Bis- and tris-chelates of NiII, CuII, CoII and FeIII bound to N,N-dialkyl/alkyl aryl-N′-benzoylthiourea ligands

Article abstract of DOI:10.1016/j.ica.2014.01.044

Bis- and tris-chelates (1-5) of Ni(II), Cu(II), Fe(III) and Co(II) with two O,S donor substituted benzoylthiourea based ligands 3,3-diethyl-1- benzoylthiourea (HL¹) and 3-methyl-3-phenyl-1-benzoylthiourea (HL²) have been synthesized

Full text of DOI:10.1016/j.ica.2014.01.044

Inorganica Chimica Acta 414 (2014) 127–133
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Inorganica Chimica Acta
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Bis- and tris-chelates of NiII, CuII, CoII and FeIII bound to N,N-dialkyl/alkyl
aryl-N0-benzoylthiourea ligands
⇑
Haridas Mandal, Debashis Ray
Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Bis- and tris-chelates (1–5) of Ni(II), Cu(II), Fe(III) and Co(II) with two O,S donor substituted benzoylthiou-
rea based ligands 3,3-diethyl-1-benzoylthiourea (HL1) and 3-methyl-3-phenyl-1-benzoylthiourea (HL2)
have been synthesized and structurally characterized by X-ray crystallography. The keto-thione form
of the free ligands transform to the keto-thiol form during coordination through neutral O and anionic
S atoms. Crystallographic characterizations with supportive spectroscopic signatures confirm the cis-con-
formation in bis-chelates and facial binding to the tris-chelates.
Received 5 November 2013
Received in revised form 13 January 2014
Accepted 22 January 2014
Available online 5 February 2014
Keywords:
Benzoylthiourea
O,S donor
Ó 2014 Elsevier B.V. All rights reserved.
Bis- and tris-chelates
X-ray structure
Bidentate
1. Introduction
enantioselective organic transformations [16–18], selective chelat-
ing extractants for precious metals [19–22] and as effective chem-
Benzylisothiocyanate (PhCH2NCS, BITC) has been shown to inhi-
bit the cell growth and induces apoptosis in few types of human
cancer cell lines through generation of reactive oxygen species
(ROS) [1,2]. The related species, benzoylisothiocyanate (PhCONCS,
BIT) readily reacts with hydrazone derivatives to provide 1,2,4-
triazoline-5-thiones [3]. Self-condensation of two benzoylisothio-
cyanate molecules have led to the formation of novel tridentate
OCS ligand [4]. It smoothly reacts with different secondary amines
to yield substituted benzoylthioureas. Complexes of iron, cobalt,
nickel and copper in O and S environments are fascinating in estab-
lishing the distortions in coordinating polyhedron around the me-
tal centers in identifying the distorted environments around these
metal ions in living organisms [5]. Planar nickel(II) complexes have
been shown to be excellent G-quadruplex DNA stabilizers [6].
Nickel(II) complex in N2S2 coordination environment has shown
model behavior for nickel-containing superoxide dismutase [7].
The redox and magnetic properties of CoII, NiII and CuII are
dependent on the nature of the ligands having varying steric and
electronic properties. The thiourea backbone is important in anti-
thyroid drug methimazole, used to treat hyperthyroidism [8].
Moreover substituted thioureas and their metal complexes are
potentially useful mainly because of their in vitro activities against
common pathogens [9–14], catalysts for alcohol oxidation [15],
ical corrosion inhibitors [23]. Mononuclear M(O,S)n (n = 2 or 3)
type complexes are thus expected to show interesting structures,
isomerism, magnetic and electrochemical properties. These O,S-
donor ligands present high inhibitory activity towards xanthine
oxidase in nanomolar concentration range [24]. Photoinduced
cis–trans isomerism in bis-chelates of similar O,S-donor ligands is
rare and interesting [25].
In this work two O,S-donor ligands, 3,3-diethyl-1-benzoylthiou-
rea (HL1) and 3-methyl-3-phenyl-1-benzoylthiourea (HL2) were
synthesized and examined for the type of complexation to Co(II),
Fe(III), Ni(II) and Cu(II) ions. The bis-chelates in cis-form are close
to ideal square planar geometries whereas the tris-chelate in dis-
torted octahedral environment remains in fac-form.
2. Experimental
2.1. Materials
Hydrated perchlorate salts of copper(II), nickel(II) and cobalt(II)
were prepared by treating corresponding metal carbonates with
1:1 conc. HClO4–water mixture and crystallized after concentra-
tion on water bath. The ligands HL1 and HL2 were synthesized fol-
lowing modified procedure [26]. The other chemicals used were
obtained from the following sources: diethylamine from SRL Chem.
(India), triethylamine and ferric nitrate nonahydrate from S. d.
Fine-Chem Ltd., benzoyl chloride from Merck, India, potassium
⇑
Corresponding author. Tel.: +91 3222 283324; fax: +91 3222 82252.
