Synthesis, crystal X-ray diffraction structure, vibrational properties and quantum chemical calculations on 1-(4-(4-Fluorobenzamido)phenyl)-3-(4- fluorobenzoyl)thiourea

Article abstract of DOI:10.1016/j.molstruc.2010.09.035

The 1-(4-(4-Fluorobenzamido)phenyl)-3-(4-fluorobenzoyl)thiourea species (1) has been synthesized and characterized by GC-MS, elemental analyses and ¹H NMR and FTIR spectroscopy techniques. The crystal structure of the novel compound - having a

Full text of DOI:10.1016/j.molstruc.2010.09.035

Journal of Molecular Structure 984 (2010) 240–245
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, crystal X-ray diffraction structure, vibrational properties
and quantum chemical calculations on
1-(4-(4-Fluorobenzamido)phenyl)-3-(4-fluorobenzoyl)thiourea
b
a
c
Aamer Saeed a, , Mauricio F. Erben , Naeem Abbas , Ulrich Flörke
⇑
a Department of Chemistry, Quaid-I-Azam University, Islamabad 45320, Pakistan
b 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
c Department Chemie, Fakultät fur Naturwissenschaften, Universitat Paderborn, Warburgerstrasse 100, D-33098 Paderborn, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The 1-(4-(4-Fluorobenzamido)phenyl)-3-(4-fluorobenzoyl)thiourea species (1) has been synthesized and
characterized by GC–MS, elemental analyses and 1H NMR and FTIR spectroscopy techniques. The crystal
structure of the novel compound – having a benzamide moiety attached to a thiourea nucleus – has been
determined by X-ray diffraction. The species crystallize in the triclinic space group P-1, Z = 4, with 2 mol-
ecules per asymmetric unit. Additionally there is one ethylacetate solvent molecule per asymmetric unit.
The carbonyl and thiourea groups are almost planar and the conformation adopted by the C@S and the
C@O double bonds is mutually antiperiplanar. Density functional theory methods have been applied to
determine the conformational space around the central –C(O)NHC(S)NH– moiety. The vibrational prop-
erties have been studied by FTIR and FT-Raman spectroscopy along with quantum chemical calculations
at the B3LYP/6-311+Gꢀ level of approximation.
Received 22 July 2010
Received in revised form 22 September
2010
Accepted 23 September 2010
Available online 29 September 2010
Keywords:
Thiourea derivative
Crystal structure
Conformation analysis
Hydrogen bonds
DFT calculations
Vibrational studies
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
Introduction of various electron-donating or -withdrawing sub-
stituents affects the hydrogen-bonding ability of the thiourea
Fluoro-substituted thioureas are excellent substrates for study-
ing the hydrogen bonding due to their ability to form intra- and
intermolecular hydrogen bonds of the N–H proton-donor groups
which depends upon the acidity of thioureido –NH protons. The
presence of amide group provides an additional bonding site for
such studies. Fluorinated aryl thioureas represent a new class of
potent anti-trypanosomal agents [17] and a novel class of potent
influenza virus neuraminidase inhibitors [18]. Very recently, the
in vitro antifungal activity of a series of isomeric fluoro-substituted
thioureas was also determined [19].
On the other hand, the benzamido core is present in compounds
with such a wide range of biological activities that it has been
called a privileged structure. N-substituted benzamides are well-
known anticancer compounds and the mechanism of action for
N-substituted benzamide-induced apoptosis has been studied,
using declopramide as a lead compound [20]. N-substituted benz-
´
to sulphur and carbonyl oxygen atoms [1–3]. Thus, N-benzoyl-N-
arylthioureas have been thoroughly investigated in connection
with the formation of intramolecular hydrogen bonding [4–7]. In
effect, it was found that the intramolecular hydrogen bond be-
tween the oxygen atom in the C@O group and the hydrogen atom
of the thiourea group is favored by the formation of a six-
membered ring [2,8,9]. Moreover, the hydrogen-bonding ability
of the thiourea moiety has extensively been used in construction
of anion receptors [10–12] and in the thiourea-based metal com-
plexes [13] and organocatalysts [14]. Very recently, Pisiewicz
et al. reported the preparation of a fluorine substituted thiourea
which forms heteroleptic monocationic Pd(II), Pt(II) and Ru(II)
complexes [15]. Moreover, ion selective electrodes for Pb(II) based
on benzoylthioureido derivatives as ionophores have been formu-
lated [16].
