Synthesis, characterization of complexes ofn-benzoyl-n'-2-nitro-4-methoxyphenyl-thiourea with Cu, Ni, Pt, Pd, Cd and Hg

Article abstract of DOI:10.1023/A:1010163012703

A scries of coordination complexes with the compositions CuL, NiL-2H₂O, ML₂Cl₂ (A/=Pt(II), Hg(II)) and M(L-H)₂ (A/=Pd(II)), Cd(II)), wlicrc J.=N-bcnzoyI-N'-2-nitro-4-methoxyphenylthiourea, were synthesized and characterized by conductance, EPR, IR and electronic spectral studies and thennogravimetric analysis. The IR and electronic spectra suggest coordination through the thiocarbonyl S and carbonyl O in the Pd(II) and Cd(II) complexes, and S bonding for the Pt(II) and Hg(ll) complexes. The Cu(II) and Ni(II) complexes have polymeric structures in which the ligand is coordinated via the N, O and S atoms.

Full text of DOI:10.1023/A:1010163012703

Journal of Thermal Analysis and Calorimetry, Vol. 61 (2000) 935–945
SYNTHESIS, CHARACTERIZATION OF COMPLEXES
OF N-BENZOYL-N’-2-NITRO-4-METHOXYPHENYL-
THIOUREA WITH Cu, Ni, Pt, Pd, Cd AND Hg
V. Cârcu1, M. Negoiu1, T. Rosu1 and S. Serban2
1Inorganic Chemistry Department, University of Bucharest, 23 Dumbrava Rosie st., Bucharest sect. 2
2ICECHIM, 202, Splaiul Independentei st., Bucharest, Romania
(Received November 19, 1999)
Abstract
A series of coordination complexes with the compositions CuL, NiL 2H2O, ML2Cl2 (M=Pt(II), Hg(II))
and M(L–H)2 (M=Pd(II)), Cd(II)), where L=N-benzoyl-N’-2-nitro-4-methoxyphenylthiourea, were
synthesized and characterized by conductance, EPR, IR and electronic spectral studies and thermo-
gravimetric analysis. The IR and electronic spectra suggest coordination through the thiocarbonyl S
and carbonyl O in the Pd(II) and Cd(II) complexes, and S bonding for the Pt(II) and Hg(II) complexes.
The Cu(II) and Ni(II) complexes have polymeric structures in which the ligand is coordinated via the
N, O and S atoms.
Keywords: complexes, EPR spectroscopy, N-benzoyl-N’-substituted phenyl thiourea, thermal
decomposition
Introduction
Extensive work has been reported on the complexing behaviour of disubstituted
thiourea [1, 2]. In these complexes, it has been shown that one of the coordination
sites is occupied by the thiocarbonyl S. N-benzoyl-N’-alkyl- and N-benzoyl-N’-aryl-
thioureas have recently attracted interest in view of their potential use as highly selec-
tive reagents for liquid-liquid extraction [3].
Satpathy and co-workers synthesized polymeric octahedral complexes of the
type ML H2O, where L=N-benzoyl-N’-phenyl- and N-benzoyl-N’-ortho-substituted-
phenylthioureas (containing nitro, chloro or methoxy groups), with the ligands linked
to the metal ions through the N, S and O atoms [4].
The potentially bidentate ligands: R1R2NC(S)NHC(O)R, where R=phenyl, and
R1, R2=alkyl, form stable neutral complexes with a variety of transition metals.
The crystal structures of such complexes for M=Cu(II) [5], Ni(II) [6], Pd(II) [7],
Pt(II) [8, 9] or Ru(III) [10] all exhibit very similar coordination to the metal ion, with
the ligand coordinated to M(II) through the S and O atoms, with concomitant loss of a
proton. In the case of d10 metal ions (Hg(II) [11], Ag(I) [12, 13] and Cu(I) [14]), this
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CÂRCU et al.: COORDINATION COMPLEXES
type of ligand can coordinate to the metal ion only through the S atom. The
S-coordination of N-benzoyl-N’-propylthiourea to Pt(II) is known [15]. We report
here the synthesis, characterization and thermal behaviour of Cu(II), Ni(II), Pt(II),
Pd(II), Cd(II) and Hg(II) complexes of N-benzoyl-N’-2-nitro-4-methoxy-
phenylthiourea:
Experimental
The ligand N-benzoyl-N’-2-nitro-4-methoxyphenylthiourea was prepared according
to the procedure described in the literature [16].
