New complexes of Ni(II) and Cu(II) with Schiff bases functionalised with 1,3,4-thiadiazole: Spectral, magnetic, biological and thermal characterisation

Article abstract of DOI:10.1007/s10973-009-0280-4

Schiff bases obtained by the condensation of 2-amino-5-mercapto-1,3,4- thiadiazole with 2,4-pentandione or 1-phenyl-1,3-butandione were synthesized and characterized in order to obtain polydentate ligands HL¹ and HL ², respectively.

Full text of DOI:10.1007/s10973-009-0280-4

J Therm Anal Calorim (2009) 97:721–727
DOI 10.1007/s10973-009-0280-4
New complexes of Ni(II) and Cu(II) with Schiff bases
functionalised with 1,3,4-thiadiazole: spectral, magnetic,
biological and thermal characterisation
Rodica Olar Æ Mihaela Badea Æ Dana Marinescu Æ
Veronica Lazar Æ Carmen Chifiriuc
ICTAC2008 Conference
´
´
Ó Akademiai Kiado, Budapest, Hungary 2009
Abstract Schiff bases obtained by the condensation of
2-amino-5-mercapto-1,3,4-thiadiazole with 2,4-pentandi-
one or 1-phenyl-1,3-butandione were synthesized and
characterized in order to obtain polydentate ligands HL1
and HL2, respectively. The complexes with these ligands of
the type M(L)ClꢀnH2O [(1) M:Ni, L:L1, n = 0.5; (3) M:Ni,
L:L2, n = 0.5]; [(2) M:Cu, L:L1, n = 1; (4) M:Cu, L:L2,
n = 0] were also synthesized and characterized. The
modifications evidenced in IR spectra of complexes were
correlated with the presence of monodeprotonate Schiff
bases. The electronic spectra display the characteristic
pattern of square-planar stereochemistry. The in vitro
qualitative and quantitative antimicrobial activity assays
showed that the new complexes exhibited variable anti-
microbial activity. The thermal analyses have evidenced
the thermal intervals of stability and also the thermody-
namic effects that accompany them. Schiff bases and
complexes have a similar thermal behaviour. Processes as
water elimination, melting, chloride anion removal as well
as oxidative degradation of the organic ligands were
observed.
Introduction
Heterocycles bearing a 1,3,4-thiadiazole moiety, represent an
interesting class of compounds displaying a wide spectrum of
biological activities such as anti-inflammatory, antiviral,
antitumor, antiulcer, antiepileptic as well as antimicrobial
properties [1–3]. Some 1,3,4-thiadiazole derivatives are good
inhibitors of matrixins and bacterial collagenases, enzymes
which can degrade the tissue leading to a variety of diseases
such as cancer, rheumatoid arthritis, multiple sclerosis, and
congestive heart failure [4, 5]. Moreover, diversified Schiff
bases derived from 1,3,4-thiadiazole have been obtained and
the inhibitory properties toward Carbonic anhydrase [6] or
antimicrobial activities both for these compounds and their
complexes have been reported [6–9].
In order to evaluate the biological properties and thermal
stability of such derivatives, we report here the synthesis and
characterization of two Schiff bases obtained by the
2-amino-5-mercapto-1,3,4-thiadiazole condensation with
2,4-pentandione or 1-phenyl-1,3-butandione. The com-
plexes of Ni(II) and Cu(II) with these ligands were also
synthesized and characterised. The Schiff bases and com-
plexes have been characterized by different analytical and
spectral methods. The antimicrobial activity of these deriv-
atives was also assayed against planktonic microbial strains.
The thermal behaviour of these derivatives was inves-
tigated in synthetic air by thermal analysis (TG, DTA).
So far, our research group reported the thermal behaviour
of other complexes with 1,3,4-thiadiazole derivatives
[10–12]. The thermal behaviour of the complexes with
other Schiff bases has attracted attention in the last years
[13–20], this attention being focused on the species that
could have some practical applications [15, 19, 20]. Data
concerning kinetic studies were also reported for such type
of compounds [15, 17–19].
