Synthesis, characterization and thermal studies of bipyridine metal complexes containing different substituted dithiocarbamates

Article abstract of DOI:10.1081/SIM-200066980

Complexes of the type [Mpy₂(dedtc)₂], and [Mpy ₂(dpdtc)₂], where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), py = pyridine, dedtc = diethyldithiocarbamate and dpdtc = diphenyldithiocarbamate, have been synthesized and characterized by elemental analyses, magnetic susceptibility, TGA/DSC and IR in the solid-state, and electronic spectroscopy and conductivity measurement studies in solution. The dithiocarbamato moiety has been found to be symmetrically bonded to the metal. The complexes are proposed to have a distorted-octahedral structure. The ligand field parameters 10 Dq, B and β have also been evaluated. The value of β indicates a considerable orbital overlap in the complexes. A two-stage decomposition pattern leading to the formation of respective metal sulfide as the end-product has been observed in all the complexes. Their molar conductance indicated them to be non-electrolyte in nitrobenzene. Copyright

Full text of DOI:10.1081/SIM-200066980

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Synthesis, Characterization and Thermal Studies of
Bipyridine Metal Complexes Containing Different
Substituted Dithiocarbamates
K. S. Siddiqi a , Shahab A. A. Nami a , Lutfullah a & Yonas Chebude b
a Department of Chemistry , Aligarh Muslim University , Aligarh , India
b Department of Chemistry , Addis Ababa University , Addis Ababa , Ethiopia
Published online: 31 Jan 2012.
To cite this article: K. S. Siddiqi , Shahab A. A. Nami , Lutfullah & Yonas Chebude (2005) Synthesis, Characterization and
Thermal Studies of Bipyridine Metal Complexes Containing Different Substituted Dithiocarbamates, Synthesis and Reactivity in
Inorganic, Metal-Organic, and Nano-Metal Chemistry, 35:6, 445-451, DOI: 10.1081/SIM-200066980
To link to this article: http://dx.doi.org/10.1081/SIM-200066980
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Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, 35:445–451, 2005
Copyright # 2005 Taylor & Francis, Inc.
ISSN: 0094-5714 print/1532-2440 online
DOI: 10.1081/SIM-200066980
Synthesis, Characterization and Thermal Studies
of Bipyridine Metal Complexes Containing
Different Substituted Dithiocarbamates
K. S. Siddiqi, Shahab A. A. Nami, and Lutfullah
Department of Chemistry, Aligarh Muslim University, Aligarh, India
Yonas Chebude
Department of Chemistry, Addis Ababa University, Addis Ababa, Ethiopia
semiconducting copper sulfide thin films (Ngo et al., 2003).
Complexes of the type [Mpy2(dedtc)2], and [Mpy2(dpdtc)2], In addition, Cu(II)dialkyldithiocarbamate is also employed in
where M 5 Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), py 5
pyridine, dedtc 5 diethyldithiocarbamate and dpdtc 5 diphenyl-
dithiocarbamate, have been synthesized and characterized by
elemental analyses, magnetic susceptibility, TGA/DSC and IR in
the solid-state, and electronic spectroscopy and conductivity
measurement studies in solution. The dithiocarbamato moiety ide dismutase (SOD) activity through the withdrawal of Cu
the preparation of single source MOVCD precursors for
mixed metal sulfide thin films, like copper-indium sulfide or
copper-doped cadmium sulfide (Ngo et al., 2003). Diethyl-
dithiocarbamate has also been shown to inhibit Cu/Zn-superox-
has been found to be symmetrically bonded to the metal. The
complexes are proposed to have a distorted-octahedral structure.
The ligand field parameters 10 Dq, B and b have also been evalu-
ated. The value of b indicates a considerable orbital overlap in the
complexes. A two-stage decomposition pattern leading to the
formation of respective metal sulfide as the end-product has infected patients (Nagano and Yoshimura, 2002).
from the protein both in vivo and in vitro systems (Cocco
et al., 1981).
Beside this, dithiocarbamates have been clinically used and
were shown to be safe and efficient in the treatment of HIV-
been observed in all the complexes. Their molar conductance
indicated them to be non-electrolyte in nitrobenzene.
One of the most striking properties of dithiocarbamate
group is its high nucleophilicity, which leads to a large
number of biologically active derivatives (Ileiv et al., 1984).
