Polynuclear transition metal complexes with thiocarbohydrazide and dithiocarbamates

Article abstract of DOI:10.1016/j.saa.2006.09.019

Sn(tch)₂{MCl₂}₂ was prepared from the precursor Sn(tch)₂ and MCl₂. It was subsequently allowed to react with diethyldithiocarbamate which yielded the trinuclear complexes of the type Sn(tch)₂{M₂(dtc)₄}, where tch = thiocarbohydrazide, M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and dtc = diethyldithiocarbamate. They were characterized on the basis of microanalytical, thermal (TGA/DSC), spectral (IR, UV-vis, EPR, ¹H NMR) studies, conductivity measurement and magnetic moment data. On the basis of spectral data a tetrahedral geometry has been proposed for the halide complexes, Sn(tch)₂{MCl₂}₂ except for Cu(II) which exhibits a square planar coordination although the transition metal ion in Sn(tch)₂{M₂(dtc)₄} achieves an octahedral geometry where the dithiocarbamato moiety acts as a symmetrical bidentate ligand. The bidentate nature has been established by the appearance of a sharp single ν(C-S) around 1000 cm^-1. A downfield shift observed in NH_a and NH_b protons on moving from Sn(tch)₂ to Sn(tch)₂{MCl₂}₂ is due to the drift of electrons toward metal atoms. A two-step pyrolysis has been observed in the Sn(tch)₂{MCl₂}₂ complexes while their dithiocarbamato derivatives exhibit a three-stage degradation pattern. Finally, the in vitro antibacterial activity of Sn(tch)₂{M₂(dtc)₄} and the mononuclear Sn(tch)₂ has been carried out on bacterial strains Escherichia coli and Salmonella typhi. The compounds were found to be active against the test organisms. The activity of the complexes is enhanced with increasing concentration. The maximum activity in both the strains was achieved by cobalt(II) dithiocarbamate complex. Minimum activity was found for Sn(tch)₂ which generally increases with the introduction of transition metal ion in the complex.

Full text of DOI:10.1016/j.saa.2006.09.019

Spectrochimica Acta Part A 67 (2007) 995–1002
Polynuclear transition metal complexes with thiocarbohydrazide
and dithiocarbamates
a,∗
a
a
b
K.S. Siddiqi , Sadaf Khan , Shahab A.A. Nami , M.M. El-ajaily
a
Department of Chemistry, Aligarh Muslim University, Aligarh 202002, India
Chemistry Department, Faculty of Science, Garyounis University, Benghazi, Libya
b
Received 14 June 2006; accepted 18 September 2006
Abstract
Sn(tch)
2
{MCl
2
}
2
was prepared from the precursor Sn(tch)
2 2
and MCl . It was subsequently allowed to react with diethyldithiocarbamate which
yielded the trinuclear complexes of the type Sn(tch)
dtc = diethyldithiocarbamate. They were characterized on the basis of microanalytical, thermal (TGA/DSC), spectral (IR, UV–vis, EPR, H NMR)
studies, conductivity measurement and magnetic moment data. On the basis of spectral data a tetrahedral geometry has been proposed for the halide
2
{M
2
(dtc)
4
}, where tch = thiocarbohydrazide, M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and
1
complexes, Sn(tch)
2
{MCl
2
}
2
except for Cu(II) which exhibits a square planar coordination although the transition metal ion in Sn(tch)
2
{M
2
(dtc)
4
}
achieves an octahedral geometry where the dithiocarbamato moiety acts as a symmetrical bidentate ligand. The bidentate nature has been established
by the appearance of a sharp single ν(C–S) around 1000 cm . A downfield shift observed in NH and NH protons on moving from Sn(tch) to
a b 2
−
1
Sn(tch) {MCl is due to the drift of electrons toward metal atoms. A two-step pyrolysis has been observed in the Sn(tch)
while their dithiocarbamato derivatives exhibit a three-stage degradation pattern.
2
Finally, the in vitro antibacterial activity of Sn(tch) (dtc) has been carried out on bacterial strains Escherichia
2
2
}
2
2
{MCl complexes
2
}
2
2
{M
2
4
} and the mononuclear Sn(tch)
coli and Salmonella typhi. The compounds were found to be active against the test organisms. The activity of the complexes is enhanced with
increasing concentration. The maximum activity in both the strains was achieved by cobalt(II) dithiocarbamate complex. Minimum activity was
found for Sn(tch)
2
which generally increases with the introduction of transition metal ion in the complex.
