Thermal studies on some organotin(iv) complexes with piperidine and 2-aminopyridine dithiocarbamates

Article abstract of DOI:10.1007/s10973-005-0461-0

The complexes of piperidine dithiocarbamate, 2-aminopyridine dithiocarbamate and organotin(IV) of the type R₃Sn(L¹), R₂Sn(L¹)₂, R₃Sn(L²), R₂Sn(L²)₂

Full text of DOI:10.1007/s10973-005-0461-0

Journal of Thermal Analysis and Calorimetry, Vol. 78 (2004) 953–964
THERMAL STUDIES ON SOME ORGANOTIN(IV)
COMPLEXES WITH PIPERIDINE AND
2-AMINOPYRIDINE DITHIOCARBAMATES
R. Sharma and N. K. Kaushik*
Department of Chemistry, Delhi University, Delhi 110007, India
(Received August 29, 2003; in revised form March 1, 2004)
Abstract
The complexes of piperidine dithiocarbamate, 2-aminopyridine dithiocarbamate and organotin(IV) of
the type R3Sn(L1), R2Sn(L1)2, R3Sn(L2), R2Sn(L2)2, [R=C6H5CH2 (benzyl), p-ClC6H4CH2 (p-chloro-
benzyl), L1=sodium piperidine dithiocarbamate and L2=sodium 2-aminopyridine dithiocarbamate] have
been synthesised and characterised by spectral studies (IR, UV, 1H NMR). Thermogravimetric (TG) and
differential thermal analytical (DTA) studies have beeen carried out for these complexes and from the
TG curves, the order and apparent activation energy for the thermal decomposition reactions have been
elucidated. The various thermal studies have been correlated with some structural aspects of the
complexes concerned. From DTA curves, the heat of reaction has been calculated.
Keywords: apparent activation energy and heat of reaction, differential thermal analysis,
organotin(IV) complexes, order of thermal reaction, thermogravimetry
Introduction
Recent studies on determination of kinetic parameters from thermal data prompted us
to analyse the variation in thermal stability of some metal complexes in terms of their
structural parameters. This follows from our interest to investigate the thermal be-
haviour of metal dithiocarbamate complexes.
The organotin compound use as efficient fungicides, because they degrade in soil
to give inorganic tin, which is nontoxic. Trialkyl and triaryl tin compounds are ideal
wood preservatives, as they are highly active vs. both fungi and insects, which attack
wood. Dialkyl and diaryl tin compounds show pronounced bacteriostatic properties to-
wards gram +ve bacteria as well as gram –ve bacteria. The most important structural
feature of the solid organotin halides is their strong tendency to increase their coordina-
tion number from four to five or six by intermolecular association.
*
Author for correspondence: E-mail: nkkaushik@chemistry.du.ac.in
1388–6150/2004/ $ 20.00
Akadémiai Kiadó, Budapest
© 2004 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

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SHARMA, KAUSHIK: ORGANOTIN(IV) COMPLEXES
The dithiocarbamates (R2NCS–2 ) are the half amides of dithiocarbonic acid. These
are sulphur analogs of carbamates (R2NCO–2 ). The strong metal binding properties of
dithiocarbamates are directly related with the presence of two donor sulphur atoms.
A large number of metal dithiocarbamates of aliphatic and aromatic amines have
been reported [1–5, 6]. Copper(II) dithiocarbamates are easily prepared and their
properties have been studied [7, 8–10]. The reaction of gold(III) chloride with (R2dtc) in
aqueous solution gives black-brown crystals of Au(R2dtc)3 [11]. Delepine first reported
the water insoluble dithiocarbamate of zinc(II) and cadmium(II) [7]. The first detail study
on arsenic(III) dithiocarbamate complexes was carried out by Melatesta [12].
Metal dithiocarbamates find applications in the field of rubber industry as
vulcanisation accelerators and antioxidants. They have been employed extensively as
inhibitors in researches on enzymes. Their usefulness as inhibitors is due to their metal
combining capacity and their ability to interact with sulfhydryl compounds. In analytical
chemistry, the insolubility of metal dithiocarbamates in water, accounts for their
usefulness for the estimations of metals. The fungicidal activity of the dithiocarbamates
was described by Martin [13] and by Tisdale and Williams [14]. The insecticidal activity
of the dithiocarbamates was reported by Guy [15, 16]. The N,N-dimethyl-S-alkyl-
sulphenyl dithiocarbamates have been patented as rodent repellents by Goodhue [17].
