Synthesis, characterization and thermal studies of 2,2′-bipyridine adduct of bis-(N-alkyl-N-phenyl dithiocarbamato-S,S′)cadmium(II)

Article abstract of DOI:10.1016/j.molstruc.2012.10.047

Three 2,2′-bipyridine adducts of alkyl-phenyl dithiocarbamate cadmium(II) formulated as [Cd(mpdtc)₂bpy] (1), [Cd(epdtc) ₂bpy] (2), [Cd(bpdtc)₂bpy] (3) have been synthesized and characterized by elemental analysis, FTIR, ¹H and ¹³C NMR spectroscopy. Two of the compounds were further characterized by single crystal X-ray diffraction analysis. The two compounds belong to the monoclinic space group P2₁/c. Single crystal X-ray analysis reveals octahedral coordination around the Cd(II) ions involving two molecules of dithiocarbamate acting as bidentate chelating ligands through the S-atom and one bidentate bipyridine through the N-atoms. Each of the compounds crystallizes with a molecule of chloroform. The thermal decomposition profiles of the compounds and EDX analysis of the residues showed that the compounds decomposed to their respective metal sulphides. They might thus serve as single molecule precursors for metal sulphides thin films or nanoparticles.

Full text of DOI:10.1016/j.molstruc.2012.10.047

Journal of Molecular Structure 1034 (2013) 249–256
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Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, characterization and thermal studies of 2,20-bipyridine adduct
of bis-(N-alkyl-N-phenyl dithiocarbamato-S,S0)cadmium(II)
⇑
Peter A. Ajibade , Damian C. Onwudiwe
Department of Chemistry, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa
h i g h l i g h t s
"
"
"
"
Bipyridine adducts of Cd(II) complexes of dithiocarbamates were synthesized and characterized.
Single crystals X-ray structures of two compounds are reported.
The compounds exist as distorted octahedral geometries in the CdS4N2 form.
The thermal properties of the compounds were studied.
a r t i c l e i n f o
a b s t r a c t
Three 2,20-bipyridine adducts of alkyl-phenyl dithiocarbamate cadmium(II) formulated as [Cd(mpdtc)2
bpy] (1), [Cd(epdtc)2bpy] (2), [Cd(bpdtc)2bpy] (3) have been synthesized and characterized by elemental
analysis, FTIR, 1H and 13C NMR spectroscopy. Two of the compounds were further characterized by single
crystal X-ray diffraction analysis. The two compounds belong to the monoclinic space group P21/c. Single
crystal X-ray analysis reveals octahedral coordination around the Cd(II) ions involving two molecules of
dithiocarbamate acting as bidentate chelating ligands through the S-atom and one bidentate bipyridine
through the N-atoms. Each of the compounds crystallizes with a molecule of chloroform. The thermal
decomposition profiles of the compounds and EDX analysis of the residues showed that the compounds
decomposed to their respective metal sulphides. They might thus serve as single molecule precursors for
metal sulphides thin films or nanoparticles.
Article history:
Received 20 August 2012
Received in revised form 21 October 2012
Accepted 22 October 2012
Available online 2 November 2012
Keywords:
Crystal structure
Cd(II) complexes
Bipyridine adduct
Dithiocarbamate
Thermal studies
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
carbamates are cleaved by monoamines in 1:1; 1:2 to give five-
coordinate [16] or six-coordinate monomers [17] respectively or
Cadmium dithiocarbamates are important because of the vast
industrial [1] and biological applications [2,3]. In recent years, it
has been recognized as precursors for the synthesis of CdS nanopar-
ticles [4–6] and also used as non-linear optical materials [7]. Cd
atom has a high affinity towards dithiocarbamates and this leads
to compounds of various structural motif [8,9]. The molecular struc-
ture of N, N-dialkyldithiocarbamato derivatives are known to exist
as binuclear species [Cd2{S(S)CNR2}4] (R = C2H5 [10,11], C3H7 [12],
i-C3H7 [13], C4H9 [2], i-C4H9 [13,14]. These binuclear molecules in-
volve two pairs of dithiocarbamates ligands with terminal chelating
and tridentate bridging structural functions. The dithioacid com-
plexes of CdL2 (LH = XCS2H or X2PS2H) type are coordinately unsat-
urated; this leads to the formation of compounds of higher
coordination number either by the addition of one or two molecules
of a Lewis base or by polymerization of CdL2 [15]. Cadmium dithio-
by bipyridine to give monomers with distorted octahedral coordina-
tion [18]. In this study, we report the synthesis, characterization and
thermal studies of 2,20-bipyridine adducts of Cd(II) complexes of
some N-alkyl-N-phenyl dithiocarbamates.