©
2006 Elsevier B.V. All rights reserved.
Keywords: Thiocarbohydrazide; Dithiocarbamates; Trinuclear complexes; Antibacterial activity
1
. Introduction
Dithiocarbamates on the other hand are organosulfur com-
pounds bearing robust synthetic and chemical properties [8,9].
They form complexes with almost all elements. Commercially,
dithiocarbamates are well known for their application as NO-
trapping agents, lubricants, vulcanizers, photovoltaic material,
holographic recording system, solar control devices [10–12].
Also they are used in the removal of heavy metals [13,14].
Dithiocarbamato derivatives of tin are considered as promis-
ing species in the treatment of carcinoma [15,16]. When such
complexes are coupled with other ligands and metal ions the
pharmacological efficacy is enhanced manifold.
In the present work, thiocarbohydrazide bridged trinuclear
metal complexes and their dithiocarbamates have been synthe-
sized and characterized in order to study their spectral, thermal
properties besides their antibacterial activity. The insertion of
tin(IV) at a central position offers an opportunity to explore the
variation in magnetic moment of transition metal ions in pres-
ence of a non-transition metal.
Macrocyclic ligands acquire significance due to their flex-
ibility under both, the neutral and deprotonated forms [1,2].
Transition metal complexes with such ligands have a wide range
of biological and chemical properties [3]. Thiocarbohydrazides
constitute an important class of N, S donor ligands possessing
interesting chemical, biological and medicinal properties [4,5].
These systems contain N–C–N structural units and form chelate
rings giving rise to mononuclear and polynuclear complexes of
varying strength and complexity [6]. The broad pharmacologi-
cal activity of these species is thought to be dependent on the
chelate formation and the cavity provided by the ring [7].
∗
Corresponding author. Tel.: +91 9837284930.
E-mail address: khwajas siddiqi@yahoo.co.in (K.S. Siddiqi).
1
386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.09.019

9
96
K.S. Siddiqi et al. / Spectrochimica Acta Part A 67 (2007) 995–1002
2
. Experimental
recorded on a RE-2X Jeol EPR, spectrometer fitted with 100 kHz
field modulation. The electronic spectra were recorded on a
Cintra 5GBC spectrophotometer in DMSO. The NMR spec-
tra were recorded on a DPX-300 spectrometer in DMSO at
room temperature. The conductivity measurements were carried
out on a CM-82T Elico conductivity bridge in DMSO. Mag-
netic susceptibility measurements were done with a 155 Allied
Research vibrating sample magnetometer at room temperature.
TGA was performed with a Perkin-Elmer (Pyris Diamond) ther-
mal analyzer under nitrogen atmosphere using alumina powder
as reference. The weight of the sample was between 8 and 12 mg
Hydrated metal chlorides (Merck), hydrazine hydrate, carbon
disulfide (s.d. fine), stannic chloride anhydrous (Loba Chem-
mie) and sodium diethyldithiocarbamate (BDH) were used as
received. Methanol was distilled prior to use. Elemental analy-
ses (C, H, N and S) were carried out with a Carlo Erba EA-1108
analyzer. The metal contents were estimated by complexometric
−
1
titration [17]. IR spectra (4000–400 cm ) were recorded on a
−
1
RXI FT-IR spectrometer as KBr disc while the 600–200 cm
range was scanned with CsI on a Nexus FT-IR Thermo Nico-
let, Madison Wisconsin. EPR spectra of copper complexes were
◦
and the heating rate was maintained at 10 C/min.
2.1. Synthesis of thiocarbohydrazide (H2tch)
To a vigorously stirred solution of 99% hydrazine hydrate
(
(
400 mmol, 20.0 mL) was dropwise added neat carbon disulfide
80 mmol, 7.8 mL) in an ice bath. After refluxing this mixture
◦
for 25 min it was cooled to 0 C to obtain a yellow crystalline
product. It was filtered and washed several times with ethanol,
chilled diethyl ether and dried in vacuo.
2.2. Synthesis of Sn(tch)2
To a hot methanolic solution (20 mL) of H2tch (8 mmol,
.85 g) was added 99% SnCl4 (4 mmol, 1.04 g) and the mix-
ture was refluxed for 3 h till it became homogeneous. A few
0
Fig. 1. Synthesis of mononuclear Sn(tch)2.
