Supramolecular synthons in fluorinated and nitrogen-rich ortho-diaminotriazoles

Article abstract of DOI:10.1007/s11224-011-9805-0

5-Substituted 3,4-diamino-1,2,4-triazoles can be obtained in moderate to good yields in a one-pot reaction starting from a carboxylic acid and dimethylaminoguanidine monohydrochloride in polyphosphoric acid (PPA) at 120 °C. Several triazoles and bistriazo

Full text of DOI:10.1007/s11224-011-9805-0

Struct Chem (2011) 22:1095–1103
DOI 10.1007/s11224-011-9805-0
ORIGINAL RESEARCH
Supramolecular synthons in fluorinated and nitrogen-rich
ortho-diaminotriazoles
•
Roberto Centore Antonio Carella
•
Sandra Fusco
Received: 23 December 2010 / Accepted: 2 May 2011 / Published online: 17 May 2011
Ó Springer Science+Business Media, LLC 2011
Abstract 5-Substituted 3,4-diamino-1,2,4-triazoles can
be obtained in moderate to good yields in a one-pot reac-
tion starting from a carboxylic acid and dimethylamino-
guanidine monohydrochloride in polyphosphoric acid
(PPA) at 120 °C. Several triazoles and bistriazoles have
been prepared in this way, with substituents ranging from
alkyl to aryl, including perfluoroaryl or perfluoroalkyl
substituents. The crystal structure analysis of three per-
fluorinated diaminotriazoles has evidenced a most stable
R22ð8Þ H bonding synthon, involving the amino CNH2
donor and the adjacent nitrogen ring acceptor; additionally,
two new synthons consisting of chains of rings have been
identified. The relevance of the short F_F intermolecular
contacts found in the structures is also discussed.
have more recently attracted interest in materials chemistry
as building blocks of conjugated active molecules in many
emerging fields of organic electronics (conducting poly-
mers [1], OFETs [2, 3], organic solar cells [4], NLO
compounds [5, 6]). In many applications in organic elec-
tronics, in particular, it has been found that reduction of the
hydrogen content or extensive replacement of hydrogen by
fluorine can significantly improve the performances of the
devices [7–9], in such a way that the development of
fluorinated aromatic heterocycles is an urging issue of the
field.
As a prosecution of our studies on the synthesis and H
bonding patterns of heterocycles and nitrogen-rich com-
pounds [10, 11], we present in this article an investigation
on 3,4-diamino-1,2,4-triazoles (Scheme 1). The synthesis
of these heterocycles has not been described comprehen-
sively in the literature; yet, they are building blocks of
nitrogen-rich, aromatic fused-ring systems potentially
interesting in organic electronics.
Keywords H bonding ꢀ Supramolecular synthon ꢀ
Organic fluorine ꢀ Heterocycles ꢀ Crystal structure
From a crystal engineering perspective, the study of
diaminotriazoles is challenging because the high number of
H bonding donor and acceptor sites present in the molecule
can induce competition among different H bonding pat-
terns; moreover, no X-ray structure of compounds corre-
sponding to Scheme 1 is found in the present version of the
Cambridge Structural database (CSD version 5.21 August
2010) [12].
Introduction
Heterocycles are key compounds of synthetic chemistry.
Besides their long standing and relevant application as
drugs and bioactive compounds, aromatic heterocycles
In this article we report the synthesis and characteriza-
tion of several diaminotriazoles with R substituents ranging
from alkyl to aryl, including perfluorinated substituents.
Their chemical diagrams are shown in the Scheme 2.
For the X-ray analysis, we have focused on perfluori-
nated triazoles 2, 4, 8 in view of the abiding interest of
structural chemists for weak interactions involving organic
fluorine [13–19], and on the nitrogen-rich bis-triazole 5.
Electronic supplementary material The online version of this
article (doi:10.1007/s11224-011-9805-0) contains supplementary
material, which is available to authorized users.
R. Centore (&) ꢀ A. Carella ꢀ S. Fusco
Department of Chemistry ‘‘Paolo Corradini’’, University
of Naples ‘‘Federico II’’, Via Cinthia, 80126 Naples, Italy
e-mail: roberto.centore@unina.it
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Struct Chem (2011) 22:1095–1103
Scheme 1 Chemical diagram
of 5-substituted-3,4-diamino-
1,2,4-triazoles
2.60 mol in case of dicarboxylic acid) were finely grinded
in a mortar. The grinded mixture was added in portions to
the PPA, and, after complete addition, the temperature of
the pasty PPA mixture was gradually raised to 120 °C
within 30 min. The starting of the reaction was clearly
evidenced by abundant evolution of gaseous HCl from the
reaction mixture, which had to be continuously stirred.
When evolution of gas has apparently finished, the mixture
was left under stirring for 4 h, then it was poured in
100 mL cold water, under stirring. The resulting mixture
was basified at pH = 8 by addition of conc. NaOH. The
formed precipitate was filtered, washed repeatedly with
water, dried and crystallized from ethanol/water or DMF/
water. In the case of 5 and 6 crystallization was from hot
glacial acetic acid (or 1 M HCl). On cooling to room
temperature, the crystalline acetate (or chloridrate) salt was
recovered by filtration and dried in oven. It was then sus-
pended in water and basified to pH = 9 with conc. aqueous
NaOH, affording the pure bistriazole that was filtered,
washed repeatedly with water and dried.