E-mail address: dray@chem.iitkgp.ernet.in (D. Ray).
http://dx.doi.org/10.1016/j.ica.2014.01.044
0020-1693/Ó 2014 Elsevier B.V. All rights reserved.

128
H. Mandal, D. Ray / Inorganica Chimica Acta 414 (2014) 127–133
thiocyanate and N-methylaniline from Aldrich Chemical Co. Inc. All
other chemicals and solvents were reagent grade materials and
were used as received without further purification.
conductance, KM: (MeCN solution at 25 °C) 6.3 S m2 molꢀ1. UV–
Vis spectra [kmax, nm (
, L molꢀ1 cmꢀ1)]: (MeCN solution) 505
(145), 293 (13330), 265 (12903).
e
2.2.4. Cis-bis-(3,3-diethyl-1-benzoylthioureato)copper(II), cis-CuL1
(2)
2
2.2. Synthesis
2.2.1. 3,3-Diethyl-1-benzoylthiourea (HL1)
This was synthesized as green solid following the same protocol
as mentioned for complex 1. Here nickel(II) perchlorate was re-
placed by copper(II) perchlorate (0.38 g, 1 mmol) and recrystalliza-
tion was made from the saturated mixture of 1:1 (v/v) MeOH–
Potassium thiocyanate (2.332 g, 24 mmol) was taken into a
250 mL round bottom flask and at about 40 mL acetone was added
followed by addition of benzoyl chloride (2.8 mL, 24 mmol). The
resulting mixture was gently refluxed at 50 °C for 45 min after that
a dilute solution of diethylamine (2.5 mL, 24 mmol) was added to
the cold reaction mixture and magnetically stirred for about
30 min followed by warming at 35 °C during next 1 h and finally
the cooled mixture was stirred overnight by adding water
(500 mL) and the white suspension thus formed was suction fil-
tered and recrystallized from methanol (Scheme 1). Yield: 4.92 g,
87%. Anal. Calc.. for C12H16N2OS (236.33 g molꢀ1): C, 60.98; H,
6.82; N, 11.85. Found: C, 60.93; H, 6.88; N, 11.91%. Selected FT-IR
MeCN. Yield: 0.390 g, 74%. Anal. Calc. for
C24H30N4O2S2Cu
(534.21 g molꢀ1): C, 53.96; H, 5.66; N, 10.49. Found: C, 53.89; H,
5.69; N, 10.53%. Selected FT-IR bands: (KBr, cmꢀ1; s = strong,
vs = very strong, m = medium, br = broad) 3446(br), 1491(s),
1417(vs), 1354(s), 1087(m), 715(m). Molar conductance, KM
(MeCN solution at 25 °C) 4.7 S m2 molꢀ1. UV–Vis spectra [kmax
nm (
, L molꢀ1 cmꢀ1)]: (MeCN solution) 571 (149), 283 (10600),
:
,
e
251 (9906).
2.2.5. Fac-tris-(3,3-diethyl-1-benzoylthioureato)iron(III), fac-FeL1
bands: (KBr, cmꢀ1
; s = strong, vs = very strong, m = medium,
3
(3ꢁH2O). Method A
br = broad) 3219(br), 2970(s), 1681(vs), 1532(vs), 1458(s),
1284(m), 1228(vs), 1134(m), 715(m). 1H NMR (CDCl3): d = 1.28 (t,
J = 6.0 Hz, 3H, CH3), 1.34 (t, J = 6.2 Hz, 3H, CH3), 3.59 (q, J = 6.0 Hz,
2H, CH2), 4.00 (q, J = 6.2 Hz, 2H, CH2), 7.42–7.45 (m, 3H, Ph), 7.85
(m, 2H, Ph), 8.51 (s, 1H br, NH) ppm. 13C NMR (CDCl3): d = 11.6
(CH3), 13.3 (CH3), 47.8 (CH2), 48.0 (CH2), 127.9, 128.9 (2C), 132.7
(Cq), 132.9(2C), 163.9 (CO), 179.5 (CS) ppm.
HL1 (0.71 g, 3 mmol) was initially dissolved separately in MeCN
(15 mL) and it was drop wise added to the methanolic solution
(15 mL) of iron(III) nitrate (0.4 g, 1 mmol) under stirring condition.
At this stage, triethylamine (0.42 mL, 3 mmol) was introduced into
the reaction vessel and immediately color changes to deep brown.
The mother liquor was filtered after additional 2 h stirring. Upon
air dry it gave microcrystalline sticky mass. Immediately it was
dissolved in THF and kept for crystallization. After about 6 days,
it produced diffraction quality brown rod-shaped single crystals.