Synthesis of CuL
The Cu(II) complex may be prepared by addition a-acetate in excess of 4 mmol of cop-
per(II) acetate in 20 ml of methanol to a methanolic solution of ligand (4 mmol in 20 ml).
The mixture is stirred during 1/2 h, when the Cu(II) complex is formed as an olive-green
solid. An excess of metal salt is required because the ligand can reduce Cu(II) to Cu(I)
[14, 17]. (%C: calc. 45.80, exp. 44.95%; %N: calc. 10.69, exp. 10.24; %Cu: calc. 16.28,
exp. 16.75.)
Synthesis of NiL×2H2O
To a suspension of [Ni(NH3)6]Br2 (2 mmol) in 15 ml of ethanol was added a solution
of ligand (2 mmol) in ethanol (10 ml). The resulting brown mixture was stirred at
50°C for 2 h. The brown solid which precipitated out was filtered off, washed with
ethanol, and then dried. (%C: calc. 42.29, exp. 41.75; %N: calc. 9.86, exp. 9.30;
%Ni: calc. 13.77, exp. 14.15.)
Synthesis of PtL2Cl2 and Pd(L–H)2
To a stirred suspension of anhydrous PtCl2 or Pd(CH3COO)2 (2 mmol) in acetone
(15 ml) was added dropwise a solution of ligand in acetone (4 mmol in 20 ml). The
mixture was stirred at room temperature for 30 min. The resulting precipitate was fil-
tered off and washed with acetone (for PtL2Cl2: %C: calc. 38.80, exp. 38.65; %N calc.
9.05, exp. 8.90; %Pt: calc. 21.01, exp. 21.15; for Pd(L–H)2: %C: calc. 46.97, exp.
46.53; %N: calc. 10.96, exp. 10.42; %Pd: calc. 13.87, exp. 14.05.)
Syntheses of Cd(L–H)2 and HgL2Cl2
These complexes were prepared as orange and yellow solids by a method similar to
that for the corresponding Pd(II) and Pt(II) complexes, but with ethanol instead of ac-
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CÂRCU et al.: COORDINATION COMPLEXES
937
etone (for Cd(L–H)2: %C: calc. 46.61, exp. 46.07; %N: calc. 10.87, exp. 10.62;
%Cd: calc. 14.54, exp. 14.72; for HgL2Cl2: %C: calc. 38.57, exp. 38.23; %N: calc.
9.00, exp. 8.73; %Hg: calc. 21.47, exp. 21.15.)
Physical measurements
Elemental analyses were performed with a Carlo Erba L1108 automatic analyzer
(C, N). Metal analyses were carried out by standard methods [18]. The molar conduc-
tivities of complexes were measured in DMF with a Radelkis OK/102 conducto-
meter. The electronic spectra of the ligand and complexes were obtained by a dif-
fuse-reflectance technique, MgO being used as dilution matrix, with a Carl Zeiss Jena
Specord M40 spectrophotometer.
The IR spectra were run on an FT-IR BioRad (FTS-135) spectrophotometer in
the range 4000–500 cm–1 in KBr pellets. The EPR spectra of the Cu(II) complex were
recorded on polycrystalline powder and in pyridine solution, with a spectrometer
ART F-5 model IFA, Bucharest. All the complexes (except that of Cd) were studied
by thermogravimetry in a static air atmosphere, at sample heating rates of 20, 10 and
5°C min–1, with a DuPont 2000 ATG.
Results and discussion
The range of values obtained in DMF for the molar conductivities of the complexes
suggests that all are non-electrolytes.
