The role of substituents in the molecular and crystal structure of 1-(adamantane-1-carbonyl)-3-(mono)- and 3,3-(di) substituted thioureas

Article abstract of DOI:10.1016/j.molstruc.2014.03.002

Three novel 1-(adamantane-1-carbonyl) thioureas were synthesized by the reaction of adamantyl isothiocyante with corresponding amines and fully characterized by spectroscopy methods. Two isomeric species, i.e. 1-(adamantane-1-carbonyl)-3-(3-nitrophenyl)thiourea (1) and 1-(adamantane-1- carbonyl)-3-(4-nitrophenyl)thiourea (2), are structurally characterized and a third related compound, namely 1-(adamantane-1-carbonyl)-3,3-(methyl-phenyl) thiourea (3) has been also included for assessing the role of the nitrogen substitution on the structural properties. As determined by X-ray analysis, compounds 1 and 2 exhibit the S conformation with the CO and CS double bonds in a pseudo-antiperiplanar orientation, whereas the U form is found for compound 3. These conformational features are mainly dictated by the substitution degree on the thiourea core and the ability of forming an intra-molecular NH-OC hydrogen bond for mono-substituted analogues 1 and 2. These dissimilar interactions affect the vibrational properties, which have been determined by infrared and Raman spectroscopies and quantum chemical calculations at the B3LYP/6-311++G^** level of approximation.

Full text of DOI:10.1016/j.molstruc.2014.03.002

Journal of Molecular Structure 1065-1066 (2014) 150–159
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Journal of Molecular Structure
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The role of substituents in the molecular and crystal structure
of 1-(adamantane-1-carbonyl)-3-(mono)- and 3,3-(di) substituted
thioureas
b
c,
Aamer Saeed a, , Ulrich Flörke , Mauricio F. Erben
⇑
⇑
a Department of Chemistry, Quaid-I-Azam University, Islamabad 45320, Pakistan
b Department Chemie, Fakultät für Naturwissenschaften, Universität Paderborn, Warburgerstrasse 100, D-33098 Paderborn, Germany
c 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
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
ꢀ
Three 1-(adamantane-1-carbonyl)-3-
substituted thioureas were prepared
for the first time.
ꢀ
ꢀ
Crystal and molecular structures
were determined.
Both intra- and inter-molecular
hydrogen bonds are found in the
crystal.
ꢀ
ꢀ
Conformational aspects are discussed
in terms of the vibrational spectra.
The role of the substituent attached
to the thiourea group is discussed.
a r t i c l e i n f o
a b s t r a c t
Article history:
Three novel 1-(adamantane-1-carbonyl) thioureas were synthesized by the reaction of adamantyl
isothiocyante with corresponding amines and fully characterized by spectroscopy methods. Two isomeric
species, i.e. 1-(adamantane-1-carbonyl)-3-(3-nitrophenyl)thiourea (1) and 1-(adamantane-1-carbonyl)-
3-(4-nitrophenyl)thiourea (2), are structurally characterized and a third related compound, namely
1-(adamantane-1-carbonyl)-3,3-(methyl-phenyl)thiourea (3) has been also included for assessing the
role of the nitrogen substitution on the structural properties. As determined by X-ray analysis, com-
pounds 1 and 2 exhibit the S conformation with the C@O and C@S double bonds in a pseudo-antiperipla-
nar orientation, whereas the U form is found for compound 3. These conformational features are mainly
dictated by the substitution degree on the thiourea core and the ability of forming an intra-molecular
NAHꢁ ꢁ ꢁO@C hydrogen bond for mono-substituted analogues 1 and 2. These dissimilar interactions affect
the vibrational properties, which have been determined by infrared and Raman spectroscopies and quan-
tum chemical calculations at the B3LYP/6-311++G** level of approximation.
Received 18 December 2013
Received in revised form 11 February 2014
Accepted 3 March 2014
Available online 11 March 2014
Keywords:
Acyl thioureas
Vibrational spectroscopy
Quantum chemical calculations
Crystal structure
Hydrogen bond
Conformational analysis
Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
1-acyl thiourea derivative. Substitution can occur on the second
nitrogen atom affording compounds with general formula
As early as 1873, Neucki reported the preparation of
CH3C(O)NHC(S)NH2, which is considered the first synthesized
RC(O)NHC(S)NR1R2. These are useful materials for the synthesis
of a wide variety of heterocyclic compounds [1,2], as ionophores
in ion selective electrodes [3–5] and versatile ‘‘collectors’’ used in
mineral extraction by froth flotation processes [6,7]. Moreover,
the potential application of this kind of compounds as smoothened
antagonist has been highlighted recently [8], and its antiviral
⇑
Corresponding authors. Tel.: +92 51 9064 2128; fax: +92 51 9064 2241 (A.
Saeed). Tel./fax: +54 221 425 9485 (M.F. Erben).
E-mail addresses: aamersaeed@yahoo.com (A. Saeed), erben@quimica.unlp.
edu.ar (M.F. Erben).
http://dx.doi.org/10.1016/j.molstruc.2014.03.002
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

A. Saeed et al. / Journal of Molecular Structure 1065-1066 (2014) 150–159
151
properties has been proved [9]. Review articles covering the syn-
thesis [10], the coordination chemistry [11,12], potential applica-
tions [10] and biological aspects of 1-acyl thioureas can be found
in the chemical literature [13].
There are, however, only a few examples in the literature of
ureas/thioureas containing the adamantyl group [14]. Accordingly,
thioureas containing the bulkier 1-adamantyl group have been
on a Bruker EQUINOX 55 FTIR spectrometer. The FT-Raman spectra
of powdered samples were recorded 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
.
