Structural and vibrational study on N-(biphenyl-2-thiocarbamoyl)-4- phenylcarboxamide

Article abstract of DOI:10.1016/j.molstruc.2010.10.013

A new thiourea derivative, N-(biphenyl-2-thiocarbamoyl)-4- phenylcarboxamide, is synthesized and characterized by elemental analysis, FTIR, NMR and the single crystal X-ray diffraction study. The title compound crystallizes with two molecules in the asymm

Full text of DOI:10.1016/j.molstruc.2010.10.013

Journal of Molecular Structure 985 (2011) 57–62
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Structural and vibrational study on
N-(biphenyl-2-thiocarbamoyl)-4-phenylcarboxamide
Aamer Saeed , Mauricio F. Erben , Michael Bolte c
a,
⇑
b
a
Department of Chemistry, Quaid-I-Azam University, Islamabad 45320, Pakistan
CEQUINOR (UNLP, CONICET-CCT La Plata), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C.C. 962 (1900). La Plata, Argentina
Institut für Anorganische Chemie, J.W.-Goethe-Universität, Max-von-Laue-Str.7, D-60438 Frankfurt/Main, Germany
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
A new thiourea derivative, N-(biphenyl-2-thiocarbamoyl)-4-phenylcarboxamide, is synthesized and
characterized by elemental analysis, FTIR, NMR and the single crystal X-ray diffraction study. The title
compound crystallizes with two molecules in the asymmetric unit. The dihedral angle between the
two aromatic rings in the biphenyl unit is 47.9(2) and 56.52(19)°, respectively, for the two molecules
in the asymmetric unit. The molecular conformation is stabilized by intramolecular NAHꢀ ꢀ ꢀO hydrogen
bond. The crystal packing shows that the molecules form centrosymmetric dimers connected by NAHꢀ ꢀ ꢀS
hydrogen bonds. The vibrational properties have been studied by FTIR and FT-Raman spectroscopy along
Received 17 September 2010
Received in revised form 6 October 2010
Accepted 6 October 2010
Available online 20 October 2010
Keywords:
Thiourea derivative
Crystal structure
Conformation analysis
Hydrogen bonds
DFT calculations
Vibrational studies
ꢁ
with quantum chemical calculations at the B3LYP/6-311 + G level of approximation. The main normal
modes related with the thioamide bands are discussed.
Ó 2010 Elsevier B.V. All rights reserved.
1
. Introduction
Various biphenyl derivatives are used in the synthesis of phar-
construction of anion receptors [7–9] and in the thiourea-based
metal complexes [10] and organocatalysts [11]. In particular,
aroylthioureas have been successfully used in environmental
control, as ionophores in ion selective electrodes [12–14]. Very re-
cently, the structural and conformational properties of N-(diet-
hylcarbamothioyl)benzamide in different phases, before and after
the interaction with a heavy metal ion were studied and the behav-
ior of the molecule as a ionophore in a typical ion selective elec-
trode membrane has been simulated [15].
maceuticals, antifungal agents like bifonazole, optical brightening
agents, dyes and polychlorinated biphenyls (PCBs). The rotation
around the single bond in biphenyls, and in particular the
ortho-substituted ones, is sterically hindered. Therefore, some
substituted biphenyls exhibit the atropisomerism; specifically,
the individual C
derivatives, as well as related molecules such as 2,2 -bis(diphenyl-
phosphino)-1,1 -binaphthyl (BINAP), find application as ligands in
asymmetric synthesis [1]. The relationship between ligand confor-
mations and complexation properties in some homoditopic biphe-
nyl thioureas has been demonstrated [2]. Some biphenyl thioureas
having structure very closely related to that of title compound have
been used as organocatalysts for electrochemical reductions [3].