N
N
R
NH2
N
NH2
1
2
3
p-O2N-C6H4
C6F5
N
N
R =
R
NH2
C7H15
N
NH2
C7F15
4
5
6
N
N
N
N
N
R
CH CH
H2N
NH2
N
NH2
R =
NH2
7
8
C12H24
C4F8
In the synthesis of 2 and 4, before raising the tempera-
ture to 120 °C, the reaction mixture must be kept at 50 °C
for 1 h, in order to reduce sublimation of the acid, which
would significantly lower the yield.
Scheme 2 Chemical diagrams of the studied triazoles
3,4-Diamino-5-p-nitrophenyl-1,2,4-triazole (1)
Experimental
C8H8N6O2. Yield 33%; Tdec = 248 °C. dH (300 MHz;
[D6]DMSO, 25 °C) 5.81 (s, 2 H), 6.04 (s, 2 H), 8.30 (s, 4
H) ppm. dH (300 MHz; [D5]Py, 25 °C) 6.83 (s, 2 H), 7.27
(s, 2 H), 8.26 (d, 2 H, 3J = 8.8 Hz), 8.65 (d, 2 H,
3J = 8.8 Hz) ppm. M (mass spectrum), 221.18 (M ? H?).
Required for C8H8N6O2 220.19.
Thermogravimetric analysis was performed with a TA
instrument SDT 2960 under flowing air, at 20 K/min
scanning rate, with simultaneous DSC–TGA recording.
Decomposition temperature was taken as the temperature
1
corresponding to 5% weight loss. H-NMR spectra were
recorded with
a Varian spectrometer operating at
300 MHz. 13C-NMR spectra were recorded with a Bruker
DRX 400 MHz spectrometer. Proton chemical shifts were
referenced to the residual solvent signal ([D6]DMSO
2.50 ppm; [D5]Py 7.20, 7.58, 8.70 ppm); 13C-NMR
chemical shifts were referenced to the solvent ([D6]DMSO
39.5 ppm). Mass spectra were recorded on a MALDI TOF
DE-PRO apparatus on a-cyano-4-hydroxycinnamic acid
matrix. All chemicals were obtained commercially and
used as received.
3,4-Diamino-5-pentafluorophenyl-1,2,4-triazole (2)
C8H4N5F5. Yield 30%; Tdec = 220 °C. dH (300 MHz;
[D6]DMSO, 25 °C) 5.55 (s, 2 H), 5.96 (s, 2 H) ppm. dC
(100.597 MHz; [D6]DMSO, 25 °C) 136.04 (m), 137.67
(m), 138.52 (m), 140.34 (m), 142.81 (m), 143.33 (m),
145.84 (s), 156.59 (s) ppm. M (mass spectrum), 266.12
(M ? H?). Required for C8H4N5F5 265.145. Single crys-
tals for X-ray analysis were obtained by slow evaporation
of an ethanol solution.
General procedure for the synthesis of 5-substituted-
3,4-diamino-1,2,4-triazoles
3,4-Diamino-5-n-heptyl-1,2,4-triazole (3)
Polyphosphoric acid (PPA, 7.5 g) was put into a beaker and
heated at 50 °C under mechanical stirring. Separately, the
organic acid (1 g of a monocarboxylic acid or 0.5 g of a
dicarboxylic acid) and diaminoguanidine monohydrochlo-
ride (1.30 mol times the mol of the monocarboxylic acid or
C9H19N5. Yield 24%; m.p. 200 °C, Tdec = 282 °C. dH
(300 MHz; [D6]DMSO, 25 °C) 0.84 (t, 3 H), 1.25 (m, 8 H),
1.58 (qintet, 2H), 2.47 (t, 2H), 5.39 (s, 2H), 5.43 (s, 2H)
ppm. M (mass spectrum), 198.28 (M ? H?). Required for
C9H19N5 197.283.
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Struct Chem (2011) 22:1095–1103
1097
refined by the full-matrix least-squares method on F2 using
SHELXL-97 program [22] with the aid of the program
WinGX [23]. Non-hydrogen atoms were refined aniso-
tropically; H atoms were located in difference Fourier
maps and their coordinates were refined, while Uiso was not
refined but set equal to 1.2 times Ueq of the carrier atom.
The analysis of the crystal packing was performed using
the program Mercury [24]. Crystal and refinement data are
summarized in Table 1. CCDC reference numbers
796663–796666 contain the supplementary crystallo-
graphic data for 2, 4, 5 and 8, respectively. These data can
be obtained free of charge at www.ccdc.cam.ac.uk/conts/
retrieving.html.
