Synthesis, spectral, thermal and structural characterization of a hexanuclear copper(I) cluster and a cobalt(III) complex of 1-ethyl-3-phenyl-thiourea

Article abstract of DOI:10.1016/j.poly.2014.10.018

1-Ethyl-3-phenyl-thiourea (Heptu, 1) forms a hexanuclear complex, [Cu₆(eptu)₆] (2), and a mononuclear complex, [Co(eptu)₃] (3), which have been characterized with the aid of elemental analyses, IR, magnetic susceptibility

Full text of DOI:10.1016/j.poly.2014.10.018

Polyhedron 85 (2015) 918–925
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, spectral, thermal and structural characterization
of a hexanuclear copper(I) cluster and a cobalt(III) complex
of 1-ethyl-3-phenyl-thiourea
a
a,
⇑
a
c
b
a,
⇑
A. Singh , M.K. Bharty , P. Bharati , A. Bharti , Sanjay Singh , N.K. Singh
a
Department of Chemistry, Banaras Hindu University, Varanasi 221005, India
Department of Chemical Sciences, Indian Institute of Science Education and Research, Mohali 140306, India
Department of Chemistry, Kirori Mal College, University of Delhi, Delhi-110007, India
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 June 2014
Accepted 11 October 2014
Available online 27 October 2014
6 6
1-Ethyl-3-phenyl-thiourea (Heptu, 1) forms a hexanuclear complex, [Cu (eptu) ] (2), and a mononuclear
complex, [Co(eptu)
susceptibility and single crystal X-ray diffraction data. The ligand (1) and [Co(eptu)
triclinic system whereas [Cu (eptu) ] (2) crystallizes in the monoclinic system, with the respective space
3
] (3), which have been characterized with the aid of elemental analyses, IR, magnetic
3
] (3) crystallize in the
6
6
ꢀ
ꢀ
groups P1, P21/c and P1. The unit cell of complex 2 consists of two identical units, each containing three
interacting Cu(I) ions. Out of which Cu1 and Cu2 are tetrahedrally bonded by two sulfur atoms, one nitro-
gen and one Cu3 ion, whereas each Cu3 ion is bridged between Cu1 and Cu2 and bonded to two sulfur
and one nitrogen, having a trigonal bipyramidal geometry. Thus Cu1 and Cu2 have coordination number
of four, while Cu3 is five coordinate. The ligand acts as uninegative tridentate in complex 2, bonding
through the thioamide nitrogen and sulfur atoms, and bridging between two copper centers, whereas
the ligand acts as uninegative chelating N,S bidentate in complex 3, forming three four-membered CNSCo
chelate rings. The crystal structures of the ligand and complexes are stabilized by various types of inter
and intramolecular hydrogen bonding, providing supramolecular frameworks. The course of the thermal
degradation of complex 2 has been investigated by TG-DTA.
Keywords:
Thiourea
Cu(I) and Co(III) complexes
Crystal structure
Supramolecular architecture
TGA
Ó 2014 Elsevier Ltd. All rights reserved.
1
. Introduction
have become a topic of interest in the last few years. It has been
reported that substituted acylthiourea ligands might act as mono-
0
N,N -Disubstituted thioureas possess a remarkable capacity for
dentate sulfur donors or bidentate oxygen and nitrogen donors [9].
These hard and soft donor atoms provide a multitude of bonding
possibilities [10]. A number of thiourea derivatives have been
reported to form complexes with 3d metal ions [11]. Recent work
on copper(I) complexes has involved the synthesis and character-
ization of polynuclear complexes with bridging ligands [12].
