Hydrogen-bonding network in the crystal of 1-(diaminomethylene)thiouron-1-ium picrate

Article abstract of DOI:10.1016/j.molstruc.2010.04.015

The single crystals of 1-(diaminomethylene)thiouron-1-ium picrate were grown using a solution growth technique. The compound crystallises in the centrosymmetric C2/c space group of the monoclinic system. The conformation of the 1-(diaminomethylene)thiouron-1-ium cation is almost planar, while the conformation of the picrate(-) anion is non-planar. Both NO₂ groups linked in ortho positions in relation to the phenolate oxygen are oppositely turned in relation to the ring plane. Arrangement of the oppositely charged components, i.e. 1-(diaminomethylene)thiouron-1-ium cations and picrate(-) anions in the crystal is mainly determined by ionic and hydrogen bonding interactions forming pseudo-one dimensional chains. The compound was also characterised by the FT-IR and Raman spectroscopy. The characteristic bands of the NH₂, NO₂, C{double bond, long}S and C_ar{single bond}O groups as well as of skeletal groups are discussed.

Full text of DOI:10.1016/j.molstruc.2010.04.015

Journal of Molecular Structure 975 (2010) 166–172
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Hydrogen-bonding network in the crystal of
1-(diaminomethylene)thiouron-1-ium picrate
b
Jan Janczak a, , Genivaldo Julio Perpétuo
*
a Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50950 Wrocław, Poland
b Departamento de Física, Instituto de Ciências Exatas e Biológicas, Universidade Federal de Ouro Preto, 35400-000 Ouro Preto, MG, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
The single crystals of 1-(diaminomethylene)thiouron-1-ium picrate were grown using a solution growth
technique. The compound crystallises in the centrosymmetric C2/c space group of the monoclinic system.
The conformation of the 1-(diaminomethylene)thiouron-1-ium cation is almost planar, while the confor-
mation of the picrate(À) anion is non-planar. Both NO2 groups linked in ortho positions in relation to the
phenolate oxygen are oppositely turned in relation to the ring plane. Arrangement of the oppositely
charged components, i.e. 1-(diaminomethylene)thiouron-1-ium cations and picrate(À) anions in the
crystal is mainly determined by ionic and hydrogen bonding interactions forming pseudo-one dimen-
sional chains. The compound was also characterised by the FT-IR and Raman spectroscopy. The charac-
teristic bands of the NH2, NO2, C@S and CarAO groups as well as of skeletal groups are discussed.
Ó 2010 Elsevier B.V. All rights reserved.
Received 25 February 2010
Received in revised form 10 April 2010
Accepted 12 April 2010
Available online 24 April 2010
Keywords:
1-(Diaminomethylene)thiouron-1-ium
picrate
Crystal structure
Hydrogen bonds
Vibrational spectroscopy
1. Introduction
[10–12]. Besides the known Pt and Pd complexes with these tau-
tomers, the 2-imino-4-thiobiuret or 1-(diaminomethylene)thio-
Strong OAHÁ Á ÁY and NAHÁ Á ÁY (Y = O, N) hydrogen bonds play an
important role in molecular recognition and self-organisation in
crystal engineering and biology [1–3]. On the other hand, much
weaker interactions like CAHÁ Á ÁY (Y = O, N) hydrogen bonds as well
urea can form salts, since they contain the N atom with lone
pair of electrons that can accept the H atom, forming positively
charged cations [13–17].
Picric acid (2,4,6-trinitrophenol) is an organic acid, which is
used, in the dyeing industry and as an explosive. The presence of
as the interactions between the
p-clouds of aromatic rings have
been recently recognized as equally important factors determining
the organisation of molecules in crystals and have found a broad
application in the crystal engineering for the design of new func-
tional materials [4–8].
The commercially available crystalline product described as 2-
imino-4-thiobiuret (amidinothiourea) by Aldrich (CAS No. 2114-
02-5) is in fact the tautomeric form of 1-(diaminomethylene)thio-
urea (Scheme 1), as has been identified by X-ray single crystal anal-
ysis [9]. Both tautomers are potentially interesting compounds that
can be used in the crystal engineering to built up extended frame-
works, since they contain complementary arrays of hydrogen
bonding sites.
three electron withdrawing nitro groups makes it as a good p-
acceptor for neutral carrier donor molecule [18–20]. In addition,
picric acid is used at human theraphy (treatment of burns, anisep-
tic and astringent agent) [21]. Several complexes or salts of the pic-
ric acid with organic molecules exhibit non-linear optical
applications [22].
In the present work, we investigate the crystal structure of 1-
(diaminomethylene)thiouron-1-ium picrate by the X-ray diffrac-
tion. The compound was also characterized by vibrational (FT-IR
and Raman) spectroscopy, and the results are discussed in compar-
ison with the data obtained for the neutral molecule of 1-
(diaminomethylene)thiourea.
Additionally, both tautomers possess several potential coordi-
nation modes, since they can act as N,N- or N,S-coordinating li-
gands and can form several different types of complexes with
metal ions. The coordination of the metals by these tautomers
is feasible with both neutral and deprotonated (anionic) forms
2. Experimental
All materials were commercially available and used as received.
The Fourier transform infrared spectra were recorded from Nujol
mulls between 400 and 4000 cmÀ1 on a Bruker IFS 113V FTIR spec-
trometer at room temperature. Elemental analyses were carried
out with a Perkin-Elmer 240 elemental analyzer.
* Corresponding author.