Fig. 2. Synthesis of Sn(tch)2{MCl2}2, where M = Mn(II), Fe(II), Co(II), Ni(II) and Cu(II).
Fig. 3. Synthesis of trinuclear transition metal complexes Sn(tch)2{M2(dtc)4}.

K.S. Siddiqi et al. / Spectrochimica Acta Part A 67 (2007) 995–1002
997
drops of triethylamine were then added to cause precipitation
and the refluxing was continued for additional 2 h. The solvent
was removed by filtration, which afforded a light-yellow solid
(Fig. 1). It was washed with methanol and dried in vacuo.
2
.3. Synthesis of Sn(tch)2{MCl2}2
To a well stirred solution of Sn(tch)2 (2 mmol) in methanol
(
15 mL) was added 10 mL solution of metal dichloride (4 mmol)
in the same solvent. This resulted in an immediate precipitation
of the complexes (Fig. 2). However, in a few cases refluxing was
also carried out in order to ensure complete precipitation. It was
filtered, washed with methanol, chilled ether and dried in vacuo.
2
.4. Synthesis of Sn(tch)2{M2(dtc)4}
A mixture of Sn(tch)2{MCl2}2 (2 mmol) and sodium
diethyldithiocarbamate (Nadtc) (4 mmol) in methanol (25 mL)
was stirred for 3 h which afforded a thick precipitate (Fig. 3). It
was filtered washed carefully with methanol and cold ether and
dried in vacuo. The purity of all the complexes was checked by
TLC (CHCl3:MeOH = 15:1)
3
. Results and discussion
The complexes Sn(tch)2, Sn(tch)2{MCl2}2 and Sn(tch)2
M2(dtc)4} were prepared as follows and gave satisfactory ele-
{
mental analyses (Table 1) (where dtc = diethyldithio-carbamate,
M = Mn(II), Fe(II), Co(II), Ni(II) and Cu(II)).
Sn(tch)2 + 2MCl2 → Sn(tch)2{MCl2}2
(1)
Sn(tch)2{MCl2}2 + 4Nadtc → Sn(tch)2{M2(dtc)4} + 4NaCl
(2)
The Sn(tch)2{MCl2}2 and its dithiocarbamato complexes
are stable at room temperature. The conductivity measurement
−3
(
10 M) in DMSO indicated their non-electrolytic nature [18].
The coloured complexes are soluble in DMSO and DMF and
are insoluble in common organic solvents so all the attempts to
recrystallize these complexes were unsuccessful.
3
.1. IR spectra
Unlike thiosemicarbazone, the thiocarbohydrazide and its
complexes have not been found to exhibit keto-enol tautomerism
[
2
19], which is evidenced by the absence of absorption bands in
600–2800 cm (Fig. 4). Although there are five donor sites,
−
1
the tch acts as a bidentate ligand. On moving from free tch to
Sn(tch)2 the ν(N–H) is blue shifted (Table 2). This band was
further lowered in Sn(tch)2{MCl2}2 suggesting the formation of
M–N coordinate covalent bond. Since the ν(C S) of tch remains
unaltered it is ascertained that it does not bind the metal ion
[
20].
The
Sn(tch)2{M2(dtc)4} (Fig. 3) exhibit single sharp ν(C S)
corresponding
metal
dithiocarbamates
of
−
1
band in 995 ± 6 cm range which is due to symmetrically

9
98
K.S. Siddiqi et al. / Spectrochimica Acta Part A 67 (2007) 995–1002
Table 2
Diagnostic IR bands of the ligand, its mononuclear and trinuclear complexes
Complex
ν(N–H)
ν(C· · ·N)
ν(C· · ·S)
ν(C S)
ν(Sn–N)
ν(M–N)
ν(M–S)
H2tch
Sn(tch)2
3220s
3198s
3171s
3172s
3170s
3174s
3168s
3146s
3153s
3162s
3155s
3154s
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
759s
763s
760s
760s
762s
763s
760s
761s
762s
763s
760s
472m
458m
454m
458m
458m
460m
461m
462m
458m
459m
465m
Sn(tch)2{MnCl2}2
Sn(tch)2{FeCl2}2
Sn(tch)2{CoCl2}2
Sn(tch)2{NiCl2}2
Sn(tch)2{CuCl2}2
Sn(tch)2{Mn2dtc4}
Sn(tch)2{Fe2dtc4}
Sn(tch)2{Co2dtc4}
Sn(tch)2{Ni2dtc4}
Sn(tch)2{Cu2dtc4}
438w
427w
432w
434w
438w
429w
425w
428w
440w
431w
–
–
–
–
1609s
1604s
1605s
1604s
1606s
1001s
992s
1000s
995s
988s
408m
385m
364m
368m
492m
range, which is in agreement with the observations made by
other workers [25].