Heterocyclic thiones, such as pyridine-2-thione [13] or 3-trimeth-
ylsilylpyridine-2-thione [14], form hexanuclear copper(I) com-
plexes which have an interesting paddle-wheel like structure
coordination with transition metals, giving rise to highly colored
chelate compounds. The complexation behavior of thiourea deriv-
atives has been reported in the literature [1,2]. Thioureas are
important organic compounds which possess high biological activ-
ity, act as corrosion inhibitors and antioxidants, and are the com-
ponent of polymers [3]. Thioureas are selective analytical
reagents, especially for the determination of metals in the presence
of other metal ions [4,5]. Acyl thiourea derivatives are well known
for a wide range of biological activities, like bactericidal, fungicidal,
herbicidal and insecticidal, and they possess regulating activity for
plant growth [6–8]. With the simultaneous presence of S, N and O
electron donors, the versatility and interesting behavior of acy-
lthioureas as building blocks in polydentate ligands for metal ions
6
with an octahedral Cu core. In these complexes each ligand, with
the thione form [–NHC(@S)–], is converted to the thiolato form
[–N–C(S–)–] and acts as an effectively tridentate ligand with a
monodentate nitrogen atom and a bridging sulfur atom [15]. A sur-
vey of the literature shows that there are no reports on the synthe-
sis and characterization of complexes of 1-ethyl-3-phenyl-thiourea
(
Heptu). Therefore, in this paper we have synthesized the ligand
⇑
Corresponding authors. Tel.: +91 542 6702452; fax: +91 542 2368127.
E-mail addresses: manoj_vns2005@yahoo.co.in (M.K. Bharty), singhnk_bhu@
Heptu and its Cu(I) and Co(III) complexes, and characterized them
by spectroscopic and single crystal X-ray diffraction data.
yahoo.com (N.K. Singh).
http://dx.doi.org/10.1016/j.poly.2014.10.018
0
277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

A. Singh et al. / Polyhedron 85 (2015) 918–925
919
EtOH
reflux
EtNH
2
+ PhNCS
NH
C
NH
S
2
H C
CH
3
[Heptu] (1)
O
Co(O
A
H 2
2.
)
Ac
c
)
O
2
2H
2
(
.
u
C
O
CH
3
CH
2
HN
S
N
CH
3
3
H C
2
H C
CH
2
S
Cu
Cu
HN
HN
N
N
S
N
Cu
N
H
N
CH
2
CH
3
N
N
Co
H
C
S
S
S
H
CH3
Cu
2
N
Cu
N
HN
Cu
S
S
2
H C
CH
3
NH
H2C
NH
S
N
2
H C
3
[Co(eptu) ] (3)
CH
3
CH
3
NH
2
H C
CH
3
[Cu
6 6
(eptu) ] (2)
Scheme 1. Syntheses of 1-ethyl-3-phenyl-thiourea (Heptu) and complexes 2 and 3.
2
. Experimental
Mo K
scan absorption correction was applied to the X-ray data of both
compounds. The structure was solved by direct methods (SHELXL
a (k = 0.71073 Å) radiation source. A semi-empirical multi
2.1. Chemicals and starting materials
-
2
0
8) and refined by full matrix least-square on F (SHELXL) using
Commercial reagents were used without further purification
anisotropic displacement parameters for all non-hydrogen atoms.
All hydrogen atoms were included in calculated position and
refined with a riding model [16]. Figures were drawn using the
programs MERCURY and ORTEP-3 [17,18].
and all experiments were carried out in the open atmosphere. Phe-
nyl isothiocyanate (Sigma Aldrich) and ethyl amine (SD Fine Chem-
icals) were used as received. All the synthetic manipulations were
carried out in the open atmosphere and at room temperature. The
solvents were dried and distilled before use following the standard
procedures.
2.4. Synthesis
2.4.1. Preparation of 1-ethyl-3-phenyl-thiourea [Heptu] (1)
A solution of phenyl isothiocyanate (6.75 g, 50 mmol) in ethanol
15 ml) was added dropwise at 15 °C to a vigorously stirred solu-
2.2. Physical measurements
(
tion of ethylamine (2.25 ml, 50 mmol) in ethyl alcohol (10 ml) over
a period of 30 min. The reaction mixture was stirred for 2 h and left
overnight at room temperature. The solvents were evaporated
slowly at room temperature which gave single crystals of the com-
pound suitable for X-ray analysis. Yield: 60%. M.p.: 140 °C. Anal.
Carbon, hydrogen and nitrogen contents were estimated on a
CHN Model CE-440 Analyser and on an Elementar Vario EL III Carlo
Erba 1108. Magnetic susceptibility measurements were performed
at room temperature on
Hg[Co(NCS) ] as the calibrant and electronic spectra were recorded
on a SHIMADZU 1700 UV–Vis spectrophotometer. IR spectra were
a Cahn Faraday balance using
4
Calc. for C
9
H
12
N
2
S (180.27): C, 59.91; H, 6.65; N, 15.53; S, 17.75.
