nitrogen, carboxylic OH, phenolic OH and
sulfonamide hydrogen, respectively. The free carboxylic form of
sulfasalazine is insoluble in water or ethanol, so that ammonical
ethanolic solutions were used (pH 6.0) at which the carboxylic
acid group is ionized. In addition, the sulfonamide NH (pKa
11.1) does not participate in bonding due to structure com-
plication. Hence, sulfasalazine can be symbolized as HSS−
(Scheme 2).
∗
Present address: Department of Chemistry, Faculty of Science, UAE Uni-
2.1. Preparation of complexes
versity, P.O. Box 17551, Al-Ain, UAE. Tel.: +971 50 7132451;
fax: +971 3 7671291.
The 1:1:1 [Ni:HSS:AA] complexes were prepared from hot
ethanolic solutions (60 ◦C) by the addition of 50 ml of the nickel
E-mail addresses: ahmed.soliman@uaeu.ac.ae,
ahmedsoliman2@hotmail.com.
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.01.035

A.A. Soliman / Spectrochimica Acta Part A 65 (2006) 1180–1185
1181
ductometric measurements of the complexes were carried out as
DMF solutions at 25 ◦C using Metrohm 660 conductivity meter.
Themolarmagneticsusceptibilitiesweremeasuredonpowdered
samples (Gouy method) using a Sherwood Scientific magnetic
susceptibility balance. Mass spectra of the solid complexes were
recorded by FAB technique at (4 10 keV) using JMS-AX500
Double focusing mass spectrometer. Thermogravimetric analy-
sis (TG) of the complexes was carried out in a dynamic nitrogen
atmosphere (20 ml min−1) at different heating rates of 5, 10 and
15 ◦C min−1 using Shimadzu TGA-50H analyzer. X-ray pow-
der diffraction (XRD) was carried out at ambient temperature
using Philips Analytical X-Ray B.V. with PC-APD, Diffraction
Software. Theinstrumentisequippedwithacopperanodegener-
˚
ating Ni-filtered Cu K␣ radiation (λ = 1.54056 A, 40 kV, 55 mA).
Diffractograms were recorded in the 2θ range between 2.0 and
90.0 with a step size (2θ) of 0.080.
3. Results and discussion
Scheme 1. Structure of sulfasalazine (H3SS).
The results of the elemental analyses and mass spectrometry
data are presented in Table 1. The results obtained are in good
agreement with those calculated for the suggested formulae of
the complexes (Ni:HSS:AA:4H2O). The molar conductance val-
ues in DMF (Table 1) for the complexes were found to be in the
range 16.90–32.00 S cm2 mol−1. The relatively low values indi-
cate the non-electrolytic nature of these complexes [11,14]. This
can be accounted for by the satisfaction of the bivalency of nickel
by the carboxylate group of sulfasalazine (used as ammonium
salt) and the amino acid carboxylic group which deprotonated
upon complex formation. This implies the coordination of the
phenolic OH of sulfasalazine and the NH2 of the amino acids
without proton displacement.
nitrate hexahydrate (2 mmol, 0.58 g) dropwisely to 50 ml of an
ammonical solution of sulfasalazine (HSS−) (2 mmol, 0.80 g)
and 2 mmole amino acid (AA) (0.18 g ala, 0.27 g asp, 0.42 g hist,
0.30 g meth and 0.21 g ser). The mixtures were adjusted to be
slightly alkaline (pH 7.5–8.5) to ensure the complete solubility
of sulfasalazine and to assist the formation of the ternary com-
plexes, which are usually formed at higher pH than the binary
ones[13]. Themixtureswerethenstirredfor1 handleftinrefrig-
erator overnight whereby the complexes were precipitated. The
isolated complexes were filtered, washed thoroughly by warm
ammonical ethanol and then by diethyl ether. The solid com-
plexes were then dried in vacuum desiccator and subjected to
elemental microanalyses.
3.1. Infrared spectra
The IR spectra of the free ligand and its metal complexes
were carried out in the range of 4000–400 cm−1 and the impor-
tant bands were listed in Table 2. The IR spectrum of sul-
fasalazine showed a medium broad band at 3439 cm−1, which
was attributed to OH of the phenolic and carboxylic OH groups.