One of them was mounted for X-ray structure analysis. Yield:
0.530 g, 68%. Anal. Calc. for C36H47N6O4S3Fe (779.84 g molꢀ1): C,
55.45; H, 6.07; N, 10.78. Found: C, 55.43; H, 6.11; N, 10.82%. Se-
2.2.2. 3-Methyl-3-phenyl-1-benzoylthiourea (HL2)
HL2 was synthesized following the above mentioned adapted
procedure and N-methylaniline was used (2.6 mL, 24 mmol) in
place of diethylamine (Scheme 1). The crystalline white solid was
directly employed for complexation. Yield: 5.40 g, 83%. Anal. Calc.
for C15H14N2OS (270.35 g molꢀ1): C, 66.64; H, 5.22; N, 10.36.
Found: C, 66.69; H, 5.26; N, 10.32%. Selected FT-IR bands: (KBr,
lected FT-IR bands: (KBr, cmꢀ1
; s = strong, vs = very strong,
m = medium, br = broad) 3447(br), 2975(m), 1490(s), 1419(vs),
1353(s), 1243(m), 1137(m), 825(m), 715(s). Molar conductance,
cmꢀ1
; s = strong, vs = very strong, m = medium, br = broad)
KM: (MeCN solution at 25 °C) 8.4 S m2 molꢀ1. UV–Vis spectra [kmax
,
3196(br), 1696(vs), 1516(vs), 1437(m), 1382(s), 1262(vs),
1117(s), 1024(m), 763(m), 708(s). 1H NMR (CDCl3): d = 3.75 (s,
3H, CH3), 7.26 (t, J1 = 4.0 Hz, J2 = 6.8 Hz, 2H, Ph), 7.32–7.37 (m,
5H, Ph), 7.45 (s, 1H, br), 7.48 (t, J1 = 6.8 Hz, J2 = 14.0 Hz, 2H, Ph),
8.49 (s, 1H br, NH) ppm. 13C NMR (CDCl3): d = 45.7 (CH3), 125.6,
127.7 (CH2), 127.9 (CH2), 128.8 (2C), 129.5 (2C), 132.8, 132.9,
145.2, 163.1 (CO), 180.7 (CS) ppm.
nm (e
, L molꢀ1 cmꢀ1)]: (MeCN solution) 505 (241), 290 (10766),
267 (10352).
2.2.6. One pot synthesis of 3ꢁH2O. Method B
Compound 3 was also synthesized in excellent yield using a
multi-components solvent-based synthetic procedure in a single
pot under stirring condition. To a 100 mL round bottom flask, solid
potassium thiocyanate (0.583 g, 6 mmol) was taken with MeCN
(20 mL) followed by carefully addition of benzoyl chloride
(0.7 mL, 6 mmol). It was heated to reflux for about 1.5 h at 70 °C.
At this stage white solid of potassium chloride formed. Under cold
condition, slight excess diethylamine (1.2 mL, 12 mmol) was added
and again it was refluxed for another 1 h. The in situ generated HL1
was reacted with methanolic solution of iron(III) nitrate (0.8 g,
2 mmol) and stirred in air for further 2 h. The resulting brown solu-
tion on standing at room temperature for 5 days resulted in needle
like brown crystals suitable for X-ray diffraction analysis. Yield:
0.550 g, 71%. Anal. Calc. for C36H47N6O4S3Fe (779.84 g molꢀ1): C,
55.45; H, 6.07; N, 10.78. Found: C, 55.41; H, 6.12; N, 10.86%. Se-
2.2.3. Cis-bis-(3,3-diethyl-1-benzoylthioureato)nickel(II), cis-NiL1 (1)
2
To a MeCN (20 mL) solution of HL1 (0.47 g, 2 mmol), a methano-
lic solution of nickel(II) perchlorate (0.37 g, 1 mmol) was added
slowly by room temperature magnetic stirring. A red solution
was developed gradually upon addition of triethylamine
(0.27 mL, 2 mmol) and the reaction mixture was stirred for 1 h fur-
ther. The solid separated thus was filtered and the filtrate was kept
for slow evaporation. On standing at room temperature it afforded
deep red crystalline complex 1. Yield: 0.430 g, 82%. Anal. Calc.. for
C
24H30N4O2S2Ni (529.35 g molꢀ1): C, 54.46; H, 5.71; N, 10.58.
Found: C, 54.39; H, 5.74; N, 10.61%. Selected FT-IR bands: (KBr,
cmꢀ1
s = strong, vs = very strong, m = medium, br = broad)
;
lected FT-IR bands: (KBr, cmꢀ1
; s = strong, vs = very strong,
3446(br), 1493(vs), 1412(vs), 1335(m), 1250(m), 708(s). Molar
m = medium, br = broad) 3447(br), 2975(m), 1490(s), 1419(vs),
1353(s), 1243(m), 1137(m), 825(m), 715(s).
2.2.7. Cis-bis-(3-methyl-3-phenyl-1-benzoylthioureato)cobalt(II), cis-
CoL2 (4ꢁCH3CN)
2
To a solution of ligand HL2 (0.54 g, 2 mmol) in MeOH (15 mL),
cobalt(II) perchlorate (0.366 g, 1 mmol) was added under stirring
which afforded pale green solution. On addition of methanolic
solution of triethylamine (0.27 mL, 2 mmol), the green product
Scheme 1.