3,4-Diamino-5-perfluoroheptyl-1,2,4-triazole (4)
C9H4N5F15. Yield 22%; Tdec = 220.5 °C. dH (300 MHz;
[D6]DMSO, 25 °C) 5.72 (s, 2 H), 6.27 (s, 2 H) ppm. dC
(100.597 MHz; [D6]DMSO, 25 °C) 98.61 (m), 108.04 (m),
110.40 (m), 111.22 (m), 113.44 (m), 115.22 (m), 118.09
(m), 138.30 (tr, 2JCF = 27.4 Hz), 158.09 (s) ppm. M (mass
spectrum), 468.11 (M ? H?). Required for C9H4N5F15
467.140. Single crystals for X-ray analysis were obtained
as for 2.
3,4-Diamino-5-(3,4-diamino-1,2,4-triazol-5-yl)-1,2,4-
triazole (5)
C4H8N10. Yield 34%; Tdec = 347.5 °C. dH (300 MHz;
[D6]DMSO, 25 °C) 5.80 (s, 4 H), 5.90 (s, 4 H) ppm. M
(mass spectrum), 197.24 (M ? H?). Required for C4H8N10
196.175.
Results and discussion
Synthetic considerations
(E)-1,2-Bis(3,4-diamino-1,2,4-triazol-5-yl)-ethene (6)
Diaminotriazoles with H or methyl in position 5 are descri-
bed in the literature and were prepared by acid catalyzed
reaction of formic or acetic acid with 1,3-diaminoguanidine-
monohydrochloride [25, 26], but the extension of this pro-
cedure to other carboxylic acids has not been reported.
Another synthetic approach reported in the literature is based
on the hydrazinolysis of 2-amino-1,3,4-oxadiazoles [27, 28],
but this procedure is applicable only to the synthesis of
5-alkyl-diaminotriazoles, having been explicitly reported
that hydrazinolysis of 5-aryl-amino-oxadiazoles does not
afford the correspondent triazoles [27]. Consequently,
5-aryl-diaminotriazoles are poorly described in the litera-
ture. The synthesis of 5-phenyl-3,4-diamino-1,2,4-triazole,
in very low yield (7%), was reported by Hoggarth by
hydrazinolysis of 1,4-dibenzoylthiosemicarbazide [29]. A
multi-step synthetic route has been reported more recently
[30, 31], based on the successive conversions of the aromatic
acid in the monohydrazide, aroylthiosemicarbazide and
5-aryl-2-amino-1,3,4-thiadiazole, respectively; hydrazinol-
ysis of the thiadiazole eventually affords the triazole. This
procedure, which is unexpected on account of the proved
stability of aryl-oxadiazoles to hydrazinolysis, and on the
expected even higher stability of thiadiazoles,1 is hardly
compatible, in principle, with the presence of oxidizing
groups (e.g., nitro) in the aromatic acid, because of the final
step of hydrazinolysis.
C6H10N10. Yield 34%; Tdec = 341.8 °C. dH (300 MHz;
[D6]DMSO, 25 °C) 5.62 (s, 4 H), 5.74 (s, 4 H), 7.23 (s, 2H)
ppm. M (mass spectrum), 223.15 (M ? H?). Required for
C6H10N10 222.212.
1,12-Bis(3,4-diamino-1,2,4-triazol-5-yl)-dodecane (7)
C16H32N10. Yield 72%; Tdec = 268 °C. dH (300 MHz;
[D6]DMSO, 25 °C) 1.30 (m, 16 H), 1.63 (quintet, 4 H),
2.53 (t, 4H), 5.43 (s, 4H), 5.46 (s, 4H) ppm. M (mass
spectrum), 365.45 (M ? H?). Required for C16H32N10
364.496.
1,4-Bis(3,4-diamino-1,2,4-triazol-5-yl)-perfluorobutane (8)
C8H8N10F8. Yield 78%; Tdec = 299 °C. dH (300 MHz;
[D6]DMSO, 25 °C) 5.68 (s, 4 H), 6.22 (s, 4 H) ppm. dC
(100.597 MHz, [D6]DMSO, 25 °C) 111.62 (m), 112.3 (m),
2
138.62 (tr, JCF = 27.4 Hz), 158.71 (s) ppm. M (mass
spectrum), 397.19 (M ? H?). Required for C8H8N10F8
396.206. Single crystals for X-ray analysis were obtained
by slow evaporation of a DMF solution.
X-ray analysis
All data for crystal structure determinations were measured
on a Bruker-Nonius Kappa CCD diffractometer using
˚
graphite monochromated Mo Ka radiation (0.71073 A) at
1
We have checked repeatedly the hydrazinolysis of 2-amino-5-
heptyl-1,3,4-thiadiazole, both according to the recipe given in [30],
and by increasing reaction times and amount of hydrazine hydrate; in
all the cases we only recovered, almost quantitatively, the unreacted
thiadiazole, without observing any significant conversion in the
triazole.