Several metal N-ethyl-N-phenyl dithiocarbamates have been prepared and their
influence on the kinetics of cure was studied by Ondrusova et al. [18].
Experimental
The following instruments were used: Elico conductivity Bridge, model CM-180 for
conductance measurements; Perkin Elmer, FTIR spectrometer, spectrum 2000 for
IR spectra; Shimadzu UV-visible spectrophotometer model 260 for UV spectra; Brucker
spectrospin advance 300 spectrometer and Hitachi R-600 FTNMR spectrometer for
1H NMR. Rigaku model 8150 Thermoanalyser (Thermaflex) was used for simultaneous
recording of TG-DTA curves in air at a heating rate of 283 K min–1. For TG, the
instrument was calibrated using calcium oxalate while for DTA calibration was done
using indium metal, both of which were supplied along with the instrument. A flat bed
type Al-crucible was used with α-alumina (99% pure) as the reference material for DTA.
Tin powder and 2-aminopyridine were purchased from CDH Pvt Ltd. Mumbai, India.
Piperidine was purchased from E-Merk, (India) Limited, Worli, Mumbai. All reagents
were of AR grade. They were used without further purification.
Preparation and characterisation of complexes
Preparation of ligands
(i) Preparation of sodium piperidine dithiocarbamate (L1): It was prepared by the
modified method given by Gilman and Blatt [19]. A three-necked 500 mL flask was
used in which the middle neck was fitted with a mechanical stirrer; second neck with
a separating funnel and the third neck was loosely stoppered. The flask was placed in
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955
a freezing mixture of common salt and ice. Sodium hydroxide (10.0 g, 0.25 mol), dis-
solved in minimum amount of water, was added to the flask. Pure carbon disulfide
(15.1 mL, 0.25 mol) was also added to the flask, through the separating funnel. To the
stirred mixture, pure piperidine (21.28 g, 0.25 mol) was added drop by drop through
the separating funnel in about 30 min. The contents were stirred mechanically for
about 30 min. The sodium piperidine dithiocarbamate precipitated out. It was dried
and recrystallised form acetone. The reaction proceeds in the manner shown below:
Analysis: found C=39.67%, H=5.95%, N=7.75%, S=35.40%; calc.: C=39.31%,
–1
----
----
H=5.46%, N=7.64%, S=35.02%; IR(KBr), cm : ν(C N), 1475; ν(C S),
964, 1025.
(ii) Preparation of sodium 2-aminopyridine dithiocarbamate (L2): This compound
was prepared by the same procedure (Gilman and Blatt [19]) as adopted in the case of
sodium piperidinedithiocarbamate the reaction proceeds in the manner shown below:
Analysis: found: C=37.65%, H=2.85%, N=14.45%, S=33.40%; calc.: C=37.47%,
–1
----
----
H=2.60%, N=14.57%, S=33.38%; IR(KBr), cm : ν(C N), 1488; ν(C S), 970, 1019.
Preparation of organotin(IV) compounds [20]
Preparation of complexes
i) Preparation of sodium piperidine dithiocarbamate complexes: A solution of sodium
piperidine dithiocarbamate (L1, 3.6 g, 0.02 mol) in 25 mL THF was added slowly to a
solution of R3SnCl (0.02 mol) or R2SnCl2 (0.01 mol) in 25 mL THF. The contents were
stirred for 10–12 h on a water bath at 70°C. After cooling, the complexes were filtered
out. These were dried in vacuum dessicator over anhydrous CaCl2.
ii) Preparation of sodium 2-aminopyridine dithiocarbamate complexes: A solution of
sodium 2-aminopyridine dithiocarbamate (L2, 3.84 g, 0.02 mol) in 25 mL THF was
added slowly to a solution of R3SnCl (0.02 mol) or R2SnCl2 (0.01 mol) in 25 mL THF.
The contents were stirred for about 5 h at room temperature. The reaction mixture was
reduced to one-fourth of its original volume by evaporating the solvent under vacuum.