E-mail address: j.janczak@int.pan.wroc.pl (J. Janczak).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.04.015

J. Janczak, G.J. Perpétuo / Journal of Molecular Structure 975 (2010) 166–172
167
Table 1
H
N
H
N
H
N
H
N
H
N
Crystallographic data for 1-(diaminomethylene)thiouron-1-ium picrate.
N
Empirical formula
C8H9N7O7S
347.28
Formula weight (g molÀ1
)
H
H
H
H
Crystal system, space group
Monoclinic, C2/c (No. 15)
12.698(2)
10.184(2)
21.354(4)
101.03(1)
2710.4(9)
8
1.702/1.70
0.293
1424
N
N
S
S
a (Å)
b (Å)
c (Å)
b (°)
V (Å3)
Z
H
H
H
(I)
(II)
Scheme 1.
Dcalc/Dobs (g cmÀ3
(mmÀ1
F(000)
)
l
)
2.1. Preparation of 1-(diaminomethylene)thiouron-1-ium picrate
Crystal size (mm)
Radiation type, wavelength, k (Å)
Temperature (K)
h range (°)
Absorption correction
0.38 Â 0.26 Â 0.20
Mo Ka, 0.71073
Commercially available 2-imino-4-thiobiuret (amidinothiourea,
Aldrich, CAS No. 2114-02-5), which is in fact the tautomeric form
1-(diaminomethylene)thiourea and picric acid (Aldrich, purity of
99%) were added to hot water in a molar proportion of 1:1. When
the solution became homogenous it was cooled slowly and kept at
room temperature. After several days, transparent yellowish crys-
tals were formed. Anal. Calculated for C8H9N7O7S: C, 27.67; H, 2.60;
N, 28.24, O, 32.27 and S, 9.22%. Found: C. 27.54; H, 2.57; N, 28.32;
O, 32.33 and S, 9.24%.
295(2)
3.04 Ä 28.95
Numerical, CrysAlis Red [23]
Tmin/Tmax
0.8997/0.9476
15,262/3364/2350
0.0231
Reflections collected/unique/observed
Rint
Refinement on
F2
0.0361
0.0988
1.004
R[F2 > 2
r
(F2)]
wR (F2 all reflections)
Goodness-of-fit, S
D
qmax
,
D
qmin (e ÅÀ3
)
+0.176, À0.269
[w(F2o À F2c )2]/
R = r
wF4o} ; wÀ1 2(F2o ) + (0.0577P)2 where P = (Fo2 + 2F2c )/3.
½
wR = {
R
2.2. X-ray data collection
X-ray intensity data for the crystal were collected using graph-
ite monochromatic Mo K
KUMA KM-4 diffractometer with a two-dimensional area CCD
detector. The -scan technique with = 1.0° for each image
a radiation on a four-circle j geometry
3. Results and discussion
x
Dx
Good quality single crystals of 1-(diaminomethylene)thiouron-
1-ium picrate suitable for the X-ray single crystal analysis were ob-
tained from water solution at room temperature. Fig. 1 shows the
molecular structure of the title compound. The X-ray single crystal
analysis revealed that the proton of the hydroxyl group of picric
acid is transferred to the N1 atom of 1-(diaminomethylene)thio-
urea forming the 1-(diaminomethylene)thiouron-1-ium cation.
These oppositely charged units interact via NAHÁ Á ÁO hydrogen
bonds forming the cation–anion complex (Fig. 1).
was used for data collection. The 760 images for six different runs
covering over 95% of the Ewald sphere were performed. The unit
cell parameters were refined by the least-squares methods on the
basis of 1826 reflections. One image was used as a standard after
every 40 images for monitoring the crystal stability and data col-
lection, and no correction on the relative intensity variations was
necessary. 15,262 reflections (3364 independent, Rint = 0.0231)
were measured up to 57.90° in 2h. Data collections were made
using the CrysAlis CCD program [23]. Integration, scaling of the
reflections, correction for Lorenz and polarisation effects and
absorption corrections were performed using the CrysAlis Red
program [23]. The structure was solved by the direct methods
using SHELXS-97 and refined using SHELXL-97 programs [24].
The hydrogen atoms joined to aromatic ring were located in their
geometrical positions and refined as riding model with the Ui-
so = 1.2Ueq of the C atoms joining H, the other H atoms were lo-
cated from difference Fourier maps and were refined. The final
difference Fourier map showed no peaks of chemical significance.
The 1-(diaminomethylene)thiouron-1-ium cation is almost pla-
nar (Table 2). This is in contrast to the neutral molecule of 1-
(diaminomethylene)thiourea in the crystal [9], where it is non-pla-
nar; both arms are turned in opposite directions around the CAN
bonds involving the central N1 atom. Thus, in the crystal the con-
formation of the neutral 1-(diaminomethylene)thiourea is twisted
(22.2(1)°), in contrast to the conformation of the 1-(diaminometh-
ylene)thiouron-1-ium cation in the present structure, which is al-
most planar. A similar non-planar conformation of the cation as
for neutral 1-(diaminomethylene)thiourea molecule is observed
in all known crystal structure of the 1-(diaminomethylene)thiou-
ron-1-ium salts: chloride, bromide and iodide [13], perchlorate,
hydrogen sulfate, dihydrogen phosphate and dihydrogen arsenate
[14], nitrate and phosphite [15]. The C1AS1 bond in the cation is
longer by ꢀ0.05 Å than the typical double bond as observed in
the thioformaldehyde CH2C@S (1.6108(9) Å) [29], which repre-
sents 100% double-bond character, and is shorter than the value
of ꢀ1.74 Å as observed in the thiolate anions that represents 50%
double-bond character [30]. Thus the bond order of the C1AS1 is
intermediate between 2 and 1.5. Three CANH2 bond distances
are in the range 1.309(2) Ä 1.321(2) Å, are thus shorter than the
typical single bond C(sp2)ANH2 of 1.341 Ä 1.363 Å [31]. The CAN
bond lengths involving the central N1 atom are significantly longer
than the three CAN bonds linking the amine groups (Table 2). The
C1AN1AC2 angle of 129.73(12)° is higher than an expected value
of sp2 hybridization due to the steric hindrance of S and NH2 group.