293 K for 2, 4, 8 and at 173 K for the acetate salt of 5.
Reduction of data and semiempirical absorption correction
were done using SADABS program [20]. The structures
were solved by direct methods (SIR97 program [21]) and
123

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Struct Chem (2011) 22:1095–1103
Table 1 Crystallographic data of triazoles 2, 4, 5, and 8
2
4
5
8
Chemical formula
M
C8H4F5N5
265.16
P21/c
C9H4F15N5
467.17
C2/c
(C4H10N10)(C2H4O2)2ꢀ2C3H3O2
436.42
C8H8F8N10
396.24
P21/c
Space group
P21/c
˚
a (A)
14.477(8)
6.181(4)
11.228(6)
108.16(4)
955(1)
4
54.58(1)
5.591(3)
9.889(5)
99.05(3)
2980(2)
8
10.236(7)
6.404(4)
14.958(7)
95.77(3)
975.5(10)
2
12.426(7)
5.786(3)
9.449(4)
92.40(3)
678.8(6)
2
˚
b (A)
˚
c (A)
b (°)
3
˚
V (A )
Z
Density (g/cm3)
1.845
2.082
1.486
1.939
T (K)
l (mm-1
293
293
173
293
)
0.189
0.262
0.125
0.208
Reflections collected
Unique reflections (Rint
R1 [I [ 2r(I)]
7,835
8,598
6,472
3,425
)
2,176 (0.049)
0.040
3,285 (0.049)
0.064
2,210 (0.068)
0.049
1,542 (0.056)
0.063
wR2 (all data)
0.1032
0.1870
0.1547
0.1732
In this article we have used a simple, one-step method
(Scheme 3), which is applicable to both 5-alkyl and 5-aryl
substituents. The method, which can be considered to be a
significant improvement of the procedure described in
Refs. [25, 26], is based on the reaction of the carboxylic
acid with diaminoguanidine monohydrochloride in poly-
phosphoric acid (PPA) at 120 °C for 4 h; it has virtually no
limitations and we have successfully confirmed it with
long-chain aliphatic acids (octanoic acid, perfluorooctanoic
acid) and aromatic acids (4-nitrobenzoic acid, pentafluo-
robenzoic acid).
thermal stability for bis(diaminotriazoles) and this could be
the consequence of a more tight pattern of H bonding in the
crystal packing. In particular, the highest thermal stability
is shown by 5, with a decomposition temperature (in air)
approaching 350 °C, a noteworthy result if we consider
that 5 is a nitrogen-rich compound, with ten nitrogen atoms
summing up 71.4% by weight, a figure higher than the
recently reported bis[3-(5-nitroimino-1,2,4-triazole)] and
its precursor bis[3-(5-amino-1,2,4-triazole)] [32]. Actually
in 5, out of 22 atoms present in the molecule, 16 are
potential H bonding donor/acceptors.
Using bicarboxylic acids, the corresponding bis(3,4-
diamino-1,2,4-triazoles) are obtained, and are described
here for the first time. We have confirmed that with oxalic,
fumaric, tetradecanedioic, and perfluoroadipic acids.
Basic physico-chemical properties of the studied tria-
zoles are provided in ‘‘Experimental’’ section. Diamino-
triazoles are easily recognized by the 1H-NMR spectrum in
DMSO which shows two characteristic singlets of equal
area in the range 5.4–6.3, corresponding to resonances of
the two amino groups (see also ‘‘Experimental’’ section).
Surprisingly, no mention of these diagnostic NMR signals
is given in Ref. [30].
Molecular structure of fluorinated triazoles 2, 4, 8
Ortep drawings of the perfluorinated triazoles are reported
in Figs. 1, 2, and 3, with thermal ellipsoids drawn at 30%
probability level.
The pentafluorophenyl and triazole rings of 2 are not
coplanar, making a dihedral angle of 43.4(1)°, because of
torsion around the C2–C3 bond. Actually, coplanarity
cannot be allowed because of the close contact between N4
˚
and F1 (2.776(3) A). The conformation of the perfluori-
nated chain in 4 is not trans but helicoidal, with torsion
angles of about -164° around each CF2–CF2 bond; this
torsion is expected as it corresponds to the 13/6 helix of
poly(tetrafluoroethylene) (PTFE) chain [33].
The thermal stability of triazoles was studied by com-
bined TGA/DSC analysis. The decomposition tempera-
tures, reported in ‘‘Experimental’’ section, indicate higher
Scheme 3 Synthetic procedure
for 5-substituted-3,4-diamino-
1,2,4-triazoles
NH
H2N NH C NH NH2 HCl
N
N
PPA, 4 h
.
+
COOH
2 H2O + HCl
R
+
R
120 °C
NH2
N
NH2
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Struct Chem (2011) 22:1095–1103
1099
pyramidal and in some cases almost trigonal (the sum of
valence angles is 338°, 357°, and 360° for 2, 4, and 8,
respectively). The conformation of the N-NH2 group is also
variable in the studied structures. In fact, two different
staggered conformations can be considered, in which the
two H atoms are from the same side (A) or from opposite
side (B) with respect to the C-NH2 group. Staggered con-
formation A is found in 2, while B conformation is found in
4 and 8. This variability could be related with the different
steric encumbrance of the R group; yet, as we shall see
below, the different conformations fit different types of H
bonding patterns.