3.2. Electronic spectra and magnetic moments
Generally, thehigh-spintetrahedralMn(II)complexesexhibit
spin-forbidden transitions unlike their octahedral analogs which
shows both spin-forbidden as well as parity-forbidden bands
[26]. This accounts for the extreme pale colour in case of octa-
hedral complex. The pale yellow coloured Sn(tch)2{MnCl2}2
−
1
in DMSO shows a solitary d–d band at 16,680 cm assigned
4
6
to T1 ← A1 transition. It also exhibits a broad strong charge
−
1
transfer band centered at 35,450 cm . The magnetic moment
of 5.77 BM is in proximity with the calculated spin-only value of
Fig. 4. IR spectrum of Sn(tch)2{Co(dtc)2}2 exhibiting bidentate dithiocarbam-
ato moiety.
5.9 BM indicating a high spin tetrahedral arrangement of Mn(II)
ion.
However, the Sn(tch)2{Mn2dtc4} depicts three weak inten-
bound dithiocarbamato moiety, although the same band splits
when it behaves as a monodentate ligand [21]. However, the
band near 1500 cm is a characteristic of NCS2 and exhibits
partial double bond character in the S2C· · ·NR2 bond. This may
be due to the delocalization of electron cloud over the S2CNR2
region leading to the following possible resonating structures.
−1
sity bands at 28,140, 21,520 and 15,490 cm
which have
4
6
4
6
been assigned to T1g(P) ← A1g, T2g(G) ← A1g and
−
1
4
6
T1g(G) ← A1g transitions, respectively [27]. The low mag-
netic moment (5.69 BM) might be due to distortion from
regular octahedral field. Thus the ligand field bands and
−
1
We have observed a strong band at 1495 cm that is inter-
mediate between ν(C–N) and ν(C N) indicating a partial double
bond character. Moreover, the ν(C· · ·N) seems to be insensitive
to the nature of the metal [22].
magnetic moment value support a distorted octahedral geometry
for Sn(tch)2{Mn2dtc4} complex [28]. The ligand field parame-
ters were calculated from Orgel energy level diagram using ν2/ν1
ratio. A low value of β (Bcomplex/Bfree-ion) may be attributed to
the low covalent character of metal ligand bond (Table 3).
All the tetrahedral Fe(II) complexes are high-spin and dis-
plays only one spin allowed d–d absorption. A strong band at
−
1
The region 350–500 cm is quite crucial in elucidating the
metal coordination. A band of medium intensity was observed at
72 cm corresponding to ν(Sn–N) and is shifted appreciably
by 10–20 cm in the complexes [23]. This bathochromic shift
implies a partial drift of electrons due to the coordination with
the metal centers. Also, the spectrum depicts medium intensity
bands occurring in the far-IR region consistent with the M–S
stretching frequency [24]. The ν(M–S) depends on the nature of
the metal ion and the substituents attached with the sulfur. We
−1
4
−
1
−1
23,474 cm was observed in case of Sn(tch)2{FeCl2}2 corre-
5
5
sponding to E ← T2 transition while the magnetic moment
value was found to be 5.35 BM corresponding to four unpaired
electrons. These observations are consistent with the tetrahe-
dral nature of Fe(II) in Sn(tch)2{FeCl2}2 [29]. However, in case
−
1
of Sn(tch)2{Fe2dtc4} a broad band centered at 19,200 cm is