amides inhibit nuclear factor-jB and nuclear factor of activated T
cells activity while inducing activator protein 1 activity in T lym-
phocytes [21]. 2-Aminotetralin-derived substituted benzamides
with mixed Dopamine D2, D3, and Serotonin 5-HT1A receptor
binding properties are a novel class of potential atypical antipsy-
chotic agents [22]. Fluoro-substituted benzamides have been also
studied, suggesting the presence of strong fluorine–hydrogen short
contacts and hydrogen bonds [23].
⇑
Corresponding author. Tel.: +92 51 9064 2128; fax: +92 51 9064 2241.
E-mail address: aamersaeed@yahoo.com (A. Saeed).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.09.035

A. Saeed et al. / Journal of Molecular Structure 984 (2010) 240–245
241
The title compound was designed to investigate the effect of the
presence of amide group as an additional bonding site in the thio-
urea moiety. It is unique in having both the benzamido and thiou-
redo moieties present in a single structural unit, which makes it an
excellent model for studying their simultaneous H-bonding inter-
actions. Here, the synthesis, characterization and vibrational prop-
erties, together with the X-ray molecular structure are reported.
gaseous helium as mobile phase. One peak at retention time
7.4 min is observed in the chromatogram, with a fragmentation
pattern dominated by the following peaks: 123 (100%, FC6H4CO),
95 (60%, FC6H4) and 75 (28%, C6H3).
2.5. Quantum chemical calculations
All quantum chemical calculations were performed with the
GAUSSIAN 03 program package [25]. The molecular geometries
were optimized to standard convergence criteria by using a DFT
hybrid method with Becke’s non local three parameter exchange
and the Lee, Young and Parr correction (B3LYP) using 6-31+Gꢀ
and the more extended 6-311+Gꢀ basis sets. The calculated vibra-
tional properties corresponded in all cases to potential energy min-
ima for which no imaginary frequency was found.
2. Experimental
2.1. Synthesis
A solution of p-phenylenediamine (1.5 mmol) in 25 ml acetoni-
trile was added dropwise to a two-necked round-bottomed flask
containing 4-fluorobenzoyl isothiocyanate (1.5 mmol) in 30 ml of
acetonitrile. The mixture was refluxed for 3 h. On cooling, the reac-
tion mixture was acidified with dil. hydrochloric acid. The 1-(4-
aminophenyl)-3-(4-fluorobenzoyl) thiourea intermediate obtained
on filtration was washed with water, died, dissolved in 30 ml of
acetonitrile and treated as such with 4-fluorobenzoyl chloride
(1.5 mmol) in 25 ml of acetonitrile. The reaction mixture was re-
fluxed further for 1 h, on cooling added to water to furnish the title
benzamido-thiourea (I) as solid. The product was recrystallized
twice from ethyl acetate to afford the crystal suitable for the
X-ray diffraction study (yield 87%). Anal. Calcd. for C21H15F2N3O2S:
C, 61.31; H, 3.67; N, 10.21; S, 7.79, Found: C, 61.24; H, 3.61; N,
10.34; S, 7.85 %. 1H NMR (300 MHz, CDCl3 d, ppm): 12.21 (br s,
1H, NH), 9.18 (br s, 1H, NH), 10.1 (br s, 1H, NH), 7.96 (m, 4H,
Ar–H), 7.41 (m, 2H, Ar–H), 7.51 (dd, J = 2.7, 6.6 Hz, 2H, Ar–H),
7.41 (m, 2H, Ar–H), 7.09 (dd, J = 2.7, 6.6 Hz, 2H, Ar–H).