Computational details. Quantum chemical calculations were
performed with the GAUSSIAN 03 program package [26]. The
molecular geometries were optimized to standard convergence cri-
teria by using B3LYP DFT hybrid methods employing the Pople-
type [27] extended valence triple-n basis set augmented with dif-
fuse and polarization functions in both the hydrogen and weighty
atoms [6-311++G**]. The calculated vibrational properties corre-
sponded in all cases to potential energy minima for which no imag-
inary frequency was found. Scott and Radom derived the scaling
factors for the theoretical harmonic vibrational frequencies at 19
levels utilizing a total of 1066 individual vibrations for small mol-
ecules [28]. Zhou and coworkers [29] demonstrated that scaled
B3LYP calculations are powerful approaches for understanding
the vibrational spectra of medium-sized organic compounds and
the recommended factors of 0.96 was used to scale the theoretical
frequencies.
used as organocatalysts for synthesis of enantiomerically pure
a-
and b-amino acids [15] and N-(1-adamantyl)-N0-(4-guanidino-ben-
zyl)urea is a highly selective non-peptidic uPA inhibitor and a lead
structure for the development of potent antimetastatic drugs [16].
Similarly N-adamantyl-N0-phenylurea derivatives are simple solu-
ble epoxide hydrolase (sEH) inhibitors [17]. A library of 1600 ada-
mantyl ureas was screened in vitro for anti tuberculosis activity
and for increasing the bioavailability of inhibitors of human soluble
epoxide hydrolase (hsEH) [18].
The use of the adamantyl group has a multidimensional signif-
icance in drug design. The hydrophobic substituent constant and
steric factors increase the drug stability and plasma half-life of this
kind of compounds [19], as recently demonstrated for polyhydr-
oxylated N-benzylbenzamide derivatives containing an adamantyl
moiety [20]. Adamantyl-1,3,4-oxadiazoles and adamantylamino-
1,3,4-thiadiazoles show antimicrobial, and anti-inflammatory
activities [21]; adamantyl triazoles are selective inhibitors of
11b-hydroxysteroid dehydrogenase type 1 [22] as are the thiazol-
idine derivatives with an adamantyl group [23]. 1-Adamantane
carboxylic acid hydrazides have promising antimicrobial activity
[24]. In this context, it should be noted that the medicinal chemis-
try of adamantane derivatives has been recently reviewed [25].
In continuation of our work focused on the chemistry and struc-
ture of acyl-thiourea compounds, herein we report the synthesis
and structural characterization of three novel 1-(adamantane-1-
carbonyl)-3-substituted thioureas (R = 1-COAC10H15). Specifically,
two isomeric mono-substituted derivatives with R1 = H and
R2 = 3-NO2AC6H4 and 4-NO2AC6H4 (1 and 2, respectively) and the
di-substituted species 1-(adamantane-1-carbonyl)-3,3-(methyl-
phenyl)thiourea (R1 = ACH3, R2 = C6H5) (3) are studied. The selected
species allowed scrutinizing the role of nitrogen substitution on the
conformational properties of the 1-(adamantane-1-carbonyl)thio-
urea moiety. For this purpose, the molecular and crystal structure
for the three species have been determined by X-ray diffraction
and the vibrational properties analyzed by a combined experimen-
tal (including infrared and Raman spectroscopy) and theoretical
calculations at the B3LYP/6-311++G** level of approximation.
2.2. X-ray data collection and structure refinement
Data were collected at 130(2) K on a Bruker AXS SMART APEX
CCD diffractometer using Mo Ka radiation. Structures solved by di-
rect methods [30], full-matrix least-squares refinement on F2. 467/
8167 Parameters/unique intensities for 1, 233/4181 for 2 and 424/
8250 for 3, respectively. All but H atoms refined anisotropically, H
atoms from difference Fourier maps refined on idealized positions
with Uiso = 1.2 Ueq(C/N) or 1.5Ueq(C methyl) and CAH distances of
0.95–0.98 Å, H(N)-positions were refined freely. H(Cmethyl) for 3
were allowed to rotate but not to tip. For 1 and 3 there are each
two crystallographically independent molecules A and B per
asymmetric unit with numbering schemes 1xx for A and 2xx for
B, respectively. Experimental data are listed in Table 1, and
Figs. 1–3 show the molecular structures.
2.3. Synthesis and general procedure
Adamantane-1-carbonyl isothiocyanate was prepared by reac-
tion of adamantane-1-carbonyl chloride (10 mmol) and ammo-
nium thiocyanate (10 mmol) in acetone (30 ml) under nitrogen. A
solution of the suitable substituted aniline (10 mmol) in acetone
(10 ml) was added and the reaction mixture refluxed for 2–4 h.
The reaction mixture was then poured into cold water and the pre-
cipitated thioureas were recrystallized by slow evaporation from
the ethyl acetate–chloroform (2:1) mixture.
2. Experimental
2.1. General
1-(Adamantane-1-carbonyl)-3-(3-nitrophenyl)thiourea (1): yield
70%, mp 161–162 °C. FT-IR (ATR (solid),
m
cmꢂ1): 3321, 2853,
Adamantane carboxylic acid, 3-nitroaniline and 4-nitroaniline
and N-methylaniline were the commercial products from Aldrich.
Analytical grade acetone (E. Merck) was dried and freshly distilled
prior to use. Melting points were recorded using a digital Gallenk-
amp (SANYO) model MPD.BM 3.5 apparatus and are uncorrected.
1H and 13C nuclear magnetic resonance (NMR) spectra were deter-
mined in CDCl3 at 300 MHz and 75.4 MHz respectively using a Bru-
ker spectrophotometer. Fourier transform infrared spectroscopy
(FTIR) spectra for pure solids were recorded using Bio-Rad Excali-
bur FTS 3000 MX spectrophotometer (Madison, Wisconsin, USA)
in the ATR mode of analysis. Mass Spectra (EI, 70 eV) on a gas chro-
matography–mass spectrometry (GC–MS) instrument Agilent
technologies, and elemental analyses were conducted using a
LECO-183 CHNS analyzer.