−
1
5
5
have observed medium intensity ν(M–S) in the 408–364 cm
observed attributing to Eg ← T2g transition. A low magnetic

K.S. Siddiqi et al. / Spectrochimica Acta Part A 67 (2007) 995–1002
999
Table 3
Magnetic susceptibility, electronic spectra and ligand field parameters of the complexes
10 Dq (cm 1)
−
−1
B (cm )
β
Complex
Magnetic
moment
Electronic
bands
log ε
(L mol cm )
Possible assignments
1
1
(cm 1)
−
(
BM)
4
5
4
3
5
4
4
5
4
3
3
2
6
Sn(tch)2{MnCl2}2
Sn(tch)2{FeCl2}2
Sn(tch)2{CoCl2}2
Sn(tch)2{NiCl2}2
Sn(tch)2{CuCl2}2
Sn(tch)2{Mn2dtc4}
5.77
5.35
4.38
3.38
1.82
5.69
16680
23474
16500, 18860
9200, 15460
12150, 17933
28140, 21520,
2.2
3.1
2.1, 3.7
2.9, 2.1
2.9, 2.1
3.2, 2.7, 2.3
T1 ← A1
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
0.30
5
E ← T2
4
4
4
T2(F) ← A2(F), T1(F) ← A2(F)
3
3
3
A2(F) ← T1(F), T1(P) ← T1(F)
2
5
2
Eg ← B1g, A1g ← B1g
6
4
6
T1g(P) ← A1g, T2g(G) ← A1g,
15075
1005
6
15490
T1g(G) ← A1g
5
Sn(tch)2{Fe2dtc4}
Sn(tch)2{Co2dtc4}
Sn(tch)2{Ni2dtc4}
2.22
4.66
3.81
19200
19608
12445, 15860,
2.4
2.6
3.5, 3.1, 2.5
Eg ← T2g
–
–
–
–
1613
–
–
0.64
4
4
4
T2(F) ← A2(F), T1(F) ← A2(F)
3
3
3
T2g(P) ← A2g, T1g(F) ← A2g,
16138
3
20980
T1g(P) ← A2g
2
2
2
2
Sn(tch)2{Cu2dtc4}
1.97
13890, 18320
1.6, 1.1
B2g ← B1g, Eg + A1g ← B1g
–
–
–
moment value (2.22 BM) obtained in the present case may be
due the low spin-high spin cross-over phenomenon, which is
quite common in dithiocarbamato complexes [30].
Generally, the intense blue tetrahedral Co(II) complexes
exhibit four d–d bands akin to pale red/purple Co(II) octa-
hedral complexes. But generally, two transitions are observed
in each case [31]. Two strong bands are observed at 12,658
dral or pseudo-tetrahedral environment in the complex [35]. The
Sn(tch)2{Cu2dtc4} consists of a broad, low intensity band cen-
−
1
2
2
tered at 13,890 and a shoulder at 18,320 cm . The Eg and T2g
states of the octahedral Cu(II) ion split under the influence of
2
2
the tetragonal distortion causing three transitions, B2g ← B1g,
2
2
2
2
Eg ← B1g and A1g ← B1g in an unresolved fashion [36].
These assignments are in agreement with the general observa-
tion that Cu(II) d–d transitions are normally close in energy [37].
−
1
4
4
and 18,182 cm
corresponding to T2(F) ← A2(F) and
T1(F) ← A2(F) transitions, characteristic of tetrahedral Co(II)
ion. However, in case of Sn(tch)2{Co2dtc4}, we observed bands
4
4
−1
A moderately intense peak observed at 23,040 cm may be due
to the ligand–metal charge transfer [38]. The magnetic moment
of 1.97 BM also falls within the range normally observed for
octahedral Cu(II) complexes further supporting an octahedral
environment around the Cu(II) ion.
−
1
4
4
at 24,540 and 17,480 cm corresponding to T1g(P) ← T1g(F)
4
4
and T2g(F) ← T1g(F) transitions, respectively. These bands in
the visible region are consistent with spin allowed d–d tran-
sition for an octahedral Co(II) ion. The magnetic moment
value of 4.38 and 4.66 BM further establishes the proposed
tetrahedral and octahedral geometry for Sn(tch)2{CoCl2}2 and
Sn(tch)2{Co2dtc4} complexes, respectively.