Fig. 1 Ortep drawing of 2
H bonding patterns of fluorinated triazoles 2, 4, 8
The crystal packing of diaminotriazoles is expected to be
conditioned by the formation of H bonds. The best donors
are the C-NH2 hydrogen atoms, while best acceptors are
N1 and N2 atoms of the ring, whose lone pairs are not
involved in the aromatic sextet, and N-NH2; in fact, it is
well known that fluorine atoms are weak H bonding
acceptors in fluorocarbons [34].
Fig. 2 Ortep drawing of 4
A forecast H bonding motif is shown in the Scheme 4.
This H bonding synthon, which was first discussed with
reference to 2-amino-pyrimidine [35, 36], has a high
probability of occurrence and is ranked among the 24 most
frequently observed bimolecular cyclic hydrogen bonded
motifs in organic crystal structures [37, 38]; it can be
realized between molecules related by an inversion center
(or by a twofold axis).
Fig. 3 Ortep drawing of 8; symmetry code (i) = 1 - x, -y, 1 - z
The ring pattern R22ð8Þ is present in the crystal packing
of the three structures: 2 (N5–H_N2i: 1.01, 2.00,
2
i
˚
3.001(3) A, 169°, i = 1 - x, 1 - y, -z), 4 (N5–H_N2 :
NH2
˚
1.01, 1.99, 2.978(5) A, 165°, i = 0.5 - x, 1.5 - y, 1 - z),
and 8 (N5–H_N2 : 1.01, 2.05, 2.986(5) A, 154(4)°,
H
i
˚
N
N
H
R
i = 2 - x, 1 - y, 1 - z). Packing diagrams are reported in
Figs. 4 and 5 for 2 and 4 as examples. In the three struc-
tures the motif is formed across inversion centers.
One C-NH2 hydrogen atom and one acceptor N atom in
the ring (i.e., N1), as well as the N-NH2 acceptor/donor, are
not involved in the ring pattern of Scheme 4. So, in addi-
tion to it, chain H bonding patterns are reasonably
expected.
H
N
N
N
N
R
N
N
H
NH2
R22( 8 )
Two very simple chain patterns possible, in principle,
for the triazoles are shown in the Scheme 5. One is formed
through the free C-NH2 donor and the N1 acceptor (CP1),
another between one N-NH2 donor and the N1 acceptor
Scheme 4 Expected H bonding synthon in diaminotriazoles
Surprisingly, in bis(triazole) 8 the perfluorinated chain is
strictly transplanar as it lies on a crystallographic inversion
center.
2
The geometric parameters of the hydrogen bond D–H_A are
given, here and throughout the paper, in the following order:
˚
˚
˚
D–H (A), H_A (A), D_A (A), D–H_A (°), symmetry code of
the acceptor atom. Moreover, for 2, 4, and 8 the N–H distances were
˚
normalized to the standard neutron diffraction value 1.01 A (see Ref.
[13]).
The geometry around N4 is pyramidal in all the com-
pounds (the sum of valence angles is 320°, 330°, and 314°
for 2, 4, and 8, respectively); on the other hand, N5 is less
123

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Struct Chem (2011) 22:1095–1103
N
N
H
N
N
N
H
N
N
N
H
N
N
H
H
H
H
H
N
N
N
N
H
Fig. 4 Partial crystal packing of 2
H
N
N
N
N
N
N
H
H
H
H
H
H
B
A
Scheme 6 Topological scheme of two complex H bonded chains
possible for diaminotriazoles
Fig. 5 Partial crystal packing of 4
of them, giving rise to chains of rings, are shown in the
Scheme 6.
At unitary level [39], their graph-set symbols are,
respectively, Cð5ÞCð5Þ (Scheme 6a) and Cð4ÞCð5Þ (Sche-
me 6b), while at secondary level, ring patterns R12ð7Þ and
R22ð8Þ show up.
N
N
H
N
N
N
N
N
H
H
N
N
H
H
Crystal packing of 2 is shown in Fig. 6. The adopted
chain pattern is that of Scheme 6a. In fact, the chain CP1 is
H
NH2
i
˚
present (N5–H_N1 : 1.01, 2.02, 3.025(3) A, 174°, i = x,
N
N
N
N
H
-1/2 - y, -1/2 ? z), but N1 acts as bifurcated acceptor
and also the chain CP2 is present through a weaker H bond
with one H atom linked to N4 (N4–H_N1i: 1.01, 2.41,
H
N
N
N
N
N
H
H
NH2
˚
H
H
3.279(3) A, 144°, i = x, -1/2 - y, -1/2 ? z), just as in
Scheme 6a; moreover, that H atom acts as bifurcated donor
CP1
CP2
with ortho F5 as the additional acceptor of a weak H bond
i
˚
(N4–H_F5 : 1.01, 2.38, 3.230(3) A, 141°, i = x, -1/2 - y,
-1/2 ? z) [34].
Scheme 5 Topological schemes of simple H bonded chains possible
for diaminotriazoles
In this way two ring systems are formed, whose second
level graph-set descriptors are R12ð7Þ and R12ð6Þ, respec-
tively, and it is also evident, from Fig. 6, that the A con-
formation of the amino groups (vide supra) is suited to fit
this multiple H bonding pattern.