In view of diverse application of dithiocarbamates (Chaurasia
et al., 1981) and various biological aspects of pyridine
Keywords diethyldithiocarbamate, diphenyldithiocarbamate, metal
complexes
(Gokhale et al., 2003) it is found worthwhile to study
complexes containing both S and pyridine. Although the
reports on metal dithiocarbamates are extensive, the studies
on transition metal complexes containing both dithiocarbamate
INTRODUCTION
moiety and pyridine ligand are scarce (Ivanov et al., 1999;
Unidentate, as well as bidentate, nature of dithiocarbamate is Yusuff et al., 1983). In this article, we are reporting the
well established (Kana et al., 2001; Law et al., 2003). Much synthesis and characterization of mixed ligand complexes of
attention has been devoted to the study of dialkyldithiocarba- the type [M(dedtc)2(py)2] and [M(dpdtc)2(py)2], where
mates (Zhu et al., 2002; Jian et al., 1999) with special reference M ¼ Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), py ¼ pyri-
to Cu(II)dialkyldithiocarbamate because of its extensive use as dine, dedtc ¼ diethyldithiocarbamate and dpdtc ¼ diphenyl-
single-source molecular precursors for the growth of dithiocarbamate.
Received 20 November 2004; accepted 25 March 2005.
One of the authors (SAAN) thanks the CSIR, New Delhi for finan-
cial assistance through grant no. 01(1783)/02/EMR-II. Mr. Aurang-
zeb Khan of this department is also thanked for recording UV-Vis.
and IR spectra.
Address correspondence to K. S. Siddiqi, Department of
Chemistry, Aligarh Muslim University, Aligarh 202002, India.
E-mail: khwajas_siddiqi@yahoo.co.in
EXPERIMENTAL
General Consideration
Diethyl amine, diphenylamine, carbon disulphide, sodium
hydroxide (Merck), pyridine (Ranbaxy) and hydrated metal
chlorides (BDH) were used as received. Methanol was distilled
before use. Elemental analyses (C, H, N and S) were carried out
445

446
K. S. SIDDIQI ET AL.
with a CE Instruments Flash EA 1112. IR spectra (4000– Synthesis of MCl.2py2 Complexes
350 cm21) were recorded on a Perkin Elmer Spectrum BX as
A methanolic solution of hydrated metal(II) chlorides
KBr discs. The conductivity measurements were carried out
with CM-82T Elico conductivity bridge in nitrobenzene. The
electronic spectra were recorded on a Cintra 5GBC spectropho-
tometer in nitrobenzene. Magnetic susceptibility measure-
ments were done with a Sherwood Scientific MSB auto at
room temperature. TGA/DSC was performed with a universal
V3.5B TA SDT Q600 V3.8 built 51 thermal analyzer. The
experiment was done under nitrogen atmosphere using
alumina powder as the reference material. The weight of the
sample was taken in between 6 to 16 mg, and the heating rate
was maintained at 108C/min.
(25 mL) was added to a methanolic solution of pyridine
(15 mL) in 1 : 2 molar ratios with continuous stirring for
about half an hour. The reaction mixture was left overnight
at room temperature to obtain the required metal precipitate
(Bailar et al., 1973), which was isolated by filtration, washed
with methanol, and dried in vacuo.
Synthesis of the Mpy2(dedtc)2
A methanolic solution of MCl.2py2 (25 mL) [where
M ¼ Mn(II), Fe(II), Co(II), Ni(II) and Cu(II)] was added to a
methanolic solution (20 mL) of sodium salt of diethyl dithio-
carbamate (dedtc) in 1 : 2 molar ratios with continuous
stirring for about one hour. A solid compound in the form of
precipitate was formed. It was left overnight at room tempera-
ture and the compound was isolated by filtration, washed with
methanol and dried in vacuo (Figure 1).
Synthesis of Sodium Diethyl Dithiocarbamate (Nadedtc)
A solution of diethyl amine (50 mmol, 5.22 mL) in 50 mL of
methanol was taken in a round bottom flask and cooled in an
ice bath. Neat carbon disulphide (50 mmol, 3.02 mL) was
added slowly with constant stirring to obtain a white precipi-
tate. To this reaction mixture, NaOH (50 mmol, 2.0 g) dis-
solved in a minimum amount of water was added dropwise
with stirring. The precipitate dissolved and the stirring was
continued for four hours. The content was then allowed to
stand overnight at room temperature to obtain needle shaped
crystals of sodium salt of diethyl dithiocarbamate (dedtc),
which was filtered, repeatedly washed with methanol and
cold diethyl ether, and dried in vacuo.