3. Results and discussion
3.1. Synthesis
The Synthetic pathway to 1-(4-(4-fluorobenzamido)phenyl)-3-
(4-fluorobenzoyl)thiourea (I) is shown in Scheme 1. Thus 4-fluor-
obenzoyl isothiocyanate was produced in situ, by reaction of
freshly prepared 4-fluorobenzoyl chloride with an equimolar
amount of potassium thiocyanate in dry acetonitrile. Treatment
of the latter with equimolar quantity of p-phenylenediamine
afforded the 1-(4-aminophenyl)-3-(4-fluorobenzoyl) thiourea as
an intermediate, in addition to some bis-thiourea product. Further
treatment of the intermediate thiourea with another mole of
4-fluorobenzoyl chloride furnished the title compound (I) in 87%
yield. The product was recrystallized twice from ethyl acetate to
afford the crystal suitable for the X-ray diffraction study.
2.2. Crystal structure determination
The 1H NMR spectrum of the compound was consistent with the
proposed structure. Thus, in addition to the signals for aromatic
protons three N–H signals are observed. The signals appearing at
d = 12.21 ppm region and in the d = 9.18 ppm are characteristic of
the thiourea moiety. The imine group proton participating in the
intramolecular hydrogen appears at low field. The N–H signal for
amide appeared at d = 10.1 ppm.
C
23H19F2N3O3S, 0.5 ethylacetate; Mr = 455.5, colorless crystal,
size 0.49 ꢁ 0.33 ꢁ 0.21 mm3, triclinic space group P-1, a =
10.1338(14), b = 12.7183(18), c = 16.930(2) Å,
a = 85.814(3), b =
80.934(3),
cm3, F(0 0 0) = 944,
fractometer, T = 120(2) K, MoK
lected 1.6 < < 26.4°, semi-empirical absorption correction from
c
= 78.508(3)°, V = 2109.6(5) Å3, Z = 4, Dcalc = 1.434 g/
= 0.202 mmꢂ1. Bruker SMART APEX CCD dif-
-radiation, 15,776 intensities col-
l
a
H
equivalents, 8333 independent reflections (Rint = 0.052). Structure
solution by direct and conventional Fourier methods, structure
refinement based on F2 and 578 parameters, all but hydrogen atoms
3.2. X-ray structure
There are two crystallographically independent molecules A
(labeling 1yz) and B (2yz) per asymmetric unit that differ only
slightly from their geometric parameters. Table 1 includes selected
geometric parameters derived from the structure refinement, as
well as those obtained from quantum chemical calculations. The
fluorobenzoyl group of the thiourea moiety is twisted by about
29.2(2)° (mol. B 20.6(2)°) along the Cx01–Cx02 bond from the thio-
urea plane. The fluorobezamido phenyl part as well is twisted, both
aromatic subunits define a dihedral angle of 15.0(1)° (mol. B
18.3(1)°). Thiourea (Cx01, Ox01, Nx01, Cx08, Sx01, Nx02) and ami-
do planes (Nx03, Cx15, Ox02) are also twisted by 34.8(1)° (mol. B
26.5(1)°) (see Fig. 1).
The structure of substituted thioureas generally shows a signif-
icant influence of intramolecular hydrogen bonding, which results
in substancial differences between the preferred conformation of
the N,N di-substituted molecules, compared with the N-substituted
analogue [26]. Koch and co-workers [13,27] and Dago et al. [6] re-
ported that an intramolecular hydrogen bond between the thio-
urea group and the oxygen atom of the amidic group stabilizes a
planar six member ring structure. Following this trend, in the title
molecule the –C(O)NHC(S)NH– unit adopt a planar structure with
refined anisotropically. H atoms were clearly resolved from
DF
maps, placed on idealized positions and refined riding on the parent
atoms with Uiso = 1.2Ueq(C or N) [24]. There are two crystallograph-
ically independent but chemically equal molecules and one
ethylacetate solvent molecule per asymmetric unit. Refinement
converged at R1(I > 2
r
(I)) = 0.052, wR2(all data) = 0.139, S =
0.933, max.(D/r) = 0.001, min./max. height in final DF map
ꢂ0.43/0.51 e/Å3.
2.3. Vibrational spectroscopy
Solid-phase IR spectra were recorded as KBr discs with a resolu-
tion of 2 cmꢂ1 in the 4000–400 cmꢂ1 range on a Bruker EQUINOX
55 FTIR spectrometer. The FT-Raman spectrum was recorder in
the region 4000–100 cmꢂ1 using a Bruker IFS 66v spectrometer
equipped with Nd:YAG laser source operating at 1.064 lm line
with 200 mW power of spectral width 2 cmꢂ1
.