2. Experimental
2.1. Materials and measurements
All solvents and chemicals were of analytical grade and used
without further purification. Microanalyses were carried out with
a Perkin-Elmer 240 elemental analyzer. The IR spectra were re-
corded as KBr discs on a Perkin Elmer 2000 FTIR spectrophotome-
ter in the range 4000–370 cmꢀ1 region. 1H and 13C NMR spectra
were recorded on 400 MHz and 101 MHz Bruker NMR
spectrometers respectively. Chemical shifts are given in ppm (d
scale) relative to tetramethylsilane (for 1H and 13C nuclei).
Thermogravimetric analysis was performed on a Perkin Elmer
⇑
Corresponding author. Tel.: +27 40 602 2055; fax: +27 40 602 2094.
E-mail address: pajibade@ufh.ac.za (P.A. Ajibade).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.10.047

250
P.A. Ajibade, D.C. Onwudiwe / Journal of Molecular Structure 1034 (2013) 249–256
Thermogravimetric analyzer (TGA 7) fitted with a thermal analysis
controller (TAC 7/DX). A flow of N2 was maintained with a heating
rate of 10 °C/min between ambient temperature and 750 °C. 10–
12 mg of the sample was loaded into an alumina cup and weight
changes were recorded as a function of temperature. The SEM
images were obtained in a Joel, JSM-6390LV apparatus, using an
accelerating voltage between 15 and 20 kV at various magnifica-
tions. Composition and energy dispersive spectra were processed
using energy dispersive X-ray analysis (EDX) attached to the SEM
with Noran System six software. For the EDX analysis, an acceler-
ating voltage of 20.0 kV and magnification of 1000 were used.
full-matrix least-squares with the program SHELXL-97 [22] refin-
ing on F2. Diagrams were produced using the program PovRay
and graphic interface X-seed [23]. For the structure of 1, all non-
hydrogen atoms were refined anisotropically. For the structure of
2, all the non-hydrogen atoms were refined anisotropically, except
that two carbon atoms (C12 and C13) and the solvent atoms (C17,
Cl1 Cl2 and Cl3) which were refined isotropically due to their high
temperature factors and possible disordered nature. For both two
structures, all the hydrogen atoms were placed in idealized posi-
tions in a riding model with Uiso set at 1.2 or 1.5 times those of
their parent atoms and fixed CAH bond lengths. The structure of
(1) was refined successfully with final R = 0.0311. The final R index
for (2) is 0.0793, which is slightly high but is acceptable. Several
high peaks with electron residuals of 1.54–2.68 e Åꢀ3 are clustered
around the solvent chloroform molecule and could not be mod-
elled. It is possible that the C12 and C13 group is disordered but
no reasonable model can be made.
2.2. Synthesis of 2,20-bipyridine adduct
The precursor complexes were prepared as reported earlier
[19]. The adducts were prepared by adding a 25 mL hot chloroform
solution of 2,20-bipyridine (2 mmol, 0.312 g) into a hot 40 mL solu-
tion of 2 mmol, ([Cd(mpdt)2], 0.952 g); ([Cd(epdtc)2], 1.008 g) and
([Cd(bpdtc)2], 1.122 g) respectively, in the same solvent. The
resulting solution was refluxed for 20 min and filtered. Addition
of 15 mL acetonitrile to the filtrate gave colourless single crystals
of [Cd(mpdt)2bpy] suitable for X-ray analysis after 5 days. Some
colourless single crystals of [Cd(epdtc)2] were obtained after 3 days
from the filtrate. The crystals thus obtained were washed with eth-
anol and then dried over CaCl2.