Other biphenyl thioureas have been used in carboxylate sensing
and the effect of the ligand substituents on the geometry of the
complexes has been reported [4]. Biphenyls thiourea derivatives
are also potent Vitronectin receptor antagonists [5] and thiourea-
based molecular clips has been used for fluorescent discrimination
of isomeric dicarboxylates [6]. Moreover, the hydrogen-bonding
ability of the thiourea moiety has extensively been used in
2
-symmetric-isomers are optically stable. Some
0
Herein, the synthesis, characterization and vibrational proper-
ties, together with the X-ray molecular structure of N-(biphenyl-
2-thiocarbamoyl)-4-phenylcarboxamide is reported. Some related
structures containing the biphenyl moiety as a part of thiourea
0
0
nucleus include the N-(biphenyl-4-carbonyl)-N -(4-chlorophenyl)-
thiourea [16], its 2-chloro- [17], 2-pyridyl methyl)- [18], and
recently reported 6-methylpyridin-2-yl [19] analogs but in all of
these compounds the biphenyl moiety is derived from the corre-
sponding isothiocyanate, whereas in present case it is obtained
from the corresponding anilino compound.
2
. Experimental
2.1. Synthesis
⇑
Corresponding author. Tel./fax: +92 51 9064 2128.
E-mail address: aamersaeed@yahoo.com (A. Saeed).
A solution of 2-aminobiphenyl (1.5 mmol) in 20 ml dry acetoni-
trile was added dropwise to a two-necked round-bottomed flask
0
022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.10.013

5
8
A. Saeed et al. / Journal of Molecular Structure 985 (2011) 57–62
containing an equimolar amount of benzoyl isothiocyanate
1.5 mmol) in 20 ml of acetonitrile. The mixture was refluxed for
h. On cooling, the reaction mixture was acidified with dilute
hydrochloric acid. The solid product obtained on filtration was
washed with water and recrystalized from an acetone:dichloro-
methane mixture (1:2). Colourless crystals were obtained on slow
evaporation (yield 91%, m.p.: 126–127 °C). Anal. Calcd. for
2.5. Quantum chemical calculations
(
3
The molecular geometries were optimized to standard conver-
gence criteria and harmonic frequencies calculated by using DFT
hybrid method with Becke’s non-local three parameter exchange
and the Lee, Young and Parr correction (B3LYP) using the 6-
ꢁ
311 + G basis sets as implemented in the GAUSSIAN 03 program
C
20
H
16
N
2
OS: C, 72.26; H, 4.85; N, 8.43; S, 9.65. Found: C, 72.01;
package [24].
1
H, 4.69; N, 8.41; S, 9.57%. H NMR (300 MHz, CDCl
2.31 (s, 1H, CONH), 9.22 (s, 1H, CSNH), 7.14 (t, 1H, J = 2.1 Hz,
bp), 7.33–7.40 (m, 4H, bp), 7.36 (m, 4H, bp), 7.66 (dd, 1H, J = 4.8,
3
d, ppm):
1
3
. Results and discussion
1
3
2
.1 Hz, ph), 8.09–8.22 (m, 2H, ph), 8.40–8.48 (m, 2H, ph).
C
3.1. Synthesis
NMR (75 MHz, CDCl3, d, ppm) 115.83, 116.13, 117.04, 117.35,
1
1
1
18.55, 123.35, 123.65, 124.41, 126.27, 126.38, 128.90, 129.87,
30.87, 137.04, 141.35, 149.80, 159.51, 162.71, 168.39 (C@S),
72.89 (C@O).