Keywords Complexes ꢀ Gram negative strain ꢀ
Gram positive strain ꢀ Thermal behaviour ꢀ
1,3,4-thiadiazole
R. Olar (&) ꢀ M. Badea ꢀ D. Marinescu
Faculty of Chemistry, Department of Inorganic Chemistry,
University of Bucharest, 90-92 Panduri Str., 050663 Sector 5,
Bucharest, Romania
e-mail: marioara.olar@unibuc.ro; rodica_m_olar@yahoo.com
V. Lazar ꢀ C. Chifiriuc
Faculty of Biology, Department of Microbiology, University
of Bucharest, 1-3 Aleea Portocalilor Str., 060101 Sector 6,
Bucharest, Romania
123

722
R. Olar et al.
Experimental
HL1: IR (KBr pellet), cm-1: mas(CH3), 2962w; ms(CH3),
2914w; TI (d(NH) ? m(C=N) ? d(CH)), 1606s; (m(C=C) ?
m(C=N)), 1524m, 1369s; das(CH3), 1421w; TII (d(NH) ?
d(CH) ? m(C=N) ? m(C=S)), 1345vs; m(C=C) ? m(C–CH),
1283w; m(C–N), 1181m; TIII (m(C=N) ? m(C=S)), 1053m;
m(N–N), 957m; d(SH), 906w; TIV (m(C=S)), 729w; mas(C–S–
C), 647w; ms(C–S–C), 536w.
All reagents were of commercial analytical quality and have
been used without further purification. Chemical analysis of
carbon, nitrogen and hydrogen has been performed using a
Perkin–Elmer PE 2400 analyzer. Nickel and chloride were
determined gravimetrically using dimethylglyoxyme and
silver nitrate, respectively, while copper was determined
volumetrically using thiosulfate method in the laboratories
of Inorganic Chemistry Department.
HL2: IR (KBr pellet), cm-1: m(CH), 3068w; mas(CH3),
2962w; ms(CH3), 2914w; TI (d(NH) ? m(C=N) ? d(CH)),
1596s; (m(C=C) ? m(C=N)), 1514m, 1453w; das(CH3),
1416w; TII (d(NH) ? d(CH) ? m(C=N) ? m(C=S)), 1337vs;
m(C=C) ? m(C–CH), 1266w; m(C–N), 1210w; TIII (m(C=N)
? m(C=S)), 1023m; d(SH), 927w; c(CH), 844w, 772w,
692w; TIV (m(C=S)), 735w; mas(C–S–C), 637w; ms(C–S–C),
546w.
IR spectra were recorded in KBr pellets with a BIO-RAD
FTIR 135 spectrometer in the range 400–4000 cm-1. Elec-
tronic spectra by diffuse reflectance technique, with MgO as
standard, were recorded in the range 280–2800 nm, on a
Jasco V 670 spectrophotometer. Magnetic measurements
were done by Faraday’s method, at room temperature, using
Hg[Co(NCS)4] as standard. The molar magnetic suscepti-
bilities were calculated and corrected for the atomic dia-
magnetism. EPR spectra were recorded on microcrystalline
samples at room temperature with a Varian E-9 spectrome-
ter. The field was calibrated using crystalline diph-
enyilpicrylhydrazyl (g = 2.0036).
The complexes were obtained following the general
procedure: to a solution of 5 mmol of MCl2 in 50 mL
ethanol was added drop wise at 50 °C, under continuous
stirring, a solution of 5 mmol Schiff base in 20 mL etha-
nol. A solution of LiOH 1% was added drop wise until the
solution turn yellow (for nickel) or brown (for copper). The
yellow or brown, sparingly soluble compound formed after
1 h was filtered out and washed with ethanol and air dried.