The bands and assignments for the vibrational spectra of the ligand and the com-
plexes prepared in this work are listed in Table 1. The assignments of the IR spectra
of substituted thioureas and their complexes have been fairly well established. When
the ligand is coordinated to the metal through S, the mainly C–S modes found at
1345 and 720 cm–1 should be either lowered or split or both, sometimes with de-
creased intensity. For all the complexes examined, there is a clear lowering by about
15–20 cm–1 of the band at 720 cm–1, indicating probable M–S bonding. This is an
agreement with the findings on most of the thiourea complexes examined so far. For
all the complexes, there were either slight increases or constancy of the various ab-
sorptions in the region 1600–1150 cm–1 (due to N–H bending and C–N stretch),
which is also consistent with previous findings on S-coordinated substituted thiourea
complexes [19–21]. The ν(CN) vibrations for the ligand are assigned to the bands at
1523(i), 1481(m), 1344(m) and 1163(m) cm–1. The same vibrations are found at
higher frequencies in the IR spectra of the complexes. This increase in frequency can
be explained as resulting from a stronger double bond upon complex formation. One
of the frequencies in the range 3110–3300 cm–1, assigned to ν(NH) vibrations, is not
present in the IR spectra of the Cu(II), Ni(II), Pd(II) and Cd(II) complexes. This indi-
cates that deprotonation of one of the N–H groups occurs upon coordination.
The position of the band at 1670 cm–1, due to νC=O vibration, broadens and be-
comes of much lower intensity, shifts to a lower frequency region or disappears from
the spectra of the Cu(II), Ni(II), Pd(II) and Cd(II) complexes. The position of this
J. Therm. Anal. Cal., 61, 2000

Table 1 IR bands (cm–1) of N-benzoyl-N’-2-nitro-4-methoxyphenylthiourea and its complexes
L
CuL
–
NiL·2H2O
3390
–
PtL2Cl2
–
Pd(L–H)2
–
Cd(L–H)2
–
HgL2Cl2
–
Assignments
–
νOH
νNH
–
3282
3110
1672
1597
1573
1523
1481
1344
1314
1269
1223
1163
1087
1067
1029
851
–
3285
3154
1687
–
–
3339
–
3290
3115
1691
–
–
3120
–
3115
1626
–
1617
1590
1570
1520
1460
1395
1308
1272
1218
–
–
νC=O
–
1593
–
δ
NH+phenyl
1570
1522
1490
1379
1307
1272
1214
1182
1093
1071
1032
858
1576
1521
1499
1352
1315
1274
1232
1178
–
1573
1515
1483
1337
1303
1282
1226
1175
–
1574
1534
1490
1353
1315
1272
1233
1166
–
–
1535
1499
1357
1307
1285
1210
1182
1085
1063
1033
862
νasN–C–N
ν
ν
C–N+νC–S
sN–C–N+νC–S
νC– NO
2
phenyl
–
νC–N
phenyl
–
1096
1068
1031
856
802
693
670
1067
1030
849
1067
1025
850
1059
1025
850
νC– OCH
3
phenyl
805
802
803
806
804
802
νC– NO
2
720
696
711
696
708
709
νC=S
664
668
670
657
678
679
phenyl

CÂRCU et al.: COORDINATION COMPLEXES
939
band is not changed in the IR spectra of the Pt(II) and Hg(II) complexes, suggesting
that the C=O group is not involved in coordination to Pt(II) and Hg(II). The Cu(II)
and Ni(II) complexes are considered to have polymeric structures in which the ligand
coordinates via the N, O and S atoms.
Table 2 Electronic spectral data* on the N-benzoyl-N’-2-nitro-4-methoxyphenylthiourea com-
plexes (nm)
Compound
L
Electronic spectra
257
243
250
241
245
367
360
329
360
380
–
–
610
390
–
–
–
CuL
418
NiL 2H2O
PtL2Cl2
Pd(L–H)2
366
523
–
426(sh)
427(sh)
–
–
*sh=shoulder
Electronic spectral results are included in Table 2. The UV-visible absorption spec-
tra of the Cu(II), Ni(II), Pt(II) and Pd(II) complexes are typical of square-planar com-
plexes of these metal ions [22]. The solid reflectance spectrum of the Cu(II) complex re-
veals a strong band at around 610 nm, corresponding to a ligand-field transition, charac-
teristic of elongated tetragonal octahedral or square-planar stereochemistry. The band
which appears at 418 nm can be considered as reflecting a charge-transfer transition.