2849, 1681, 1544, 1516, 1350, 1153, 889, 869. 1H NMR
(300 MHz, CDCl3): d 13.08 (br s, 1H, NH, D2O exchangeable); 9.58
(br s, 1H, NH, D2O exchangeable); 8.61 (s, 1H, Ar); 7.89 (d, 2H,
J = 2.6 Hz Ar), 7.97 (d, 2H, J = 2.6 Hz Ar), 2.1 (brs, 3H, adaman-
taneACH), 1.96 (s, 6H, adamantaneACH2), 1.83 (m, 6H, adaman-
taneACH2); 13C NMR (75 MHz, CDCl3): 179.4 (C@S); 178.7 (C@O),
145.0 (Ar), 144.3 (Ar), 124.5 (Ar), 122.9 (Ar), 120.6 (Ar), 41.9,
39.4, 38.5, 36.4, 36.0, 31.6, 28.0, 27.7, (adamantaneACs). EI-MS,
m/z (Rel. Int.): 221 (14), 202 (17), 180, 179, 163 (100), 135 (88),
137 (28), 122, 93, 80, 79, 67, 41, 39. Anal. Calcd for C18H21N3O3S
(359.44): C, 60.15; H, 5.89; N, 11.69; S, 8.92%; Found: C, 59.95;
H, 5.83; N, 11.72; S, 8.97%.
1-(Adamantane-1-carbonyl)-3-(4-nitrophenyl)thiourea (2): yield
70%, mp 165 °C, FT-IR (ATR (solid),
m
cmꢂ1): 3310, 2849, 1686,
Furthermore, solid-phase (as KBr pellets) infrared spectra were
1547, 1508, 1350, 1299, 1150, 896, 852. 1H NMR (300 MHz, CDCl3):
recorded with a resolution of 2 cmꢂ1 in the 4000–400 cmꢂ1 range
d 13.08 (br s, 1H, NH, D2O exchangeable); 8.58 (br s, 1H, NH, D2O

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A. Saeed et al. / Journal of Molecular Structure 1065-1066 (2014) 150–159
Table 1
Crystal data and structure refinement for compounds 1–3.a
Compound
1
2
3
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C18 H21 N3 O3
359.4
Monoclinic
P 21/n
7.2067(7)
17.2759(16)
27.553(3)
94.185(2)
3421.2(6)
8
S
C18 H21 N3 O3
359.4
Monoclinic
P 21/c
12.6285(10)
9.8576(8)
14.1746(11)
107.507(2)
1682.8(2)
4
S
C19 H24 N2 O S
328.5
Monoclinic
P 21/n
21.627(5)
7.7396(18)
21.627(5)
107.09
3460.2(14)
8
b (Å)
c (Å)
b (°)
V (Å3)
Z
Dc (Mg mꢂ3
)
1.396
0.212
1.419
0.216
1.261
0.194
Absorp. coeff. (mmꢂ1
)
F(000)
1520
760
1408
Crystal size (mm3)
0.43 ꢃ 0.28 ꢃ 0.12
9 6 h 6 9
ꢂ22 6 k 6 21
ꢂ36 6 l 6 36
31,617
0.42 ꢃ 0.29 ꢃ 0.25
ꢂ16/16
ꢂ13/13
ꢂ17/18
16,009
4181
0.49 ꢃ 0.37 ꢃ 0.30
ꢂ28/28
ꢂ10/10
ꢂ28/28
31,923
h
k
l
Data collected
Unique reflections
R(int)
8167
0.041
8250
0.036
0.029
Parameters
GooF
467
1.02
0.044
0.111
233
1.03
0.043
0.121
424
1.03
0.055
0.149
R1 [I > 2sigma(I)]
wR2 (all data)
Max/min
D
F (e Åꢂ3)
0.38/ꢂ0.22 e Åꢂ3
882901
0.58/ꢂ0.26
0.94/ꢂ0.86
CCDC deposition
882900
912608
a
Further conditions and refinement comments: temperature 130(2) K, wavelength 0.71073 Å. Absorption correction: semi-empirical from equivalents. Refinement
method: full-matrix least-squares on F2.
Fig. 1. Molecular structure of 1 with displacement ellipsoids plotted at 50% probability level. Only one molecule A shown.
Fig. 2. Molecular structure of 2 with displacement ellipsoids plotted at 50% probability level.
exchangeable); 8.26 (d, 2H, J = 8.6 Hz, Ar), 8.0 (d, 2H, J = 8.6 Hz, Ar),
1-(Adamantane-1-carbonyl)-3,3-(methyl-phenyl)thiourea
(3):
2.12 (brs, 3H, adamantaneACH), 1.93 (s, 6H, adamantaneACH2),
1.80 (m, 6H, adamantaneACH2); 13C NMR (75.5 MHz, CDCl3):
179.1 (C@S); 178.5 (C@O), 145.0 (Ar), 144.7 (Ar), 124.5 (Ar);
122.9 (Ar), 42.0, 41.9, 39.2, 38.5, 36.4, 36.0, 31.6, 28.0, 27.7, (ada-
mantaneACs). EIMS, m/z (Rel. Int.): 221 (11), 180, 179, 163 (100),
135 (69), 137 (33), 122, 93, 80, 79, 67, 41, 39. Anal. Calcd for C18-
H21N3O3S (359.44): C, 60.15; H, 5.89; N, 11.69; O, 13.35; S,
8.92%; Found: C, 59.03; H, 5.86; N, 11.73; S, 8.87%.
yield 74%, mp 115 °C. FT-IR (ATR (solid),
m
cmꢂ1): 2906, 1700,
1508, 1435, 1376, 1224, 1184, 1118, 871, 800. 1H NMR
(300 MHz, CDCl3): d 7.83 (br s, 1H, NH, D2O exchangeable); 7.23–
7.33 (m, 3H, Ar); 7.38–7.43 (m, 2H, Ar); 3.17 (s, 3H, NACH3);
2.08 (s, 3H, adamantaneACH), 1.69 (s, 6H, adamantaneACH2),
1.58 (q, 6H, adamantaneACH2, J = 8.6 Hz); 13C NMR (75 MHz,
CDCl3): 182.2 (C@S); 169.92 (C@O); 143.05 (C-9); 45.47 (NACH3),
41.51, 39.25, 38.69, 38.49, 36.44, 28.05, 27.78, (adamantaneAC).