[Ni(L1)Cl]ꢀ0.5H2O (1): Analysis, found: Ni, 19.43; C,
27.93; Cl, 11.78; H, 2.86; N, 14.01; S, 21.23 NiC7ClH8-
N3O0.5S2 requires: Ni, 19.53; C, 27.98; Cl, 11.80; H, 2.68;
N, 13.98; S, 21.35; IR (KBr pellet), cm-1: m(OH), 3414w;
mas(CH3), 2960m; ms(CH3), 2910m; TI (d(NH) ? m(C=N)
? d(CH)), 1606s; (m(C=C) ? m(C=N)), 1523m, 1385s;
das(CH3), 1435m; TII (d(NH) ? d(CH) ? m(C=N) ?
m(C=S)), 1360vs; m(C=C) ? m(C–CH), 1279s; m(C–N),
1180m; TIII (m(C=N) ? m(C=S)), 1054m; m(N–N), 957m;
TIV (m(C=S)), 702w; mas(C–S–C), 660m; ms(C–S–C), 535w.
The qualitative screening of the susceptibility spectra of
different microbial strains to the complexes was performed
by adapted diffusion techniques, while the quantitative
assay of minimal inhibitory concentration (MIC, lg/cm3)
value was based on liquid medium serial microdilutions
[21]. The compounds were solubilised in DMF to a final
concentration of 1 mg/mL. The in vitro biological screen-
ing effects were tested against a microbial inoculum of
*1.5 9 108 UFC/cm3, corresponding to 0.5 McFarland
density, represented by Enterobacteriaceae (E. coli,
Salmonella sp., Shigella sp., Proteus sp., Klebsiella pneu-
moniae) Pseudomonadaceae (Pseudomonas aeruginosa,
Acinetobacter boumani), Micrococcaceae (Staphylococcus
aureus), Bacillaceae (Bacillus sp.), and Candida strains,
reference ones and recently isolated from clinical samples.
The heating curves (TG and DTA) were recorded using
a Labsys 1200 SETARAM instrument, with a sample mass
of 6–17 mg over the temperature range of 20–1000 °C,
using a heating rate of 10 K/min. The measurements were
carried out in synthetic air atmosphere (flow rate
16.66 cm3/min) by using alumina crucibles.
1
UV–Vis (MgO pellet), cm-1: 1A1 ? A2: 17543; leff, lB: 0.
[Cu(L1)Cl]ꢀH2O (2): Analysis, found: Cu, 20.18; C,
26.88; Cl, 11.38; H, 2.75; N, 13.37; S, 20.49 CuC7ClH9
N3OS2 requires: Cu, 20.22; C, 26.75; Cl, 11.28; H, 2.89; N,
13.37; S, 20.41; IR (KBr pellet), cm-1
: m(OH),
3450m; mas(CH3), 2940m; ms(CH3), 2890m; TI (d(NH) ?
m(C=N) ? d(CH)), 1610m; (m(C=C) ? m(C=N)), 1530m,
1375s; das(CH3), 1435w; TII (d(NH) ? d(CH) ? m(C=N) ?
m(C=S)), 1355m; m(C=C) ? m(C–CH), 1275w; m(C–N),
1180w; TIII (m(C=N) ? m(C=S)), 1055m; m(N–N), 957m;
TIV (m(C=S)), 705w; mas(C–S–C), 660w; ms(C–S–C), 530w.
Synthesis of the complexes
UV–Vis (MgO pellet), cm-1: CT: 28570; dxy ? dx2-y2
16390; leff, lB: 0.75.
:
The syntheses of Schiff bases were performed by heating
for 4 h a mixture of 2-amino-5-mercapto-1,3,4-thiadiazole
with 2,4-pentandione or 1-phenyl-1,3-butandione for molar
ratio 1:1 in the presence of metal chloride. Structural data
for Schiff bases will be presented elsewhere. These com-
pounds were characterised by elemental analysis and IR
data.
[Ni(L2)Cl]ꢀ0.5H2O (3): Analysis, found: Ni, 16.09; C,
39.77; Cl, 9.82; H, 2.81; N, 11.65; S, 17.69 NiC12ClH10-
N3O0.5S2 requires: Ni, 16.15; C, 39.65; Cl, 9.75; H, 2.77;
N, 11.56; S, 17.65; IR (KBr pellet), cm-1: m(OH), 3400m;
m(CH), 3080m; mas(CH3), 2960m; ms(CH3), 2930m; TI
(d(NH) ? m(C=N) ? d(CH)), 1600vs; (m(C=C) ? m(C=N)),
1518vs, 1386m; das(CH3), 1420m; TII (d(NH) ? d(CH) ?