The carboxylic OH group was not considered in the spectra of
complexes since ammonical solution of sulfasalazine was used
in which the carboxylic group was used as an ammonium salt.
The existence of water of hydration in the spectra of the com-
plexes rendered it difficult to get conclusion from the phenolic
OH group of the sulfasalazine, which would be overlapped by
those of the water molecules. The participation of the pheno-
lic group was deduced by clarifying the effect of chelation on
the ␯(C O) stretching vibration. The shift in ␯(C O) of phe-
nolic group, from 1281 cm−1 in the free sulfasalazine ligand to
1268–1260 cm−1 in the complexes indicated the participation
of the phenolic group in complex formation [14–17]. Also the
participation of the OH group was apparent from the shift in
position of the ␦(OH) in-plane bending from 1393 cm−1 in the
free sulfasalazine ligand to 1388–1346 cm−1 in the complexes.
The presence of water molecules in the above mentioned
complexes was ascertained by the appearance of bending vibra-
2.2. Measurements
Elemental analyses (C, H, N and S) were performed in the
Centeral Laboratory Unit (CLU) of UAE University; the analy-
ses have been repeated twice. The IR spectra have been recorded
using NEXUS 470 FT-IR spectrometer, Thermo Nicolet Corpo-
ration, running under OMNIC software package in wave number
region 4000–400 cm−1. The spectrum recorded as a KBr pel-
lets. UV–vis measurements for the binary and ternary complexes
were performed using Cary 50 Conc UV–vis spectrophotome-
ters, VARIAN; in the wavelength range 200–900 nm. The con-
Scheme 2. HSS− (R = –N2PhSO2NHPy; py = pyridine).

1182
A.A. Soliman / Spectrochimica Acta Part A 65 (2006) 1180–1185
tion modes of the water molecules; ␦(OH2), found in the
range 996–962 cm−1. The other bending vibration of the water
molecules; ␦(OH2), is usually around 1600 cm−1 which always
interferes with the skeleton vibration of the benzene ring (C C
vibration).
The participation of the carboxylic group in chelation could
be indicated from the changes of the bands of the asymmetric
and symmetric stretching vibrations of the carboxylate group
upon complex formation. The spectrum of sulfasalazine showed
medium strong bands at 1625 and 1475 cm−1 assigned for asym-
metric and symmetric stretching vibrations of the carboxylate
moiety, respectively. These two bands are either slightly shifted
to lower frequencies (≈1600 cm−1) or remained but decreased
markedly in intensity. This indicates that the carboxylate group
was participated in complex formation with the metal ions [18].
Participation of the phenolic and carboxylic OH groups is also
confirmed by the appearance of new bands in the spectra of the
complexes in the 472–439 cm−1 regions which may be assigned
to the ␯(M O) stretching vibration [19].
The amino acid was found to be a bidentate ligand and bound
tothecentralnickelionthroughthecarboxylicOHandtheamino
+
group. The ␦NH3 band, which is a characteristic for the zwit-
ter ion, disappeared in the spectra of the complexes. This fact
indicates that the NH2 group must be involved in coordination.
This is supported by the appearance of broad and split bands
in the spectra of the complexes, in the regions 3429–3405 and
3266–3200 cm−1 (␯NH2) as well as sharp bands in the region
1520–1516 cm−1 (in-plane deformation; ␦NH2), assigned for
the coordinated amino group [20–22]. The bands in the regions
1594–1586 and 1412–1408 cm−1, due to ␯
(COO−) and
asym
␯
sym
(COO−) of the amino acids appeared in the complexes
at 1550–1540 and 1391–1389 cm−1. The shift of these two
bands suggests the involvement of the carboxylic groups of the
amino acids in complex formation [23,24]. Hence, the amino
acid moiety is chelated to the metal ion through five-member
ring. However, the lower values of the two carboxylic vibrations
compared to those of the free ligand suggests that the carboxylic
group interacts weakly with the metal ions.