The planarity of the amine groups indicates the sp2 hybridization
of the orbitals on the amine nitrogen atoms with the lone pair of
The largest peaks on the final
Dq map were +0.176 and
À0.269 eÅÀ3. Details of the data collection parameters, crystallo-
graphic data and final agreement parameters are collected in
Table 1. Visualisation of the structure was made with the Dia-
mond 3.0 program [25]. The geometrical parameters are collected
in Table 2.
2.3. Quantum calculations
Ab initio molecular orbital calculations full geometry optimiza-
tion were performed with the Gaussian98 program package [26].
All calculations were performed by the density functional three-
parameter hybrid (B3LYP) methods [27,28] with the 6 – 31 + G* ba-
sis set starting from the X-ray geometry. As convergence criterions
the threshold limits of 0.00025 and 0.0012 a.u. were applied for the
maximum force and the displacement, respectively. The geometri-
cal parameters of the MO-claculated structure are contained in
Table 2.

168
J. Janczak, G.J. Perpétuo / Journal of Molecular Structure 975 (2010) 166–172
Table 2
S1
H4
Bond lengths (Å) and angles (°) for 1-(diaminomethylene)thiouron-1-ium picrate.
N3
1-(diaminomethylene)thiouron-1-ium cation
X-ray
ab initio
H5
S1AC1
C1AN2
C1AN1
N1AC2
C2AN4
C2AN3
N2AC1AN1
N2AC1AS1
N1AC1AS1
C2AN1AC1
N4AC2AN3
N4AC2AN1
N3AC2AN1
S1AC1AN1AC2
N3AC2AN1AC1
1.6640(15)
1.321(2)
1.662
1.348
1.421
1.368
1.343
1.319
111.4
122.9
125.7
129.9
121.3
117.0
121.8
À9.9
C1
1.3837(18)
1.3720(18)
1.3087(19)
1.3096(18)
112.87(13)
121.21(12)
125.91(11)
129.73(12)
122.36(14)
115.80(13)
121.84(14)
0. 9(2)
N1
H3
N2
H2
C2
N4
H7
H6
H1
C7
O1
C3
O72
N7
O51
N5
O52
À0.6(2)
6.1
picrate(À) anion
C3AC4
C4AC5
C5AC6
C6AC7
C7AC8
C3AC8
O1AC3
C4AN5
C6AN6
C8AN7
N5AO51
N5AO52
N6AO62
N6AO61
N7AO71
N7AO72
O1AC3AC8
O1AC3AC4
C8AC3AC4
C5AC4AN5
C5AC4AC3
N5AC4AC3
C4AC5AC6
C5AC6AC7
C5AC6AN6
C7AC6AN6
C8AC7AC6
C7AC8AC3
C7AC8AN7
C3AC8AN7
O51AN5AO52
O51AN5AC4
O52AN5AC4
O62AN6AO61
O62AN6AC6
O61AN6AC6
O71AN7AO72
O71AN7AC8
O72AN7AC8
C3AC4AN5AO51
C3AC8AN7AO72
O71
1.4523(19)
1.3678(18)
1.3810(19)
1.3855(18)
1.3734(18)
1.4461(18)
1.2446(16)
1.4514(17)
1.4427(16)
1.4476(18)
1.2251(17)
1.2257(17)
1.2231(16)
1.2256(15)
1.2259(16)
1.2267(16)
124.84(13)
123.78(12)
111.38(12)
116.07(12)
124.91(12)
119.01(12)
118.71(12)
121.32(12)
119.63(12)
119.05(12)
119.15(12)
124.33(12)
115.85(12)
119.82(12)
122.61(13)
118.94(13)
118.43(13)
122.64(12)
118.68(12)
118.68(12)
122.82(13)
118.65(12)
118.51(12)
36.5(2)
1.475
1.378
1.406
1.406
1.378
1.475
1.257
1.449
1.426
1.449
1.265
1.282
1.282
1.282
1.282
1.265
124.0
124.0
112.0
116.3
123.9
119.8
119.9
120.3
119.9
119.8
119.9
123.9
116.3
119.8
122.5
119.5
118.0
121.9
119.0
119.0
122.5
118.0
119.5
35.0
C8
H71
C4
C5
H51
C6
O62
O61
N6
Fig. 1. A view of 1-(diaminomethylene)thiouron-1-ium picrate showing displace-
ment ellipsoids at the 50% probability level and H atoms as a sphere of arbitrary
radii. Dashed lines represent the hydrogen bonds.
the twisted conformation of the cation (Table 2). Thus the interac-
tions with the picrate counter-ion with the formation of NAHÁ Á ÁO
hydrogen bonds make the 1-(diaminomethylene)thiouron-1-ium
cation almost planar.