3. Results and discussion
3.1. Synthesis
The precursor complexes, (N-alkyl-N-phenyl dithiocarbamato)
Cd(II)) were refluxed in chloroform in the presence of 2,20-bipyri-
dine in 1:1 of the stoichiometric amount to afford the final product
(2,20-bipyridine) bis (N-alkyl-N-phenyl dithiocarbamato)Cd(II) [al-
kyl = methyl, ethyl and butyl]. The Cd(II) dithiocarbamate adducts
are formulated as [Cd(mpdtc)2bpy] (1), [Cd(epdtc)2bpy] (2),
[Cd(bpdtc)2bpy] (3). All the complexes are air stable; compounds
1 and 2 crystallized with incorporation of the chloroform solvent
molecule in the crystal lattice. The structure of 1 and 2 are very
similar and therefore will be discussed together.
[Cd(mpdtc)bpy], (Yield: 1.12 g, 88%; M.p. 201–202 °C). Anal.
Calc. for C26H24N4S4Cd: C, 49.38; H, 3.82; N, 8.85; S, 20.25. Found:
C, 49.53; H, 4.07; N, 9.12; S, 20.69%.
Selected IR, (cmꢀ1): 1435
t(C@N), 1262 t(C2AN), 972 t(C@S).
1H NMR (CDCl3): (NAC6H5) d = 7.22–7.46 (m); (C6H5(bpy))
d = 7.89–7.93 (m), 8.10–8.12 (d), 8.96–8.97 (d), 3.74 (s).
13C NMR (CDCl3): (C6H5) d = 121.06, 125.45, 125.96, 127.40,
129.14; C6H4(bpy) d = 149.77, 148.80, 138.71; (NACH3): d = 48.33.
[Cd(epdtc)2bpy], (Yield: 1.05 g, 79%; M.p.222–224 °C). Anal.
Calc. for C28H28N4S4Cd: C, 50.86; H, 4.27; N, 8.47; S, 19.39. Found:
C, 50.12; H, 4.06; N, 8.68; S, 19.21%.
3.2. Spectroscopic studies
Selected IR, (cmꢀ1): 1436
t
(C@N), 1269
t
(C2AN), 998
t(C@S).
In adducts, the t(CAN) stretching frequencies has been used as
a measure of the thioureide form to the complexes [24]. A compar-
1H NMR (CDCl3): (NAC6H5) d = 7.22–7.43 (m); (C6H5(bpy))
d = 7.87–7.91 (t); 8.10–8.12 (d); 8.92–8.93 (d); (
4.21(4H, q); (CH3) d = 1.25–1.22 (t).
a-CH2) d = 4.26–
ison of the cadmium complexes with their respective adducts re-
vealed that the
a lower wave number, appearing at 1358 and 1393 cmꢀ1 respec-
tively. The reduction in (CAN) bond for these adducts is most
t(CAN) in both adducts (1) and (2) has shifted to
13C NMR (CDCl3): (C6H5) d = 121.05, 125.31, 127.06, 127.53,
129.10; C6H4(bpy) d = 149.75, 146.64, 138.57; (NACH2) d = 55.03;
(CH3) d = 12.53.
t
probably due to the change in coordination number from tetrahe-
dral to octahedral and the steric effect exerted by 2,20-bipyridine
[25]. A higher shift is observed in compound 2, 1408 cmꢀ1 com-
[Cd(bpdtc)bpy], (Yield: 1.10 g, 76%; M.p.205-208 °C). Anal. Calc.
for C32H36N4S4Cd: C, 53.58; H, 5.06; N, 7.81; S, 17.88%. Found: C,
53.81; H, 5.26; N, 7.68; S 17.97%.
pared to compound 1, 1358 cmꢀ1
. A prominent peak at
Selected IR, (cmꢀ1): 1438
t
(C@N), 1269
1H NMR (CDCl3): (NAC6H5) d = 7.20–7.42 (m); (C6H5(bpy))
d = 7.85–7.91 (t); 8.07–8.10 (d); 8.90–8.93 (d); ( -CH2) d = 4.25–
–CH2) d = 1.20–1.22
t
(C2AN), 998
t(C@S).
1593 cmꢀ1 common to the two adducts and their parent com-
plexes is ascribed to the phenyl rings while the characteristic band
due to 2,20-bipyridine is found at 1635 cmꢀ1. Other bands due to
the bipyridines are masked by those of the dithiocarbamate
a
4.18(4H, t); (b–CH2) d = 1.74–1.69 (4H, q); (
(4H, q), (CH3) d = 0.86 (6H, t).
c
ligands. The
t(CAS) are observed as single bands at 973 and
13C NMR (CDCl3): (C6H5) d = 120.01, 125.28, 126.19, 127.50,
998 cmꢀ1 in 1 and 2 respectively. This support the bidentate
coordination of the dithiocarbamate to the metal centre [26]. The
structures of both compounds are discussed below.