A. Saeed et al. / Journal of Molecular Structure 1065-1066 (2014) 150–159
153
Fig. 3. Molecular structure of 3 with displacement ellipsoids plotted at 50% probability level. Only one molecule A shown.
EIMS, m/z (Rel. Int.): 328 (M+, 41), 313, 222, 179 (42), 163 (100),
135 (88), 149 (23), 122, 106, 93, 80. Anal. Calcd for C19H24N2OS
(328.47): C, 69.47; H, 7.36; N, 8.53; S, 9.76%; Found: C, 69.51; H,
7.40; N, 8.56; S, 9.71%.
The mass spectra of compounds 1 and 2 did not show the
molecular ion peaks; the base peak at m/z 163 is derived from
the adamantoyl cation followed by next intense signal for adaman-
tyl cation at m/z 135 is which further fragments to weaker signals
at m/z = 93, 80, 79, 67, 41 and 39. The other major fragments at m/
z = 180 and 179 correspond to those of the N-McLafferty rearrange-
ment. The mass spectrum of 3 showed the molecular ion peak at
m/z = 328, the other important peaks appeared at m/z 313, 222,
179, 163 (100), 135, 149. The observed fragmentation pattern is
in agreement with the mass spectra study reported by Martínez-
Alvarez et al. [34] on a series of acylthiourea species, which the
3. Results and discussion
3.1. Synthesis and characterization
The synthesis of title acyl thioureas was adapted from the origi-
nal method of Douglas–Dains [31] involving the reaction of acyl
isothiocyanates produced in situ with suitable anilines in dry ace-
tone or acetonitrile [32]. A similar method was recently used for
the synthesis of related adamantyl thioureas [33]. Thus, freshly
prepared adamantane-1-carbonyl isothiocyanate was treated with
an equimolar quantity of 3-nitro-, 4-nitro- and N-methylaniline
respectively in acetone to afford compounds 1–3, respectively
(Scheme 1).
main fragment is produced by
a-cleavage to the carbonyl group
to form a well-stabilized acylium cation.
Further characterization includes the X-ray diffraction analysis
and the vibrational spectra (including infrared and Raman) dis-
cussed in the following sections.
3.2. X-ray crystal structure
In the 1H NMR the characteristic signals of adamantyl moiety: a
6H quartet at d 1.75–1.79 (adamantaneACH2), a 6H, singlet at
1.95–1.98 (adamantaneACH2) and a 3H, singlet around 2.08 (ada-
mantaneACH), besides singlets at d 8.5–8.7 and 12.7–13.0 ppm
were observed for HN(1) and HN(2) except for the secondary
amine (3) where the HN(2) was absent. In the 13C NMR character-
istic signals at for adamantyl moiety at d 27.7, 36.1–36.4, 38.6–38.5
and 41.5 ppm, as well those at d = 182–179 ppm for thiocarbonyl
and d = 170–178 ppm for carbonyl carbons were observed.
Compounds 1 and 3 crystallize with each two independent mol-
ecules per asymmetric unit, denoted A and B. All cyclohexane rings
adopt a chair conformation. The dihedral angle between the best
plane through the thiourea moiety OCNCSN and the phenyl plane
measures 47.21(5)° and 45.06(5)° for molecules A and B of 1 and
30.72(4)° for 2. The molecular conformations of 1 and 2 are stabi-
lized by intra-molecular NAHꢁ ꢁ ꢁO hydrogen bonds forming six-
membered rings. On the other hand, molecules of 3 are strongly
Scheme 1. Synthesis of 1-(adamantane-1-carbonyl)-3-substituted thioureas.

154
A. Saeed et al. / Journal of Molecular Structure 1065-1066 (2014) 150–159
twisted with torsion angles SACx12ANx01ACx01 of 126.8(2)°
(x = 1 for A) and 130.6(2)° (x = 2 for B), respectively.
the intra-molecular NAHꢁ ꢁ ꢁO@C hydrogen bond. On the other
hand, the N(1)ACAN(2) bond angles found for compounds 1 and
2 [115.6(1)°] are lower than that of 3 [117.5(2)°], accounting for
the steric effects of the latter due to the di-substitution on the N(1).
It is worthy noticing that as is shown in Table 2, quantum
chemical calculations at the B3LYP/6-311++G** reproduce the geo-
metrical parameters in general good agreement with the experi-
mental data for each compound, as well as the tendencies found
when the three compounds are compared each other [44].
Additionally, all three crystal packings of 1, 2 and 3 show
NAHꢁ ꢁ ꢁS inter-molecular interactions that link molecules into
non-crystallographic centro-symmetric dimers with Hꢁ ꢁ ꢁS dis-
tances ranging from 2.55 to 2.77 Å and NAHꢁ ꢁ ꢁS angles 152° to
171°. The crystal packing pattern for 1 (Fig. 4) shows the inter-
molecular N102AHꢁ ꢁ ꢁS2 and N202AHꢁ ꢁ ꢁS1 bridges that link each
an A/B molecule pair forming non-crystallographic centro-sym-
These conformational differences observed between com-
pounds 1–2 and 3 are in agreement with the a recent article by
Becker and coworkers [35] where 739 structures containing the
AC(C@O)N(C@S)NA moiety found in the Cambridge Crystallo-
graphic Database were analyzed. As vastly documented for 1-ben-
zoyl-3-alkyl substituted thioureas, a local planar structure of the
central AC(O)ANHAC(S)ANHA moiety is preferred, with opposite
orientation between the C@O and C@S double bonds (‘‘S-shape’’).