H. Mandal, D. Ray / Inorganica Chimica Acta 414 (2014) 127–133
129
precipitated out. After stirring at room temperature for further
conductivity meter with a solute concentration of about 10ꢀ3
M
and a Shimadzu 1601 UV–Vis–NIR spectrophotometer using 1 cm
quartz cell pairs. In each measurement, background was sub-
tracted using reference solvent to one of the cuvettes.
45 min, it was filtered, washed with methanol and finally dried un-
der vacuum over P4O10. A saturated solution in MeCN gave deep
green single crystals suitable for X-ray analysis. Yield: 0.490 g,
78%. Anal. Calc. for C32H29N5O2S2Co (638.67 g molꢀ1): C, 60.18; H,
4.58; N, 9.23. Found: C, 60.13; H, 4.60; N, 9.25%. Selected FT-IR
2.4. Crystal data collection and refinement for 2, 3ꢁH2O, 4ꢁCH3CN and 5
bands: (KBr, cmꢀ1
; s = strong, vs = very strong, m = medium,
br = broad) 3447(br), 3052(m), 2926(m), 1508(m), 1490(m),
1420(vs), 1374(vs), 1274(s), 1103(m), 904(s), 718(s), 696(m),
550(m). Molar conductance, KM: (MeCN solution at 25 °C) 5.6
The diffraction data of the complexes 2, 3ꢁH2O, 4ꢁCH3CN and 5
were collected on a Bruker APEX-II CCD X-ray diffractometer using
single crystals that uses graphite-monochromated Mo K
a radiation
S m2 molꢀ1. UV–Vis spectra [kmax, nm ( , L molꢀ1 cmꢀ1)]: (MeCN
e
(k = 0.71073 Å) by -scan method at 293 K. Information concern-
x
solution) 579 (36.6), 278 (9128), 209 (9225).
ing X-ray data collection and structure refinement of the com-
pounds are summarized in Table 1. For complex 2, a total of
5988 reflections were recorded with Miller indices hmin = ꢀ13,
hmax = 13, kmin = ꢀ24, kmax = 24, lmin = ꢀ13, lmax = 17. For complex
3ꢁH2O, a total of 4013 reflections were recorded with Miller indices
hmin = ꢀ23, hmax = 23, kmin = ꢀ23, kmax = 19, lmin = ꢀ12, lmax = 12.
For complex 4ꢁCH3CN, a total of 5041 reflections were recorded
with Miller indices hmin = ꢀ12, hmax = 13, kmin = ꢀ16, kmax = 16,
lmin = ꢀ22, lmax = 22 whereas for complex 5, a total of 6815 reflec-
tions were recorded with Miller indices hmin = ꢀ13, hmax = 13,
kmin = ꢀ17, kmax = 17, lmin = ꢀ28, lmax = 28. In the final cycles of
full-matrix least squares on F2, all non-hydrogen atoms were as-
signed anisotropically. The H atoms were introduced in calculated
positions and refined with fixed geometry with respect to their car-
rier atoms. The structures were solved using the SHELX-97 pro-
gram system [27] and were drawn using DIAMOND v. 2.1e
programs [28].
2.2.8. Cis-bis-(3-methyl-3-phenyl-1-benzoylthioureato)nickel(II), cis-
NiL2 (5)
2
Complex 5 was synthesized following same reaction protocol as
mentioned for the synthesis of complex 1. Here HL2 was used in-
stead of HL1. The block shaped deep brown single crystals formed
from the reaction mixture after 5 days. One of them was used for
structure determination using X-ray diffractometer. Yield:
0.495 g, 83%. Anal. Calc. for C30H26N4O2S2Ni (597.38 g molꢀ1): C,
60.32; H, 4.39; N, 9.38. Found: C, 60.29; H, 4.36; N, 9.37%. Selected
FT-IR bands: (KBr, cmꢀ1; s = strong, vs = very strong, m = medium,
br = broad) 3447(br), 3059(m), 2928(m), 1511(m), 1491(m),
1419(vs), 1378(vs), 1272(s), 1107(m), 906(s), 719(s), 692(vs),
556(s). Molar conductance, KM: (MeCN solution at 25 °C) 6.2 S m2 -
molꢀ1. UV–Vis spectra [kmax, nm ( , L molꢀ1 cmꢀ1)]: (MeCN solu-
e
tion) 504 (152), 291 (13410), 264 (12927).
2.3. Physical measurements
3. Results and discussion
The elemental analysis (C, H, N) were performed with a Perkin-
Elmer model 240 C elemental analyzer. Fourier transform infrared
(FT-IR) spectra were recorded on a Perkin-Elmer RX1 spectrometer.