129.11; C6H4(bpy) d = 148.85, 145.64, 136.01; (
a–CH2) d = 60.03;
(b–CH3) d = 40.53; ( –CH2) d = 26.82; (CH3) d = 10.25.
c
The 1H and 13C NMR spectra of the compounds in chloroform
confirmed the presence of the 2,20-bipyridine in the molecular
structure of the compounds. 1H NMR spectra of the adducts ob-
tained from 2,20-bipyridine show signals for the hydrogen of the
methyl, integrated as six protons, in three distinctly separate posi-
tions, at d = 3.78 (6H, s), 1.30 (6H, t) and 0.93 (6H, t) for the Zn(II);
3.74 (6H, s), 1.23 (6H, t) and 0.86 (6H, t). The 13C NMR spectra of
the compounds show five signals in the region d = 120.00–
129.00 ppm and 124–129 ppm for the 2,20-bipyridine which corre-
spond to the aromatic carbons from the phenyl substituent of the
dithiocarbamate ligand. The resonant peaks due to 2,20-bipyridine
carbons appeared around d = 137.00–149.00 ppm. Only slight
2.3. X-ray crystallography
X-ray single crystal intensity data for both structures were col-
lected on a Nonius Kappa-CCD diffractometer using graphite
monochromated MoKa radiation (k = 0.71073 Å). Temperature
was controlled by an Oxford Cryostream cooling system (Oxford
Cryostat). The strategy for the data collections was evaluated using
the Bruker Nonius ‘‘Collect’’ program. Data were scaled and re-
duced using DENZO-SMN software [20]. Empirical absorption cor-
rections using the program SADABS [21] were applied. Both
structures were solved by direct methods and refined employing

P.A. Ajibade, D.C. Onwudiwe / Journal of Molecular Structure 1034 (2013) 249–256
251
Table 2
differences were observed in the resonant peaks of these carbons
Selected bond length (Å) for complexes 1 and 2.
as they appeared not to be influenced by either the central metal
atoms or the alkyl substituents.
Bond length (1)
Bond length (2)
Cd(1)AN(4)
Cd(1)AN(3)
Cd(1)AS(1)
Cd(1)AS(4)
Cd(1)AS(3)
Cd(1)AS(2)
S(1)AC(11)
S(2)AC(11)
S(3)AC(13)
S(4)AC(13)
2.3733
Cd(1)AN(2)
Cd(1)AN(1)
Cd(1)AS(1)
Cd(1)AS(4)
Cd(1)AS(3)
Cd(1)AS(2)
S(1)AC(11)
S(2)AC(11)
S(3)AC(14)
S(4)AC(14)
2.343(6)
2.430(6)
2.4113(2)
2.6251(6)
2.6662(6)
2.6874(7)
2.7558(7)
1.724(3)
1.710(2)
1.715(2)
1.715(2)
3.3. Description of the crystal structures
2.6017(19)
2.6658(19)
2.700(2)
2.794(2)
1.733(8)
1.705(7)
1.727(7)
1.711(8)
Details of crystal data and structure refinements are provided in
Table 1. Selected length and bond angles for 1 and 2 are shown in
Tables 2 and 3. The molecular structures of the complexes are
shown Figs. 1 and 3 while the packing diagrams are shown in Figs. 2
and 4 respectively. The structure of the complexes are typically
represented with empirical formula [Cd(S2CNRR0)2L] where L is
an adduct; bipyridine. The two complexes belong to P21/c space
group. The complexes are isostructural, with the cadmium atom
in a highly distorted octahedral environment, [CdS4N2], (Figs. 2
and 3). The two nitrogen atoms belong to a bidentate bipyridine
ligand and the sulphur atoms from the bidentate dithiocarbamate.
The two dithiocarbamate ligands in both compounds 1 and 2 are
cis to each other. The distortion of the octahedral geometry is
mainly due to the small bite angle of the planar bipyridine ligand;
N(4)ACd(1)AN(3) [68.42(7)] for compound 1 and N(2)ACd(1)A
N(1) [68.6(2)] for compound 2. These values are similar to those
found in other complexes containing NN donor adducts [25,27–
29]. There are also noticeable reductions in the SACdAS bites as
well.