(CP2). In both cases, the graph-set symbol is Cð5Þ and the
motif can be built up by glide reflection, binary screw
rotation or simple translation.
Partial crystal packing of 4 is shown in Fig. 7. Along
i
The two patterns of Scheme 5 are common in nitrogen
containing amino-heterocycles. In fact, for CP1, a CSD
search limited to pentatomic rings gave 44 hits. In 33 out of
the 44 hits is present the CP1 pattern and in 26 out of the 33
are present both the CP1 and the R22ð8Þ patterns. For CP2,
the search gave 31 hits. In 19 out of the 31 hits is present
the CP2 pattern (see Supplementary material).
˚
with the chain CP2 (N4–H_N1 : 1.01, 2.34, 3.046(5) A,
126°, i = x, 1 - y, -1/2 ? z), an additional chain motif is
observed, having graph-set descriptor Cð4Þ, due to a
(weaker) H bond formed between the H atom bonded to
N5, and not involved in the dimer pattern of Scheme 4, and
N2 which acts as trifurcated acceptor (N5–H_N2i: 1.01,
˚
2.53, 3.368(5) A, 140°, i = x, 1 - y, -1/2 ? z). In this
However, in the case of diaminotriazoles discussed in
this article, for which no CSD hit is present, the over-
crowding of the donor groups could favor N1 and N2 to act
as multifurcated acceptors so, besides the simple chains of
Scheme 5, more complex chain patterns can be also
expected which are specific of ortho-diaminotriazoles; two
way, another second level ring pattern R22ð8Þ is formed and
the overall arrangement is that of Scheme 6b.
An analogous situation is found in 8, with the CP2
i
˚
pattern (N4–H_N1 : 1.01, 2.66, 3.018(6) A, 101°, i = x,
1/2 - y, -1/2 ? z) and the additional Cð4Þ chain
123

Struct Chem (2011) 22:1095–1103
1101
Fig. 6 H bonded chain in 2
Fig. 8 Short F_F contacts in 4
Fig. 7 H bonded chain in 4
i
˚
(N5–H_N2 : 1.01, 2.50, 3.276(5) A, 134°, i = x, 1/2 - y,
-1/2 ? z); moreover, in 8, the N4–H donor involved in the
CP2 pattern is actually a bifurcated donor, being also
involved in a weak N–H_F bond (N4–H_F1i: 1.01, 2.48,
˚
3.373(5) A, 147°, i = x, -1/2 - y, -1/2 ? z).
Fig. 9 Short F_F contacts in 8
Intermolecular F_F contacts in fluorinated triazoles
2, 4, 8
ii = x, -1 ? y, ?z for 4; N4–H_N2ii: 1.01, 2.52,
˚
Besides H bonding, we have searched for other interactions
that can play a role in the packing of the perfluorinated tri-
azoles. Some F_F contacts less than the sum of van der
Waals radii are present in each structure. Of potential rele-
3.474(6) A, 159°, ii = x, -1 ? y, ?z for 8), and the F_F
contact could be simply the outcome of perfluorinated
molecules which are H bonded in the b direction; in this
view, the shorter F_F contact observed in 8 could be
simply due to the stronger cooperative effect of two H
bonds in 8 as compared with one in 4.
vance seem to be some type I F_F contacts [40] present in 4
i
(C3–F1_F4 = 2.885(3) A, \C3–F1_F4i = 141.2(2)°,
˚
i = x, -1 ? y, z) and, mostly, in 8 (C4–F4_F4i =
2.704(4) A, \C4–F4_F4 = 160.8(3)°, i = 1 - x, 1 - y,
1 - z), and shown in Figs. 8 and 9.
In order to explore the reliability of this (putative) F_F
synthon, we have searched in the CSD for structures con-
taining a chain of at least 2 CF2 groups, finding 249 hits
(see Supplementary material). In 73 structures of this set
(29%) there is effectively a short F_F contact between
molecules related by a unit cell translation (22 of the 73
structures are perfluorinated, i.e., they contain only C–F
bonds and no C–H bonds) and the value of the cell axis is
in several cases similar to 4 and 8, with higher values being
found if the fluorinated chain is tilted with respect to the
translation axis. If the structural probability [38] Ps (i.e.,
the frequency of occurrence of structures containing the
i
˚
The contacts are very similar in the two structures, as
they link molecules adjacent along b, with the CF2 chain
being approximately perpendicular to b and, in fact, the
b axis is similar in the two structures (5.591(3) and
˚
5.786(3) A, respectively) and similar to the values found in
the low temperature polymorphs of PTFE (5.59 and
˚
5.66 A) [33, 41]. However, in both the structures, mole-
cules adjacent along b are linked also by a weak H bonding
ii
˚
N4–H_N2 (N4–H_N2 : 1.01, 2.69, 3.642(5) A, 157°,
123

1102
Struct Chem (2011) 22:1095–1103
60
50
40
30
20
10
0
chain, as it is also shown in Fig. 10. This indicates that the
F_F contact found in 4 and 8 has a scarce reliability as
supramolecular synthon and is essentially a close-packing
contact of H bonded molecules. Given that the contact is
ancillary, it remains, however, the experimental fact that, in
˚
8, it is 0.24 A shorter than two times the Bondi van der
˚
Waals radius of fluorine (1.47 A).