Solution electrical conductivity measurements and electronic
spectra were carried out using a Unitech type U131C digital
The ligands 3,3-diethyl-1-benzoylthiourea (HL1) and 3-methyl-
3-phenyl-1-benzoylthiourea (HL2) have been synthesized
quantitatively following modified literature procedure (Scheme 1).
The powered ligands thus obtained were next employed for
complexation reaction with perchlorate salts of Ni(II), Cu(II) and
Table 1
Crystallographic data of complex 2, 3ꢁH2O, 4ꢁCH3CN and 5.
Complex
2
3ꢁH2O
4ꢁCH3CN
5
Formula
M g molꢀ1
Space group
Crystal system
a (Å)
C
24H30N4O2S2Cu
C36H47N6O4S3Fe
779.839
P3
hexagonal
16.6660(10)
16.6660(10)
8.5087(5)
90.00
C32H29N5O2S2Co
638.65
P21/c
monoclinic
11.3573(4)
14.6264(6)
19.4019(8)
90.00
C30H26N4O2S2Ni
597.38
P21/c
monoclinic
9.8051(11)
13.2791(15)
21.669(2)
90.00
534.21
P21/n
ꢀ
monoclinic
10.620(4)
18.319(7)
13.464(5)
90.00
b (Å)
c (Å)
a
(°)
b (°)
102.946(12)
90.00
2552.7(18)
293
90.00
120.00
2046.7(2)
293
104.3970(10)
90.00
3121.8(2)
293
91.597(4)
90.00
2820.3(5)
293
c
(°)
V (Å3)
T (K)
Z
4
2
4
4
Dcalc (g cmꢀ3
F(000)
)
1.390
1116
10.47
1.262
818
5.64
1.359
1324
7.21
1.407
1240
8.71
l
(Mo K
a
) (cmꢀ1
)
Measured reflections
Unique reflections
Rint
33744
5988
0.0386
29989
4013
0.0284
34026
5041
0.0525
37838
6815
0.1138
Observed reflections [I P 2
r(I)]
4057
2967
3457
3471
hmin–hmax/°
Index ranges
1.91–27.96
ꢀ13 6 h 6 13,
ꢀ24 6 k 6 24,
ꢀ13 6 l 6 17
0.0562
1.41–30.63
ꢀ23 6 h 6 23,
ꢀ23 6 k 6 19,
ꢀ12 6 l 6 12
0.0617
1.76–24.27
ꢀ12 6 h 6 13,
ꢀ16 6 k 6 16,
ꢀ22 6 l 6 22
0.0440
1.80–28.26
ꢀ13 6 h 6 13,
ꢀ17 6 k 6 17,
ꢀ28 6 l 6 28
0.0607
R(F2) (observed reflections)
wR(F2) (all reflns)
0.2541
0.2112
0.1300
0.2480
No. of variables
298
0.978
1.273; ꢀ0.614
151
1.033
1.217; ꢀ0.413
379
1.063
0.393; ꢀ0.372
352
0.652
0.539; ꢀ0.327
Goodness-of-fit (GOF) on F2
D
qmax
;
D
qmin (e Åꢀ3
)

130
H. Mandal, D. Ray / Inorganica Chimica Acta 414 (2014) 127–133
Scheme 2.
Co(II) in 2:1 M ratios in MeOH–MeCN mixture in presence of tri-
ethylamine for the synthesis of 1, 2, 4ꢁCH3CN and 5.
providing oxygen and sulfur donor atoms. Each ligand underwent
coordination driven thiolization and deprotonation, responsible
for the generation of neutral bis- and tris-chelates depending upon
the coordination environments. All the above changes in the
stretching vibrations support the coordination of thiol forms of
the ligands as opposed to the thione forms.
For the synthesis of complex 3ꢁH2O, two separate methods were
followed in 3:1 M ratios of ligand and metal salts. The preliminary
X-ray data analysis from unit cell determination, FT-IR spectrum
and elemental analysis confirmed the formation of isostructural
compounds in both the methods. In method A, triethylamine was
used to deprotonate the ligand HL1. The in situ generated ligand
HL1 was used in method B where excess diethylamine acts as base
to abstract the proton. All these complexes were obtained as
microcrystalline solid except complex 3ꢁH2O in moderate to high
yield (ꢂ68–87%). The single crystals for 3ꢁH2O were grown from
the saturated solution of THF from method A whereas the same
chemical structure was obtained following method B from the sat-
urated solution of 1:1 (v/v) MeOH–MeCN mixture. The single crys-
tals suitable for X-ray diffraction of complex 5 were grown both
from MeOH and DMF separately whereas the complex 2 and 4ꢁCH3-
CN were generated from MeOH-MeCN mixtures. The methoxido or
hydroxido bridged dinuclear complexes were not obtained under
varying alkaline conditions (complex 3, Scheme 2) [29,30].