The synthetic pathway to N-(biphenyl-2-thiocarbamoyl)-4-
phenylcarboxamide, (I) is shown in Scheme 1. Thus benzoyl
isothiocyanate was produced in situ, by reaction of freshly pre-
pared benzoyl chloride with an equimolar amount of potassium
thiocyanate in dry acetonitrile. Treatment of the latter with equi-
molar quantity of 2-aminobiphenyl afforded the title compound
2.2. Crystal structure determination
C
20
16
H N
2
OS,
M
r
= 332.41, colorless crystal, size 0.36 ꢂ
.33 ꢂ 0.29 mm , triclinic space group P-1, a = 10.2091(7),
= 84.103(5), b = 77.217(5),
(
I). Colourless crystals suitable for the X-ray diffraction study were
3
0
obtained on slow evaporation from an acetone: dichloromethane
mixture (1:2).
b = 10.9563(6), c = 15.7563(10),
a
c =
3
8
6
9.164(5), V = 1709.57(19), Z = 4, Dcalc = 1.291 g/cm , F(0 0 0) =
1
In the H NMR spectrum of the compound in addition to the sig-
ꢃ1
96,
l = 0.202 mm . STOE IPDS-II diffractometer [20] using Mo
nals for aromatic protons, the characteristic NAH singlets at d12.31
K
a
radiation (k = 0.71073 Å) at T = 173 K. An absorption correction
13
for CONH and 9.22 for CSNH ppm and in C NMR the peaks for car-
was applied using the MULABS [21] option in PLATON [22]. The
structure was solved by direct methods [23] and refined by full-ma-
trix least-squares using SHELXL-97 against F using all data [23]. All
bonyl and thiocarbonyl were observed d172.89 and 168.39 ppm
respectively.
2
non-H atoms were refined anisotropically. H atoms were positioned
geometrically at distances of 0.95 Å (aromatic CH) and 0.98 Å
3.2. X-ray structure
(
methyl groups) from the parent C atoms; a riding model was used
The title compound crystallizes with two crystallographically
during the refinement process and the Uiso(H) values were con-
strained to be 1.2Ueq(aromatic C) or 1.5Ueq(methyl C). The H atoms
bonded to N were freely refined. Crystallographic data for the struc-
ture reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre. Copies of the data CCDC-745277 can
be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [e-mail: deposit@ccdc.cam.ac.uk]. Any re-
quest to the CCDC for this material should quote the full literature
citation and the reference number 745277.
independent molecules in the asymmetric unit. Table 1 includes
selected geometric parameters derived from the structure refine-
ment, as well as those obtained from quantum chemical calcula-
tions. The dihedral angle between the two aromatic rings in the
biphenyl unit is 47.9(2) and 56.52(19)° for the two molecules in
the asymmetric unit, respectively. Also the orientation of the
C@O and the phenyl ring in the benzoyl group shows a slightly dif-
ferent orientation when both molecules are compared (see Table 1).
The X-ray molecular structures of the two crystallographically
independent molecules are shown in Fig. 1.
2.3. Vibrational spectroscopy
Solid-phase IR spectra were recorded as KBr discs with a resolu-
tion of 2 cm in the 4000–400 cm range on a Bruker EQUINOX
O
ꢃ1
ꢃ1
5
5 FTIR spectrometer. The FT-Raman spectrum was recorded in
ꢃ1
the region 4000–100 cm using a Bruker IFS 66v spectrometer
S
C
N
equipped with Nd:YAG laser source operating at 1.064
l
m line
ꢃ1
with 200 mW power of spectral width 2 cm
.4. GC–MS determination
The GC–MS measurements were recorded in a GCMS-QP2010
.
NH2
2
Dry acetonitrile
SHIMADZU instrument using gaseous Helium as mobile phase with
the pressure in the column head equal to 100 kPa. The column used
was a 19091J-433 HP-5 of 30 m ꢂ 0.32 mm ꢂ 0.25 mm film thick-
O
S
3
ness. A 1 lL volume of the compounds dissolved in CHCl was
chromatographed under the following conditions: injector temper-
ature was 210 °C, the initial column temperature (100 °C) was held
for 3 min, then increased to 200 °C at 20 °C/min and held for 2 min
after elevated to 300 °C at 35 °C/min and held for 2 min. In the
spectrometer the source was kept at 200 °C. One peak at retention
time 8.5 min is observed in the chromatogram, with a fragmenta-
tion pattern dominated by the following peaks: 211 (100%,
N
H
N
H
(
1)
+
+
+
C
1
12
H
9
NCS ), 178 (86%, C
H
6 5
CONHCSN ), 151 (35%, C12
H
7
) and
Scheme
phenylcarboxamide.