[Mn(py)2(dedtc)2] yield (54%); m. p. . 3008C; LM ¼ 23
ohm21cm2mol21 Found (calcd. for C20H30MnN4S4) C, 46.96
(47.13), H, 5.8(5.93), N, 10.54(10.99), S, 25.45(25.16), Mn,
10.67(10.78). IR (KBr): nmax/cm21 1497s (C. . .N), 1190 m
(ring vib.), 397 m (Mn-S), 355 (Mn-N).
[Fe(py)2(dedtc)2] yield (66%); m. p. 2578C; LM ¼ 30
ohm21cm2mol21 Found (calcd. for C20H30FeN4S4) C, 46.88
(47.02), H, 5.57(5.92), N, 10.67(10.97), S, 25.27(25.11), Fe,
10.8(10.93). IR (KBr): nmax/cm21 1494s (C. . .N), 1194 m
(ring vib.), 397 m (Fe-S), 377 (Fe-N).
Synthesis of Sodium Diphenyl Dithiocarbamate (Nadpdtc)
[Co(py)2(dedtc)2] yield (60%); m. p. 2978C; LM ¼ 39
A methanolic solution (50 ml) of diphenylamine (50 mmol, ohm21cm2mol21 Found (calcd. for C20H30CoN4S4) C, 46.53
8.46 g) was taken in a round bottom flask and cooled in an ice (46.77), H, 5.77(5.88), N, 10.72(10.91), S, 25.26(24.97), Co,
bath. Neat carbon disulphide (50 mmol, 3.02 mL) was added 11.23(11.47). IR (KBr): nmax/cm21 1486s (C. . .N), 1190 m
dropwise with stirring to obtain an immediate white precipi- (ring vib.), 403 m (Co-S), 371w (Co-N)
tation. To this, a solution of NaOH (50 mmol, 2.0 g) dissolved
[Ni(py)2(dedtc)2] yield (68%); m. p. 2498C; LM ¼ 36
in minimum amount of water was slowly added with continu- ohm21cm2mol21 Found (calcd. for C20H30NiN4S4) C, 46.59
ous stirring to obtain a yellow colored solution. The stirring (46.79), H, 5.74(5.89), N, 10.77(10.91), S, 25.18(24.98), Ni,
was continued for four hours. The content was then allowed 11.33(11.43). IR (KBr): nmax/cm21 1504s (C. . .N), 1195 m
to stand overnight to obtain needle shaped crystals of sodium (ring vib.), 417 m (Ni-S), 377w (Ni-N)
salt of diphenyl dithiocarbamate (dpdtc), which was filtered, [Cu(py)2(dedtc)2] yield (74%); m. p. 2098C; LM ¼ 41
repeatedly washed with methanol and cold diethyl ether, and ohm21cm2mol21 Found (calcd. for C20H30CuN4S4) C, 46.28
dried in vacuo. (46.35), H, 5.69(5.83), N, 10.69(10.81), S, 24.91(24.75), Cu,
FIG. 1. Synthesis of the complexes Mpy2(dedtc)2, where M ¼ Mn(II), Fe(II), Co(II), Ni(II) and Cu(II), py ¼ C5H5N and dedtc ¼ S2CN(C2H5)2.

STUDIES OF BIPYRIDINE METAL COMPLEXES
447
12.08(12.26). IR (KBr): nmax/cm21 1504s (C. . .N), 1194 m
(ring vib.), 393 m (Cu-S), 354w (Cu-N)
[Zn(py)2(dpdtc)2] yield (73%); m. p. 2258C; LM ¼ 17
ohm21cm2mol21 Found (calcd. for C36H30N4S4Zn) C,
[Zn(py)2(dedtc)2] yield (70%); m. p. 2088C; LM ¼ 42 60.39(60.68), H, 4.05(4.24), N, 7.51(7.86), S, 18.06(17.99),
ohm21cm2mol21 Found (calcd. for C20H30N4S4Zn) C, 46.07 Zn, 9.47(9.22). IR (KBr): nmax/cm21 1497s (C. . .N), 1190 m
(46.16), H, 5.69(5.81), N, 10.68(10.77), S, 24.87(24.64), Zn, (ring vib.), 413 m (Zn-S) and 372w cm21 (Zn-N).