Table 3
Selected bond angles (°) for complex 1 and 2.
Bond Angles (1)
Bond Angles (2)
N(4)ACd(1)AN(3)
N(3)ACd(1)AS(1)
N(4)ACd(1)AS(3)
N(3)ACd(1)AS(3)
S(1)ACd(1)AS(3)
S(4)ACd(1)AS(3)
S(1)ACd(1)AS(2)
S(4)ACd(1)AS(2)
S(3)ACd(1)AS(2)
68.42(7)
93.52(5)
N(2)ACd(1)AN(1)
N(1)ACd(1)AS(1)
N(2)ACd(1)AS(3)
N(1)ACd(1)AS(3)
S(1)ACd(1)AS(3)
S(4)ACd(1)AS(3)
S(1)ACd(1)AS(2)
S(4)ACd(1)AS(2)
S(3)ACd(1)AS(2)
68.6(2)
92.58(16)
104.57(17)
87.28(15)
112.30(7)
67.25(6)
67.17(6)
90.65(6)
155.69(6)
104.87(5)
87.60(5)
111.25(2)
67.289(19)
67.432(19)
90.37(2)
154.53(2)
The length of the NAC bond of the dithiocarbamate linkage is
1.35 Å, which is considerably shorter than would be expected for
a typical single CAN bond (1.47 Å), and closer to that of a CAN dou-
ble bond (1.28 Å) [27]. This demonstrates the high covalent charac-
ter of the metalAsulphur bonds, typical of a third row transition
metal complex. The two CdAN bond length are similar in both
complexes and the four CdAS bond lengths in the complexes varies
between 2.6017(19) Å and 2.794(2) Å with compound 2 having the
shortest and the longest CdAS bond lengths. It is interesting to
note that the shortest CdAS bond is in complex 2, Cd(1)AS(1)
[2.6017(19) Å] is associated with the longest CAS, S(1)AC(11)
[1.733(8) Å]. Also, the longest CdAS bond lengths in both
complexes can be found in compound 2, Cd(1)AS(2), [2.794(2) Å]
is also associated with the shortest CAS bond, S(2)AC(11)
[1.705(7) Å]. The CdAS bond lengths that are relatively longer than
the other in compounds 1 and 2 may be due to the steric influence
of the bipyridine ligand. The thioureide CAN distance in the com-
pound are between 1.326(10)–1.349(9) Å, indicating a partial dou-
ble bond nature. Packing of compounds 1 and 2 (Figs. 2 and 4)
showed that they asymmetric unit are parallel to each other with
the chloroform molecule sandwich between them.
Table 1
Summary of crystal data and structure refinement.
Compound
1
2
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C
27H25CdCl3N4S4
C29H29CdCl3N4S4
780.55
173(2) K
0.71073
Monoclinic
P21/c
752.50
173(2) K
0.71073
Monoclinic
P21/c
Unit cell dimensions
a (Å)
b (Å)
7.1412(1)
26.3063(6)
16.9393(4)
98.975(1)
3143.23(11)
4
1.590
1.240
1512
7.1204(4)
27.7575(9)
17.0776(7)
98.948(2)
3334.2(3)
4
1.555
1.172
1576
c (Å)
b (°)
Volume (A3)
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
)
Crystal size (mm)
Theta range (°)
Limiting indices
Reflections collected
Independent reflection
Refinement method
Completeness to h = 26.35
Data/restraints/parameters/
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
0.26 ꢁ 0.23 ꢁ 0.20
0.24 ꢁ 0.23 ꢁ 0.19
2.43–26.35
2.51–27.50
ꢀ8 6 h 6 8, ꢀ32 6 k 6 32, ꢀ21 6 1 6 21
108770
6404 [R(int) = 0.0684]
Full-matrix least-squares
99.9
6404/0/354
1.117
R1 = 0.0311, wR2 = 0.0569
R1 = 0.0467, wR2 = 0.0626
0.491 and ꢀ0.557
ꢀ9 6 h 6 9, ꢀ36 6 k 6 36, ꢀ22 6 1 6 22
104979
7643 [R(int) = 0.1019]
Full-matrix least-squares
99.7
0.8080 and 0.7662
1.046
R1 = 0.0793, wR2 = 0.2032
R1 = 0.1329, wR2 = 0.2405
2.679 and ꢀ2.256
Largest diff. peak and hole (e Åꢀ3
)

252
P.A. Ajibade, D.C. Onwudiwe / Journal of Molecular Structure 1034 (2013) 249–256
Fig. 1. Molecular structure of 1 showing the atomic labelling. Displacement ellipsoids are drawn at the 40% probability level. All H-atoms are omitted for clarity.