3.2. Magnetic susceptibility measurements
The magnetic moment values of the complexes are calcu-
lated and reported in Table 1. The tetra-coordinated nickel
species in the [Ni(HSS)(AA)]·4H2O tris complexes has μeff
of 2.62–3.0 BM, which is close to the value of two unpaired
electrons. This suggests that the complexes have a tetrahedral
geometries with a slight orbital contribution to the magnetic
moment [11].
3.3. The electronic absorption spectra
The electronic absorption spectra of sulfasalazine displayed
a broad band at 360 nm assigned to the n–␲* transition from
the solvent to sulfasalazine moiety. This band was found to
be shifted to higher wavelengths in the spectra of the binary
(385 nm) and ternary complexes (395–405 nm). This may be
related to the chromophoric groups (N N, SO2) affected by

A.A. Soliman / Spectrochimica Acta Part A 65 (2006) 1180–1185
1183
Table 2
Selected IR data for sulfasalazine and its binary and ternary complexes
Compound
␯(NH2)
␯
asym
(COO)
␦(NH2)
␯
sym
(COO)
␦(CH)
␯(C O) (phenolic)
␥H2O
␯(M O)
␯(M N)
SS
Ni–SS
–
–
1625s
1600s
–
–
1427m
1420m
13908m
1389m
1390m
1390m
1391m
1393s
1386s
1281
–
–
–
–
1266m
1260m
1267m
1268m
1265m
1268m
962w
964m
978m
996m
990w
993m
611s
615m
616m
616m
615m
617m
[Ni(HL)(ala)]·4H2O
[Ni(HL)(asp)]·4H2O
[Ni(HL)(hist)]·4H2O
[Ni(HL)(meth)]·4H2O
[Ni(HL)(ser)]·4H2O
3429s
3422s
3405s
3428s
3406s
1550m
1544m
1543m
1545m
1540s
1517m
1517m
1516m
1517m
1520m
1346m
1346m
1347m
1346m
1348m
578m
577m
578m
578m
580m
Fig. 1. TG and DTG data of [Ni(HSS)(meth)]·4H2O complex.
overall electronic environment change of sulfasalazine upon
complex formation.
[Ni(HSS)(ala)]·4H2O was thermally decomposed in five
successive decomposition steps within the temperature range
304–783 K. The first decomposition step with an estimated
mass loss of 11.70% (calc. mass = 72) within the temperature
range 304–388 K, may be attributed to the liberation of the four
hydrated water molecules. The second and third decomposition
steps found within the temperature range 403–617 K with an
estimated mass losses of 7.15 and 14.31% (calc. mass losses
44, 88), which are reasonably accounted for by the removal
of one CO2 and the alanine moieties, respectively. The rest
3.4. Thermogravimetric analysis
The thermogravimetric (TG) and the derivative thermogravi-
metric (DTG) plots of the complexes were represented in Fig. 1.
The assignment of the different decomposition steps were given
in Table 3. The decomposition schemes of the complexes can be
approached as follows.
Table 3
Thermal analytical data for the ternary complexes
Molecular formula
Molecular
weight
DTGmax
(◦K)
Decomposition
temperature (◦C)
Mass loss
(%)
Mol. mass
found (Calc.)
Eliminated species
Solid residue (%)
[Ni(HL)(ala)]·4H2O
615.48
343
470
580
668
750
304–388
403–524
530–617
622–735
733–783
11.27
7.18
14.56
23.08
72.00
44.02
88.12
142.18
209.08
4H2O
CO2
C3H6NO2
C5H4NSO2
C21H27N5NiO11
S
C
12H9N3
NiO (12.03)
NiO (11.22)
NiO (10.86)
NiO (10.93)
NiO (11.72)
[Ni(HL)(asp)]·4H2O
C22H27N5NiO13
659.49
681.54
675.60
631.48
340
573
631
310–381
400–570
570–647
12.47
13.25
56.53
76.84
81.65
348.38
4H2O
CO2
S
(C17H13N4O3S + C4H7NO4)
[Ni(HL)(hist)]·4H2O
C24H29N7NiO11
347
568
628
306–386
400–570
570–647
13.25
11.75
57.98
81.65
72.40
357.27
4H2O
CO2
S
(C17H13N4O3S + C6H8N3O2)
[Ni(HL)(meth)]·4H2O
337
582
623
313–402
404–559
557–675
12.75
11.75
56.09
78.57
72.40
345.63
4H2O
CO2
C23H31N5NiO11S2
(C17H13N4O3S + C5H11NO2S)
[Ni(HL)(ser)]·4H2O
340
559
632
310–378
386–561
563–686
12.50
10.75
55.01
77.025
66.24
338.97
4H2O
CO2
C21H27N5NiO12
S
(C17H13N4O3S + C3H7NO3)

1184
A.A. Soliman / Spectrochimica Acta Part A 65 (2006) 1180–1185
Scheme 3. Decomposition of [Ni(HSS)(ala)]·4H2O.