Microanalysis and solution conductivity measurements con-
firmed the chemical formula and non-electrolytic nature of the
synthesized complexes. All of these complexes were characterized
by a combined spectroscopic technique both in solid and solution
phases and four of them were structurally determined from X-
ray crystallography. The FTIR spectra of both the ligands and their
corresponding metal complexes confirmed that the keto-thione
forms are stable in the free ligands and but during complexation,
tautomerized keto-thiol forms stabilized and coordinated to the
metal centers.
3.2. Structural descriptions
The crystallographic refinement data for complexes 2, 3ꢁH2O,
4ꢁCH3CN and 5 are given in the experimental section (Table 1)
and the selected bond angles and bond lengths are collected in
Table 2.
Complex 2 crystallizes in monoclinic P21/n space group is
shown in Fig. 1. Here Cu(II) center is surrounded by two sulfur
and two oxygen atoms of two deprotonated HL1 ligands in an
approximately square planar arrangement where both oxygen
and sulfur atoms are located in cis-conformation. The six-mem-
bered chelate rings (NC2OS–Cu) so formed are twisted about the
central N-atoms in order to attain suitable Oꢁ ꢁ ꢁS bite distances
in the 3.018–3.048 Å range. The amount of distortion from the
ideal square planar geometry around Cu(II) ion is reflected from
deviation of the cis and trans angles of 86.3–93.8° and
173.0–179.7° from ideal range of 90°and 180°, respectively. The
closeness of the C–N bonds residing on the oxygen and sulfur
sides indicate the facile delocalization of the single negative
charge between these two donor atoms but the significantly long-
er C–S bond lengths (1.740–1.742 Å) compare to C–O distances
(1.261–1.265 Å) is a clear indication that the negative charge is
mostly on sulfur atom. Within the square-planar arrangement
the Cu–O bond distances (1.92–1.93 Å) are significantly shorter
than Cu–S distances (2.22–2.23 Å) as expected [31]. The six-mem-
bered chelate rings deviate from the planarity as indicated from
the O–C–N–C and C–N–C–S torsion angles of 6.07–9.93° and
5.59–16.98° respectively. The dihedral angle between two O–
Cu–S planes is 6.97° for a slight D2d distortion from the ideal
square-planar geometry.
3.1. FTIR spectra
The FT-IR spectra (Figs. S1 and S2 in the Supporting informa-
tion) of the free ligands and their metal complexes clearly indicate
the spectral patterns of the free and metal-bound states of the li-
gands. The backbone N–H stretching vibrations in the region of
3190–3220 cmꢀ1 present in the free ligands disappear in the spec-
tra of corresponding metal complexes which are in good agree-
ment with the presence of deprotonated ligands in the respective
complexes. The C@O stretching vibration in the region of
1681–1697 cmꢀ1 and C@S band within 1228–1262 cmꢀ1 of the
free ligands are shifted to the lower wave-number by ca.
112–190 cmꢀ1 and 93–134 cmꢀ1 respectively upon complexation,
confirming the lowering of C@O and C@S bond orders during
coordination [vide supra]. The FTIR data clearly indicate the
coordination of the ligands through C@O and C–Sꢀ groups
Molecular structure of 3ꢁH2O with atom numbering scheme
ꢀ
shown in Fig. 2 crystallizes in a hexagonal P3 space group. The lat-
tice water molecules occupy the void space between monomeric
units. Three ligands around FeIII ion yielded a distorted octahedral
O3S3 environment with a stereochemical preference for a facial
geometry [29,30]. Six-membered O,S chelate rings (NC2OS–Fe) pro-
vide a distorted octahedral geometry with an average Oꢁ ꢁ ꢁS bite
distance of 3.01 Å in the complex. The substantial distortion from
ideal coordination geometry is seen for the cis and trans angles at
85.5–88.1° and 169.7 from 90° and 180° respectively. The Fe–O

H. Mandal, D. Ray / Inorganica Chimica Acta 414 (2014) 127–133
131
Table 2
Selected bond lengths (Å) and bond angles (°) of complex 2, 3ꢁH2O, 4ꢁCH3CN and 5.