. . . .
12.49(12.62). IR (KBr): nmax/cm21 1497s (C
(ring vib.), 408 m (Zn-S) 362w (Zn-N)
N), 1193 m
RESULTS AND DISCUSSION
The mixed ligand complexes of the type [M(py)2(dedtc)2],
and [M(py)2(dpdtc)2], where M ¼ Mn(II), Fe(II), Co(II),
Ni(II), Cu(II), Zn(II), py ¼ pyridine, dedtc ¼ diethyldithiocar
bamate and dpdtc ¼ diphenyldithiocarbamate, were readily
obtained by the reaction of [M(py)2Cl2] with Nadedtc and
Nadpdtc. The complexes are formed by the replacement of
two chlorine atoms from [M(py)2Cl2] by dedtc and dpdtc
(Figure 1). The metal complexes are stable to light and are
amorphous powder.
Synthesis of the Mpy2(dpdtc)2
A methanolic solution of MCl.2py2 (25 mL) [where
M ¼ Mn(II), Fe(II), Co(II), Ni(II) and Cu(II)] was added to a
methanolic solution (20 mL) of sodium salt of diphenyl dithio-
carbamate (dpdtc) in 1 : 2 molar ratios with continuous stirring
for about two hours. A precipitate was formed, which was
isolated by filtration, washed with methanol, and dried in
vacuo (Figure 2).
[Mn(py)2(dpdtc)2] yield (40%); m. p. 2258C; LM ¼ 28
ohm21cm2mol21 Found (calcd. for C36H30MnN4S4) C,
61.49(61.61), H, 4.18(4.31), N, 7.69(7.98), S, 18.48(18.27),
Mn, 7.69(7.83). IR (KBr): nmax/cm21 1497s (C. . .N), 1195 m
(ring vib.), 395 m (Mn-S), 370w (Mn-N).
Mð pyÞ Cl2 þ 2Nadedtc ! Mð pyÞ2ðdedtcÞ þ 2NaCl
Mð pyÞ2Cl2 þ 2NadpdtcMð pyÞ ðdpdtcÞ þ 22NaCl
2
2
2
Conductance Measurements
The molar conductance value of 1023 M solution of all the
metal complexes measured in nitrobenzene fall well below
those reported for univalent electrolyte at room temperature,
indicating their non-electrolytic nature (Geary, 1971). The
metal contents were determined by complexometric titration
(Reilly et al., 1959).
[Fe(py)2(dpdtc)2] yield (60%); m. p. 1628C; LM ¼ 39
ohm21cm2mol21 Found (calcd. for C36H30FeN4S4) C,
61.29(61.53), H, 4.05(4.3), N, 7.66(7.97), S, 18.51(18.25),
Fe, 8.06(7.95). IR (KBr): nmax/cm21 1492s (C. . .N), 1190 m
(ring vib.), 398 m (Fe-S), 375w (Fe-N).
[Co(py)2(dpdtc)2] yield (63%); m. p. 1588C; LM ¼ 37
ohm21cm2mol21 Found (calcd. for C36H30CoN4S4) C,
61.08(61.26), H, 4.11(4.28), N, 7.81(7.94), S, 17.98(18.17),
Co, 8.52(8.35). IR (KBr): nmax/cm21 1492s (C. . .N), 1194 m
(ring vib.), 419 m (Co-S), 354w (Co-N).
IR Spectra
Literature survey reveals that almost all the dithiocarba-
mates studied to date, the region 950–1050 cm21 is considered
[Ni(py)2(dpdtc)2] yield (70%); m. p. 2128C; LM ¼ 43 as highly diagnostic in deciding the nature of the coordination
ohm21cm2mol21 Found (calcd. for C36H30NiN4S4) C, of the dithiocarbamato moiety (Bonati et al., 1967). According
61.15(61.28), H, 4.15(4.29), N, 7.66(7.94), S, 18.03(18.18), to the criterion laid by Brinkhoff and Grotens (1971) the
Ni, 8.44(8.31). IR (KBr): nmax/cm21 1495s (C. . .N), 1190 m presence of only one band in the 1000 + 70 cm21 region is
(ring vib.), 415 m (Ni-S), 360w (Ni-N).