123

New complexes of Ni(II) and Cu(II) with Schiff bases
723
m(C=N) ? m(C=S)), 1360s; m(C=C) ? m(C–CH), 1290m;
m(C–N), 1185m; TIII (m(C=N) ? m(C=S)), 1025vs; c(CH),
840w, 720w, 690w; TIV (m(C=S)), 730w; mas(C–S–C), 630w;
1
ms(C–S–C), 560w. UV–Vis (MgO pellet), cm-1: 1A1 ? A2:
17700; leff, lB: 0.
[Cu(L2)Cl] (4): Analysis, found: Cu, 17.68; C, 40.38; Cl,
9.91; H, 2.48; N, 11.74; S, 17.82 CuC12ClH9N3S2 requires:
Cu, 17.73; C, 40.22; Cl, 9.89; H, 2.53; N, 11.73; S, 17.90; IR
(KBr pellet), cm-1: m(CH), 3069m; mas(CH3), 2960m;
ms(CH3), 2935m; TI (d(NH) ? m(C=N) ? d(CH)), 1595s;
(m(C=C) ? m(C=N)), 1513m, 1384 m; das(CH3), 1410m; TII
(d(NH) ? d(CH) ? m(C=N) ? m(C=S)), 1350m; m(C=C) ?
m(C–CH), 1270w; m(C–N), 1180w; TIII (m(C=N) ? m(C=S)),
1040m; c(CH), 844w, 720w, 690w; TIV (m(C=S)), 726w;
mas(C–S–C), 635w; ms(C–S–C), 550w. UV–Vis (MgO pellet),
cm-1: CT: 29410; dxy ? dx2-y2: 17857; leff, lB: 1.29.
Fig. 1 X-band EPR spectrum of complex (2) on polycrystalline
sample at room temperature
In the complexes spectra the bands assigned to TIII
vibration mode are shifted towards lower wavenumbers.
This behaviour indicates the mercapto group deprotonation
of the and its involvement in coordination. In the charac-
teristic ranges for water a large band about 3400 cm-1 for
the complexes can be assigned to m(OH) stretching vibra-
tions, except for complex (4) [25].
Results and discussions
Physico-chemical characterisation of complexes
In this article, we report the preparation, physico-chemical
and biological characterisation of some Schiff bases
(HL1 and HL2) resulted in 2-amino-5-mercapto-1,3,
4-thiadiazole condensation with 2,4-pentandione or 1-phenyl-
1, 3-butandione for 1:1 molar ratio. The structure of these
compounds as resulted from X-ray determination is:
The electronic spectra of compounds show the charac-
teristic pattern of the square-planar stereochemistry. The
1
1
bands about 17500 cm-1 are assigned to A1 ? A2 tran-
sition while the intense ones at higher energy are associated
with charge transfer for Ni(II) compounds. The electronic
spectra of Cu(II) complexes display a broad band centred at
16390/17857 cm-1 assigned to dx2-y2 ? dxy spin allowed
transition [26].
SH
-
N
The Ni(II) complexes are diamagnetic as is expected for
a square planar specie. The EPR spectrum of complex (2)
(Fig. 1) display a low intensity isotropic signal with a value
of factor g = 2.115. Moreover, a second narrow signal
with g = 2.011, value closer to the free electron one, have
origin in a charge transfer metal to ligand.
+
S
R
N
1
HL : R=CH3;
2
HL : R=C6H6
N
CH3
Compound (4) is EPR silent suggesting the possibility of
polymerisation and the appearance of an antiferromagnetic
coupling between paramagnetic ions mediated by the
bridging ligands. This behaviour is also according with the
smaller value of the magnetic moment at room temperature.
The square planar surrounding of the M(II) centres are
supposed to be realised through both chloride and sulphur
bridges, assembling poly-nuclear entities in the solid state
of the compound (as is shown below).