The asymmetric unit 1-(diaminomethylene)thiouron-1-ium
picrate contains the 1-(diaminoethylene)thiouron-1-ium cation
and the picrate anion where the hydroxyl group is deprotonated.
Deprotonation of the hydroxyl group in picrate anion results in
the shortening of the C3AO1 bond (1.2446(18) Å) close to the value
of the double C@O bond (1.214–1.224 Å) [31], as well as in the
opposite rotation of both NO2 groups attached in orto positions
in relation to the carbon atom linking the deprotonated hydroxyl
group, due to the repulsive interaction between the negative polar-
ized NO2 groups and the negative charged oxygen (O1). The torsion
O51AN5AC4AC3 and O72AN7AC8AC3 angles describing the ori-
entation of the NO2 groups in relation to the plane of the ring are
36.5(2)° and 29.9(2)°, respectively. Thus the conformation of the
picrate anion is non-planar and plays a pivotal role in hydrogen
bonding with the 1-(diaminomethylene)thiouron-1-ium cation
29.9(2)
34.9
Table 3
Hydrogen-bond geometry (Å, °).
electrons on the p orbital that is perpendicular to the plane of the
NH2 groups. Additionally, the p orbitals of the C, S and N atoms
DAHÁ Á ÁA
DAH
HÁ Á ÁA
DÁ Á ÁA
DAHÁ Á ÁA
forming the
also perpendicular to the plane, therefore the partial delocalisation
of the -bonds over the CANH2 bonds linking the amine groups,
p bond of the C1AS1 and C2AN1 double bonds, are
N1AH1Á Á ÁO1
0.91(2)
0.84(2)
0.89(2)
0.89(2)
0.91(2)
0.86(2)
0.86(2)
0.92(2)
0.92(2)
0.78(2)
1.93(2)
2.08(2)
2.43(2)
2.59(2)
2.26(2)
2.42(2)
2.47(2)
1.94(2)
2.35(2)
2.25(2)
2.793(2)
2.909(2)
3.149(2)
3.366(2)
2.978(2)
3.084(2)
3.198(2)
2.771(2)
3.024(2)
3.032(2)
157.3(14)
172.3(19)
138.0(16)
145.9(16)
135.6(15)
134.9(15)
142.6(16)
148.4(15)
129.6(14)
176.6(18)
N2AH2Á Á ÁO72
N2AH3Á Á ÁO71i
N2AH3Á Á ÁO62ii
N3AH4Á Á ÁS1
p
due to symmetry of the p orbitals, is possible. Therefore, the double
C1@S1 and C2@N1 bonds are longer and the other single CAN
bonds linking the amine groups shorter than the typical values of
the double C@S and C@N bonds or single CAN bond [32]. A similar
correlation between the bond lengths and angles is observed in the
gas phase, as predicted for an isolated 1-(diaminomethylene)thi-
ouron-1-ium cation by the density functional theory [13], however
the molecular orbital calculation, in contrast to the crystal, results
N3AH5Á Á ÁO61iii
N3AH5Á Á ÁO52iv
N4AH6Á Á ÁO1
N4AH6Á Á ÁO51
N4AH7Á Á ÁO51iv
Symmetry code: i = Àx + ½, Ày À ½, Àz + 1; ii = x, Ày, z + ½; iii = x À ½, Ày + ½,
z + ½; i
= Àx, Ày + 1, Àz + 1.
v

J. Janczak, G.J. Perpétuo / Journal of Molecular Structure 975 (2010) 166–172
169
and leads to the formation of intermediate NAHÁ Á ÁO hydrogen
bonds (Table 3). The conformation of the picrate anion is different
from the conformation of the picric acid, in which one of two NO2
groups in orto position is coplanar with the ring due to the forma-
tion of intramolecular hydrogen bond with the hydroxyl group
[33]. The third NO2 group joined in para position in relation to
the hydroxyl or deprotonated hydroxyl group is coplanar with
the ring in both neutral picric acid molecule and deprotonated pic-
rate(À) anion. The orientation of this NO2 group is stabilised by the
intramolecular interaction with the H atoms (O61Á Á ÁH71 and
O62Á Á ÁH51). The CAC bonds involving the C atom linking the
deprotonated hydroxyl group are significantly longer than the
remaining four CAC bonds within the ring (Table 2). The repulsive
interactions of the deprotonated oxygen atom O1 with the electron
withdraw NO2 groups attached in the ortho positions in relation to
the O1 are responsible for the lengthening of the C3AC4 and
C3AC8 bonds as well as for the significant differences between
the internal CACAC angles within the ring. Both CACAC angles
joining the NO2 groups (C3AC4AC5 and C3AC8AC7) are signifi-
cantly greater and the C4AC3AC8 angle joining the deprotonated
hydroxyl group is significantly smaller than the expected angle
for C sp2 hybridization (Table 2). The partially double in character
of C'O bond linked the phenolic oxygen as well as the relatively
long C3AC4 and C3AC8 bonds can be explained by the resonance
structures presented in Scheme 2.