ꢀ1
Found: C, 59.91; H, 6.98; N, 15.33; S, 17.76% IR (KBr, cm ):
ꢀ1
recorded in the 4000–400 cm region as KBr pellets on a Varian
m
(NH) 3215, 3117; [b(NH) +
(CN) + b(NH)] (thioamide-II) 1375;
300 MHz, DMSO-d , d ppm): 11.06 (s, 1H, NH, attached to phenyl
m
(CN)] (thioamide-I) 1407;
1
13
Excalibur 3100 FT-IR spectrophotometer. H and C NMR spectra
were recorded in DMSO-d on a JEOL AL300 FT-NMR spectrometer
using TMS as an internal reference. Thermogravimetric analyses
TG-DTA) were performed on a Netzsch STA 449 thermal analyzer
at a heating rate of 5 °C/min in a N atmosphere.
(C@S) 956. 1H NMR
[m
m
6
(
6
ring), 4.49 (s, 1H, NH, attached to ethyl group), 7.11–7.64 (m, aro-
(
13
matic protons), 2.49 (–CH
ppm): 187.31 (>C@S), 137.86 (>C–N), 117.95–134.32 (aromatic
carbons), 65.17 (–CH ), 14.03 (–CH ).
2 3 6
), 1.32 (–CH ). C NMR (DMSO-d , d
2
2
3
2.3. X-ray crystallography
6 6
2.4.2. Preparation of [Cu (eptu) ] (2)
Crystals suitable for X-ray analyses of complexes 1 and 2 were
A methanolic solution of Cu(OAc)
2
2
.H O (0.199 g, 1 mmol) was
grown at room temperature. X-ray diffraction data were measured
at 293(2) K on an Oxford Diffraction Gemini diffractometer
equipped with CrysAlis Pro., using a graphite monochromated
added to a methanol solution of Heptu (1.038 g, 2 mmol) with con-
tinuous stirring for 30 min. The resulting solution was filtered and
the filtrate was kept for 5 days, whereupon orange crystals of com-

9
20
A. Singh et al. / Polyhedron 85 (2015) 918–925
Fig. 1. TG-DTA curves for complex 1.
Table 1
Crystallographic data for the ligand Heptu (1), complexes 2 and 3.
Parameters
1
2
3
Empirical formula
Formula weight
Crystal system
Space group
T (K)
C
9
H
12
N
2
S
C
54
H
66Cu
6
N
12
S
6
C
27 6 3
H33CoN S
180.27
triclinic
P1ꢀ
293(2)
1456.91
monoclinic
P21/C
596.73
triclinic
P1ꢀ
293(2)
293(2)
k, Mo K
a (Å)
b (Å)
a
(Å)
0.71073
0.71073
13.4167(9)
14.0585(10)
17.0847(9)
90.00
103.134(6)
90.00
3138.2(3)
2
1.542
2.241
1488
0.29 ꢁ 0.27 ꢁ 0.25
2.96–29.16
ꢀ18 6 h 6 17
ꢀ10 6 k 6 18
ꢀ21 6 l 6 23
15887
0.71073
9.3310(7)
9.7037(8)
12.0974(10)
12.2300(10)
89.337(7)
84.504(7)
85.224(7)
1424.1(2)
6
12.1688(7)
13.1694(9)
79.445(5)
84.574(6)
80.533(5)
1446.82(17)
2
1.370
0.837
624
0.29 ꢁ 0.27 ꢁ 0.25
3.26–32.45
ꢀ13 6 h 6 14
ꢀ17 6 k 6 18
ꢀ17 6 l 6 19
16050
c (Å)
a
(°)
b (°)
(°)
c
3
V (Å )
Z
q
l
calc (g cmꢀ3)
(mm
1.261
0.863
576
ꢀ
1
)
F(000)
Crystal size (mm )
h range for data collections (°)
Index ranges
3
0.29 ꢁ 0.27 ꢁ 0.25
3.17–29.03
ꢀ10 6 h 6 13
ꢀ
ꢀ
16 6 k 6 9
16 6 l 6 15
No. of reflections collected
6893
No. of independent reflections (Rint
)
7599
8478
10420
No. of data/restrains/parameters
5656/0/325
1.046
0.0659, 0.0977
0.1643, 0.1959
0.552, ꢀ0.595
7151/0/352
1.028
0.0593, 0.1296
0.1189, 0.1559
0.541, ꢀ0.502
9362/0/324
0.998
0.0766, 0.1662
0.1886, 0.2413
0.680, ꢀ0.652
2
Goodness-of-fit on F
a
a
b
b
R
R
1
, wR
, wR
2
[I > 2
(all data)
r
(I)]
1
2
Largest difference in peak/hole (e Åꢀ3)
P
P
a
R
R
1
=
||F
o
| ꢀ |F
c
|| |F
o
|.