2.4. GC–MS determination
The GC–MS measurements were recorded in a GCMS-QP2010
SHIMADZU instrument with a 19091J-433 HP-5 column, using
the C@O group interacting with the N102–H amidic group in a sim-
ilar manner. The nonbonding distance O101ꢃ ꢃ ꢃN102 is 2.635(2) ÅA,
0

242
A. Saeed et al. / Journal of Molecular Structure 984 (2010) 240–245
O
HO
O
i) SOCl2
F
F
N
S- K+
ii)
S
C
N
/ dry acetone
H2N
NH2
Dry acetone
O
S
F
NH
H2N
NH
Cl
O
F
F
H
N
H
N
O
O
S
N
H
(1)
F
Scheme 1. Synthetic pathway to 1-(4-(4-Fluorobenzamido)phenyl)-3-(4-fluorobenzoyl) thiourea.
Table 1
these species [26], the lengths increasing in the order C108
–
Experimental and calculated selected geometric parameters (values in Å and degrees)
for the title species.
N102 < C101–N101 < C108–N101 (see Table 1). For comparison, the cor-
responding C–N bond length in the benzoyl amide group (C115
–
0
Experimental
B3LYP/6-311+Gꢀ
N103) amounts 1.347(3) ÅA, slightly shorter than the C101–N101 bond.
The patterns of packing adopted by thiourea derivatives were
Bond lengths
C
C
101@O101
115@O102
1.225(3)
1.226(3)
1.654(2)
1.374(3)
1.347(3)
1.323(3)
1.400(3)
1.228
1.221
1.674
1.380
1.378
1.345
1.415
rationalized by McBride et al. in terms of molecular structure, sol-
vent of crystallization, and energies and efficiencies of packing
[29]. For the title species, the crystal packing is dominated by inter-
molecular N101–Hꢃ ꢃ ꢃS@C (ꢂx, ꢂy, ꢂz + 1) and 0 N201–Hꢃ ꢃ ꢃS201@C
(ꢂx + 1, ꢂy, ꢂz + 1) hydrogen bonds [2.546(1) ÅA] connect mole-
cules into centrosymmetric dimers that are stacked in parallel
sheets along the [1 0 0] plane. This is a well-known crystal motif
for N-benzoyl-thiourea compounds [5,30]. The presence of ethyl
acetate molecules in the crystal seems to play a minor role in the
X-ray molecular structure and crystal packing. It was reported that
the crystallization of bis(thiourea) derivatives containing the 1,3-
dimetrhyl-adamantane linker from ethyl acetate affords crystals
containing disordered solvent molecules [31]. In the present case,
C@S
C
101–N101
N103–C115
N102–C108
N101–C108
Bond angles
101@C101–N101
101–N101–C108
O
123.1(2)
127.7(2)
117.91(18)
126.48(18)
123.3(2)
115.3(2)
122.7
130.4
116.3
129.7
123.7
114.9
C
N101–C108–S101
N102–C108–S101
N103–C115@O102
N103–C115–C116
Dihedral angles
101–C101–N101–C108
O
7.2(4)
1.8(4)
ꢂ4.4
1.2
the main interaction is given by C@Oꢃ ꢃ ꢃH–N103 hydrogen bonds
0
C
C
101–N101–C108–N102
108–N102–C109–C110
[3.311(1) ÅA] involving the carbonyl ester group of the solvent mol-
ecule and the amide group of the title species.
ꢂ3.3(4)
ꢂ0.8(4)
41.4(4)
ꢂ24.2(3)
27.8(4)
ꢂ1.8
ꢂ2.4
ꢂ6.2
ꢂ26.3
ꢂ20.9
O
C
O
C
102–C115–N103–C112
113–C112–N103–C115
102@C115–C116–C121
103–C102–C101@O101
3.3. Quantum chemical calculations
The molecular structure and conformational flexibility are
important properties for determining the donor–acceptor capabil-
ities on thiourea derivatives [32,33]. Fabbrizzi et al. reported that
substituted-phenyl urea compounds interacts through hydrogen
bonding with a variety of oxoanions to give bright colored
complexes [34] and a variety of receptors containing the urea
and the thiourea groups were designed for anion recognition
[35]. These effects are closely related with the conformational
´
similar to that found in other N-benzoyl N-substituted thioureas,
0
which are reported in the range of 2.618(4)–2.654(2) ÅA [3,28].