Scheme 4. Decomposition of [Ni(HSS)(meth)]·4H2O.
of sulfasalazine molecule was removed on the fourth and fifth
steps within the temperature range 622–783 K (calc. mass
losses = 142, 195). The decomposition of the ligand molecule
ended with a final oxide residue of NiO (12.11%, mass = 74)
(Scheme 3).
3.5. XRD analysis
The metallic residue for all complexes obtained at 800 ◦C
were grounded and subjected to XRD analysis. All metallic
residues had the same diffraction pattern (Fig. 2), which indi-
cates that they reach the same metallic moiety at high temper-
ature. The XRD data are listed in Table 4. It is clear from the
data that the final decomposition product of all complexes was
[Ni(HSS)(meth)]·4H2O decomposed in three steps within
the temperature range 313–675 K. The first decomposition
step, observed within the temperature range 304–388 K, with
an estimated mass loss of 10.64% (calc. mass = 72) may
be attributed to the liberation of the four hydrated water
molecules. The second decomposition step associated with
the removal of CO2 moiety was observed in the tempera-
ture range 404–559 K with an estimated mass loss of 6.50%
(calc. mass = 44). The third step observed in the temperature
range 563–686 K with an estimated mass loss of 69.91% (calc.
masses = 337 + 104) which was assigned to the removal of the
sulfasalazine and amino acid moieties. The mass of the metallic
residue remained at the end of the decomposition was 11.72%
(calc. mass = 74) which was assigned for NiO (Scheme 4). The
other ternary complexes have the same decomposition scheme of
[Ni(HSS)(meth)]·4H2O.
Table 4
Comparison of the X-ray powder diffraction data of Ni metallic residue
Angle 2θ
Observed
Referencea
b
˚
˚
˚
d-Value (A)
I/Io
49.3
100
76.7
33.0
24.4
d-Value (A)
I/Io
ꢀd (A)
36.75
42.81
62.45
74.98
78.97
2.44
2.11
1.48
1.26
1.211
2.41
2.09
1.48
1.26
1.21
91
100
57
16
13
0.03
0.03
0.00
0.00
0.00
a
JCPDS-ICDD 4-835.
b
ꢀd = dobsd. − dref
.

A.A. Soliman / Spectrochimica Acta Part A 65 (2006) 1180–1185
1185
Fig. 2. XRD powder diffractogram of the metallic residue of the complexes.
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NiO whose XRD data matches the reference for nickel oxide
(JCPDS-ICDD 4-835). This conclusion is consistent with the
results of the TG analysis.
3.6. Conclusion
As a general conclusion, the sulfasalazine participated in
bonding to nickel as monobasic bidentate (OO) ligand and the
amino acids as monobasic bidentate (NO) ligand with a total
of four coordination sites around the metal ion whose charges
are neutralized by the deprotonation of the sulfasalazine and
the amino acid carboxylates. The non-electrolytic nature of the
complexes was evidenced from the low values of the molar con-
ductance of the complexes. The elemental analysis suggested the
presence of four water molecules, which is evidenced, from the
thermal analysis to be hydrated water. All the tetra-coordinated
nickel (d8 configuration) complexes have net magnetic values,
which suggest a tetrahedral geometry (Scheme 5).
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