Ab-initio full-optimised molecular orbital calculation per-
formed for an isolated picrate anion shows similar correlation be-
tween the bond lengths and distances as found in the crystal (Table
2). However, the small differences between the X-ray and MO cal-
culated values are noticeable but understable if we take into ac-
count the interactions with oppositely charged partner in the
crystal. The ab initio MO calculations confirm the non-planar con-
formation of picrate anion observed in the crystal. In the gas phase
structure the NO2 groups attached to the ring in ortho position in
relations to deprotonated O1 atom are turned around the C4AN7
and C8AN7 bonds by ꢀ35.0°. The deprotonation of the hydroxyl
group (O1) increases the steric effect of the lone electron pairs at
O1 and causes the rotation of the ortho NO2 group. The steric effect
of the lone pair of electrons at the O1 atom makes the internal
C4AC3AC8 angle significantly smaller than 120° and both
O1AC3AC4 and O1AC3AC8 angles greater than 120° and is in
agreement with the valence shell electron pair repulsion model
(VSEPR), according to which the lone-pair of electrons occupies a
wider region as the bonding pair [34]. In addition, the steric effect
of the lone pair of electrons at O1 together with the interaction the
negatively polarized NO2 groups are responsible for the angle dis-
tortions within the ring from 120° as expected for
hybridization.
C
sp2
The oppositely charged units, i.e. 1-(diaminomethylene)thiou-
ron-1-ium cation and picrate anion interact via NAHÁ Á ÁO hydrogen
bonds forming hydrogen bonded cation–anion complex. These
cation–anion complexes related by an inversion interact via addi-
tional NAHÁ Á ÁO hydrogen bonds forming pseudo-one dimensional
hydrogen bonded polymer (Fig. 2). In the crystal, the hydrogen-
bonded polymers are located almost parallel to the (212) and (2-
12) planes forming layers parallel to the (0 0 1) crystallographic
plane (Fig. 3). Within one layer the almost planar 1D-polymers
interact via
of picrate anions and the planar 1-(diaminomethylene)thiouron-
1-ium cations in which the electrons of the double C1AS1 and
p–p clouds between the aromatic six-membered ring
p
C2AN1 bonds are delocalized over the whole cation. The distance
between the ring of picrate anion and the mean plane of the 1-
(diaminomethylene)thiouron-1-ium cation are 3.56 Å indicating
on the weak
structure.
p–p interactions that stabilise the three dimensional
The FT-IR and Raman spectra of the 1-(diaminomethylene)thiou-
ron-1-ium picrate are show in Figs. 4 and 5, respectively. Bands cor-
responding to vibration of the functional groups were identified
with the aid of infrared correlation charts [35,36]. In addition the
spectra were compared with the spectra of 1-(diaminomethyl-
ene)thiourea and picric acid that are also illustrated in Figs. 4 and
5. The title compound has several functional and skeletal groups
_
O
O
O
O
O2N
NO2 O2N
NO2 O2N
NO2
O2N
NO2
-
-
-
NO2
NO2
NO2
NO2
(a)
(b)
(c)
(d)
Scheme 2.
O52
O71
O72
O1
O51
H6
H2
H3
H1 N4
N1
H7
H5
N2
N3
Fig. 2. Pseudo-one dimensional hydrogen bonded chain of 1-(diaminomethylene)thiouron-1-ium picrate.

170
J. Janczak, G.J. Perpétuo / Journal of Molecular Structure 975 (2010) 166–172
6
(a)
4
2
0
0.60
(b)
0.45
0.30
0.15
0.00
2.4
(c)
1.8
1.2
0.6
0.0
c
b
a
3500
3000
2500
2000
1500
1000
500
Wavenumber [cm-1]
Fig. 5. Room temperature Raman spectra of picric acid (a), 1-(diaminomethyl-
ene)thiourea (b) and 1-(diaminomethylene)thiouron-1-ium picrate (c).
Fig. 3. Molecular packing of 1-(diaminomethylene)thiouron-1-ium picrate in the
unit cell.
such as three NH2, C@S, CANAC, NACAN and NAC@S in the cation
and three NO2, Car ANO2, CarAOÀ and six-membered skeletal aro-
maticringinthe anion. Acareful inspectionof theIR spectrumshows
three medium-strong intensity bands in the range between 3439
and 3322 cmÀ1 that can be attributed to the asymmetric stretching
of the three NH2 groups of 1-(diaminomethylene)thiouron-1-ium
cation and three weaker bands in the spectral region of 3210–
3062 cmÀ1 attributedto thesymmetricstretchingof the NH2 groups.
The strong intensity band at 1616 cmÀ1 in IR with weak intensity Ra-
man counterparts at 1611 cmÀ1 is attributed to NH2 asymmetric
deformation mode. The X-ray data reveal that all NH2 groups of
the 1-(diaminomethylene)thiouron-1-ium cation are involved in
nine NAHÁ Á ÁO hydrogen bonds with bond lengths ranging from
ꢀ2.77 to ꢀ3.37 Å (the distance between donor and acceptor). This
is reflected in the infrared spectrum as a broad band in the range
3300–2750 cmÀ1. Additionally, the broad band in the range of
1400–1100 cmÀ1 overlapped with the msym stretching NO2 points
to the presence of the NAHÁ Á ÁO hydrogen bonds. The vibrations of
the NAC(S)AN group in the thiourea are observed in the range be-
tween 1480 and 1130 cmÀ1. The band at 1419 cmÀ1 observed in
the IR spectrum of 1-(diaminomethylene)thiourea (Fig. 4b) corre-
sponds to the 1414 cmÀ1 of thiourea, and is a contributions of the
0.8 (a)
0.6
0.4
N
0.2
0.0
1.0
(b)
0.8
0.6
0.4
N
0.2
0.0
1.0
NH2 rocking and NACAN vibrations [37]. The
observed at 730 cmÀ1, while in several thiourea metal complexes
the
(C@S) band is observed in the range 715–700 cmÀ1 [32]. Vibra-
m(C@S) in thiourea is
(c)
0.8
0.6
0.4
m
tion of the C@S bond is coupledwiththe bending vibration of thepic-
rate(À) ring and the band is observed at the 705 cmÀ1. Similar band
is also observed in other picrate slats.