1. Synthetic
pathway
to
N-(biphenyl-2-thiocarbamoyl)-4-
+
05 (12%, C
6
5
H CO ).

A. Saeed et al. / Journal of Molecular Structure 985 (2011) 57–62
59
Table 1
the order C2AN2 < C1AN1 < C1AN2 (see Table 1). This tendency
Selected experimental and calculated geometrical parameters (values in
degrees) for the central AC(O)NHC(S)NHA moiety for the title species.
Å
and
is also reproduced by the quantum chemical calculations (B3LYP/
ꢁ
6
-311 + G , see Table 1) suggesting that intramolecular electronic
Parametera
Experimental
B3LYP/6-311 + G
ꢁ
effects -rather than crystal packing effects- are responsible for
the observed NAC bond lengths values.
Molecule A
Molecule B
The molecular structure and conformational flexibility are
important properties for determining the donor–acceptor capabil-
ities on thiourea derivatives [28,29]. For example, Fabbrizzi et al.
reported that substituted-phenyl urea compounds interacts
through hydrogen bonding with a variety of oxoanions to give
bright colored complexes [30] and a variety of receptors containing
the urea and the thiourea groups have been designed for anion rec-
ognition [31]. These effects are closely related with the conforma-
tional properties and the presence of intra- and intermolecular
hydrogen bonding interactions on the thiourea group [31]. The title
species possesses intramolecular and intermolecular hydrogen
bonding interactions, as shown in Table 2. In effect, N-benzoyl-
C@O
C@S
C2AN2
C2AN1
C1AN1
S@CAN2
S@CAN1
O@CAN1
C1AN1AC2
O@CAN1AC2
N2AC2AN1AC1
O@CAC11AC16
C23AC22AC31AC32
C21AC22AC31AC36
1.2321(16)
1.6661(14)
1.3291(17)
1.4034(16)
1.3761(17)
124.06(10)
119.72(10)
121.96(12)
127.28(12)
0.9(2)
1.2302(16)
1.6777(14)
1.3289(17)
1.3979(16)
1.3783(18)
124.57(10)
119.17(10)
122.64(11)
127.33(11)
1.0(2)
1.225
1.673
1.344
1.408
1.383
127.5
117.6
122.7
130.0
2.6
5.9(2)
4.3(2)
32.5(2)
44.01(19)
47.9(2)
0.2
21.7
54.2
55.8
ꢃ8.78(19)
54.2(2)
56.52(19)
0
a
N -arylthioureas have been thoroughly investigated in connection
For atom numbering see Fig. 1.
with the formation of intramolecular hydrogen bonding [32–35].
It was found that the intramolecular hydrogen bond between the
oxygen atom in the C@O group and the hydrogen atom of the thio-
urea group is favored by the formation of a six-membered ring
The amidic N1AC1 [1.377(2) Å] and thioamide N1AC2
1.401(2) Å] and N2AC2 [1.329(2) Å] bond lengths (mean values
[
[
36,37]. In the title species, the molecular conformation is stabi-
are given) are both shorter than CAN single bond [25], indicating
a partial double bond character. This observation indicates that
resonance interactions are extended over the whole planar
AC(O)NHC(S)NHA moiety, in accordance with the behavior re-
cently reported for thiocarbamate species [26]. Moreover, it is
worth noting that a definite trend in the CAN bond distances has
been recognized for these species [27], the lengths increasing in
lized by such an NAHꢀ ꢀ ꢀO hydrogen bond. The non-bonding dis-
tances O1ꢀ ꢀ ꢀN2 and O1Aꢀ ꢀ ꢀN2A are 2.616(1) and 2.627(1) Å,
respectively in agreement with intramolecular hydrogen bonding
0
found in other N-benzoyl N -substituted thioureas, which are re-
ported in the range of 2.618(4)–2.654(2) Å [38,39]. Moreover, an
intermolecular interaction involving these groups is observed be-
tween the crystallographically independent molecules through an
N1AHꢀ ꢀ ꢀO1A hydrogen bond, with
.045(1) Å.