characteristic of a bidentate nature for the dithiocarbamato
[Cu(py)2(dpdtc)2] yield (70%); m. p. 2548C; LM ¼ 39 moiety, while the splitting of the same band within a difference
ohm21cm2mol21 Found (calcd. for C36H30CuN4S4) C, of 20 cm21 in the same region is due to the monodentate
60.59(60.86), H, 4.08(4.26), N, 7.59(7.89), S, 18.19(18.05), binding of dithiocarbamate ligand. In the present study, a
Cu, 9.08(8.94). IR (KBr): nmax/cm21 1490s (C. . .N), 1190 m single sharp peak is observed in all the synthesized complexes
(ring vib.), 409 m (Cu-S), 363w (Cu-N).
in the 991–1023 cm21, confirming the symmetrical bonding of
FIG. 2. Synthesis of the complexes Mpy2(dpdtc)2, where M ¼ Mn(II), Fe(II), Co(II), Ni(II) and Cu(II), py ¼ C5H5N and dpdtc ¼ S2CN(C6H5)2.

448
K. S. SIDDIQI ET AL.
dithiocarbamato moiety in all the cases. The thioureide band Electronic Absorption Spectra
(S2C. . .NR2), which is another cardinal band of dithiocarba-
mato complexes, appears in the range 1486–1504 cm21
The electronic spectral bands and the magnetic moments of
the complexes are listed in Table 1. In and octahedral environ-
ment, Mn(II) complex gives spin forbidden as well as parity-
forbidden bands (Cotton et al., 1999). In addition to the band
due to n-pꢀ transition the electronic spectrum of Mn(II)
complex in DMF exhibit three more bands in the region
,
which is intermediate between a n(C55N) band (1690–
1640 cm21) and a n(C–N) band (1360–1250 cm21), indicating
a partial double bond character between carbon and nitrogen.
Some new bands are also observed in the far IR region,
which might be due to M-S stretching frequencies (Bradley
and Gitlitz, 1969).
31,104 to 30,350 cm21; 22,542 to 20,533 cm21 and 17,513 to
4
16,890 cm21, which have been assigned to T1g(P) 6A1 g
;
TABLE 1
Magnetic susceptibility, electronic spectra and ligand field parameters of the complexes
Magnetic
Electronic
Log 1
(mol21cm2)
10Dq
(cm21
B
(cm21
Compounds
moment (B.M.) bands (cm21
)
Possible assignments
)
)
b
C20H30MnN4S4
[Mn(py)2(dedtc)2]
(509.68)
5.84
5.30
30,350
20,533
17,513
15,772
2.9
2.7
2.6
2.8
4T1 g(P) (6A1 g
4T2 g(G) (6A1 g
4T1 g(G) (6A1 g
5Eg 5T2 g
17,760
15,722
12,030
11,760
427
—
0.83
C20H30FeN4S4
[Fe(py)2(dedtc)2]
(510.59)
—
C20H30CoN4S4
[Co(py)2(dedtc)2]
(513.67)
4.18
20,790
15,552
11,146
22,371
15,847
11,764
17,452
11,824
2.7
2.5
2.2
2.6
2.2
1.8
2.7
2.7
4T1 g(P) 4T1 g(F)
4A2 g(F) 4T1 g(F)
4T2 g(F) 4T1 g(F)
3T1 g(P) (3A2 g(F)
3T1 g(F) (3A2 g(F)
3T2 g(F) (3A2 g(F)
2Eg 2B1 g
334
392
0.65
0.62
C20H30NiN4S4
[Ni(py)2(dedtc)2]
(513.44)
3.21
C20H30CuN4S4
[Cu(py)2(dedtc)2]
(518.29)
1.93
2B2 g 2B1 g
—
—
—
C20H30ZnN4S4
[Mn(py)2(dedtc)2]
(520.44)
Diamagnetic
5.91
—
—
—-
—
—
—
C36H30MnN4S4
[Mn(py)2(dpdtc)2]
(701.86)
31,104
22,542
16,890
2.9
2.7
2.4
4T1 g(P) (6A1 g
4T2 g(G) (6A1 g
4T1 g(G) (6A1 g
16,885
439
0.85
C36H30FeN4S4
[Fe(py)2(dpdtc)2]
(702.76)
5.44
15,082
12,080
12,380
—
—
15,082
2.8
5Eg 5T2 g
C36H30CoN4S4
[Co(py)2(dpdtc)2]
(705.85)
4.21
22,321
16,474
11,272
22,779
15,384
12,544
18,248
11,325
2.5
2.4
2.5
2.4
1.7
1.4
2.8
2.8
4T1 g(P) (4T1 g(F)
4A2 g(F) 4T1 g(F)
4T2 g(F) (4T1 g(F)
3T1 g(P) (3A2 g(F)
3T1 g(F) (3A2 g(F)
3T2 g(F) (3A2 g(F)
2Eg 2B1 g
402
279
0.78
0.44
C36H30NiN4S4
[Ni(py)2(dpdtc)2]
(705.62)
3.34
C36H30CuN4S4
[Cu(py)2(dpdtc)2]
(710.46)
1.98
2B2 g 2B1 g
—
—
—
—
—
—
C36H30ZnN4S4
[Zn(py)2(dpdtc)2]
(712.62)