N
N
0.2
The picrate being the 2,4,6-trinitrophenolate(À) anion has char-
acteristic bands of the deprotonated phenol, the bands of three NO2
groups and the bands of the six-membered aromatic ring. As can be
seen from Fig. 4a, the band at 3106 cmÀ1 observed in the spectrum
of pure picric acid disappeared in the spectrum of picrate (Fig. 5c).
0.0
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber [cm-1]
The relatively low wavenumber (3106 cmÀ1
)
points to the
Fig. 4. Room temperature FTIR spectra of picric acid (a), 1-(diaminomethyl-
ene)thiourea (b) and 1-(diaminomethylene)thiouron-1-ium picrate (c).
presence of the intramolecular OAHÁ Á ÁO interaction that was

J. Janczak, G.J. Perpétuo / Journal of Molecular Structure 975 (2010) 166–172
171
confirmed by the X-ray single crystal analysis of picric acid [33].
Thus the absence of the OAH stretching confirms a proton transfer
from picric acid to 1-(diaminomethylene)thiourea molecule with
the formation of the picrate(À) anion and 1-(diaminomethyl-
ene)thiouron-1-ium cation. Apart from this, the other functional
groups existing in the picrate(À) anion are the nitro NO2 groups
and the phenolic CarAOÀ group. The CAC ring stretching modes
are observed as expected at 1616, 1488 and 1467 cmÀ1 (Table 4)
in the spectrum of 1-(diaminomethylene)thiouron-1-ium picrate
as well as in the spectrum of picric acid. The CAH bending mode
is assigned as a medium intensity band at 824 cmÀ1 in Raman
spectrum and at 843 cmÀ1 in the IR spectrum of the salt. Picric acid
absorbs strongly at 1345 cmÀ1 as a result of symmetric stretching
vibration of nitro groups. The acid also displays two closely spaced
bands at 1562 and 1530 cmÀ1 due to the NO2 asymmetric stretch-
ing vibration mode. Besides the mentioned above bands, in the
acid only one of two orto NO2 group is rotated, the other is copla-
nar with the aromatic ring due to the formation of the intramolec-
ular OAHÁ Á ÁO hydrogen bond between the hydroxyl group and the
oxygen atom of the NO2 group. This conformation together with
the intermolecular NAHÁ Á ÁO hydrogen bonds leads to the splitting
of the msym (NO2) band. The band at 1282 cmÀ1 in the IR spectrum
is assigned to phenolic O vibration, m(CarAO) mode as was assigned
in several picrate salts [38–43]. The appearance of a medium inten-
sity band at 1285–1255 cmÀ1 in the metal picrate complexes is
attributed to the m(CarAO) mode due to the coordination of pheno-
lic oxygen after deprotonation [21]. For the lanthanide picrates,
this band is observed at ꢀ1275 cmÀ1 [44–46]. The origin and nat-
ure of the relatively strong and narrow band at 1707 cmÀ1 in the IR
spectrum of the salt (Fig. 4c), which is not observed in pure picric
acid (Fig. 4a) and pure 1-(diaminomethylene)thiourea (Fig. 4b) are
not clear. In the 1:1 and 2:1 complexes of N-methylmorpholine
betaine with picric acid the band in this spectral region
(ꢀ1730 cmÀ1 in the complex of 1:1 and 1727 cmÀ1 in the complex
present crystal, the Raman spectrum exhibits,
a band at
1368 cmÀ1 and a very strong band at 1299 cmÀ1; both are not
observed in the spectrum of pure picric acid. Comparing the con-
formation of the picrate(À) anion in the 1-(diaminomethylene)thi-
ouron-1-ium picrate with the conformation of molecule of pure
picric acid [33] it should be stated that they are different. Both
NO2 groups of the picrate(À) anion are linked to the ring in orto
positions in relation to the phenolic oxygen (COÀ) and are oppo-
sitely rotated in relation to the plane of the ring, whereas in picric
of 2:1) has been attributed to the
m
(Car@O) of picrate(À) anion [47].
However, as shown by the X-ray analysis in both complexes the
CAO bond lengths of 1.260(5) and 1.221(6) Å [47] are very close
to the value of 1.2446(16) Å observed in the present structure as
well as in other picrate salts [48]. Since in the spectra of several
picrate salts the band above 1700 cmÀ1 is not observed [38–46],
therefore the band at 1707 cmÀ1 can not be assigned to the pheno-
lic oxygen vibration. Nevertheless, this band could be ascribed to
the stretching of an imine bond of the 1-(diaminomethylene)thiou-
ron-1-ium cation, since a similar band is observed in some imines
and their picrate slats [49]. The stretching vibration of an imine
bond frequency goes from ꢀ1667 cmÀ1 in some free imines to
ꢀ1704 cmÀ1 in their picrates [49]. The observed frequencies and
their assignments are listed in Table 4.
Table 4
FT IR and Raman spectral data for 1-(diaminomethylene)thiouron-1-ium picrate.
Infrared,
(cmÀ1
m
Raman,
(cmÀ1
m
Assignment
)
)
3439m
3389s
3322s
3210w
3138w
NH2 asym stretch.