In this conformation the C@O and HAN groups form a pseudo 6-
membered ring, favoring an intra-molecular interaction through
a hydrogen bond [36]. When the formation of suitable hydrogen
bond is prevented, as in 3,3-disubstituted derivatives, the anticlinal
geometry, with uSCCO ꢄ 120° is preferred [37]. This conformation is
also referred as ‘‘U-shape’’ and found for example in 1-furoyl-3,3-
disubstituted thioureas [38].
metric dimers which are stacked along [100]. For
2 the
The geometrical parameters of compounds 1–3 around the cen-
tral 1-acyl thiourea moiety derived from the X-ray analysis are
listed in Table 2, together with the values for close related adaman-
tane 1-carbonyl thiourea species, as determined previously [14].
Table 1 also contains the geometrical data available for related 1-
acyl 3,3-(methyl, phenyl) di-substituted thiourea [39], which is
structurally related with compound 3, and allows to compare the
effect of the 3,3-disubstitution on the nitrogen atom. Moreover,
the computed parameters for the compounds here studied are also
listed in Table 2. It has been reported that the B3LYP method with
moderate large basis sets (6-311++G**) predicts the bond length
around the thiourea group very well, including the C@S bond.
NAHꢁ ꢁ ꢁS(ꢂx + 1, ꢂy + 1, ꢂz) inter-molecular bonds link molecules
also to centro-symmetric dimers stacked along [010] (Fig. 5). Fi-
nally, for 3 (Fig. 6) the N102AHꢁ ꢁ ꢁS201(ꢂx + 0.5, y ꢂ 0.5, ꢂz + 0.5)
and N202AHꢁ ꢁ ꢁS101(ꢂx + 0.5, y + 0.5, ꢂz + 0.5) interactions result
in a similar A/B linking as for 1 but now stacked along [010]. It
is worthy to notice that NAHꢁ ꢁ ꢁS@C hydrogen bonds are commonly
encountered in 1-acyl-thioureas, probably due to the fact that
nearly planar molecular dimeric chain are formed through centro-
symmetric R22ð8Þ packing motif [45].
3.3. Vibrational analysis
The amidic-NAC(O) and thioamidic-like bond lengths (ca. 1.38
Taking into account the structural features determined for com-
pounds 1–3, it is interesting to analyze their infrared and Raman
spectra for determining how the inter- and intra-molecular inter-
actions affect the vibrational properties. Table 3 collects the infra-
red and Raman data measured for the three compounds here
studied. These results are analyzed with the help of quantum
chemical calculations at the B3LYP/6-311++G** level. The joint
analysis of both infrared and Raman spectroscopy have showed
to be appropriate for study the effect on the substitution for a ser-
ies of mono- and di-substituted thioureas [38]. Moreover, the anal-
ysis includes a tentative assignment of the main bands observed in
the spectra which is done by comparison with reported vibrational
data available in the literature for similar molecules [41,46–56].
As listed in Table 3, strong absorptions at 3321 and 3310 cmꢂ1
are found in the infrared spectra of compounds 1 and 2, respec-
0
and 1.34 ÅA, respectively) shows little deviation for the three com-
pounds here studied, being shorter than CAN single bond [40], as
expected from their partial double bond character [12]. On the
other hand, the N(1)AC(S) connecting both groups amounts
0
1.383(2) and 1.386(2) ÅA for compounds 1 and 2, respectively, and
0
it is slightly longer [1.398(3) ÅA] for compound 3. This observation
suggest that resonance interactions are favored in the case of 1
and 2 – probably facilitated by the planar AC(O)NHC(S)NHA group
[41,42]–, and disfavored in the case of the non-planar structure of 3.
The CAN(1)AC bond angle of compounds 1 and 2 [128.6(1) and
128.8°, respectively] are very similar to that determined for the
other 1-acyl-3-mono-substitued thioureas listed in Table 2 [43].
It should be noted that for compound 3 the value is significantly
lower 123.8(2)°. This difference is probably related with the fact
that the S conformation adopted by compounds 1 and 2 optimizes
tively, which can be associated with the
m(N(1)AH) stretching
Table 2
Experimental X-ray and calculated (B3LYP/6-311++G**) selected geometric parameters (Å and °) of the central 1-acyl-thioamide group for compounds 1–3. Available geometrical
parameters for related molecules are also given.
Parametera
1 Expl.b/calc.
2 Expl./calc.
3 Expl.b/calc.
Ref. [33]c
Ref. [14]d
Ref. [33]e
Ref. [39]f
C@O
C@S
1.222(2)/1.226
1.670(2)/1.668
1.387(2)/1.383
1.383(2)/1.409
1.340(2)/1.353
1.416(2)/1.407
121.2(2)/121.9
128.6(1)/130.7
115.6(1)/113.5
125.6(1)/132.1
125.2(1)/129.3
1.222(2)/1.226
1.671(1)/1.668
1.392(2)/1.385
1.386(2)/1.407
1.344(2)/1.355
1.412(2)/1.403
121.0(1)/121.9
128.8(1)/130.7
115.6(1)/113.4
128.1(1)/132.4
126.1(1)/129.5
1.216(2)/1.212
1.667(2)/1.674
1.383(2)/1.401
1.398(3)/1.408
1.347(2)/1.352
1.434(2)/1.442
121.7(2)/122.4
123.8(2)/125.8
117.5(2)/116.4
123.9(1)/122.8
123.1(1)/124.7
1.223(2)
1.664(2)
1.383(2)
1.390(2)
1.343(2)
1.407(2)
121.1(1)
128.4(2)
114.4(1)
128.0(2)
126.8(1)
1.211(2)
1.675(2)
1.377(3)
1.377(2)
1.325(3)
1.425(2)
120.8(2)
129.9(2)
117.7(2)
119.5(2)
124.7(1)
1.214(2)
1.658(2)
1.374(2)
1.388(2)
1.328(2)
1.418(2)
121.8(2)
128.4(1)
115.6(1)
123.6(1)
126.5(1)
1.221(2)
1.680(2)
1.387(2)
1.405(2)
1.343(2)
1.447(2)
122.8(1)
124.1(1)
117.3(1)
123.5(1)
123.2(1)
C(8)AN(2)
N(2)AC(S)
C(1)AN(1)
N(1)AC(Ph)
O@CAN(2)
(O)CAN(2)AC(S)
N(1)AC(1)AN(2)
C(1)AN(1)AC(Ph)
S@CAN(1)
a
b
c
d
e
f
For atom numbering see Figs. 1–3.