The complexes were precipitated on addition of dry petroleum ether. These were dried in
vacuum dessicator over anhydrous CaCl2.
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Characterisation
Satisfactory result of elemental analysis and spectral studies revealed that the com-
plexes were of good purity. The complexes obtained were crystalline or powder-like
and colourless. Conductance for these complexes were <10 ohm–1 mol–1 cm2 indicat-
ing that these complexes were nonelectrolytes. These complexes were soluble in
DMSO and insoluble in most of the organic solvents.
In IR spectra, the absorption at 1450–1550 cm–1 in case of the ligand was
----
----
assigned to ν(C N) vibration of S2C NR2 bond. The second region in the range
950–1050 cm–1 was associated with the ν(C S) vibration. The
----
region 300–400 cm–1 was assigned to M—S stretching vibration. In dithiocarbamate
complexes one strong band around 1000 cm–1, indicating that all the dithiocarbamate
ligands are bidentate and symmetrically bounded, in case of monodentate
dithiocarbamate [21, 22] ligand a doublet arises around 1000 cm–1 separated
by >20 cm–1 which is due to non-equivalence of two C---S stretching vibration. Far
IR spectra contained the M—S stretching frequencies [23] in region 352–365 cm–1.
The band at ~370 cm–1 was assigned to M—Cl vibrations. The C—H stretching
–1
----
appeared in the region 2900–3000 cm . The ν(C C) aromatic stretching
frequencies, coupled with the symmetric and asymmetric inplane stretching vibra-
tional bands appeared in the region 1400–1600 cm–1 [24]. The C—H asymmetric
in-plane aromatic deformation occurs at ~1370, ~1300, ~1070 cm–1. The IR band
at ~800 cm–1 was assigned to C—H out of phase deformation.
In UV spectra of sodium piperidine dithiocarbamate two bands at 270 nm
(logε=1.765) and 288 nm (logε=1.790) were observed due to π–π* transition of
*
---- ----
N
C
S groups and n–π electronic transition involving lone pair of electrons
located on the sulphur atom, respectively. Two absorption bands were observed for
sodium-2-aminopyridine dithiocarbamate at 275 nm (logε=1.740) and 290 nm
(logε=1.608). These bands shifted to lower wavelength on complexation, showing
the involvement of NCS2 group in complexation in all the complexes. In all the
dithiocarbamate complexes one band at 350–354 nm appeared which was due to
metal→ligand charge transfer.
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957
The 1H NMR spectra of piperidine dithiocarbamate complexes showed signals in δ
6.7–7.2 (m, 15H, Ar-H), 1.7–1.9 (t, 6Ha, –CH2), 3.4–3.5 (d, 4Hb, –CH2), 3.3 (S, 6H,
–CH2) regions. In free sodium piperidine dithiocarbamate ligand, the signals have been
reported in δ 1.62 (t, 6Ha, –CH2) and δ 3.1–3.2 (d, 4Hb, –CH2). The 1H NMR spectra of
2-aminopyridine dithiocarbamate complexes showed signals in δ 7.0–7.2 (m, 15H,
Ar–H), 3.2–3.5 (S, 6H, –CH2), 7.3–7.5 (m, 1Ha, –CH), 7.5–7.6 (m, 1Hb, –CH), 8.0–8.2
(m, 1Hc, –CH), 8.6–8.8 (d, 1Hd, –CH), 5.0–5.2 (S, 1He, –NH). In free sodium
2-aminopyridine dithiocarbamate ligand, the signals have been reported in δ 6.9–7.0 (m,
1Ha, –CH), 7.42–7.45 (m, 1Hb, –CH), 7.7–7.8 (m, 1Hc, –CH), 8.45 (d , 1Hd, –CH) and
4.7–4.9 (S, 1He, –NH) regions.
A downfield shift in the position of resonance signals of the complexes in com-
parison to the free ligands may be attributed as a result of co-ordination of the ligand
to metal ion. The spectra showed no trace of the free ligands, indicating that the com-
plexes did not dissociate on dissolution.
Results
(C6H5CH2)3Sn(L1) complex
The TG curve (Fig. 5) indicates that the complex starts decomposing at 423 K and
continues to decompose till 650 K, this step corresponds to the loss of all the three
benzyl groups. The expected and observed mass losses are 49.54 and 48%,
respectively. The final step corresponding to the decomposition of organic part L1
and subsequent conversion of Sn to SnO2, lies in the temperature range 650–960 K.