Diamagnetic
—
—
—

STUDIES OF BIPYRIDINE METAL COMPLEXES
449
4T2g(G) 6A1 g and 4T1g(G) 6A1 g transitions, respect- field parameters, viz., 10Dq, B (Racah parameter), b (Nephe-
ively. The high spin d5 configuration gives an essentially lauxetic ratio) are almost identical for Nipy2(dedtc)2 and
spin-only magnetic moment of ꢀ 5.9 B.M. and is temperature Nipy2(dpdtc)2. Values of ligand field parameters reflect that
independent. The Mn(II) complex under consideration has the the M-L bond is sufficiently strong, which in turn suggest
value of 5.84 B.M. and 5.91 B.M. for ethyl and phenyl dithio- enough overlapping of metal orbitals with those of the ligand
carbamates, respectively, which are very close to the calculated orbitals. The compounds are paramagnetic with a room temp-
value. Thus, the ligand field bands and magnetic moment value erature magnetic moment values ranging in between 3.21–
support a distorted octahedral geometry around the metal ion. 3.34 B.M. One of the interesting features regarding the
For the octahedral spin-free Fe(II) complexes, the magnetic magnetic moments of octahedral Ni(II) complexes is their
moment values lies at about 5.5 B.M., and is nearly indepen- non-dependency in case of small departures from octahedral
dent of temperature. In the present case, the magnetic symmetry (Cotton, 1964).
moment values are found to be 5.30 and 5.44 B.M. for Fepy2(-
Generally the octahedral Cu(II) complexes exhibit three
dedtc)2 and Fepy2(dpdtc)2 complexes, respectively. The slight transitions in the 18,000 to 12,000 cm21 range with poorly sep-
deviation in magnetic moment value might be due to the devi- arated bands. However, in the present study, a broad band
ation from the regular octahedral geometry (Cotton, 1964) maxima in the 11,905–11,765 cm21 and 11,628–
(Table 1).
11,111 cm21 range owing to the overlap of two bands corre-
2
Octahedral cobalt(II) complexes have been widely studied. sponding to the B2g 2B1g transition (Figgis, 1976) for
The spectra of Copy2(dedtc)2 and Copy2(dpdtc)2 have identical Cupy2(dedtc)2 and Cupy2(dpdtc)2 complexes was observed.
features, indicating similar stereochemistry around the In addition to this,
a
shoulder at 17,452 cm21 and
Co(II) ion. They show absorptions at 20,790; 15,552 and 18,248 cm21 for ethyl and phenyl analogue assigned to
11,146 cm21 in case of Copy2(dedtc)2 and 22,321; 16,474 2B2 g 2B1 g transition was also observed and might be due
and 11,272 cm21 in case of Copy2(dpdtc)2. The low frequency to the distorted octahedral geometry around Cu(II) ion (Rana
band at around 11,000 cm21 is characteristic of Co(II) in a et al., 1982). It is difficult to predict the solution structure of
distorted octahedral symmetry (Wang et al., 2003). The the Cu(II) complexes from electronic spectroscopy alone
observed magnetic moment values for the Copy2(dedtc)2 and because of a wide range of possible geometrical distortions
Copy2(dpdtc)2 are 4.18 and 4.21 B.M., respectively, which and the typically poor resolution of absorption bands (Lever,
are within the predicted high-spin value for an octahedral 1984). The observed magnetic moment value lies in the
Co(II) complex with considerable orbital contribution to the range between 1.93–2.01 B.M., which further supports the
overall magnetic moment (Gebbink et al., 2002).
above proposed geometry.