Mean values determined from crystallographically independent molecules.
1-(Adamantane-1-carbonyl)-3-(2,4-dichlorophenyl).
1-(Adamantan-1-ylcarbonyl)-3-(2,6-difluoro-4-hydroxyphenyl)thiourea.
1-(Adamantane-1-carbonyl)-3-(2-bromo-4,6-difluorophenyl)thiourea.
1-(3-Chlorobenzoyl)-3,3-(methyl-phenyl)thiourea.

A. Saeed et al. / Journal of Molecular Structure 1065-1066 (2014) 150–159
155
Fig. 4. Crystal packing of 1 viewed along a-axis with inter-molecular NAHꢁ ꢁ ꢁS pattern drawn as dotted lines. H-atoms not involved are omitted.
Fig. 5. Crystal packing of 2 viewed along b-axis with inter-molecular NAHꢁ ꢁ ꢁS pattern drawn as dotted lines. H-atoms not involved are omitted.
mode [33]. In effect, as predicted by the quantum chemical
calculations, the formation of the intra-molecular N(1)AHꢁ ꢁ ꢁO@C
hydrogen bond produces a red-shift and a strong intensification
central AC(O)NHC(S)NHA skeleton are expected to appear.
Singularly, the region of the (CO) stretching vibration is of main
interest for analyzing the presence of the intra-molecular hydrogen
bond [59]. As can be seen in Fig. 7, (CO) for 3 appears as strong
absorption at 1700 cmꢂ1 (1703 cmꢂ1 Raman), whereas 1 and 2
m
of the
amide
m
m
(N(1)AH) normal mode as compared with the other thio-
(N(2)AH) stretching [57]. However, as has been also
m
pointed out, the contribution of Fermi resonance effects with the
species show strong infrared absorptions at 1681 and 1686 cmꢂ1
,
m
(C@C) first overtone and (C@C) + d(NAH) combinations modes
m
with counterparts at 1679 and 1684 cmꢂ1 in the Raman spectra,
respectively. Quantum chemical calculations at the B3LYP/
6-311++G** level of approximation for the molecules isolated in a
cannot be rule out for explaining the strong intensity displayed
by this absorption [58]. As expected, this feature is absent in the
vibrational spectra of 3. Several other
m(CAH)arom and
m(CAH)adam
vacuum agree with this description, with computed
of 1650 and 1654 cmꢂ1 for 1 and 2, respectively, and 1693 cmꢂ1
for 3. Thus, it becomes clear that the (CO) red-shift of ca.
20 cmꢂ1 observed for 1 and 2 respect to compound 3, denotes
m(CO) values
stretching modes can be observed in the 2800–3200 cmꢂ1 region.
Fig. 7 shows the 1800–1300 cmꢂ1 region of the infrared and
Raman spectra of 1–3, where the most important modes for the
m

156
A. Saeed et al. / Journal of Molecular Structure 1065-1066 (2014) 150–159
Fig. 6. Crystal packing of 3 viewed along b-axis with inter-molecular NAHꢁ ꢁ ꢁS pattern drawn as dotted lines. H-atoms not involved are omitted.
the influence of the NAHꢁ ꢁ ꢁO@C intra-molecular hydrogen bond in
the former species.
corresponding band appears at 1376 cmꢂ1. It is plausible that both,
the donating electron nature of the methyl group and the reso-
nance effect between the nitrogen atom with the phenyl group
contribute to this higher frequency for compound 3. It should be
The region between 1500 and 1600 cmꢂ1, where the d(NAH)
deformation mode (thioamide band I) appears, could also serves
a signature for identify intra- and/or inter-molecular hydrogen
bonds [59]. The analysis of the infrared spectra (see Fig. 7) reveals
the presence of very strong and rather broad absorptions at around
1544 (1541 cmꢂ1 Raman) and 1547 cmꢂ1 (1550 cmꢂ1 Raman) for 1
and 2, respectively, which can be assigned to this normal mode
stressed, also, that contribution of the ms(NO2) symmetric stretch-
ing modes are also expected in this region for compounds 1 and 2.
Taking into account the vibrational properties reported for the
simple thiourea molecule [63], it is expected that the correspond-
ing symmetric motion of the CAN stretching modes at around
1150 cmꢂ1 [64,65]. Thus, following the quantum chemical calcula-
[60]. Contributions from m(C@C) stretching modes from the phenyl
ring cannot be excluded, as also suggested by quantum chemical
calculations (see the computed intensity values in Table 3). More-
over, a second superposed absorption can be determined at 1516
and 1508 cmꢂ1 for 1 and 2, respectively. Quantum chemical calcu-
tion description, the ms(NCN) symmetric stretching modes (usually
assigned as thioamide band III), are assigned to the 1153 (1146)
and 1150 (1143) cmꢂ1 intense absorptions found in the infrared
spectra of 1 and 2 and to the 1176 cmꢂ1 (1171 cmꢂ1) band for 3
(Raman values are given in parentheses). Again, a slightly higher
frequency value is observed for compound 3, probably associated
with electronic contributions from the 3,3-methyl-phenyl substit-
uents through inductive and resonance interactions.
lations suggest that these modes are due to the mas(NO2) stretching.
As expected, this last mode is absent in the molecule 3. It is obvious
that the thioamide band I is not expected to occurs for 3,3-substi-
tuted thioureas, thus the intense band at 1598 cmꢂ1 in the Raman
spectrum of compound 3 is assigned with confidence to
stretching modes, in agreement with previous studies [61].
m
(C@C)
The adamantyl group is responsible for the very strong band
observed in the Raman spectrum at 766, 771 and 769 cmꢂ1 for
1–3, respectively, which can be assigned with confidence to the
‘‘breathing mode’’, in agreement with the Raman spectra observed
for adamantane isotopomers [66].