P
P
b
2
2
2
2|2]1/2.
2
= [ w(|F
o
| ꢀ |F
c
|) / w|F
o
Table 2
Selected bond lengths (Å) and angles (°) for [Heptu] (1).
plex 2 suitable for X-ray structural investigation were obtained.
Anal. Calc for C54 (1456.78): C, 44.48; H, 4.53; N,
1.53; S, 13.17%. Found: C, 44.50; H, 4.52; N, 11.53; S, 13.17%.
H
6 12 6
66Cu N S
1
Bond lengths (Å)
C1–C2
Bond angles (°)
ꢀ1
1.389(5)
1.377(5)
1.420(4)
1.348(4)
1.657(3)
1.311(4)
1.443(4)
1.481(5)
C6–C1–C2
C6–C1–N1
C2–C1–N1
C7–N1–C1
C7–N2–C8
N2–C7–N1
N1–C7–S1
N2–C7–S1
120.0(3)
123.7(3)
116.2(3)
129.5(3)
120.4(3)
112.4(3)
122.6(3)
125.0(3)
M.p.: 245(d) °C. IR (KBr, cm ):
amide-I) 1446; [ (CN) + b(NH)] (thioamide-II) 1386;
(Cu–N) 500; (Cu–S) 424. H NMR (300 MHz, DMSO-d
6
m
(NH) 3120; [b(NH) +
m
m
(CN)] (thio-
(C@S) 901;
, d ppm):
C1–C6
N1–C1
m
1
m
m
N1–C7
S1–C7
13
4
.39 (s, 1H, NH), 7.18–7.72 (m, aromatic protons).
C NMR
N2–C7
N2–C8
C9–C8
6
(DMSO-d , d ppm): 138.69 (>C–N), 115.05–133.89 (aromatic car-
2 3
bons), 64.10 (–CH ), 15.08 (–CH ). UV–Vis [kmax, Nujol mulls,
nm]: 253, 336.

A. Singh et al. / Polyhedron 85 (2015) 918–925
921
for crystalization. Dark green needle shaped crystals of 3 suitable
for X-ray analyses were obtained by slow evaporation of the above
solution over a period of 20 days. M.p.: 205 °C. Anal. Calc. for C27-
H
33CoN
6 3
S (596.73): C, 54.29; H, 5.53; N, 14.07; S, 16.08. Found:
ꢀ1
C, 54.29; H, 5.52; N, 14.06; S, 16.08%. IR (KBr, cm ):
m
(NH) 3120
(CN)] (thioamide-I) 1457 (Calc. 1464);
(CN) + b(NH)] (thioamide-II) 1396 (Calc. 1466); (C@S) 896;
(Co–N) 510 (Calc. 511); (Co-S) 420 (Calc. 349). UV–Vis [kmax
Nujol mulls, nm]: 350,384, 414, 450.
(
[
Calc. 3593); [b(NH) + m
m
m
m
m
,
3
. Results and discussion
Fig. 2. ORTEP diagram of Heptu (1) with a 30% ellipsoid probability level. Hydrogen
atoms are omitted for clarity.
The ligand 1-ethyl-3-phenyl-thiourea (Heptu) (1) reacts with
copper(II) and cobalt(II) acetates and forms the complexes [Cu
eptu) ] (2) and [Co(eput) ] (3). The thiourea ligand acts as a reduc-
ing agent and converts Cu(II) to Cu(I) with concomitant formation
of the disulfide ligand EtNHPhNCSSCNPhNHEt [19]. Co(II) is
converted to Co(III) by aerial oxidation in the presence of the
6
2.4.3. Preparation of [Co(eput)
3
] (3)
(
6
3
Methanolic solutions of Co(OAc)
Heptu (1.038 g, 2 mmol) were mixed together and stirred continu-
ously for 2 h. The resulting green solution was filtered off and kept
2
2
.2H O (0.178 g, 1 mmol) and
Fig. 3. Crystal packing of Heptu (1) along the b axis showing N–Hꢂ ꢂ ꢂS hydrogen bonding.