The total expected and observed mass losses, after the complete formation of SnO2
are 72.80 and 74.99%, respectively.
In the DTA profile (Fig. 5) step I is shown as one exothermic peak at 533 K and
the final step is marked by an endothermic peak with Tmax at 920 K. The heat of
reaction (∆H) for step I is 26.98 J g–1and for step II it is 79.21 J g–1.
(C6H5CH2)2Sn(L1)2 complex
The TG curve indicated that the first decomposition step which lies in the tempera-
ture range 493–673 K, corresponds to loss of both the benzyl groups. The expected
and observed mass losses for this step were 29.35 and 28%, respectively. The final
step (673–970 K) corresponded to the decomposition of the organic part L1 and the
subsequent formation of SnO2, until which the total observed mass loss is 76% and
the total calculated mass loss was 75.85%.
In DTA profile one exothermic peak with Tmax at 590 K corresponded to the step I
and the endothermic peak with Tmax at 910 K corresponded to the final step. The heat of
reaction (∆H) for step I was 28.01 J g–1and for the final step ∆H 76.50 J g–1.
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(p-ClC6H4CH2)3Sn(L1) complex
The first step of thermal degradation initiated at 473 K and continued upto 673 K. The
observed mass loss of 53% corresponded to the loss of all the three p-chlorobenzyl
groups. The expected mass loss for this step was 57.48%. Final step, which corresponded
to the decomposition of the organic part L1 and the formation of SnO2, lies in the
temperature range 673–990 K. The total observed mass loss after the completion of this
step was 79%, while the expected mass loss was 77.63%.
In the DTA curve, step I was shown as one exothermic peak with Tmax 600 K and
the final step was marked by an endothermic peak with Tmax at 905 K. For step I the
heat of reaction (∆H) was 20.16 J g–1 and for the final step (∆H) was 74.92 J g–1.
(C6H5CH2)3Sn(L2) complex
Step I of thermal degradation, which initiated at 470 K and continued up to 593 K
corresponds to the loss of all the three benzyl groups. The expected and observed
mass losses were 48.75 and 47.70%, respectively. After the completion of the final
step, which corresponded to the decomposition of the organic part L2 and the forma-
tion of SnO2, the total expected and observed mass losses were 73.23 and 75%,
respectively. This step lies in the temperature range 593–973 K.
The DTA profile showed two thermal effects. The exothermic peak with Tmax
at 523 K (∆H=28.42 J g–1) corresponded to step I and an endothermic peak with Tmax
at 920 K (∆H=110.00 J g–1) corresponded to the final step.
(C6H5CH2)2Sn(L2)2 complex
The TG curve indicated that the complex decomposed in two steps. Step 1, corresponded
to the loss of both the benzyl groups lies in the temperature range 446–675 K. The
expected mass loss was 28.52% while the observed mass loss was 27%. Final step,
which corresponded to the decomposition of the organic part L2 and formation of SnO2
lies in the temperature range 675–1043 K. The total expected and observed mass losses
after the complete formation of SnO2 were 76.53 and 78.5%, respectively.
The DTA profile showed three thermal effects. The first endothermic peak with
max at 460 K corresponded the fusion of the compound. Step I was represented by an
T
exothermic peak with Tmax at 540 K (∆H=26.22 J g–1). The final step appeared in the
form of an endothermic peak with Tmax at 1001 K (∆H=125.91 J g–1).
(p-ClC6H4CH2)3Sn(L2) complex
Step I of thermal degradation (Fig. 6) initiates at 483 K and continues upto 623 K.
This step corresponds to the loss of all the three benzyl groups. The expected and
observed mass losses for step I are 56.63 and 55%, respectively. After the completion
of the final step, which corresponds to the decomposition of the organic part L2 and
the formation of SnO2, the total expected and observed mass losses are 77.35 and
78.4%, respectively. This step lies in the temperature range 623–973 K.
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959
The DTA profile (Fig. 6) shows two thermal effects. Step I is shown as an
exothermic peak with Tmax at 577 K (∆H= 26.56 J g–1), while the final step appears as
an endothermic peak with Tmax at 940 K (∆H=120.29 J g–1).