The second d(NAH) fundamental, associated with the
AC@SANAHA moiety, appears at lower wavenumbers, also as in-
tense absorptions at 1451 (1440), 1448 (1437) and 1453 (1457)
cmꢂ1 for 1, 2 and 3, respectively (Raman shift in parenthesis).
These values are in agreement with the previously reported data
for related species [38,62].
For the parent the thiourea molecule, the
m(C@S) stretching
mode is reported at 1094 cmꢂ1 in the infrared spectrum
(1105 cmꢂ1 Raman) [63]. However, as has already been pointed
out [62], lower values were found for this mode (also named as
the thioamide band IV) in substituted thiourea derivatives, typi-
cally in the 600–800 cmꢂ1 range [3,38,61,67]. This strong variation
The thioamide band II, mainly associated with the
mas(NCN)
antisymmetric stretching, is expected to occurs as a strong absorp-
tion around 1350 cmꢂ1. Reguera et al. [38] showed that this mode
is sensitive to the substitution, 3,3-disubstitued thioureas appear-
ing at higher wavenumbers (up to 1395 cmꢂ1) than that of the
3-monosubstituted ones, below 1350 cmꢂ1. In agreement with this
trend, the absorptions at 1350 cmꢂ1 observed in the infrared
spectra of 1 and 2 are assigned to this mode, whereas for 3, the
is an indication that the frequency of the m(C@S) stretching mode is
very sensitive to the presence of inter-molecular interactions
involving the C@S group [46]. Moreover, it is expected that the
polarizability of the C@S bond originates an intense Raman disper-
sion [68]. Based on these considerations, we tentatively assigned

A. Saeed et al. / Journal of Molecular Structure 1065-1066 (2014) 150–159
157
Table 3
FTIR and FT-Raman experimental data (in cmꢂ1) for compounds 1–3, together with the computed B3LYP/6-311++G** values and tentative normal mode assignment.
1
2
3
Tentative
assignmentc
FTIRa
Ramana
Calculatedb
FTIRa
Ramana
Calculatedb
FTIRa
Ramana
Calculatedb
3459 (7.4)
3463 (8.1)
3187 (84.2)
3115 (5.3)
3077 (6.2)
2954 (10.0)
2955 (7.1)
3467 (6.4)
3178 (67.2)
3111 (1.5)
2931 (17.8)
2929 (5.0)
m
m
m
(N(2)AH)
(N(1)AH)
(CAH)arom
3321 s
3310 m
2927 sh
2909 m
3111 m
3093 m
2930 w
2908 w
3082 vw
2951
vw,sh
2921 s
2896 w,sh
2852 m
3160 br
3075 w
2926 sh
2906 m
3065 (2.3)
3058 (4.3)
3048 (5.8)
3096 vw
2923 vs
2909 s,sh
3077 w
2948 w,sh
2915 s
2894 w,sh
2853 m
2853 s
2930 (23.5)
2929 (7.3)
2849 m
2916 (9.9)
2913 (14.1)
2848 m
2849 m
2957 (6.9)
2933 (12.7)
2929 (6.3)
2927 (28.1)
2908 (26.8)
1693 (46.4)
1572 (2.6)
m
(CAH)adam
1681 m
1679 m
1616 m
1650 (26.1)
1584 (86.6)
1686 m
1605 m
1684 w
1654 (16.8)
1592 (46.0)
1572 (21.4)
1557 (93.2)
1504 (28.5)
1700 s
1596 w
1703 m
1598 s
m
m
C@O
C@C
1593 sh
1544 br
1592 s
1541 m,br
1542 (100)
1524 (50.2)
1601 s
1550 m,br
m
C@C
1547 s
d(NAH)
Thioamide band I
1516, s
1522 w
1482 (86.4)
1508 vs br
1515 m
1493 m
1481 (62.9)
1464 (17.6)
m
asNO2/mC@C
1508 vs br
1509, vvw
m
C@C
1521 m, br
1457 w
1446 vw 1436 m
1451 m
1350 s
1440 s
1451 (14.1)
1326 (12.3)
1448 s, sh
1350 m
1437 m
1347 vs
1456 (2.7)
1453 m
1435 s
1482 (100)
1462 (5.0)
1403 (32.1)
1333 (88.3)
d(NAH)
ds(CH3)
1351 vs
1308 (23.9)
1376 vs
1376 m
m
as(NCN)
Thioamide band II
s(NO2)
d(CAH)adam
1319 m, br
1286 m
1318 w
1286 vvw
1312 (89.3)
1297 (27.5)
1284 (40.5)
1256 (4.5)
1344 m
1321 m
1299 s
1258 m
1333 sh
1300 m
1256 m
1292 (45.5)
1280 (100)
1278 (42.3)
1224 (13.2)
m
1320 w
1296 w
1282 m
1266 m
1224 s
1184 s
1321 vw
1298 w
1277 w
1257 w
1224 w
1184 m
1286 (2.3)
1270 (4.8)
1246 (30.1)
1236 (5.6)
1177 (19.1)
1146 (26.0)
1255 m
1215 m
1255 s
1213 w
1189 w
1178 w
1146 m
1216 (8.7)
1211 m
1184 w
1176 w
1150 m
1210 w
1187 m,br
1178 (4.5)
1158 (4.6)
1147 (11.4)
1111 (34.1)
mas(NC)arom
d(CAH)adam
d(CAH)adam
1179 w
1153 vs
1144 (10.1)
1109 (50.8)
1143 vw
1176 m
1171 w
1138 (27.3)
m
s(NCN)
Thioamide band III
(NACH3)
das(CH3)
1118 s
1106 s, br
1120 vw
1104 m, br
1093 (20.6)
1091 (13.5)
1078 (7.5)
1053 (1.8)
1026 (8.2)
1003 (2.0)
978 (0.8)
m
1099 m, br
1102 m, br
1056 (12.6)
1101 w
1077 (22.6)
1076 w
1060 m
1025 m
1005 w
1058 vw
m
(CAC)adam
1061 m
1045 w,br
1001 vw
976 w
936 w
914 w
1062 vw
1045 vvw
1002 s
979 m
939 w
914 w
1036 (2.0)
1010 (1.6)
973 (1.0)
957 (2.0)
907 (1.9)
889 (1.4)