H
2
HN
S
C
CH
3
(
i) -2
NH
[
Cu (eptu) ]
2Cu S + 2CuS
2
6
6
H
2
C
245 -280 ºC
HN
CH3
(ii) -4
N
+ N2 280-784 ºC
2
Cu S + 2CuS .xN
2
2
-
N2
>784 ºC
2
Cu S + 2CuS
2
Scheme 2. Possible decomposition pathway for complex 2.

9
22
A. Singh et al. / Polyhedron 85 (2015) 918–925
Fig. 4. ORTEP diagram of [Cu
6
(eptu)]
6
(2) with a 30% ellipsoids probability level. Hydrogen atoms are omitted for clarity.
Table 3
Selected bond lengths (Å) and angles (°) for [Cu
6
6
(eptu)] (2).
Bond lengths (Å)
Cu1
Cu2
Cu3
Cu1–Cu3
Cu1–Cu2
Cu1–S2
Cu1–S1
N5–Cu1
N5–C2
2.7958(10)
2.9257(10)
2.2386(16)
2.2448(16)
2.011(5)
Cu2–N1
Cu2–S2
Cu2–S3
Cu2–Cu3
C19–N1
N1–C1
2.025(4)
Cu3–N2
Cu3–S3
Cu3–S1
Cu3–Cu1
N2–C22
N2–C7
2.007(5)
2.2434(17)
2.2468(17)
2.8766(10)
1.287(6)
2.2318(16)
2.2385(17)
2.7958(10)
1.291(6)
1.289(7)
1.412(7)
1.422(7)
Bond angles (°)
Cu1
Cu2
Cu3
S2–Cu1–Cu3
S1–Cu1–Cu3
N5–Cu1–Cu2
S2–Cu1–Cu2
S1–Cu1–Cu2
N5–Cu1–S1
Cu1–Cu3–Cu2
N5–Cu1–Cu3
N5–Cu1–S2
S2–Cu1–S1
78.32(4)
N1–Cu2–S2
N1–Cu2–S3
S2–Cu2–S3
N1–Cu2–Cu3
S2–Cu2–Cu3
S3–Cu2–Cu3
N1–Cu2–Cu1
S2–Cu2–Cu1
S3–Cu2–Cu1
Cu3–Cu2–Cu1
116.76(16)
116.90(15)
118.99(6)
85.51(13)
76.50(4)
133.91(5)
85.51(14)
135.24(5)
75.19(4)
N2 Cu3 S3
N2 Cu3 S1
S3 Cu3 S1
119.83(14)
116.85(14)
115.49(6)
86.33(13)
78.20(4)
133.69(5)
85.16(13)
134.96(5)
76.25(4)
131.56(5)
85.04(13)
134.07(5)
75.11(4)
116.49(15)
65.90(2)
87.22(13)
121.21(15)
115.39(6)
N2 Cu3 Cu1
S3 Cu3 Cu1
S1 Cu3 Cu1
N2 Cu3 Cu2
S3 Cu3 Cu2
S1 Cu3 Cu2
Cu3–Cu1Cu2
Cu1 Cu3 Cu2
C25 S3 Cu3
66.63(2)
65.11(3)
65.90(2)
105.1(2)
substituted thiourea to yield the non-labile Co(III) complex [20].
Complex 2 is soluble in CHCl and DMSO, but complex 3 is insolu-
ble, even in DMF and DMSO, and both complexes are stable
the formation of the Cu(I) and Co(III) complexes with Heptu ligand.
The TG and DTA curves show that the copper complex is stable up
to 245 °C (according to the first weight loss). A weight gain of
10.24% at 286 °C may arise due to the adsorption of nitrogen by
3
towards air and moisture. The ligand Heptu (1), like in similar thio-
ureas, is an N,S-bidentate ligand in complex 3, but behaves as N,
l
2
-
2
CuS and Cu S and the final weight loss of 10.12% at 784 °C shows
S tridentate in the hexanuclear copper(I) complex. Scheme 1 shows
desorption of nitrogen.