The patterns of packing adopted by thiourea derivatives were
a
N1ꢀ ꢀ ꢀO1A distance of
3
rationalized by McBride et al. [40] in terms of molecular structure,
solvent of crystallization, and energies and efficiencies of packing.
In the title molecule, the crystal packing shows (Fig. 3) that both
crystallographically independent molecules form centrosymmetric
dimers connected by N1AHꢀ ꢀ ꢀS (x ꢃ 1, y, z) and N1AAHꢀ ꢀ ꢀS
(x + 1, y, z) hydrogen bonds, adopting a well-known crystal motif
for N-benzoyl-thiourea compounds [33,41]. These non-bonding
Nꢀ ꢀ ꢀS distances are 3.396(1) and 3.625(1) Å, respectively.
3.3. Vibrational analysis
The observed infrared absorptions and the FT-Raman frequen-
cies along with their relative intensities and probable assignments
are summarized in Table 3. A tentative assignment of the observed
bands was carried out by comparison with spectra of related mol-
ecules [42–48]. Very recently, the vibrational properties of the
thiourea molecule – the idealized parent species – were revisited
by Srinivasan et al. [49]. However, in many case a clear assignment
of the observed infrared absorptions and Raman signals to a spe-
cific vibration is unclear. To further improve this situation, an
assignment of the observed vibrational spectra can be assisted by
a systematic comparison with the theoretically calculated one.
Table 2
Hydrogen bonds [Å and °] for the title species.
DAHꢀ ꢀ ꢀA
d(DAH)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
<(DHA)
ª
N(1)AH(1)ꢀ ꢀ ꢀS(1A)#1
N(2)AH(2)ꢀ ꢀ ꢀO(1)
0.872(19)
0.848(18)
0.861(18)
0.908(18)
2.535(19)
1.969(17)
2.780(19)
1.891(17)
3.3957(12)
2.6271(14)
3.6250(13)
2.6164(14)
169.1(16)
133.7(15)
167.3(15)
135.3(15)
a
N(1A)AH(1A)ꢀ ꢀ ꢀS(1)#2
N(2A)AH(2A)ꢀ ꢀ ꢀO(1A)
Fig. 1. Molecular structure of the two crystallographically independent molecules
in the asymmetric unit of the title compound with displacement ellipsoids drawn at
the 50% probability level.
a
Symmetry transformations used to generate equivalent atoms: #1 x ꢃ 1, y, z, #2
x + 1, y, z.

6
0
A. Saeed et al. / Journal of Molecular Structure 985 (2011) 57–62
Table 3
when substituted benzoylthiourea compounds are analyzed [50].
ꢁ
ꢃ1
Observed and theoretical (B3LYP/6-311 + G ) vibrational data (cm ) with a tentative
assignment for the title species.
Thus, the molecular structure of the studied compound has been
optimized at the DFT-B3LYP level of approximation by using the
FTIRa
Ramana
B3LYP/6-311 + G
ꢁb
Tentative assignment
ꢁ
triple-zeta 6-311 + G basis sets. The geometrical parameters are
3
3
3
1
1
1
1
289 m, br
135 s, br
089 m, br
662 s
601 w
581 w
3626 (5.9)
3421 (49.9)
3212–3159c
m
m
m
m
m
(N1AH)
(N2AH)
(CAH)
(C@O)
(C@C)
in very good agreement with the experimental ones (see Table 1)
and the computed harmonic frequencies are gathered in Table 3.