Fig. 2. Projection viewed along [100] for complex 1. All H atoms are omitted for clarity.
3.4. Thermal studies
As shown in the superimposed TG/DTG curves of [Cd(mpdtc)2bpy],
[Cd(epdtc)2bpy], and [Cd(bpdtc)2bpy] over their precursor com-
plexes, the thermogram of the adducts indicates that there is a
reduction in the initial decomposition temperature with the
introduction of the Lewis base. This shows the increase in volatil-
ity of compounds upon the formation of adducts and could be as-
cribed to the effect caused by the introduction of the lone pair of
electron on nitrogen into the d-orbital of the cadmium ion [32–
34].
The thermogram of the adduct [Cd(mpdtc)2bpy] is given in
Fig. 6A. This compound is found to be stable only up to 154 °C.
The decomposition is seen starting at 154 °C and gradually pro-
gressed to 247 °C, with the peak of decomposition occurring at
227 °C. The weight loss of this decomposition is 18% and corre-
sponds to the breaking off of the 2,20 bipyridine fragments, which
completed the octahedral geometry of the adducts, leaving back
the four-coordinated species. The mass loss observed during this
stage (1.87 mg) is in close agreement with the theoretical value
of 1.97 mg. In the second stage, the decomposition started at
260 °C and continues up to 353 °C, with the decomposition peak
at 225 °C. The mass loss observed was 64% leaving a residue with
The temperature ranges and percentage mass losses during the
decompositions as well as the temperature corresponding to the
maximum rate of decomposition, DTG, the product obtained and
the theoretical percentage mass losses are given in Table 4. The
overlapped TG curves of the three compounds, [Cd(mpdtc)2bpy],
[Cd(epdtc)2bpy] and [Cd(bpdtc)2bpy], are presented in Fig. 4. The
thermograms of each adduct superimposed over its respective pre-
cursor complex are shown in Fig. 5. In the 2,20-bipyridine adducts
of cadmium, the major decomposition peaks were observed below
360 °C. Unlike in the zinc adducts analogue [30], the variation of
the alkyl group on the nitrogen atom appears to have a pronounced
effect on the thermal properties of the cadmium adducts. The
replacement of an alkyl by another group in dithiocarbamates
chelate compounds has been found to result into varied thermal
property [31]. Here, the thermograms displayed non-similar
decomposition patterns. While [Cd(mpdtc)2bpy] showed only
two decomposition peaks leading to the formation of the CdS, the
[Cd(epdtc)2bpy] showed three intense peaks and [Cd(bpdtc)2bpy]
displayed two intense and one diminished peak (Fig. 5).

P.A. Ajibade, D.C. Onwudiwe / Journal of Molecular Structure 1034 (2013) 249–256
253
Fig. 3. Molecular structures of (2). The atomic labelling of the asymmetric unit is shown. All H atoms are omitted for clarity. Displacement ellipsoidal is drawn at 40%
probability. Atoms C12, C13, C17, Cl1, Cl2 and Cl3 in are drawn with arbitrary radii.
Fig. 4. Projection viewed along [100] for complex 2. All H atoms are omitted for clarity.
Table 4
Temperature values for decomposition along with corresponding weight loss values and product obtained.
Compounds
Decomposition range (°C)
Peak temperature (°C)
Total weight loss (%)
Product obtained
Mass changes
Calc.
Found
[Cd(mpdtc)2bpy]
[Cd(epdtc)2bpy]
154–247
260–353
227
325
18
82
[Cdmpdtc)]
CdS
1.97
2.38
1.87
1.88
105–159
160–248
252–358
147
230
325
18
37
82
[Cd(epdtc)]
Undefined
CdS
2.10
2.85
2.61
1.91
2.43
2.03
[Cd(bpdtc)2bpy]
101–126
142–252
254–360
114
223
326
1.2
18
77
[Cd(bpdtc)2bpy]
[Cd(bpdtc)]
CdS
–
2.78
2.70
–
2.20
2.57
mass of 1.88 mg. This could be attributed to the decomposition of
the four coordinate species yielding CdS (calculated, 2.38).