Discussion
The results of the TG and DTA evaluations are compiled in Table 1 and the mass loss
data are summarized in Table 2. From the TG curves, the order (n) and activation
energy (Ea) of the thermal decomposition reaction have been elucidated by the
method of Coats and Redfern [25]. From the DTA curves the heat of reaction (∆H)
and Tmax have been calculated.
The linearization curves are shown in Figs 1–4. The TG and DTA curves are
shown in Figs 5 and 6. The order of reaction for the thermal decomposition of the
Fig. 1 Linearisation curves of step I of a – (C6H5CH2)3Sn(L1); b – (C6H5CH2)2Sn(L1)2;
c – (p-ClC6H4CH2)3Sn(L1)
Fig. 2 Linearisation curves of step II of a – (C6H5CH2)3Sn(L1); b – (C6H5CH2)2Sn(L1)2;
c – (p-ClC6H4CH2)3Sn(L1)
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SHARMA, KAUSHIK: ORGANOTIN(IV) COMPLEXES
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SHARMA, KAUSHIK: ORGANOTIN(IV) COMPLEXES
Mass loss observed (calc.)/%
961
Table 2 Mass loss data
Compounds
Nature of products
Step I
Step II
(C6H5CH2)3Sn(L1)
(C6H5CH2)2Sn(L1)2
(p-ClC6H4CH2)3Sn(L1)
(C6H5CH2)3Sn(L2)
(C6H5CH2)2Sn(L2)2
(p-ClC6H4CH2)3Sn(L2)
48.00 (49.54)
28.00 (29.35)
53.00 (57.48)
47.70 (48.75)
27.00 (28.52)
55.00 (56.63)
74.99 (72.80)
76.00 (75.85)
79.00 (77.63)
75.00 (73.23)
78.50 (76.53)
78.40 (77.35)
SnO2
SnO2
SnO2
SnO2
SnO2
SnO2
above complexes was one. A comparison of the activation energy data for complexes
reveals that the Ea values of the second step of the thermal degradation of the
dithiocarbamate complexes were more than the first step.
Fig. 3 Linearisation curves for step I of a – (C6H5CH2)3Sn(L2); b – (C6H5CH2)2Sn(L2)2;
c – (p-ClC6H4CH2)3Sn(L2)
Fig. 4 Linearisation curves for step II of a – (C6H5CH2)3Sn(L2);
b – (C6H5CH2)2Sn(L2)2; c – (p-ClC6H4CH2)3Sn(L2)
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Fig. 5 TG and DTA curves of (C6H5CH2)3Sn(L1) complex
Fig. 6 TG and DTA curves of (p-ClC6H4CH2)3Sn(L2) complex
From the thermal data the following conclusion have also been drawn.
The activation energy (Ea) value for step I was lower in organotin(IV) complexes
with three R groups as compare to the complexes with two R groups, (R=C6H5CH2–
and p-ClC6H4CH2–), because of greater steric hindrance in the former type of
complexes as the complexes with R=p-Cl C6H4CH2– have lower Ea value for step I as
compare to the complexes with same number of R groups, but R=C6H5CH2–, because
the electron withdrawing effect of chlorine atom makes the R–Sn bond weak and hence
make its thermal degradation easy. Thus the Ea values followed the order.
R2Sn(L1)2 or R2Sn(L2)2>R3Sn(L1) or R3Sn(L2)
The heat of reaction (∆H) has been calculated for the thermal effects [26]. The
temperature dependent calibration coefficient was obtained from Curell equation [27].
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963
Conclusions
Thermal behaviour of the complexes has been investigated and Ea values have been
found to follow the order:
R2Sn(L1)2 or R2Sn(L2)2>R3Sn(L1) or R3Sn(L2)
It was, therefore, evident that the nature of metal ion in the organic moiety con-
tributed to the variation in the activation energy for the thermal degradation of the
complexes. The energy of activation, in turn, reflected the kinetic liability of the
complexes. The compounds with lower Ea values were more labile as compared to
those with higher Ea values.
The TG data of the complexes was supplemented by DTA studies. The heat of
reaction (∆H) has been enumerated from the DTA curves. The temperature
dependent calibration coefficient has been obtained from the Curell equation.
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