Ps
Pm
2
3
4
6
7
8
Molecular and crystal structure of bistriazole 5
n CF2
Bistriazole 5 is poorly soluble in most solvents. It is soluble
in acids from which, by slow cooling, single crystals
suitable for X-ray analysis can be obtained. We have
investigated single crystals obtained from glacial acetic
acid. The X-ray molecular structure, shown in Fig. 11,
indicates that the compound crystallizes as the diacetate
salt (acetic acid disolvate), and that protonation occurs at
the N2 atom, instead of amino atoms N4 and N5.
Fig. 10 Frequency of occurrence of structures with short F_F
contacts between translated molecules versus the length of the
perfluorinated chain
The bistriazolium cation is planar, lying on crystallo-
graphic inversion centers. The amino N5 atom is trigonal
(the sum of valence angles at N5 is 359°), while N4 is
pyramidal (sum is 325°) and their mutual arrangement is
B-type (vide supra). An R22ð8Þ motif involving N2 and N5
is present also in this structure, but as the result of the
cation and the acetate anion facing to each other through
charge aided hydrogen bonds [46, 47] (N2–H_O1:
Fig. 11 Ortep drawing of the acetate salt of 5. The solvent acetic acid
molecule present in the independent unit is omitted for clarity;
symmetry code (i) = -x, -y, -z
˚
0.91(3), 1.79(2), 2.693(3) A, 170(2)°; N5–H_O2: 0.91(3),
˚
1.95(3), 2.849(3) A, 169(2)°) and giving rise, through other
H bonds, to flat ribbons of H bonded molecules, Fig. 12
left. The ribbons lie on the planes of the family with Miller
˚
F_F contact), is evaluated for subsets containing per-
fluorinated chains of fixed length, the histogram of Fig. 10
is obtained.
indices 302 (d320 ¼ 3:213 A), and the 302 reflection is the
most intense of the whole diffraction pattern, as all atoms
of the independent unit lie onto or very near to those
planes. The ribbons, which are piled up along (a - c/4),
Fig. 12 right, are held fast by H bonding too, involving
NNH2 donors and carbonyl acceptors of acetate ions and
acetic acid molecules lying in adjacent planes (N4–
It can be seen that the frequency of occurrence of
structures containing the F_F contact increases with the
length of the chain. This finding, which is expected on
statistical grounds, cannot discriminate, on its own, if the
short F_F contact is the consequence of a specific (weak)
attraction between fluorine atoms [42, 43] or it is simply
the result of close-packing approach of parallel perfluori-
nated chains [44, 45]. However, if we evaluate the proba-
bility of formation of the motif [38], Pm, we find a small
value, close to 8% and little dependent on the length of the
i
˚
H_O2 : 0.90(3), 2.31(3), 3.032(3) A, 138(2)° i = -x, -1/
i
˚
2 ? y, 1/2 - z; N4–H_O4 : 0.88(2), 2.33(2), 3.116(3) A,
148(2)° i = x, -1 ? y, z); from Fig. 12 right, it is also
evident that ribbons adjacent along the piling up direction
are related with respect to each other by a 21 operation,
Fig. 12 Acetate salt of 5.
Ribbon of H bonded molecules
viewed along (a - c/4) (left);
partial view of the cell along
b showing two edge-sighted
ribbons linked by H bonds
(right)
123

Struct Chem (2011) 22:1095–1103
1103
16. Reddy LS, Nangia A, Lynch VM (2004) Cryst Growth Des
4:89–94
17. Metrangolo P, Meyer F, Pilati T, Resnati G, Terraneo G (2008)
Angew Chem Int Ed 47:6114–6127
which is a very efficient way to satisfy the ‘‘bumps in
hollows’’ golden rule of close packing of layers [48].
¨
18. Thakur TS, Kirchner MT, Blaser D, Boese R, Desiraju GR (2010)
CrystEngComm 12:2079–2085
19. Collas A, De Borger R, Amanova T, Blockhuys F (2011)
CrystEngComm 13:702–710
Conclusion
Ring pattern R22ð8Þ involving amino CNH2 donor and the
adjacent nitrogen ring acceptor is the fundamental H
bonding synthon in 5-substituted 3,4-diamino-1,2,4-tria-
zoles. Another recurrent feature is the capability of nitro-
gen atoms of the ring (N1 and N2) to act as bifurcated or
even trifurcated H bonding acceptors, leading to two dif-
ferent types of complex chain patterns. The adopted chain
pattern seems to be related with the relative conformation
of the two ortho amino groups. F_F interactions, even if
they are very short, seem to have ancillary character in
determining the crystal packing, and are mainly the result
of close packing approach of molecules held by H bonds.
