Two derivatives of 1,5-disubstituted tetra-zoles: 1-(4-nitro-phen-yl)-1H- tetra-zol-5-amine and {(E)-[1-(4-ethoxy-phen-yl)-1H-tetra-zol-5-yl]imino-methyl} dimethyl-amine

Article abstract of DOI:10.1107/S0108270108019707

The geometric features of 1-(4-nitro-phenyl)-1H-tetra-zol-5-amine, C7H6N6O2, correspond to the presence of the essential inter-action of the 5-amino group lone pair with the π system of the tetra-zole ring. Inter-molecular N - H...N and N - H...O hydrogen bonds result in the formation of infinite chains running along the [110] direction and involve centrosymmetric ring structures with motifs R 2 ²(8) and R 2 ²(20). Mol-ecules of {(E)-[1-(4-ethoxy-phenyl)-1H-tetra-zol-5-yl] imino-methyl}dimethyl-amine, C12H16N6O, are essentially flattened, which facilitates the formation of a conjugated system spanning the whole mol-ecule. Conjugation in the azomethine N=C - N fragment results in practically the same length for the formal double and single bonds.

Full text of DOI:10.1107/S0108270108019707

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
the crystal structures was studied. It is of interest to investigate
similar effects in compounds with other N-containing groups,
for example, with the azomethine fragment. For this purpose,
we have also investigated {(E)-[1-(4-ethoxyphenyl)-1H-tetra-
zol-5-yl]iminomethyl}dimethylamine, (II) (Fig. 2). This com-
pound has practical importance, being useful both as a
synthetic intermediate and as a pharmaceutical and agro-
ISSN 0108-2701
Two derivatives of 1,5-disubstituted
tetrazoles: 1-(4-nitrophenyl)-1H-tetra-
zol-5-amine and {(E)-[1-(4-ethoxy-
phenyl)-1H-tetrazol-5-yl]imino-
methyl}dimethylamine
ˆ
chemical agent (Tisler, 1983; Granik, 1983; Oshovskii &
Pinchuk, 2000), and can be utilized as a tetrazole-containing
building block for the synthesis of complex molecules or as a
polytopic ligand in bioinorganic, medicinal and supra-
molecular chemistry. No structural data for tetrazole azo-
methines are available in the literature.
Alexander S. Lyakhov,a* Andrey N. Vorobiov,b Ludmila S.
Ivashkevicha and Pavel N. Gaponika
aResearch Institute for Physico-Chemical Problems, Belarusian State University,
Leningradskaya Street 14, Minsk 220030, Belarus, and bScientific Pharmaceutical
Center, JSC Belmedpreparaty, Fabritsiusa Street 30, Minsk 220007, Belarus
Correspondence e-mail: lyakhov@bsu.by
Received 24 June 2008
Accepted 27 June 2008
Online 5 July 2008
In both title compounds, the tetrazole ring geometries are
similar. The formal double bonds (N2 N3 and N4 C5) are
The geometric features of 1-(4-nitrophenyl)-1H-tetrazol-5-
amine, C7H6N6O2, correspond to the presence of the essential
interaction of the 5-amino group lone pair with the ꢀ system of
the tetrazole ring. Intermolecular N—Hꢀ ꢀ ꢀN and N—Hꢀ ꢀ ꢀO
hydrogen bonds result in the formation of infinite chains
running along the [110] direction and involve centrosymmetric
ring structures with motifs R22(8) and R22(20). Molecules of
{(E)-[1-(4-ethoxyphenyl)-1H-tetrazol-5-yl]iminomethyl}-
dimethylamine, C12H16N6O, are essentially flattened, which
facilitates the formation of a conjugated system spanning the
whole molecule. Conjugation in the azomethine N C—N
fragment results in practically the same length for the formal
double and single bonds.
Figure 1
The asymmetric unit of (I), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 30% probability level and H
atoms are shown as small spheres of arbitrary radii.
Comment
5-Aminotetrazoles attract considerable attention because
many of them reveal biological activity (Wittenberger, 1994;
Schelenz, 2000; Katritzky et al., 2003, and references therein).
In particular, the use of 1-aryl-5-aminotetrazoles as anti-
inflammatory agents has been described (Enkoji et al., 1970),
while 5-amino-1-nitrophenyltetrazoles have been found to be
active in treating and preventing coccidiosis in poultry
(Mrozik, 1974). However, only two examples of 5-amino-1-
aryltetrazoles have been structurally characterized to date
(Lyakhov et al., 2003). In the present work, we report the
crystal structure of a new compound, viz. 1-(4-nitrophenyl)-
1H-tetrazol-5-amine, (I) (Fig. 1).
In our previous investigations of 5-aminotetrazoles
(Lyakhov et al., 2001, 2003, 2008), the influence of the conju-
gation of the 5-amino group lone pair with the ꢀ system of the
tetrazole ring on the geometric features of the molecules in
Figure 2
The asymmetric unit of (II), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 30% probability level and H
atoms are shown as small spheres of arbitrary radii.
o414 # 2008 International Union of Crystallography
doi:10.1107/S0108270108019707
Acta Cryst. (2008). C64, o414–o416