In the infrared spectra a series of broad absorptions are ob-
3067
1662 s
1602 vs
1582 m
1538 vw
1719 (36.3)
ꢃ1
ꢃ1
1650d
served at 3289, 3135 and 3089 cm . The 3289 and 3135 cm
bands could be assigned to the NꢃH stretching modes [47,51,26],
the red-shifted absorption is most likely due to the
528 vvs
1591 (77.6)
d(N2AH)
Thioamide band I
m
(N2ꢃH)
stretching mode, related with the formation of C@Oꢀ ꢀ ꢀNAH intra-
1509 vvs
1492 s,sh
1476 s, sh
1451 m, sh
1324 s
1508 m
1493 w
1477 vw
1455 sh
1324 vw
1563 (100.0)
d(N1AH)
molecular hydrogen bond, as observed in the X-ray analysis. A sin-
1650–1400d
ꢃ1
m(C@C)
gle well-defined Raman signal is observed at 3067 cm
,
characteristic of the CAH vibrations of the phenyl groups. These
features are in agreement with the calculated frequencies (see
1377 (90.1)
mas(NACAN)
Thioamide band II
Table 2), with the
m(N2AH) stretching mode computed as an strong
intensity band located at lower frequencies than the corresponding
1
1
1
1
1
267 m, sh
254 m
229 sh
181 w
154 vs
1300 m
1301 (2.6)
1266 (27.6)
1242 (2.0)
1213
1177 (47.6)
m
m
m
(C22AC31)
(C1AN1)
(C2AN21)
m(N1AH) fundamental.
1255 m
1183 w
1158 m
Fig. 2 shows the Raman and IR spectra of the title compound in
e
d(CAH)
ꢃ1
the 1800–600 cm range. A large number of signals are observed
with pronounced overlapping and for the title species, many of
these signals result from both the central thiourea moiety as well
as from the substituent groups. In the infrared spectrum, the strong
m (NACAN)
s
Thioamide band III
e
1
1
1
1
1
1
1
9
9
9
9
9
8
8
7
144 vs
109 w
086 w
072 sh
049 w
026 w
009 w
99 w
74 w
38 w
31 m
14 w
1146 sh
d(CAH)
ꢃ1
ꢃ1
1
662 cm (1663 cm Raman) band corresponds to the m(C@O)
mode, which is similar in frequency to the C@Oꢀ ꢀ ꢀHAN hydrogen
1050 w
1034 m
bonding found in many small-molecule studies [52]. Calculated
ꢁ
(
1
B3LYP/6-311 + G ) frequencies for these fundamental amounts
ꢃ1
719 cm . The relative low value observed for the
m(C@O) funda-
999 vs
941 m
964 (1.2)
958 (1.5)
d(CN1C)
d(CN2C)
q(CAH)
mental is in accordance with the presence of a intramolecular
C@Oꢀ ꢀ ꢀHAN interaction in the AC(O)NHC(S)NHA moiety [53].
Alternatively, this behavior has been also interpreted as being a re-
sult of conjugated resonance interactions between the carbonyl
and the phenyl ring in N-benzoyl substituted thiourea compounds
e
931
74 vw
54 m
73 w
875 m
854 m
775 m
866 (3.8)
783 (2.5)
d(NCN)
(C@S)
Thioamide band IV
m
759 w
741 m
720 w
701 m
672 m
621 w
552 vw
523 m
480 w
451 vw
757 (8.2)
q
(CAH)
741 w
717 m
743 (13.4)
q(N2AH)
f
729
d(CC)
oop (NCN)
697 (4.3)
661 (4.5)
607 (5.1)
671 w
615 w
547 vw
q(N1AH)
oop C@S
f
557
q(CC)
IV
451 w
II
409 vw
348 vw
306 w
276 m
212 m
216 m
349 (1.5)
q(C@O)
ν(C=O)
III
I
a
FTIR of solid in KBr pellets, FT-Raman of finely powdered solid. Band intensity:
vs = very strong, s = strong, m = medium, w = weak, vw = very weak, vvw = very
very weak.
b
In parentheses relative band strengths, IR intensities [100% ꢄ 538 km/mol].
c
The 14
m
(CAH) stretching modes expected for the molecule are computed in the
ꢃ1
3
1
212–3159 cm range as low intensity infrared absorptions.