A. Singh et al. / Polyhedron 85 (2015) 918–925
923
3.1. IR spectra
3.4. Thermal gravimetric analysis
The IR spectrum of the ligand 1-ethyl-3-phenyl-thiourea
The thermal properties of [Cu
6
(eptu)
6
] (2) were studied by TG
ꢀ1
(
Heptu) shows bands at 3215 and 3117 cm , which may be
and DTA in the temperature range 30–800 °C under a nitrogen
atmosphere. Thermogravimetric analysis of complex 2 shows that
the complex starts decomposing at 245 °C and the thermogram
exhibits three distinct decompositions at 245, 286 and 784 °C.
The weight loss (65%) at 245 °C could be ascribed to the loss of
ꢀ1
assigned to m(NH), and that at 956 cm to m(C@S). Furthermore,
ꢀ1
the bands around 1407 and 1375 cm may be assigned to thioam-
ide-I [b(NH) + (CN)] and thioamide-II [ (CN) + b(NH)], respec-
tively. Persistence of a band at around 3120 cm due to
m
m
ꢀ1
m(NH)
0
in the spectra of both complexes indicates the presence of an NH
two 1-ethyl-3-phenylisothiourea ligands and four N-ethyl-N -phe-
group adjacent to the ethyl group which does not take part in
nylformamidine moieties in the temperature range 245–280 °C, for
which the corresponding endothermic peak at 267 °C was
obtained. The second peak at 286 °C shows a weight gain
(10.24%) which may be due to adsorption of nitrogen by CuS and
bonding. However, the disappearance of the
3
m
(NH) band around
215 cm suggests the loss of the thioamide proton adjacent to
the phenyl group and participation of the deprotonated thioamide
nitrogen in bonding with the metal ion. The band due to (C@S)
ꢀ1
m
Cu
desorption of nitrogen. After 784 °C, the residue of 35.38% left cor-
responds to 2CuS + 2Cu S, for which corresponding endo and exo-
2
S, and the final weight loss of 10.12% at 784 °C indicates
ꢀ
1
suffers a negative shift of 55–60 cm suggesting bonding of the
ligand via the thioamide sulfur atom to the metal ion. In addition,
the thioamide I and thioamide II bands suffer positive shifts of 50–
2
thermic peaks in the DTA at 329 and 431 °C were obtained (Fig. 1).
The results of the thermal decomposition of the complex can be
explained on the basis of two types of coordination environment
adopted by the copper atoms. Looking at the structure of the com-
plex (Fig. 4) it can be seen that four copper atoms, which have a
coordination number of four, lose four ligand moieties without sul-
fur, whereas the other two copper atoms, having a coordination
number of five, lose two complete ligand moieties along with sul-
ꢀ1
1
1 cm in the spectra of the complexes, supporting bonding of the
ligand through the thioamide sulfur atom. The IR spectra show that
Heptu (1) is N,S bidentate in complex 3 and N, -S tridentate in the
hexanuclear copper(I) complex 2. Other bands around 500 and
l
2
ꢀ1
4
24 cm are assigned to m(M–N) and m(M–S), respectively [21].
3.2. Electronic spectra and magnetic moments
fur, leading to the formation of a mixture of 2Cu
.5. Crystal structure description of Heptu (1)
The crystallographic data and structural refinement details for
2
S + 2CuS.
3
The electronic spectrum of complex 2 in a MeOH–CHCl mix-
3
ture exhibits two strong absorptions at 253 and 336 nm due to
intraligand/charge transfer transitions [22]. Complex 3 is diamag-
netic indicating the presence of Co(III) in a low spin octahedral
geometry. It shows two bands at 450 and 414 nm which may be
Heptu are given in Table 1. The bond distances and bond angles
for the free ligand are given in Table 2. Fig. 2 shows the ORTEP dia-
gram of Heptu (1), with the atomic numbering scheme. The asym-
metric unit of 1 contains three crystallographically independent
molecules with similar geometries. The crystal packing of the
ligand is stabilized by means of an extended system of N–Hꢂ ꢂ ꢂS
hydrogen bonds, leading to the formation of a supramolecular
architecture (Fig. 3). Intermolecular N–Hꢂ ꢂ ꢂS hydrogen bonds are
present between the thioamide sulfur and NH hydrogen of a
nearby molecule of the ligand. The C–S bond distance of
1
1 g 1
A g ? E A g ? A2, transitions respec-
and 1
1
1
attributed to the
tively, for six coordinate octahedral Co(III) center. Other high
energy bands at 384 and 350 nm may be assigned to charge trans-
fer/intraligand transitions.