20. Bruker-Nonius (2002) SADABS. Bruker-Nonius, Delft, The
Netherlands
21. Altomare A, Burla MC, Camalli M, Cascarano GL, Giacovazzo C,
Guagliardi A, Moliterni GG, Polidori G, Spagna R (1999) J Appl
Crystallogr 32:115–119
22. Sheldrick GM (2008) Acta Crystallogr Sect A 64:112–122
23. Farrugia LJ (1999) J Appl Crystallogr 32:837–838
24. Macrae CF, Bruno IJ, Chisholm JA, Edgington PR, McCabe P,
Pidcock E, Rodriguez-Monge L, Taylor R, van de Streek J, Wood
PA (2008) J Appl Cryst 41:466–470
25. Gaiter A (1915) Gazz Chim Ital 45:450–461
26. Trust RI, Albright JD, Lowell FM, Perkinson NA (1979) J Het-
erocyclic Chem 16:1393–1403
¨
27. Gehlen H, Robish G (1963) Liebigs Ann Chem 663:119–123
28. Kochhar MM (1972) J Heterocyclic Chem 9:153–154
29. Hoggarth E (1950) J Chem Soc 614–617
30. Padhy AK, Nag VL, Panda CS (1999) Indian J Chem 38B:
998–1001
31. Gupta M (2007) J Heterocyclic Chem 44:1023–1027
32. Wang R, Xu H, Guo Y, Sa R, Shreeve JM (2010) J Am Chem Soc
132:11904–11905
33. Bunn CW, Howells ER (1954) Nature 174:549–551
34. Brammer L, Bruton EA, Sherwood P (2001) Cryst Growth Des
1:277–290
35. Scheinbein J, Schempp E (1976) Acta Crystallogr Sect B
32:607–609
36. Etter MC, Adsmond DA (1990) J Chem Soc Chem Commun
589–591
37. Allen FH, Raithby PR, Shields GP, Taylor R (1998) Chem
Commun 1043–1044
38. Allen FH, Motherwell WDS, Raithby PR, Shields GP, Taylor R
(1999) New J Chem 23:25–34
39. Bernstein J, Davis RE, Shimoni L, Chang NL (1995) Angew
Chem Int Ed Engl 34:1555–1573
40. Ramasubbu N, Parthasarathy R, Murray-Rust P (1986) J Am
Chem Soc 108:4308–4314
References
1. Heeger AJ (2010) Chem Soc Rev 39:2354–2371
2. Zaumseil J, Sirringhaus H (2007) Chem Rev 107:1296–1323
3. Wen Y, Liu Y (2010) Adv Mater 22:1–15
4. Li J, Grimsdale AC (2010) Chem Soc Rev 39:2399–2410
5. Jang SH, Jen AK (2008) In: Sun SS, Dalton LR (eds) Introduction
to organic electronic and optoelectronic materials and devices.
CRC Press, Boca Raton
6. Centore R, Roviello A (2010) In: Russo MV (ed) Advances
in macromolecules, perspectives and applications. Springer,
Dordrecht
7. Facchetti A, Mushrush M, Katz HE, Marks TJ (2003) Adv Mater
15:33–38
8. Casado J, Hernandez V, Ruiz Delgado MC, Ortiz RP, Lopez
Navarrete JT, Facchetti A, Marks TJ (2005) J Am Chem Soc
127:13364–13372
`
`
¨
9. Wobkenberg P, Ball J, Bradley DDC, Anthopoulos TD, Kooistra
41. Clark ES, Muus LT (1962) Z Kristallogr 117:119–127
42. Prasanna MD, Guru Row TN (2001) J Mol Struc 562:55–61
43. Choudhury AR, Urs UK, Guru Row TN, Nagarajan K (2002)
J Mol Struc 605:71–77
44. Desiraju GR, Parthasarathy R (1989) J Am Chem Soc 111:8725–
8726
F, Hummelen JC, de Leeuw DM (2008) Appl Phys Lett
92:143310–143313
10. Centore R, Fusco S, Peluso A, Capobianco A, Stolte M, Archetti
G, Kuball HG (2009) Eur J Org Chem 3535–3543
11. Centore R, Carella A, Tuzi A, Capobianco A, Peluso A (2010)
CrystEngComm 12:1186–1193
12. Allen FH (2002) Acta Crystallogr Sect B 58:380–388
13. Desiraju GR, Steiner T (1999) The weak hydrogen bond in
structural chemistry and biology. Oxford University Press Inc,
New York
14. Thalladi VR, Weiss HC, Blaser D, Boese R, Nangia A, Desiraju
GR (1998) J Am Chem Soc 120:8702–8710
15. Choudhury AR, Guru Row TN (2004) Cryst Growth Des 4:47–52
45. Thalladi VR, Weiss HC, Boese R, Nangia A, Desiraju GR (1999)
Acta Crystallogr Sect B 55:1005–1013
46. Ferretti V, Bertolasi V, Pretto L (2004) New J Chem 28:646–651
47. Thanigaimani K, Devi P, Muthiah PT, Lynch DE, Butcher RJ
(2010) Acta Crystallogr Sect C 66:o324–o328
48. Kitaigorodskii AI (1961) Organic chemical crystallography.
Consultant Bureau, New York
¨
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