845 (7.1)
1062 m
977 w
1061 vw
1014 vw
1036 (2.8)
951 (2.5)
1025 m
1006 s
d(CAH)adam
977 vw
939
vw,br
897 m
974 w
938 w
921 m
871 w
977 m
937 w
922 w
870 m
950 (2.1)
942 (1.2)
897 (2.5)
846 (0.8)
952 w
896 w
946 (0.7)
871 (2.4)
m
m
(CAC)adam
889 m
889 m
(C@S) Thioamide
band IV
869 m
809 m
867 w
811 m
803 (11.7)
784 (3.6)
860 m
852 s
813 vw
859 m
814 w
835 (10.1)
837 (8.3)
821 (3.1)
784 (0.7)
777 (0.4)
837 vw
800 s
800 vw
814 (0.6)
776 (3.6)
751 (3.9)
q(CAH)adam
774 w
766 s
748 (1.4)
773 w, br
771 m
763 s
769 vs
Breathing
s(CAC)adam
(CAH)arom
(CAC)adam
m
746 m
736 m
753 vw
738 vw
727 (1.4)
706 (3.8)
756 w
739 m
721 w
695 w
678 w
665 w
627 w
613 m
567 vw
493 w
434 w
741 (0.8)
723 (3.3)
701 (0.7)
669 (1.6)
647 (1.6)
638 (0.4)
613 (0.7)
610 (5.1)
549 (1.0)
480 (1.8)
q
738 w
725 w
708 m
698 s
670 m
647 sh
621 w
591 w
707 vw
704 (1.0)
691 (5.1)
679 (8.2)
625 (7.1)
607 (0.8)
596 (6.6)
571 (1.3)
m
720 w,br
693 vw
677 sh
668 m,br
629 w
615 m
569 vw
493 vw
690 m
673 m
664 m
642 w, sh
607 m
690 m
674 w
663 w
640 w
611 m, br
566 vw
520 vw
482 vw
444 w
421 vw
405 vw
381 vw
331 w
663 (5.7)
653 (2.6)
633 (0.6)
628 (0.4)
613 (7.7)
523 (0.8)
503 (6.3)
479
445
421
410
380
671 s
645 vw
q(CAH)arom
623 m
593 vw
d(CAC)arom
567 vw
524 m
dNO2
d(CAC)adam
547 m
489 vw
548 w
488 vw
441 vw
335 w
320 m
535 (6.4)
485 (0.5)
453 (0.6)
336
413 w
430
d(NC@O)
d(CNC)
d(NC@S)
d(CAC)adam
d(CAC)adam
308
382 w
325 w
381
341
336
268
271 m
(continued on next page)

158
A. Saeed et al. / Journal of Molecular Structure 1065-1066 (2014) 150–159
Table 3 (continued)
1
2
3
Tentative
assignmentc
FTIRa
Ramana
Calculatedb
FTIRa
Ramana
203 vw
Calculatedb
206
FTIRa
Ramana
Calculatedb
247 w
223 w
202 w,sh
190 vw
146 m
127 s
241
218
196
180
169
126
296 w
250 vw
215 m
170 w
d(CAC)adam
s
s
s
s
s
a
Solid samples as KBr pellets (FTIR), and powders (Raman). Band intensities and shape: vs = very strong; s = strong; m = medium; w = weak; vw = very weak, sh: shoulder,
br: broad.
b
Scaled computed frequency and intensity values at the B3LYP/6-311++G** level of approximation. In parentheses relative band strengths, IR relative intensities
[100% ꢅ 494, 674 and 392 km/mol for compounds 1, 2 and 3, respectively]. The computed Raman spectra are given as Supplementary material in Fig. S2.
c
m
: Stretching (subscripts s and as refer to symmetric and antisymmetric modes, respectively), d: deformation, oop: out of plane deformation modes, q: rocking mode, s:
torsional mode.
4. Conclusion
Structural properties of three novel 1-(adamantane-1-carbonyl)
thiourea derivatives (1–3) were determined by using single crystal
X-ray diffraction analysis. The X-ray molecular structure is similar
for compounds 1 and 2, with the central AC(O)NHC(S)NHA moiety
adopting a nearly planar structure with the C@O and C@S double
bond oriented toward opposite directions (‘‘S-shape’’). This confor-
mation is favored by a strong C@Oꢁ ꢁ ꢁHAN intra-molecular hydro-
gen bond forming a (pseudo)six-membered ring. This structural
motif is not present in compound 3 because the di-substitution
prevents the formation of intra-molecular hydrogen bond. For
compound 3 the non-planar ‘‘U-shape’’ conformation is adopted.
The effects on the vibrational properties have been analyzed by
using infrared and Raman spectroscopies. A clear m(CO) red-shift
of ca. 20 cmꢂ1 observed for 1 and 2 respect to compound 3, denot-
ing the influence of the NAHꢁ ꢁ ꢁO@C intra-molecular hydrogen
bond. The characteristic thioamide band II [mas(NCN)] and thioam-
ide band III [ms(NCN)] showed a small but clear shift toward higher
frequencies for compound 3, indicating the electronic effects
exerted by the methyl (inductive) and phenyl (resonance)
substitutions.
Acknowledgments
MFE is member of the Carrera del Investigador of CONICET
(República Argentina). The Argentinean author thanks to the Cons-
ejo Nacional de Investigaciones Científicas y Técnicas (CONICET),
the ANPCYT and to the Facultad de Ciencias Exactas, Universidad
Nacional de La Plata for financial support.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molstruc.
2014.03.002.
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