1
13
3
.3. H and C NMR spectra
The 1H NMR spectrum of Heptu (1) exhibits signals at d 11.06
and 4.49 ppm for the NH protons attached to the phenyl ring and
ethyl group, respectively. The five protons of the phenyl ring
1
.657(3) Å (Table 2) in 1 agrees well with those formed in other
related compounds and comes in the range observed for C@S dou-
ble bonds [1.56 Å] [23] (See Scheme 2).
appear as a multiplet in the region d 7.11–7.64 ppm. The –CH
and –CH protons appear at d 2.49 and 1.32 ppm, respectively.
The H NMR spectrum of [Cu (eptu) ] shows the absence of a sig-
2
3
1
6
6
6 6
3.6. Crystal structure description of [Cu (eptu) ] (2)
nal for the –NH proton attached to the phenyl ring, while the –NH
proton attached to ethyl group appears at d 4.39 ppm, indicating
that the metal is bonded to the ligand via the deprotonated nitro-
gen atom attached to the phenyl ring.
The ORTEP diagram of complex 2, together with the atom num-
bering scheme, is presented in Fig. 4. Selected bond distances and
angles are listed in Table 3. The crystal structure of complex 2 is
ꢂ ꢂ ꢂ
Fig. 5. C–H S interactions forming a paddle-wheel like structure.

9
24
A. Singh et al. / Polyhedron 85 (2015) 918–925
Fig. 6. ORTEP diagram of [Co(eptu)
3
] (3) with a 30% ellipsoids probability level. Hydrogen atoms are omitted for clarity.
to 3.306 Å, suggesting that they are strongly influenced by the
Table 4
Selected bond lengths (Å) and angles (°) for [Co(eptu)
characteristics of the ligand and the nuclearity of the complex. It
is observed that the Cu–Cu distance in complex 2, (Table 3)
together with the Cu–S–Cu bridging moieties are longer than those
bridged by the copper ion. The Cuꢂ ꢂ ꢂCu distances in the hexanucle-
3
] (3).
Bond lengths (Å)
Bond angles (°)
Co–N2
Co–N6
Co–N4
Co–S3
Co–S1
Co–S2
1.935(3)
1.956(3)
1.957(3)
2.2796(13)
2.2928(13)
2.2979(13)
1.715(5)
1.723(4)
1.734(4)
1.303(5)
1.420(4)
1.295(5)
1.420(5)
N2–Co–S1
N4–Co–S2
N6–Co–S3
N6–Co–S2
N2–Co–S3
N4–Co–S1
S1–Co–S2
S3–Co–S2
S3–Co–S1
C12–N4–C13
C12–N4–Co
C3–N2–Co
C21–N6–Co
72.17(10)
71.83(10)
72.05(9)
93.84(11)
92.42(10)
94.82(10)
99.22(5)
98.76(5)
96.04(5)
125.2(3)
100.4(3)
100.3(3)
99.3(3)
ar units of the [Cu
6
(eptu)
6
] octahedron (2) are in the 3.596–3.629 Å
-S–Cu3–
-S–Cu3–Cu2] units are in the 3.133–3.255 Å range for
the triangle formed by Cu1ꢀCu3ꢀCu2. The structure of complex
is stabilized by C–Hꢂ ꢂ ꢂS hydrogen bonding, leading to the forma-
tion of a paddle-wheel like structure (Fig. 5).