ν(C=O)
d
The
m
(C@C) stretching modes due to the phenyl rings are computed in the
ꢃ1
II
650–1400 cm range as low to medium intensity infrared absorptions.
III
e
N
ge
re-
eqa
k d(CAH) deformation and
q(CAH) rocking normal modes are
I
IV
ꢃ1
computed below 1213 and 931 cm , respectively.
f
ꢃ1
The d(CAC) and
q(CAC) appear in the computed IR near 730 and 570 cm as
low to medium intensity absorptions.
1800
1600
1400
1200
1000
800
600
Quantum chemical calculations and normal coordinate analysis
have been applied [36] and recently density functional theory
-1
Wavenumber (cm )
(
DFT) methods at the B3LYP/6-31G(d) basis set was used to predict
Fig. 2. FT-Raman and IR spectra (solid) for the title compound in the 1800–
the vibrational frequencies of related species [39,47]. The use of
more extended basis set certainly leads to a good performance
ꢃ1
600 cm region. The characteristic carbonyl stretching mode and the ‘‘thioamide
bands’’ are identified.

A. Saeed et al. / Journal of Molecular Structure 985 (2011) 57–62
61
It is well-known that the thiourea group presents characteristic
ꢃ1
a band in the 1500–1600 cm range of the IR spectrum, originated
by the NAH deformation mode [d(NAH)]. For the title species, a
very strong and rather broad absorption with defined maxima at
ꢃ1
1
528 and 1509 cm can be assigned to the d(N2AH) (thioamide
band I) and d(N1AH) modes, respectively. The Raman counterparts
are observed as signals of low and medium intensities at 1538 and
ꢃ1
ꢁ
1
508 cm , respectively. B3YLP/6-311 + G computations predict
the presence of strong bands in the infrared spectrum due to the
ꢃ1
d(N2AH) and d(N1AH) normal modes at 1591 and 1563 cm
,
respectively, in reasonable agreement with the proposed assign-
ment. Nevertheless, it should be noted that several (C@C) stretch-
m
ing modes from the aromatic groups also contribute to absorptions
in this region. The strong and medium intensity signals centered at
ꢃ1
ꢃ1
ꢃ1
1
602 (1601 cm infrared, weak) and 1582 cm (1581 cm infra-
red, weak) in the Raman spectrum could be assigned with confi-
dence to symmetric
m
(C@C) stretching modes.
ꢃ1
The region between 1400 and 800 cm in the vibrational spec-
tra of thioureido compounds is usually rich in medium intensity
bands from skeletal motions, especially vibrations containing con-
tributions from the
tense bands can be observed at 1324 and 1154 cm in the IR
m
(CAN) motion in the thiourea core [53]. In-
ꢃ1
spectrum of the studied compound with the corresponding coun-
ꢃ1
terpart in the Raman spectrum at 1324 and 1158 cm as very
weak and medium intensity signals, respectively. Taking into ac-
count the vibrational properties reported for the simple thiourea
molecule [49], it is expected that the CAN stretching modes, which
are usually coupled in symmetric and antisymmetric motions, ap-
pear in this region [54]. Thus, following the quantum chemical cal-
culation description, the m(NCN) antisymmetric (thioamide band II)
and symmetric (thioamide band III) stretching modes of the thio-
urea moiety, are respectively assigned to these bands. Computed
ꢃ1
frequency values are 1377 and 1177 cm , respectively, both
modes displaying strong dipole moment derivatives.