Table 1 shows the carbon–nitrogen bond lengths determined
for the central –C(O)NHC(S)NH– moiety. It is observed that both
the amidic [(O)C101–N101 1.374(3) ÅA] and thioamide [N102–C108(S)
1.323(3) ÅA] bonds have a partial double bond character. Moreover,
a definite trend in the C–N bond distances has been recognized for
0
0

A. Saeed et al. / Journal of Molecular Structure 984 (2010) 240–245
243
Fig. 1. Molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level. Only one molecule (A) present in the asymmetric unit is
shown, the second molecule (B) follows labeling scheme with 2xx.
properties and the presence of intra- and intermolecular hydrogen
bonding interactions on the thiourea group [35].
probably corresponding to a transition state structure. When the
second dihedral angle involving the thiourea group [d(O@C101
101C)] is studied the potential energy curve shows the presence
–
Thus, the conformational space and the molecular structures for
the main conformations of the studied compound have been ana-
lyzed by using quantum chemical calculations at the DFT-B3LYP
level of approximation. The comparison between experimental
X-ray results with the corresponding computed structure for the
molecule isolated in a vacuum allows for a better understanding
of the conformational transferability observed for substituted thio-
ureas. In principle, the studied compounds may adopts several
conformations mainly depending on the orientation around the
thiourea moiety, the relative position of the C@O and C@S double
bonds and the orientation of substituted-phenyl rings. Thus, in
order to define the conformational flexibility of the title molecule,
in a first approximation the potential energy functions for internal
rotation around the dihedral angles of the central –C(O)
NHC(S)NH– group have been calculated. The B3LYP method with
the moderate 6-31G basis sets has been applied allowing geometry
optimizations with the corresponding dihedral angle varying from
0° to 360° in steps of 20°. The potential energy curves obtained
around the N101–C108 and C101–N101 single bonds are shown in
Fig. 2.
N
of a well-defined minimum at d(O@C101–N101C) = 0°, correspond-
ing to the expected planar synperiplanar orientation of the C@O
double bond with the N101–C108 bond. The curve is symmetrical
with respect to the antiperiplanar orientation d(O@C101–N101C) =
180°, which seems to be located in a local maximum of the poten-
tial curve, higher in energy by ca. 14 kcal molꢂ1. It is worthy to
note that in the most stable form, the C@O and C@S double bonds
are mutually oriented in opposite directions. Additionally, the
N101–H and N102–H bonds in the thiourea group adopt a syn and
anti conformation with respect to the C@S double bond,
respectively.
Also, full geometry optimizations and frequency calculations
were computed for each of the more stable structures with the
B3LYP method and the 6-31+Gꢀ basis sets. The optimized molecular
structures for the two main conformers of the studied compound
are shown in Fig. 3. The corresponding conformer analogous to
those found in the X-ray analysis was further optimized by using
the more extended triple-zeta 6-311+Gꢀ basis sets and selected
computed geometrical parameters are gathered in Table 1. The geo-
metrical parameters obtained at the B3LYP/6-311+Gꢀ are in very
good agreement with the experimental ones.
The potential energy curve for the rotation around the N101
–
C108 bond in the thiourea moiety (Fig. 2, left) shows a deep mini-
mum at d(CN101ꢂC108@S) = 180°, corresponding to a structure with
the thiourea group adopting a planar form with the C@S double
bond and the N101–C101 bond in mutual anti conformation. The
syn form [d(CN101ꢂC108@S) = 0°] is located in a local maximum,
Of particular interest, the C108–N101 bond length is computed as
the longest nitrogen–carbon bond in the molecule, in fine agree-
ment with the structure determined by X-ray diffraction. Thus, it
is quite likely that intramolecular electronic effects (especially res-
H
O
N
S
C
C
N
R
1
R
2
H
16
8
16
H
R
N
1
S
C
O
H
N
H
N
C
N
R
1
C
O
R
C
S
2
H
R
2
8
0
H
R
N
1
S
C
O
C
N
0
R
2
H
0
60
120
180
240
300
360
0
60
120
180
240
300
360
δ (CN101-C108=S)
δ (O=C101-N101C)
Fig. 2. Calculated (B3LYP/6-31G) potential energy function for internal rotation around the N101–C108 (left) and C101–N101 (right) single bonds in the central –C(O)NHC(S)NH–
moiety (for atom numbering see Fig. 1). The molecular schemes have been inserted for better visualization of the conformational space (R1 = C6H4F– and R2 = C6H4–NHC(O)–
C6H4F).