range, whereas the Cuꢂ ꢂ ꢂCu distances in the triangular [
Cu1] and [
l
l
S3–C21
S1–C3
2
S2–C12
N2–C3
N2–C4
N4–C12
N4–C13
3.7. Crystal structure description of [Co(eptu)
3
] (3)
Fig. 6 shows the ORTEP diagram of complex [Co(eptu)
3
] (3),
built up of two trinuclear copper units bridged by a tridentate 1-
ethyl-3-phenyl thiourea (eptu) anion. This results in a hexanuclear
complex with two pairs of crystallographically different tetra-coor-
dinated copper centers, Cu3N5Cu1S1S2 and Cu3N5Cu2S1S2, and a
together with the atom numbering scheme. The structural refine-
ment data related to complex 3 are listed in Table 1 and selected
bond distances and bond angles are given in Table 4. The elements
of the structure are joined to each other in the crystal packing by
means of an extended system of H-bonds, where a hydrogen atom
belonging to the phenyl ring participates in the structure. The
2
pair of pentacoordinated Cu N2S1Cu3S2Cu1 copper centers. Thus,
two pairs Cu1 and Cu2 are equivalent and four coordinate tetrahe-
dral, while the Cu3 pairs are structurally similar to each other but
different from Cu1 and Cu2 and are five coordinate trigonal bipyra-
midal involving one nitrogen, two sulfur and Cu1–Cu3–Cu2 bridge
bonding. The six copper atoms form a distorted octahedron and the
eight surfaces of the octahedron are capped by six uninegative eptu
ligands. The average Cu–N and Cu–S distances of 2.01 and 2.250 Å,
respectively, are comparable to those reported for four coordinate
copper(I) complexes [24]. The computed average Cu–N and Cu–S
distances of 2.056 and 2.356 Å, respectively, are very close to the
observed crystal data. The shorter N(1)–C(2) distance (1.28 Å)
and longer carbon–sulfur distance (2.23 Å), as compared to those
found in the ligand (Heptu), shows delocalization of charge within
the chelate ring. The literature shows that Cu–Cu distances bridged
by sulfur atoms in this class of complexes range widely from 2.616
3 3
metal center is coordinated in an N S manner by three negatively
charged ligand moieties utilizing thioamide sulfur and nitrogen
atoms, forming three four membered chelate rings. In general,
the ligand is expected to lose a proton from the thioamide nitrogen
adjacent to the phenyl ring due to a resonance effect, and thus act
as a single charged bidentate ligand. The carbon-sulfur and car-
bon–nitrogen distances within the chelate rings are shorter than
the bond lengths in Heptu but longer than C@S and C@N double
bonds, which suggest delocalization of charge within the chelate
ring. The chelate and phenyl rings are tilted towards each other,
making a dihedral angle of 65.36°. Complex 3 forms three four
membered CSNCo chelate rings with bite angles of 71.17(10)°,
81.83(10)° and 72.05(9)°, which represents minor deviation from
an octahedral geometry. The Co–S bond distances for the three

A. Singh et al. / Polyhedron 85 (2015) 918–925
925
ꢂ ꢂ ꢂ
Fig. 7. C–H S interactions forming a linear structure.
CSNCo chelate rings are 2.2796(13), 2.2988(13) and 2.2979(13) Å,
which are comparable to the bond lengths reported for [Co{S2-
(3), respectively. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Center, 12 Union Road, Cam-
bridge CB2 IEZ, UK; fax: (+44)1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
CN(CH
compared with the computed DFT data of 2.359, 2.361 and
.357 Å, respectively. The average bond lengths, C3–S1 = 1.723(4),
2 2 2 2 2 3
CH CH NMe ) } ] [25]. These Co-S bond distances can be
2
C12–S2 = 1.734(4), C21–S3 = 1.715(5), C3–N2 = 1.303(5), C12–
N4 = 1.295(5) and C21–N6 = 1.290(5) Å, suggest considerable delo-
calization of charge [26]. The C–S bond distances are 1.743, 1.746
and 1.746 Å, respectively, and the Co-N bond distances are 1.968,
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Cu (eptu) ] (2) and a mononuclear Co(III) complex [Co(eptu) ]
[
6
6
with 1-ethyl-3-phenyl thiourea. The thiourea ligand acts as a
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[
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3
ligand and the complexes are stabilized by inter/intramolecular
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ligand and complex 3.
[
[
[
(
2011) 1410.
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Appendix A. Supplementary material
CCDC 907776, 907777 and 907778 contain the supplementary
crystallographic data for Heptu (1) [Cu (eptu) ] (2) and [Co(eput) ]
6 6 3