NH2 asym stretch.
NH2 sym stretch.
NH2 sym stretch.
NAH
4. Conclusion
The single crystals of 1-(diaminomethylene)thiouron-1-ium
picrate were grown using a solution growth technique. The 1-
(diaminomethylene)thiouron-1-ium cation is planar. This is in con-
trast to the neutral molecule of 1-(diaminomethylene)thiourea in
the crystal as well as in other known crystals of 1-(diaminometh-
ylene)thiouron-1-ium salts, in which the conformation is non-pla-
nar. In the picrate(À) anion both orto NO2 groups in relation to the
deprotonated hydroxyl group are oppositely turned in relation to
the six-membered aromatic ring, due to the repulsive interaction
between the negatively charged phenolic oxygen and the oxygen
atoms of NO2 group. Deprotonation of the picric acid leads to dis-
appearance of the OAH stretching vibration band at 3106 cmÀ1
(observed in picric acid, Fig. 4a) and to appearance of the phenolic
O stretching vibration band at 1170 cmÀ1 (observed in the salt,
Fig. 4c). In the crystal, nine NAHÁ Á ÁO hydrogen bonds exist, which
are manifested in the IR spectrum as a broad band between the
3300 and 2750 cmÀ1 and in the range of 1400–1100 cmÀ1. These
bands overlapped with the msym stretching NO2 as well as with
the NAC(S)AN skeletal group of the cation and with the skeletal
aromatic ring of picrate anion. An arrangement of the oppositely
charged components, i.e. 1-(diaminomethylene)thiouron-1-ium
cations and picrate(À) anions in the crystal is mainly determined
by the ionic and hydrogen bonding interactions forming pseudo-
one dimensional chains.
3082vw
NAH
NAH
3062m
2618vw
2262vw
1712vw
Overtones and combination bands
Overtones and combination bands
Imine bond stretch.
Imine bond stretch.
NH2 asym def.
1707s
1658m
1616vs
NH2 asym def.
1611w
1553m
1522w
1551s
1520m
1498m
m
m
m
m
m
(CAN) and NO2 asym stretch.
(CAN) and NO2 asym stretch.
(CAC) ring stretch.
(CAC) ring stretch.
(CAC) ring stretch. overlapped with
1485w
1467s
Nujol
m(CAO)
1366m
1344vs
1299vs
1360s
NO2 sym stretch. overlapped with Nujol
NO2 sym stretch.
NO2 sym stretch.
NO2 sym stretch.
Phenolic O
1330vs
1282s
1170m
1091
1170m
1084m
948m
CAN stretch.
CAC stretch.
CAC stretch.
NO2 def.
NO2 def., CAH def.
x(NO2)
C@S stretch. overlapped with d(ring)
CAC@O def.
919m
843m
824s
745w
705w
746m
705m
631w
604
5. Supplementary material
571m
519w
512w
336m
CACACAC ph ring def.
CACACAC ph ring def.
Additional material comprising full details of the X-ray data col-
lection and final refinement parameters including anisotropic ther-
mal parameters and full list of the bond lengths and angles have
vs, very strong; s, strong; m, medium; w, weak.

172
J. Janczak, G.J. Perpétuo / Journal of Molecular Structure 975 (2010) 166–172
[26] J.M. Frisch, G.W. Trucks, H.B. Schlegel, P.M.W. Gill, B.G. Johnson, M.A. Robb, J.
Cheeseman, T. Keith, G.A. Petersson, J.A. Montgomery, K. Raghavachari, M.A.
Al-Laham, V.G. Zakrzewski, J.V. Ortiz, J.B. Foresman, J. Cislowski, B.B. Stefanov,
A. Nanayakkara, M. Challacombe, C.Y. Peng, P.Y. Ayala, W. Chen, W.M. Wong,
J.L. Andres, E.S. Replogle, R. Gomperts, R.L. Martin, D.J. Fox, J.S. Binkley, D.J.
Defrees, J. Baker, B.B. Stewart, M. Head-Gordon, C. Gonzales, J.A. Pople,
Gaussian98, Revision A.3, Gaussian, Inc., Pittsburgh, PA, 1998.
[27] A.D. Becke, J. Chem. Phys. 104 (1996) 1040.
been deposited with the Cambridge Crystallographic Data Center
in the CIF format as supplementary publications No. CCDC
767502. Copies of the data can be obtained free of charge on the
application to CCDC, 12 Union Road, Cambridge, CB21EZ, UK,
(fax: +44 1223 336 033; email: deposit@ccdc.cam.ac.uk).
[28] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B37 (1988) 785.
[29] D.R. Johnson, F.X. Powell, W.H. Kirchhoff, J. Mol. Spectrosc. 39 (1971) 136.
[30] R. Fausto, L.A.E. Batista de Carvalho, J.J.C. Teixeira-Dias, M.N. Ramos, J. Chem.
Soc. Faraday Trans. 2 (1989) 1945.
[31] F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, A.G. Orpen, R. Taylor, J. Chem.
Soc. Perkin Trans. 2 (1987) S1–S19.
[32] F.H. Allen, C.M. Bird, R.S. Rowland, P.R. Raithby, Acta Crystallogr. B53 (1997)
680.
[33] M. Soriano-Garcia, T. Srikrishnan, R. Parthasarathy, Acta Crystallogr. A34
(1978) S114.
[34] R.J. Gillespie, Chem. Soc. Rev. 21 (1992) 59.