3.3. EPR spectra
The 300 K EPR spectra of the powdered Sn(tch) {CuCl }
2
2 2
The tetrahedral Ni(II) complexes exhibit strong
bands as compared to their octahedral counterparts. The
|| ⊥
and Sn(tch) {Cu dtc } exhibit g and g regions but do not
2
2
4
reveal the nitrogen coupling. The spectrum is typically axial with
−
1
Sn(tch)2{NiCl2}2 shows two bands at 9200 and 15,460 cm
d
as the ground state. Since the spectrum was recorded at
2
2
x −y
3
3
3
3
corresponding to A2(F) ← T1(F) and T1(P) ← T1(F)
room temperature, hyperfine splitting was not observed which
is diagnostic in determining the number of nitrogen atoms coor-
dinated to the Cu(II) ion. The absence of any signal around
1600 ± 100 G for Sn(tch) {CuCl } and Sn(tch) {Cu dtc }
transitions, respectively. A low value of magnetic moment
(
3.38 BM) obtained in the present case, might be due to the
deviation from the regular tetrahedral field [32].
2
2
2
2
2
4
The Sn(tch)2{Ni2dtc4} complex gives a room tempera-
ture magnetic moment of 3.81 BM which is in the range
observed for octahedral complexes (2.9–3.3 BM) [33]. Three
well resolved d–d bands are observed at 12,445, 15,860 and
complexes are indicative of zero exchange interaction between
the two peripheral Cu(II) atoms. This implies that the bridg-
ing thiocarbohydrazide moiety does not transfer any coupling
betweenthetwoCu(II)ions[39]. TheEPRparameters(g = 2.28
||
2 2
−
1
3
3
3
3
2
0,980 cm corresponding to T2g ← A2g, T1g(F) ← A2g
⊥
and g = 2.06) obtained in case of Sn(tch) {CuCl } are in
2
3
3
and T1g(P) ← A2g transitions, respectively. The spectrum
close agreement for a cubic ligand field in square planar com-
plexes [40] which is also corroborated from their UV–vis data.
However, the EPR spectrum of Sn(tch) {Cu dtc } gave sig-
also shows two strong charge transfer bands at 29,490 and
−
1
3
0,280 cm . Thus an octahedral geometry for the Ni(II) ion
2
2
4
is ascertained [33]. The Racah parameters (B and β) obtained in
the present case, indicates a considerable covalent character of
the metal ligand bond (Table 3).
nals corresponding to g = 2.18 and g = 2.14, consistent with
||
⊥
an axially elongated geometry with g > g > 2.06, suggest-
ing that the unpaired electron probably resides in the d
orbital [41]. Moreover, the broadening and splitting of the g
might be due to the overlap of g and g components con-
||
⊥
2
2
x −y
The electronic spectrum of Sn(tch)2{CuCl2}2 shows two
⊥
−
1
assigned to 2Eg ← B1g
2
bands at 12,150 and 17,933 cm
||
⊥
2
2
and A1g ← B1g transitions, respectively, and is interpreted
firming a lowered site symmetry [42]. Thus, the EPR data
in terms of square-planar geometry [34]. The absence of any
supports a distorted octahedral geometry for Sn(tch) {Cu dtc }
2
2
4
−
1
band below 10,000 cm rules out the possibility of a tetrahe-
[43].

1
000
K.S. Siddiqi et al. / Spectrochimica Acta Part A 67 (2007) 995–1002
Table 4
1
H NMR spectra of Sn(tch)2 and its complexes
Complex
δ NHa
ppm)
δ NHb
(ppm)
δ(CH2)
(ppm)
δ(CH3)
(ppm)
(
Sn(tch)2
8.59
8.64
8.68
8.66
8.69
8.70
8.81
8.80
8.83
8.84
8.80
8.92
8.97
8.94
8.96
8.98
8.98
8.88
8.92
8.94
9.93
8.95
–
–
–
–
–
–
–
–
–
–
–
–
Sn(tch)2{MnCl2}2
Sn(tch)2{FeCl2}2
Sn(tch)2{CoCl2}2
Sn(tch)2{NiCl2}2
Sn(tch)2{CuCl2}2
Sn(tch)2{Mn2dtc4}
Sn(tch)2{Fe2dtc4}
Sn(tch)2{Co2dtc4}
Sn(tch)2{Ni2dtc4}
Sn(tch)2{Cu2dtc4}
3.48 q
3.52 q
3.58 q
3.51 q
3.44 q
1.01 t
1.05 t
0.98 t
1.06 t
1.09 t
3
.4. 1H NMR spectra
1
The H NMR spectra of Sn(tch)2 in DMSO exhibits two
peaks at δ 8.59 and 8.92 corresponding to NHa and NH protons,
b
respectively. The downfield shift in the NH proton might be due
b
the coordination with the Sn-atom [44]. These peaks are further
lowered in the halide complexes, Sn(tch)2{MCl2}2 complexes
indicating a partial drift of electrons towards the peripheral metal
ions (Table 4).