ꢃ1
The medium intensity signal at 775 cm in the Raman spec-
ꢃ1
trum, with a weak counterpart in the infrared at 773 cm , is ten-
tatively assigned to the thioamide band IV, mainly due to the
m(C@S) stretching mode, in agreement with previously studied
thiourea derivatives [39,53]. However, it should be mentioned that
higher values have been reported for this fundamental. For exam-
ple, in the parent thiourea molecule, this mode appeared at
ꢃ1
ꢃ1
1
094 cm
in the infrared spectrum (1105 cm
Raman) [49],
ꢃ1
and even higher values – up to 1325 cm – have been also re-
ported in related compounds [36,45]. A definite assignment should
take into account strong coupling between fundamentals, as re-
ported for simple alkyl derivatives of thiourea, where the CAN
and C@S stretching modes contribute to a variety of fundamentals
Fig. 3. Crystal packing of the title species viewed along [1 0 0] with displacement
ellipsoids drawn at the 50% probability level.
[
59]. Moreover, the formation of C@Sꢀ ꢀ ꢀHAX intermolecular hydro-
gen bonds seems to strongly effect the frequency of the
mode [42].
m(C@S)
[
36]. It is worthy to mention that the C@O stretching mode is
appreciably coupled with the CAN stretching and with the NAH
bending mode, as observed for related compounds [54–56].
In (thio)amide compounds several infrared absorption bands
which are called ‘‘(thio)amide bands’’ are important for studying
structural and electronic properties because they are sensitive to
intermolecular hydrogen bonding and conformational changes
4. Conclusion
The title compound was synthesized and characterized by spec-
troscopic and X-ray diffraction techniques and the vibrational
properties have been studied by FTIR and FT-Raman spectroscopy
along with quantum chemical calculations at the B3LYP/6-
[
57]. This approach has recently been applied also in the analysis
of urethane [57] and thiourea derivatives [53]. In compounds con-
taining the thioamide group give rise to four characteristic vibra-
tional bands, the thioamide bands I, II, III and IV have a large
ꢁ
311 + G level of approximation. A strong intramolecular hydrogen
bond between the C@O and HAN1 groups forming a 6-membered
ring is present in the crystal. From the joint analysis of both IR and
Raman spectra the main normal modes related with the thioamide
group (‘‘thioamide bands’’) have been tentatively assigned as fol-
contribution from d(NAH) (I), m(CAN) (II and III) and m(C@S) (IV)
motions and are usually reported around 1500, 1300, 1100 and
ꢃ1
7
50 cm , respectively [58]. These bands emerge in a region which
ꢃ1
ꢃ1
is plenty of absorptions from substituent groups, making difficult
their identification. The joint analysis of both IR and Raman spectra
arises necessary for an unambiguous identification [53].
low: 1528 cm
[d(N2AH), thioamide band I], 1324 cm
ꢃ1
[m
as(NACAN), thioamide band II], 1154 cm
s
[m (NACAN), thioam-
ꢃ1
ide band III] and 775 cm
[m(C@S), thioamide band IV].

6
2
A. Saeed et al. / Journal of Molecular Structure 985 (2011) 57–62
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox,
Acknowledgments
H.P. Hratchian, J.B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann,
O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K.
Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S.
Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K.
Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J.
Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L.
Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M.
Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez and
J.A. Pople, Gaussian, Inc., Pittsburgh PA, 2003.
MFE is a member of the Carrera del Investigador of CONICET
and gratefully acknowledges to the Consejo Nacional de Investigac-
iones Científicas y Técnicas, the ANPCYT and to the Facultad de
Ciencias Exactas, Universidad Nacional de La Plata for financial
support.
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Appendix A. Supplementary material
Tables of atomic coordinates and equivalent isotropic displace-
ment parameters, full intramolecular bond distances and angles,
atomic anisotropic displacement parameters and hydrogen atoms
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