The complexes M(L)ClꢀnH2O ((1) M:Ni, L:L1, n = 0.5;
(3) M:Ni, L:L2, n = 0.5); ((2) M:Cu, L:L1, n = 1; (4)
M:Cu, L:L2, n = 0) were also synthesized and character-
ised. The major goal of this article was to evidence the
thermal behaviour of these Schiff base and their complexes
that also present in vitro an antibacterial activity.
The major IR spectral features of complexes presented
at experimental part indicate that the bands corresponding
to the combined vibration modes of the thioamide group
from the 1,3,4-thiadiazole moiety are present in the spectra
of both ligands and complexes [22–24]. Also the bands due
to amine group are absent in spectra of compounds
according with the condensation processes. New bands
appear in the region characteristic for the heterocyclic
m(C=C) ? m(C=N) vibrations [25].
R'
Cl
Cl
S
M
M
S
R'
123

724
R. Olar et al.
Biological activity
The complexes were tested also in vitro for anti-HIV
activity but it was not evidenced any significant activity.
This behaviour could be assigned either to degeneration or
rapid metabolisation of the complexes in the cultures
conditions.
The antimicrobial activity of the tested compounds was
performed against 15 microbial strains, the majority of them
being recently isolated from different clinical samples and
exhibiting different resistance patterns, i.e., Enterobacteri-
aceae (E. coli—enteropathogenic epec strains, as well as
strains producing extended spectrum beta-lactamases-esbl
rendering them resistant to all beta-lactams, Salmonella sp.,
Shigella flexneri and Shigella sp., Proteus sp., Klebsiella
pneumoniae) Pseudomonadaceae (Pseudomonas aerugin-
osa, Acinetobacter boumani—both microorganisms being
known for their high natural resistance to antibiotics),
Micrococcaceae (Staphylococcus aureus methicillin resis-
tant—MRSA), Bacillaceae (Bacillus sp.) and Candida
albicans strains. The values of minimum inhibitory con-
centration (MIC, lg/mL) are presented in Fig. 2.
Thermal behaviour of complexes
The results concerning the thermal decomposition/degra-
dation of the Schiff bases and complexes are presented in
the following (Table 1).
Schiff bases display the same thermal behaviour and the
general aspect of the DTA and TG curves excepting that
the HL1 melts at 210 °C, process that is not observed for
HL2 (Figs. 3, 4). This behaviour is consistent with a higher
molar mass corresponding to HL2.
Thermal decomposition follows in three exothermic
steps. For HL1, the melting is immediately followed by the
thermal decomposition that starts in the first step with CS2
elimination and preservation of the six-member ring
resulted after condensation. The following steps are an
overlapping of at least four processes as both TG and DTA
indicates and corresponds with the gradually oxidative
degradation of the remaining organic part. It is worth to be
mentioned that the thermal decomposition is not finished at
1000 °C for HL2, the graphite residue being identified in
the crucible.
All tested compound exhibited good antimicrobial
activity (with MIC values ranging from 32 to 256 lg/cm3).
The new copper complexes presented the best antimi-
crobial activity against Gram-positive microorganisms,
with an improved MIC comparing with the free ligand, i.e.,
complex (2) exhibited a MIC of 64 lg/mL against meth-
icilin resistant Staphylococcus aureus while compound (4)
display a similar MIC against Bacillus subtilis.
The antimicrobial activity of all four new complexes
was superior comparatively to the free ligand in case of
Pseudomonas aeruginosa and Acinetobacter boumani
strains.
In exchange, the Schiff bases proved to be more or
equally active comparatively with the new complexes
against Gram-negative, enterobacterial and fungal strains.
It must be mentioned that the used solvent, DMF, do
not influenced the antimicrobial activity of the tested
compounds at the working concentrations.
Thermal decomposition of [Ni(L1)Cl]ꢀ0.5H2O
The TG and DTA curves corresponding to the complex (1)
heated in the 20–900 °C temperature range indicate that
decomposition follows three steps (Fig. 5).