[35] G. Socrates, Infrared Characteristic Group Frequencies;, Wiley-Interscience,
Chichester, UK, 1980.
[36] G. Socrates, Infrared and Raman Characteristic Group Frequencies, third ed.,
Wiley, New York, USA, 2001.
[37] G.M.S. El-Bahy, B.A. El-Sayed, A.A. Shabana, Vib. Spectrosc. 31 (2003) 101.
[38] M.B. Mary, V. Sasirekha, V. Ramakrishnan, Spectrochim. Acta A65 (2006) 955.
[39] Y.L. Guo, Y.W. Wang, W. Dou, J.R. Zheng, W.S. Liu, C.Y. Su, Inorg. Chim. Acta 360
(2007) 3361.
References
[1] J.C. MacDonald, G.R. Whitesides, Chem. Rev. 94 (1994) 2382.
[2] G.R. Desiraju, T. Steiner, The Weak Hydrogen Bond in Structural Chemistry and
Biology, Oxford University Press, Oxford, 1999.
[3] G.R. Desiraju, Angew. Chem. Int. Ed. 34 (1995) 2311.
[4] G.R. Desiraju, Chem. Commun. (1997) 1475.
[5] T. Steiner, Angew. Chem. Int. Ed. 41 (2002) 48.
[6] C.A. Hunter, K.R. Lawson, J. Perkins, C.J. Urch, J. Chem. Soc. Perkin Trans. 2
(2001) 651.
[7] J.A. Zerkowski, J.C. MacDonald, G.M. Whitesides, Chem. Mater. 6 (1994) 1250.
[8] G.R. Desiraju, Acc. Chem. Res. 29 (1996) 441.
[9] J. Janczak, G.J. Perpétuo, Acta Crystallogr. C64 (2008) o114.
[10] K. Chakrabarty, T. Kar, S.P.S. Gupta, Acta Crystallogr. C46 (1990) 2065.
[11] M.K. Kabir, K. Yamada, K. Adachi, M. Kondo, S. Kawata, Acta Crystallogr. E58
(2002) m580.
[12] E. Doxiadi, R. Vilar, A.J.P. White, D.J. Williams, Polyhedron 22 (2003) 2991.
[13] G.J. Perpétuo, J. Janczak, Acta Crystallogr. C64 (2008) o264.
[14] J. Janczak, G.J. Perpétuo, Acta Crystallogr. C64 (2008) o330.
[15] J. Janczak, G.J. Perpétuo, Acta Crystallogr. C65 (2009) o118.
[16] M. Hołyn´ ska, M. Kubiak, Acta Crystallogr. C64 (2008) o609.
[40] E. Pinto Marinho, D.M. Araújo Melo, L.B. Zinner, E.E. Castellano, J. Zukerman-
Schpector, P.C. Isolani, G. Vicentini, Polyhedron 16 (1997) 3519.
[41] V. Tomašic´, Lj. Tušek, A. Višnjevac, B. Kojic´-Prodovic´, N. Filipovic´-Vincekovic´, J.
Colloid Interface Sci. 227 (2000) 427.
[42] Y.L. Guo, Y.W. Wang, W.S. Liu, W. Dou, X. Zhong, Spectrochim. Acta A67 (2007)
624.
´
[17] M. Hołynska, M. Kubiak, Acta Crystallogr. C65 (2009) o191.
[18] P.G. Farrell, F. Terrier, R. Schaal, Tetrahedron Lett. 26 (1985) 2435.
[19] G.C. Franchini, A. Marchetti, L. Tassi, G. Tosi, J. Chem. Soc. Faraday Trans. 1 84
(1988) 4427.
[43] A. Chandramohan, R. Bharathikannan, J. Chandrasekaran, P. Maadeswaran, R.
Renganathan, V. Kandavelu, J. Cryst. Growth 310 (2008) 5409.
[44] T. Yongchi, L. Yingqiu, N. Jiazan, J. Mol. Sci. (Int. Ed.) 5 (1987) 83.
[45] B. Ji, Q. Du, K. Ding, Y. Li, Z. Zhou, Polyhedron 15 (1996) 403.
[46] Y.W. Wang, W.S. Liu, N. Tang, M.Y. Tan, K.B. Yu, J. Mol. Struct. 660 (2003) 41.
[47] Z. Dega-Szafran, A. Katrusiak, M. Szafran, E. Sokołowska, J. Mol. Struct. 615
(2002) 73.
[20] M.A.F. Elmosallamy, Anal. Sci. 20 (2004) 285.
[21] R.C. Maurya, P. Sharma, S. Roy, Synth. React. Inorg. Metal. Org. Chem. 33 (2003)
683.
[22] R.P. Sharma, R. Sharma, R. Bala, P. Venugopalan, J. Coord. Chem. 58 (2005) 899.
[23] CrysAlis CCD and CrysAlis Red, Version 171.32.8, Oxford Diffraction
Poland,Wrocław, Poland, 2006.
[24] G.M. Sheldrick, SHELXS97, SHELXL97, Programs for Crystal Sturctures Solution
and Refinement, University of Göttingen, Göttingen, Germany, 1997.
[25] K. Brandenburg, H. Putz, DIAMOND Version 3.0, Crystal Impact GbR, Bonn,
Germany, 2006.
[48] F.H. Allen, Acta Crystallogr. B58 (2002) 380.
[49] J. Favrot, D. Vocelle, C. Sandrofy, Photochem. Photobiol. 28 (1979) 417.