The thermogram of [Cd(epdtc)bpy] (Fig. 6B) shows an initial
decomposition which started around 105 °C and terminated at
159 °C with a loss in mass of about 18%. The thermal decomposi-
tion of dithiocarbamates adducts are usually associated with the
expulsion of the Lewis base fragments as its first decomposition
step. The calculated weight loss corresponding to this decomposi-

254
P.A. Ajibade, D.C. Onwudiwe / Journal of Molecular Structure 1034 (2013) 249–256
tion stage in this compound is 17.92%. Thus, the first decomposi-
tion is ascribed to the liberation of the 2,20 bipyridine by breaking
the MAN bond on heating. The calculated mass loss (2.10 mg) is in
perfect agreement with the observed value (1.91 mg).
The second stage of decomposition initiated immediately at
160 °C and ended at 240 °C, with a mass loss of about 19%. The
decomposition of dithiocarbamate to its respective metal sulp-
hides could be completed either via the formation of metal thiocy-
anate as an intermediate, which further decomposes to give metal
sulphide or the metal sulphide could be obtained directly in a sin-
gle step decomposition [35]. Thus, the loss of the bipyridine mole-
cule was expected to be followed with either the formation of
cadmium thiocyanate or CdS. For the formation of thiocyanate
molecules, a mass loss of 57.85% was expected whereas the mass
loss observed (stage II) was only 24.79%. This anomaly between
the theoretically expected mass of the residue and the observed
may be explained as either due to the loss of two molecules of ben-
[Cd(MPDTC)bpy]
[Cd(EPDTC)bpy]
[Cd(BPDTC)bpy]
Fig. 5. Thermograms of [Cd(mpdtc)2bpy], [Cd(epdtc)2bpy] and [Cd(bpdtc)2bpy].
A
B
C
Fig. 6. Superimposed TG/DTG curves and the TG curve of the precursor complexes for [Cd(mpdtc)2bpy] (A), [Cd(epdtc)2bpy] (B) and [Cd(bpdtc)2bpy].

P.A. Ajibade, D.C. Onwudiwe / Journal of Molecular Structure 1034 (2013) 249–256
255
Fig. 7. EDX of residue obtained at the end of the thermal decomposition of [Cd(mpdtc)2bpy].
zene from the complex, since the weight loss calculated for the loss
of two molecules of benzene is 26.50% which agrees with the ob-
served value of 28.90%; or may be because the second stage of
decomposition initiated before the completion of the first stage
of decomposition. The third stage of decomposition initiated at
252 °C and ended at 358 °C. The peak temperature of this stage is
325 °C. The mass loss was found to be 45% leaving a residual mass
of 2.03 mg which is in agreement with the theoretical value of
2.85 mg, expected for CdS.
From the superimposed thermogram and DTG curve given in
Fig. 6C, a little expulsion was observed in the temperature range
101–126 °C and corresponds to 1.2% weight loss. This could be as-
cribed to the extrusion of volatiles which were entrapped during
recrystallization. The compound is thermally stable up to 142 °C,
after which a gradual decomposition was initiated until 252 °C
with a peak temperature of 223 °C. The weight loss during the
stage II amounts to 17.1%. The weight loss corresponds to the re-
lease of the Lewis base (2,2 bipyridine). The calculated value
(2.78 mg) is in fair agreement with the found (2.20 mg). The third
stage of decomposition started immediately at 254 °C and ended at
360 °C, with a mass loss corresponding to 59% (stage III) leaving
behind a 33% mass as residue. This stage could be attributed to
the decomposition of the intermediate to CdS. The mass of the res-
idue observed (2.54 mg) in the thermogram agrees well with the
theoretical value of 2.70 mg.
phide (MS) indicating that the complexes will be good single
source precursors for MS semiconductor nanoparticles.
Supplementary materials
CCDC 737048 and 740847 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif or from The Director, CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44 1223 336 033;
e-mail: deposit@ccdc.cam.ac.uk).
Acknowledgement
The authors gratefully acknowledge the contribution of Dr.
Hong Su and financial support of GMRDC, University of Fort Hare,
South Africa.
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