Bond lengths (Å)
Complex 2
Cu1–O1
Cu1–O2
Cu1–S1
Cu1–S2
O2–C19
N3–C20
1.918(4)
1.929(4)
2.221(2)
2.233(2)
1.261(5)
1.339(6)
S2–C20
S1–C8
O1–C7
N1–C8
N1–C7
N3–C19
1.742(4)
1.740(5)
1.265(6)
1.338(6)
1.324(6)
1.318(6)
Complex 3ꢁH2O
Fe–O1
Fe–S1
1.986(2)
2.4221(8)
1.726(3)
N1–C8
C7–N1
C7–O1
1.353(3)
1.319(3)
1.247(3)
S1–C8
Complex 4ꢁCH3CN
Co1–O2
Co1–O1
Co1–S2
Co1–S1
1.926(3)
1.920(3)
2.225(11)
2.217(11)
1.270(4)
1.336(5)
C7–N1
1.320(4)
1.718(4)
1.273(4)
1.321(4)
1.334(5)
1.719(4)
S2–C23
O2–C22
C22–N3
N3–C23
S1–C8
C7–O1
N1–C8
Complex 5
Ni1–O1
Ni1–O2
Ni1–S2
Ni1–S1
S2–C23
N3–C23
1.865(4)
1.858(4)
2.135(17)
2.142(17)
1.728(6)
1.335(7)
S1–C8
1.724(6)
1.263(7)
1.257(7)
1.322(8)
1.322(7)
1.344(7)
O1–C7
O2–C22
N3–C22
N1–C7
N1–C8
Bond angles (°)
Complex 2
O1–Cu1–O2
O1–Cu1–S1
O2–Cu1–S2
S1–Cu1–S2
86.40(16)
93.32(12)
93.87(11)
86.39(6)
O2–Cu1–S1
O1–Cu1–S2
C8–N1–C7
179.71(13)
173.04(15)
125.4(4)
Fig. 1. The molecular structure of complex 2 with atom numbering scheme. Color
code: Cu, brown; N, blue; O, red; S, yellow; C, grey; H, teal. (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of
this article.)
C19–N3–C20
125.8(4)
Complex 3ꢁH2O
O1–Fe–O1#
O1#–Fe–S1
O1–Fe–S1ꢃ
87.52(9)
85.55(6)
99.77(7)
O1–Fe–S1#
S1–Fe–S1ꢃ
C7–N1–C8
169.70(7)
88.13(3)
125.2(2)
Symmetry code: ꢃ = (1 ꢀ y, x ꢀ y, ꢀ1 + z) and # = (1 ꢀ x + y, 1 ꢀ x, ꢀ1 + z)
Complex 4ꢁCH3CN
O1–Co1–O2
O2–Co1–S2
O1–Co1–S1
S1–Co1–S2
84.92(11)
93.57(8)
93.11(8)
88.48(4)
O1–Co1–S2
O2–Co1–S1
C8–N1–C7
176.33(9)
177.54(9)
124.9(3)
125.4(3)
C22–N3–C23
Complex 5
O1–Ni1–O2
S2–Ni1–S1
O2–Ni1–S2
O1–Ni1–S1
84.08(18)
85.39(6)
95.24(14)
95.27(14)
O1–Ni1–S2
O2–Ni1–S1
C7–N1–C8
C22–N3–C23
179.08(15)
177.94(18)
123.8(5)
124.3(5)
separation (1.98 Å) is significantly shorter than Fe–S distance
(2.42 Å). Thus the M–O and M–S distances in octahedral geometry
are longer in trivalent state than the same in square-planar geom-
etry in +2 state as observed in case of 2 [32]. In facial geometry the
iron(III) ion is sandwiched by a slightly bigger S3 face (average Sꢁ ꢁ ꢁS
distance 3.37 Å) and smaller O3 face (average Oꢁ ꢁ ꢁO distance
2.75 Å). The phenyl rings of the benzoyl ends of the ligands remain
coplanar with the OCNCS–Fe chelate ring.
The perspective view of compound 4ꢁCH3CN is shown in Fig. 3.
The single crystal of the compound obtained from a saturated solu-
tion in MeOH-MeCN (1:1 v/v) crystallizes in monoclinic Cc space
group. The Co(II) center is enclosed by two sulfur and two oxygen
donor atoms of two deprotonated {L2}ꢀ ligands in an approxi-
mately cis-square-planar arrangement. In cis orientation the
Co–O separations (1.91–1.92 Å) are also shorter than and Co–S
separations (2.21–2.22 Å) [32]. The dihedral angle between the
two O–Co–S chelate planes is 3.55°. The inter-planar angle
between the phenyl rings from C–O and C–S sides is 87.88°.
The molecular view of compound 5 displayed in Fig. 4 is in
monoclinic P21/c space group.
Fig. 2. Molecular structure of 3ꢁH2O with partial atom numbering scheme. Solvent
water molecule is removed for clarity. Symmetry code: * = (1 ꢀ y, x ꢀ y, ꢀ1 + z) and
# = (1 ꢀ x + y, 1 ꢀ x, ꢀ1 + z). Color code: Fe, steel; N, blue; O, red; S, yellow; C, grey;
H, teal. (For interpretation of the references to color in this figure legend, the reader
is referred to the web version of this article.)