244
A. Saeed et al. / Journal of Molecular Structure 984 (2010) 240–245
Fig. 3. Molecular models for the main conformers of the title species found theoretically (B3LYP/6-31+Gꢀ). In the most stable conformer (left) the C@S and C@O bond are
oriented in opposite directions.
onance interactions) rather than crystal packing effects dominate
the trend observed for the N–C bond lengths.
being a result of conjugated resonance interactions between the
carbonyl and the phenyl ring [2].
Finally, it is worthy to mention that a strong intramolecular
hydrogen bond between the C@O and H–N102 groups seems to be
favored in the most stable form also in the vacuum isolated spe-
It is well-known that both the amide and thiourea groups present
a characteristic band in the 1500–1600 cmꢂ1 range of the IR spec-
trum, originated by the NꢂH deformation mode [d(NꢂH)]. For the ti-
tle species, strong IR absorptions with defined maxima at ca. 1603
and 1526 cmꢂ1, are assigned to these modes. The most intense Ra-
man signal is located in this region at 1607 cmꢂ1. B3YLP/6-311+Gꢀ
computations predict a strong band due to the d(N102ꢂH) normal
mode at 1666 cmꢂ1, whereas the d(N103ꢂH) and d(N101ꢂH) are
predicted at lower frequencies (1646 and 1622 cmꢂ1, respectively).
In relation to the spectroscopic peculiarities of phenyl groups,
characteristic group frequencies are observed. A series of absorp-
tions in the 1620–1500 cmꢂ1 range, with a strong band at 1511
cmꢂ1, are mainly originated in the several C–C stretching vibrations
of the benzene and substituted fluorobenzyl rings of the molecule
[48].
cies. This interaction forms a 6-membered ring, with N101 and
0
C
108, and a short non-bonded contact of ca. 2.692 ÅA is computed
(B3LYP/6-311+Gꢀ) for the C@O101ꢃ ꢃ ꢃN102 distance, in very good
agreement with the observed value in the crystal structure.
3.4. Vibrational analysis
The observed and calculated (B3LYP/6-311+Gꢀ) infrared absorp-
tions, the FT-Raman frequencies along with their relative intensi-
ties and probable assignments are summarized in Table S1, in
the supporting information. A tentative assignment of the ob-
served bands has been carried out by comparison with the spectra
of related molecules [27,36–41]. Very recently, the vibrational
properties of the thiourea molecule – the idealized parent species
– were revisited by Srinivasan et al. [42].
In the infrared spectra a series of broad absorptions of medium
intensity are observed at 3286, 3190 and 2923 cmꢂ1, which could
be assigned to the NꢂH stretching modes [40,43,44]. The most in-
tense of these band at 2923 cmꢂ1 could be tentatively assigned to
Strong bands can be observed at 1360 and 1329 cmꢂ1 in the
Raman spectrum of the studied compound, with strong counter-
parts at 1352 and 1329 cmꢂ1 in the infrared spectrum. Taking into
account the vibrational properties reported for the simple thiourea
molecule [42], it is expected that the C–N stretching modes, which
are usually coupled in symmetric and antisymmetric motions,
appear in this region [47]. Thus, following the quantum chemical
calculation description of these normal modes, the NCN antisym-
metric stretching mode of the thiourea moiety is assigned to the
intense band centered at 1352 cmꢂ1. The computed value at the
B3LYP/6-311+Gꢀ level of approximation is 1398 cmꢂ1 and corre-
sponds to the most intense absorption, in good agreement with
the experimental evidence.