Octahedral Ni(II) complex is known to exhibit three spin
allowed electronic transitions within the visible region
(Lepetit and Che, 1996). In the present case of the Nipy2(-
dedtc)2, three absorption bands at 22,371 cm21 (n1),
15,847 cm21 (n2) and 11,764 cm21 (n3) have been observed,
while for the Nipy2(dpdtc)2 complex, these bands appear at
22,779 cm21 (n1) 15,384 cm21 (n2) and 12,544 cm21 (n3)
range. The n1 is due to one of the spin allowed electronic tran-
sitions in the visible region, and is assigned to
3T2 g(F) 3A2 g(F). The position of middle band (n2) has
TGA/DSC
Thermogravimetric analysis is a useful technique for the
determination of thermal stability and structural elucidation
of various insoluble and infusible compounds (Bajpai and
Tiwari, 2004), but to date, only a limited number of reports
concerning thermal data and solution thermochemistry of
metal dithiocarbamates have been appeared in the literature
(Burkinshaw et al., 1983; Airoldi and Chagas, 1992; Szafranek
and Szafranek, 1995; Lanjewar and Garg, 1992).
3
been attributed to T1 g(F) 3A2 g transition. The ligand
TABLE 2
Degradation of various fragments in the complex M(py)2(dedtc)2 (where M ¼ Mn(II), Fe(II), Co(II), Ni(II) and Cu(II))
Temperature
Fragments
range (8C) Mn(py)2(dedtc)2 Fe(py)2(dedtc)2 Co(py)2(dedtc)2 Ni(py)2(dedtc)2 Cu(py)2(dedtc)2
Mass loss of the
total organic moiety.
found (calc.), %
Mass loss of the
metal sulfide. found
(Calc.), %
85–500
75.91 (76.64)
75.73 (76.30)
76.44 (76.04)
75.90 (76.07)
81.50 (81.55)
500–650
24.04 (23.35)
23.88 (23.49)
23.71 (23.95)
23.59 (23.92)
17.97 (18.44)

450
K. S. SIDDIQI ET AL.
Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. Advanced
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In the present study, a two stage decomposition process is
observed for M(py)2(dedtc)2, where M ¼ Mn(II), Fe(II),
Co(II), Ni(II) and Cu(II) indicating similar structural features
of the complexes. A literature survey reveals that the dithiocar-
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residue or decompose to yield respective metal sulfide (Bajpai
and Tiwari, 2004). However, mixed ligand diethyldithiocarba-
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volatile with 17 to 55% residual weight (Lanjewar and Garg,
1992). In our study, the first thermolytic cleavage starts from
85 to 5008C with 76% loss of weight corresponding to whole
organic moiety (found 75.5%) (Table 2). The second stage
ranges between 500 to 6508C, after which a straight line is
observed, indicating no change above this temperature range.
The remaining weight loss corresponds to the respective
metal sulfide (Bajpai and Tiwari, 2004).
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Figgis, B. N. Introduction to Ligand Fields; Wiley Eastern Limited:
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Gokhale, N. H.; Padhye, S. B.; Billington, D. C.; Rathbone, D. L.;
Croft, S. L.; Kendrick, H. D.; Anson, C. E.; Powell, A. K. Synthesis
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In case of Cu(py)2(dedtc)2, the final product was heated
under nitrogen atmosphere and CuS was detected quantitat-
ively among the volatile products.
Ivanov, A. V.; Mitrofanova, V. I.; Kritikos, M.; Antzutkin, O. N.
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The DSC profile exhibits enthalpic changes from endother-
mal and exothermal bands and peaks. In the present case, the
DSC peaks correlate well with the TGA data. A broad exother-
mic peak is obtained between 300–4008C due to the pyrolysis
of the whole organic moiety. However, there is no well defined
exotherm or endotherm corresponding to the last step of
formation of metal sulfide.
Jian, F.; Wang, Z.; Bai, Z.; You, X.; Fun, H.; Chinnakali, K.;
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