The first step of compound transformation consists in an
endothermic elimination of water molecules (Table 1). The
temperature range corresponding to the lost indicates their
nature as crystallisation water. The anhydrous specie is
stable over a 50 °C temperature range. The second step,
exothermic, is not a single one being an overlap of at least
two processes as both TG and DTA curves indicate. This
step corresponds to the partial Schiff base oxidative deg-
radation that leads to 2-mercapto-1,3,4-thiadiazolyl frag-
ment that remain coordinated. This behaviour could be
generated by the fact that monoanionic Schiff base is
coordinated through exocyclic sulphur to metallic ion and
this interaction stabilises the thiadiazole ring. Next step,
exothermic also, corresponds to organic part oxidative
degradation together with chloride loss. This consists in at
least four processes (according to TG and DTA curves
profile). The final product is NiO (found/calcd. overall
mass loss: 75.2/75.1).
512
448
1 Shigella flex neri
2 Shigella sp.
384
3 Salm onella sp.
4 Web siella pneum oniae ESBL
5 Proteus sp.
320
6 E. coli EPEC
7 E. coli ESBL 1
8 E. coli ESBL 2
256
9 E. coli ATCC 25922
10 Acinetobacter boumani
192
11 Pseudomonas aeruginosa 1700
12 Ps. aeruginosa 1829
13 Bacillus subtilis
128
14 Staphyloc occus aureus MRSA
15 Candida albicans
64
0
1
2
(1)
(2)
(3)
(4)
HL
HL
Fig. 2 The representation of the antimicrobial activity (MIC values)
of the tested compounds (white columns—Gram negative, enterobac-
terial bacterial strains, grey columns—Gram negative, pseudomonade
strains, black columns—Gram-positive bacterial strains, dark upward
diagonal columns—Candida albicans)
123

New complexes of Ni(II) and Cu(II) with Schiff bases
725
Table 1 Thermal behaviour
Complex
Step
Thermal effect
Temperature
range/°C
Dmexp/%
Dmcalc/%
data (in synthetic air
atmosphere) for Schiff bases
and complexes
HL1
Endothermic
Strong exothermic
Exothermic
210*
0
0
1.
2.
3.
1.
2.
3.
1.
2.
3.
210–240
240–410
410–1000
194–280
280–890
890–1000
70–130
38.1
27.0
34.8
29.2
44.8
13.3
2.9
38.4
27.3
34.3
29.3
45.0
25.7
3.0
Exothermic
HL2
Strong exothermic
Exothermic
Exothermic
[Ni(L1)Cl]ꢀ0.5H2O
Endothermic
Exothermic
170–320
320–900
26.8
45.4
24.8
5.7
26.6
45.5
24.9
5.7
Exothermic
Residue NiO
[Cu(L1)Cl]ꢀH2O
1.
2.
3.
Endothermic
70–140
Exothermic
Exothermic
170–260
260–730
25.5
43.5
25.3
2.5
25.5
43.5
25.3
2.5
Residue CuO
[Ni(L2)Cl]ꢀ0.5H2O
1.
2.
3.
Endothermic
70–130
Exothermic
Exothermic
180–430
430–800
39.3
37.6
20.5
21.5
56.3
22.2
39.4
37.6
20.6
21.5
56.3
22.2
Residue NiO
[Cu(L2)Cl]
1.
2.
Exothermic
Exothermic
170–290
290–860
Residue CuO
*melting point
Fig. 3 TG and DTA curves of HL1
Fig. 4 TG and DTA curves of HL2
Thermal decomposition of [Cu(L1)Cl]ꢀH2O
DTA) can be noticed in the last step. Finally, the oxidative
degradation leads to CuO in accord with the overall mass
loss (found/calcd: 74.6/74.7).
The decomposition of complex (2) comprises also three
steps and starts with water elimination, process that also
occurs at low temperatures (Fig. 6).