the
low
m
m
(N102ꢂH) stretching mode. Weiqun et al. [2] also reported a
(NꢂH) frequency value (3086 cmꢂ1) for the related N-(4-
´
chloro)benzoyl-N(4-tolyl)thiourea species. Quantum chemical cal-
culations for the most stable conformer of the title compound iso-
lated in a vacuum compute that the
m
(N102ꢂH) stretching mode
appears as a very intense absorption at 3384 cmꢂ1 (not corrected),
The
m
(CꢂF) stretching modes originate medium intensity infra-
shifted to lower frequencies as compared with both the
m
(N102ꢂH)
red absorptions at 1258 and 1231 cmꢂ1, with counterparts at
1262 cmꢂ1 and 1233 cmꢂ1 in the Raman spectrum, respectively.
The medium intensity IR absorption observed at 756 cmꢂ1 is
and
m
(N103ꢂH) fundamentals (3621 cmꢂ1). This red-shift observed
for the
m
(NꢂH) stretching mode could be related with the forma-
tion of C@Oꢃ ꢃ ꢃN–H intramolecular hydrogen bond, as observed in
the X-ray analysis. Interestingly, the computed vibrational spec-
trum for the second stable conformer – for which intramolecular
hydrogen bonds are not expected – shows the presence of three
tentatively assigned to the
m(C@S) mode. This assignment is in
agreement with previously studied thiourea derivatives [3,46].
However, it should be mentioned that for the parent the thiourea
molecule, this mode appeared in the 1094 cmꢂ1 in the infrared
spectrum (1105 cmꢂ1 Raman) [42], and higher values – up to
1325 cmꢂ1 – have been also reported [2,38]. The formation of
C@Sꢃ ꢃ ꢃH–X intermolecular hydrogen bonds seems to strongly
absorptions with similar intensity at 3613, 3579 and 3572 cmꢂ1
.
Strong IR absorptions at 1674 and 1645 cmꢂ1 were assigned to
the (C@O) modes, frequency values which are similar to that
m
found in many small-molecule having C@Oꢃ ꢃ ꢃH–N hydrogen bond-
ing [45]. The respective Raman bands are observed at 1672 and
1644 cmꢂ1, respectively. Calculated (B3LYP/6-311+Gꢀ) frequencies
for these fundamentals amount 1731 and 1720 cmꢂ1 for the
affect the frequency of the m(C@S) mode [36].
4. Conclusion
m(C115@O102) and m(C101@O101) stretching modes, respectively.
The lower value computed for the –C(O)NHC(S)NH– carbonyl as
compared with the amidic group is in accordance with the pres-
ence of a intramolecular C@OꢃꢃꢃH–N interaction in the –C(O)
NHC(S)NH– moiety. These facts are in agreement with the compre-
hensive vibrational study of Reguera et al. for substituted thioureas
displaying intramolecular hydrogen bonding [46]. It is worthy to
mention that the C@O stretching mode is appreciably coupled with
the C–N stretching and with the N–H bending mode, as observed
for related compounds [47–49]. Moreover, the relative low fre-
The title compound having benzamido and thiourea moieties in
a single structural unit has been synthesized and characterized by
spectroscopic and X-ray diffraction techniques. The presence of
amide carbonyl group provides an additional bonding site in addi-
tion to the thioureido carbonyl and thiocarbonyls, thus increasing
its bonding potential as a versatile ligand for coordination to met-
als. DFT methods have been used to determine the conformational
space around the central –C(O)NHC(S)NH– moiety and the vibra-
tional properties have been studied by FTIR and FT-Raman spec-
troscopies along with quantum chemical calculations at the
B3LYP/6-311+Gꢀ. A strong intramolecular hydrogen bond between
quency values observed for the
m(C@O) stretching mode in N-ben-
zoyl substituted thiourea compounds has been also interpreted as

A. Saeed et al. / Journal of Molecular Structure 984 (2010) 240–245
245
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N.A. gratefully acknowledges the research scholarship from HEC
Islamabad under the HEC Indigenous PhD Scholarship 5000
Scheme. MFE is a member of the Carrera del Investigador of
CONICET and gratefully acknowledges to the Consejo Nacional de
Investigaciones Científicas y Técnicas, the ANPCYT and to the
Facultad de Ciencias Exactas, Universidad Nacional de La Plata for
financial support.
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