Fig. 1 EPR spectra of Cu(II) complex: a – polycrystalline powder, and pyridine solu-
tion at b – room temperature; or at c – 77 K
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CÂRCU et al.: COORDINATION COMPLEXES
The EPR spectra obtained for the polycrystalline sample at room temperature and
77 K are presented in Fig. 1a, and those in pyridine solution in Fig. 1b and 1c. The spec-
trum recorded at 77 K is very similar to the room-temperature spectrum, indicating no
significant change in stereochemistry. The broad isotropic feature found for solid CuL
suggests a significant interaction between Cu(II) centers (g=2.079). The g values for the
frozen pyridine solution are different from that found for the powder compound, suggest-
ing axial interaction with the pyridine molecules (g||=2.255, g =2.014). The Cu(II) spec-
trum in solution has four well-defined copper hyperfine lines (A0=69 G at room tempera-
ture, and A||=162 G and A =23 G in frozen solution at 77 K). The compound therefore
possesses a square-planar configuration with the values of hyperfine splitting constants
typical of the D4h symmetry of the Cu(II) ion. From the above parameters, α2 is evaluated
by using the following approximate expression [23]:
α2=A||/0.036+(g||–2.0023)+3/7(g –2.0023)+0.04
where A|| is the parallel coupling constant expressed in cm–1. The large value of α2
(0.75) for the Cu(II) complex suggests O and N bonding [24].
Fig. 2 TG and DTG curves for a – ligand L; b – CuL; c – NiL·2H2O; d – PtL2Cl2;
e – Pd(L–H)2 and f – HgL2Cl2
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CÂRCU et al.: COORDINATION COMPLEXES
941
Thermal behaviour
The thermal decompositions of these complexes were studied by TG. In air, the Cu,
Pd and Ni complexes thermally degrade to CuO, PdO and NiO, while the Pt complex
does so to the metal. There is very good agreement between the theoretical and ob-
served mass losses (Table 3).
Table 3 Thermogravimetric analysis data in air
Overall mass loss/%
Stepped mass loss/%
Compound
CuL
Temp.
range/°C
Calc.
Found
Temp. range/°C
Mass loss
100–800
79.65
78.03
84.16
100–230
230–680
680–800
20–125
56.72
17.45
3.86
(CuO)
NiL 2H2O
120–520
82.36
(NiO)
7.65
125–280
280–400
400–625
120–275
275–520
150–330
330–475
110–340
340–475
475–605
30.29
11.94
34.14
43.21
36.50
54.31
27.41
49.48
30.75
18.65
PtL2Cl2
120–520
150–475
110–605
78.98
(Pt)
77.09
82.76
100
Pd(L–H)2
HgL2Cl2
84.03
(PdO)
100
The Cu complex (Fig. 2b) decomposes in three steps. The first two steps corre-
spond to the actual decomposition of the complex and the final step involves conver-
sion of the sulphide to the oxide (theoretical loss: 4.07, experimental loss: 3.86%).
The thermogravimetric curve of the complex NiL 2H2O (Fig. 2c) reveals four steps.
The first, in the range 20–125°C, corresponds to the loss of two water molecules (the-
oretical loss: 8.47; experimental loss: 7.65%). The other three steps correspond to the
decomposition of the complex. The Pt complex decomposes in essentially two stages.
The first stage of decomposition is a sequential combination of dehalogenation of the
complex, followed by the loss of one molecule of ligand (theoretical loss: 43.32; ex-
perimental loss: 43.20%). The second stage of decomposition corresponds to the loss
of the second molecule of ligand (theoretical loss: 35.67; experimental loss: 36.50%).