However, the dithiocarbamto complexes show two more sig-
nals in addition to peaks for NHa and NH protons. A quartet
b
in 3.44–3.58 ppm range was observed for the methylene protons
while the methyl protons were found to resonate as triplet in
0
.98–1.09 ppm range [45].
3
.5. TGA/DSC
The mass losses, temperature ranges and final decomposi-
tion product for the complexes are presented in Table 5. The
TGA curve of the mononuclear complex, Sn(tch)2 shows two
major breaks. The first thermolytic break of Sn(tch)2 ranges
◦
between 170 and 198 C which corresponds to the liberation
of two N2 molecules contributing 17.14% weight loss (calcd.
◦
1
7.01%). However, the second stage between 200 and 490 C
is consistent with the decomposition of the total organic moiety
leaving behind tin as the end product [46]. These findings are
consistent with the DSC curves of Sn(tch)2 which exhibits peaks
◦
◦
at 180, 280 and 465 C and a small hump at 640 C. The first
peak is sharp and endothermic in nature implying that the loss of
N2 is an endothermic process. The degradation of organic moi-
ety exhibits a two-peak composite pattern; a sharp endothermic
◦
◦
peak at 280 C and a broad exothermic hump centered at 465 C.
However, the small exotherm observed at 640 C might be due
◦
to the formation of elemental tin.
The TGA profile of the trinuclear complexes
Sn(tch)2{MCl2}2 is relatively simple and consists of three
discreet stages. The first decomposition corresponds to the
◦
loss of two N2 molecules in the temperature range 45–170 C
(
4
Table 5). The second stage is ascribed to a weight loss of about
0% of the total weight of the complex corresponding to the
decomposition of remaining organic moiety {C2H8N4Cl4}.

K.S. Siddiqi et al. / Spectrochimica Acta Part A 67 (2007) 995–1002
1001
The third stage is attributable to the formation of elemental
◦
tin in 395–650 C range, which accounts for 20% weight loss.
Metal sulfides are obtained as the end products in all the cases
[
47]. The TGA results are in close accord with the DSC curves.
◦
A sharp endotherm observed at 92 C is attributable to the
liberation of two N2 molecules whereas a strong exothermic
peak observed at 250 C may be suggested to be due to the
◦
degradation of organic moiety. A strong hump centered at
◦
5
85 C can be corroborated to the formation of elemental tin.
Moreover there is no well-defined exotherm and endotherm for
the formation of metal sulfide.
The thermal analysis curves suggest that the decomposition
of Sn(tch)2{M2dtc4} is in good agreement with the general
pyrolysis pattern of metal dithiocarbamato complexes. Gener-
ally, the metal dithiocarbamates, on pyrolysis volatilize leav-
ing some residue or decompose to the corresponding metal
sulfide [48]. In the present study, the first stage of decom-
position is due to the liberation of eight ethene, six hydro-
gen and two N2 molecules contributing to about 29% of the
Fig. 5. Biological activity of Sn(tch)2 and its complexes Sn(tch)2{M2(dtc)4}.
◦
total weight loss. The pyrolysis begins at 50 C and contin-
4. Conclusion
◦
ues up to 190 C. This is a common feature of dithiocarba-
◦
mates [49]. The second stage ranges from 220 to 390 C and
The halide and dithiocarbamato complexes of Sn(tch) were
2
is consistent with the degradation of remaining organic moi-
prepared and characterized by various analytical and spectral
ety {C H4N8S8}. The DSC curves of the complexes depict
techniques. The anti-microbial activity of the dithiocarbamato
complexes was evaluated by disc diffusion technique. The com-
pounds were found to be active against the bacterial strains E.
coli and S. typhi and the maximum activity is found in case of
cobalt(II) dithiocarbamate complex.
6
typical endotherms characteristic of liberation of ethene, hydro-
gen and N2 molecules. A sharp exothermic peak is obtained at
◦
2
78 C, associated with the loss of remaining organic moiety. A
◦
broad exothermic hump is centered at 480 C, is attributable
to the formation of elemental tin while there is no distinct
peak or hump for the last process of formation of metal
sulfide.
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