Thermal decomposition of [Ni(L2)Cl]ꢀ0.5H2O
The anhydrous specie is stable over a 30 °C temperature
range. The thermal degradation of this intermediate starts
at 170 °C and comprises two steps. The second step occurs
in two exothermic processes as both TG and DTA profile
indicate. At least four processes (according to both TG and
According to the TG profile the decomposition of
[Ni(L2)Cl]ꢀ0.5H2O (3) occurs in three, well-defined steps
(found/calcd. overall mass loss: 79.4/79.5) (Fig. 7).
123

726
R. Olar et al.
Fig. 7 TG and DTA curves of [Ni(L2)Cl]ꢀ0.5H2O
Fig. 5 TG and DTA curves of [Ni(L1)Cl]ꢀ0.5H2O
Fig. 6 TG and DTA curves of [Cu(L1)Cl]ꢀH2O
Fig. 8 TG and DTA curves of [Cu(L2)Cl]
After water loss in the the 50–130 °C range, the anhy-
drous specie is stable over a 50 °C temperature range. The
next step corresponds to the Schiff base partial oxidative
degradation. According to mass loss the 2-mercapto-1,3,
4-thiadiazolyl fragment remain also coordinated as result
of stabilisation induced by the Ni(II). The step consists in
at least two processes as both TG and DTA indicate. The
chloride elimination together with the rest of organic part
leads to NiO in the final step. The TG and DTA profiles are
consistent with at least four processes.
Next step comprises at least three processes (according to
TG and DTA) and consists in the remaining organic frag-
ment and chloride elimination. The final product is also
CuO (found/calcd. overall mass loss: 77.8/77.8).
Conclusions
Two Schiff bases derived from 2-amino-5-mercapto-1,3,
4-thiadiazole and the corresponding Ni(II) and Cu(II)
complexes were characterised in order to obtain new
effective antibacterial agents with a large spectrum of
biological activity.
Thermal decomposition of [Cu(L2)Cl]
Complex (4) is anhydrous and as result is very stable up to
170 °C (Fig. 8). As a consequence the decomposition
comprises only two steps and starts with the oxidative
degradation of a part of the organic ligand. The mass loss
corresponds to the benzene ring removal. For the first one
the TG and DTA curves indicate two interfering processes.
Electronic and EPR spectra of complexes are charac-
teristic for a square planar stereochemistry. The modifica-
tions in the IR spectra of ligands are in accord with
the condensation process. The low values of magnetic
123

New complexes of Ni(II) and Cu(II) with Schiff bases
727
triazole and -1-tetrazolo-10-triazole with antimicrobial properties.
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tive of interaction between paramagnetic ions at room
temperature.
10. Badea M, Olar R, Brezeanu M, Marinescu D, Segal E. Thermal
stability and non-isothermal kinetic study of three coordination
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Soradi C, et al. Thermal stability and non-isothermal decomposi-
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characterisation and thermal behaviour of some complexes with
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The antimicrobial activity of all new complexes was
superior comparatively to the free ligand in case of Pseu-
domonas aeruginosa and Acinetobacter boumani strains.
The copper complexes presented the best antimicrobial
activity against Staphylococcus aureus and Bacillus sub-
tilis strains. In exchange, the free ligands proved to be more
or equally active comparatively with the complexes against
Gram-negative, enterobacterial and fungal strains.
Thermal decomposition of complexes allowed us to
establish the number and nature of water molecule, the
composition of complexes and also the intervals of thermal
stability. The thermal degradation occurs in three steps for
the organic derivatives and the HL1 melting was observed
before decomposition. After water elimination up to
140 °C, the complexes decompose in two steps leading at
metal (II) oxides as final products. The results are in good
concordance with the complexes composition.
ˇ
13. Konstantinoviæ SS, Radovanoviæ BC, Krkljes A. Thermal
behaviour of Co(II), Ni(II), Cu(II), Zn(II), Hg(II) and Pd(II)
ˆ
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studies of bis salicylidene adipic dihydrazone derivatives and
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Acknowledgements The VIASAN Romanian National Research
Program 142/2006 financially supported this study.
17. Modi CK, Patel MN. Synthetic, spectroscopic and thermal
aspects of some heterochelates. J Therm Anal Calorim. 2008;94:
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