Coordinated chloride is slowly evolved initially (Fig. 2d). Bourne and Koch have re-
cently shown [15] by means of X-ray diffraction that the cis isomer is obtained
through reaction of the Pt(II) salt with N-benzoyl-N’-propylthiourea. One of the rea-
sons is that the carbonyl oxygen atom is locked into a ring by an N–H…O hydro-
gen-bond. It may be presumed that the cis isomer also predominates in the case of the
J. Therm. Anal. Cal., 61, 2000

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CÂRCU et al.: COORDINATION COMPLEXES
Fig. 3 Isotherms of mass loss of CuL
Fig. 4 Plots of log(heating rate) vs. 1/T for isothermal decomposition of CuL
Pt(II) complex with N-benzoyl-N’-2-nitro-4-methoxyphenylthiourea. In view of the
high trans effect [25] of unidentate thioureas, the initial elimination of coordinated
chloride is expected. In contrast, the presence of the trans isomer should lead to the
initial evolution of the two thiourea molecules. Thus, the presence of the cis isomer is
more probable than that of the trans isomer.
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CÂRCU et al.: COORDINATION COMPLEXES
943
Fig. 5 DSC curve of CuL
The Pd complex decomposes in the temperature range 150–475 and a pro-
nounced discontinuity occurs in the region of 350°C, at a mass loss of about 54%.
The discontinuity represents a combination of desulphurization followed by conver-
sion of the sulphide residue to the oxide (84.03% mass loss at 475°C) (Fig. 2e). In this
case, we can conceive that M–S links are retained and extended, owing to metal sul-
phide formation, during the thermal decomposition [26].
Figure 3 illustrates the isothermal mass loss (as a percentage of the initial mass)
vs. time at 80, 90, 100, 110, 115, 120 and 125°C for the Cu(II) complex. There is a
relatively slow change in mass with time at 80, 90 and 100°C, but at temperatures
greater than 100°C the initial period is characterized by a very fast mass loss. For
∆m=const., a plot of log(heating rate) vs. 1/T (Fig. 4) should be a straight line with a
slope which relates to the activation energy. Figure 4 shows such straight lines for
10≤%∆m≤70. In this range of %∆m, the values of the activation energy are located in
the range 129.9–167.9 kJ mol–1 (Table 4). For the Cu(II) complex, the DSC curve was
also recorded (at a heating rate of 5°C min–1); this is depicted in Fig. 5.
Table 4 Kinetic parameters at different conversion levels for isothermal decomposition of CuL
% Conversion
Ea/kJ mol–1
165.8
logA/min–1
18.6
10
20
50
70
138.9
15.4
129.9
14.5
167.9
19.4
Ea is the activation energy, and A is the pre-exponential factor
From the TG curves for the Ni, Pt, Pd and Hg complexes, the reaction order (n)
and activation energy (Ea) of the thermal decomposition were obtained by the method
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944
CÂRCU et al.: COORDINATION COMPLEXES
Fig. 6 Linearization plots for a – NiL·2H2O; b – Pd(L–H)2; c – PtL2Cl2 and
d – HgL2Cl2
of Coats and Redfern [27]. The linearization plots for the complexes are shown in
Fig. 6. The order of reaction in each case is unity (Table 5).
Table 5 Non-isothermal kinetic parameters
Compound
NiL 2H2O
Pd(L–H)2
PtL2Cl2
n
1
1
1
1
Ea/kJ mol–1
34.2
r
0.9875
0.9934
0.9856
0.9965
46.6
67.4
HgL2Cl2
34.4
r is the correlation of the linear regression
It is obvious that the activation energy depends on the electronegativity of the
metal atom and follows the sequence Ni(II)<Hg(II)<Pd(II)<Pt(II).
Conclusions
The initial elimination of coordinated chloride leads to the conclusion that the cis iso-
mer probably predominates in the case of the Pt(II) complex.
There is a significant difference between the thermal decompositions of the com-
plexes containing the monodentate-bound thiourea ligand (Pt(II) and Hg(II)) and the
other complexes.
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