Like Cu(II) and Co(II) complexes, two sulfur and two oxygen
atoms of two monoanionic HL2 ligands bind Ni(II) ion in square
planar cis-conformation. The six-membered (OCNCS–Ni) chelate

132
H. Mandal, D. Ray / Inorganica Chimica Acta 414 (2014) 127–133
3.3. Electronic absorption spectra
The electronic absorption spectra (Figs. S3–S5 in the Supporting
information) measured for all the five complexes using 10ꢀ3 M sol-
ute concentration in MeCN showed strong absorption bands from
charge transfer transitions in near UV range. In case of nickel(II)
complexes of 1 and 5, the spin forbidden d–d transitions observed
at 505 nm (
cmꢀ1
can be assigned to
region the bands at 293 nm
265 nm
= 12,903 L molꢀ1 cmꢀ1
= 13,410 L molꢀ1 cmꢀ1) and 264 nm (
complex 5 were observed for nickel(II)-bound intraligand n-p⁄ and
p⁄ charge transfer transitions overlapping with alternative MLCT
transitions. For complex the observed band positions for
electronic transitions were 571 nm (
= 159 L molꢀ1 cmꢀ1), 283 nm
= 10600 L molꢀ1 cmꢀ1 = 9906 L molꢀ1 cmꢀ1
and 251 nm
e
= 145 L molꢀ1 cmꢀ1) and 504 nm (
1g?B1g transition [33]. In UV
= 13,330 L molꢀ1 cmꢀ1
and
for complex and 291 nm
= 12,927 L molꢀ1 cmꢀ1) for
e
= 152 L molꢀ1
)
A
(
e
)
(e
)
1
(e
e
p-
2
e
(e
)
(
e
)
respectively. The low energy transition may be assigned to d–d
transition band centered on chelated copper(II). The two other high
energy transitions were observed for copper(II)-bound intraligand
n-p⁄ and
p-
p⁄ charge transfer transitions. In case of octahedral
iron(III) complex 3ꢁH2O, one of the ligand field transition appears
at 505 nm (
= 241 L molꢀ1 cmꢀ1) . Here high energy transitions
were observed at 290 nm (10766 L molꢀ1 cmꢀ1
and 267 nm
(11156 L molꢀ1 cmꢀ1) for iron(III)-bound intraligand n-p⁄ and
p⁄ charge transfer transitions. For square planar cobalt(II)
complex 4ꢁCH3CN, the ligand field transitions appear at 579 nm
= 36.6 L molꢀ1 cmꢀ1) whereas the intraligand n–p⁄ and
charge transfer transitions appear at 278 nm (
= 9128 L molꢀ1 cmꢀ1
and 209 nm (
= 9225 L molꢀ1 cmꢀ1) respectively.
e
Fig. 3. The molecular structure of complex 4ꢁCH3CN with atom numbering scheme.
Solvent acetonitrile molecule is removed for clarity. Color code: Co, pink; N, blue; O,
red; S, yellow; C, grey; H, teal. (For interpretation of the references to color in this
figure legend, the reader is referred to the web version of this article.)
)
p
-
(e
p–
p⁄
e
)
e
4. Concluding remarks
Two benzoylthiourea based ligands have been examined for
their coordination potential to FeIII, CoII, NiII and CuII. The unsym-
metrical O,S donor anionic ligands show systematic preferences
for facial and cis isomers in mononuclear octahedral and square-
planar geometries around these metal ions. The spectroscopic sig-
natures both in solution and solid states and X-ray crystallography
confirm keto-thiol tautomerization during metal binding as well as
delocalization of negative charge over the six membered chelate
rings. The unique properties of square-planar 3d metal complexes
reported in this paper can be successfully used to probe the duplex
DNA and G-quadruplex DNA structure in live cells to elucidate the
role of planar structures with perpendicular N-phenyl pendent
ends. The N,N-diethyl ends of complex 2 make it almost planar
molecule for good stacking and intercalation.
Acknowledgements
Fig. 4. The molecular structure of complex 5 with atom numbering scheme. Color
code: Ni, green; N, blue; O, red; S, yellow; C, grey; H, teal. (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of
this article.)
HM is thankful to the Council of Scientific and Industrial Re-
search, New Delhi for the financial support. The authors also thank
to DST, New Delhi, for providing the Single Crystal X-ray Diffrac-
tometer facility to the Department of Chemistry, IIT Kharagpur un-
der its FIST program.
rings so formed showed twisting about the central N-atoms in or-
der to maintain suitable Oꢁ ꢁ ꢁS bite distances of 2.956–2.966 Å. The
Ni–O (1.858–1.865 Å) and Ni–S (2.135–2.142 Å) bond lengths are
considerably shorter than the corresponding values for Cu(II) and
Co(II) complexes. The dihedral angle between the two O–Ni–S
planes is smallest (2.12°) for a close ideal square-planar arrange-
ment compared to cobalt(II) and copper(II) complexes. Around
the NiO2S2 coordination environment, the inter-planar angle be-
tween the phenyl rings of the benzoyl moieties and the phenyl
rings of the N-methylaniline parts is 87.48°.
Appendix A. Supplementary material
CCDC 922997, 922998, 922999 and 923000 contain the supple-
mentary crystallographic data for 2, 3ꢁH2O, 4ꢁCH3CN and 5, respec-
tively. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at http://dx.doi.org/10.1016/
j.ica.2014.01.044.

H. Mandal, D. Ray / Inorganica Chimica Acta 414 (2014) 127–133
133
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