organic compounds
could be caused by essential conjugation of the N6 atom lone
pair with the N5 C14 bond. This conjugation also takes place
in solution, as seen in the observed difference in the chemical
shifts of signals of formally equivalent N-methyl groups in the
1H and 13C NMR spectra. Thus, two singlets of the same
1
intensity were observed in the H NMR spectrum (2.99 and
3.16 p.p.m.) and two similar methyl signals were observed in
the 13C NMR spectrum (34.3 and 40.4 p.p.m.), which is indi-
cative of the absence of free rotation around the N6—C14
bond in solution. Analysis of the data presented in the
Cambridge Structural Database (Version 5.29 of November
2007; Allen, 2002) show that in azomethines with the
dialkylamino group at the C atom, the relation between the
two bond lengths in the N C—N fragment is rather different,
namely the formal double bond may be shorter, equal to or
even longer than the formal single bond, which may be caused
by the different influence of the fragments bonded to the
azomethine N atom.
Figure 3
The hydrogen-bonded polymeric chain in (I) running along the [110]
direction. Dashed lines indicate hydrogen bonds. Symmetry codes (i) and
(ii) correspond to those in Table 2.
the shortest in the ring, while the other three ring bonds lie in a
rather narrow range (Tables 1 and 3). The tetrazole rings are
essentially planar, with the mean deviations of the tetrazole
In (II), the C5—N5 bond (Table 3) is longer than the C5—
amino bond in 5-aminotetrazoles, which may be an indicative
N
˚
ring atoms from their least-squares plane being 0.0018 (6) A
˚
for (I) and 0.0013 (10) A for (II). The geometries of the
of less conjugation between the lone pair of the azomethine N
atom and the tetrazole ring ꢀ system in (II) compared with
5-aminotetrazoles. The azomethine fragment is in the E
configuration. There are no direction-specific interactions
between adjacent molecules in (II).
benzene rings are normal. In (I), the benzene and tetrazole
rings are essentially noncoplanar, with a dihedral angle of
54.41 (5)ꢁ, while in (II) the corresponding dihedral angle has a
rather low value of 4.15 (11)ꢁ. This noncoplanarity of the rings
in (I) may be caused by steric hindrance due to a 5-amino-
group H atom. This assumption agrees with the essential
noncoplanarity of the benzene and tetrazole rings in the
molecules of all 5-amino-1-aryltetrazoles investigated to date
(Lyakhov et al., 2003).
Quantum chemical and X-ray investigations of 5-amino-
tetrazoles (Lyakhov et al., 2001, 2003, 2008) show that the
conjugation of the 5-amino group lone pair with the ꢀ system
of the tetrazole ring results in a planar configuration of the
amino group, essential shortening of the exocyclic C5—Namino
bond and, to a lesser extent, elongation of the C5 N4
tetrazole ring bond. Moreover, the hydrogen bonds formed by
the 5-amino group in these crystal structures enhance this
effect. For all 5-aminotetrazoles studied to date, the length of
the C5—Namino bond lies in the narrow range 1.330 (2)–
Experimental
1-(4-Nitrophenyl)-1H-tetrazol-5-amine, (I), was prepared from 1-(4-
nitrophenyl)-1H-tetrazole using the one-pot technique reported by
Vorobiov et al. (2006). Single crystals suitable for X-ray crystal
structure analysis were grown by slow evaporation from a tetra-
hydrofuran–benzene solvent system (2:1 v/v) at room temperature.
For the preparation of {(E)-[1-(4-ethoxyphenyl)-1H-tetrazol-5-yl]-
iminomethyl}dimethylamine, (II), a solution containing 1-(4-ethoxy-
phenyl)-1H-tetrazol-5-amine (0.01 mol) in methanol (30 ml) was
treated with N,N-dimethylformamide dimethyl acetal (0.02 mol). The
reaction mixture was boiled under reflux for 2 h, cooled and kept at
273 K for 10 h. The precipitate which formed was filtered off, washed
with cold methanol and dried under reduced pressure (yield 95%,
m.p. 421–422 K). 1H NMR (500 MHz, DMSO-d6): ꢁ 1.34 (t, 3H, CH3),
2.99 (s, 3H, CH3), 3.16 (s, 3H, CH3), 4.08 (q, 2H, CH2), 7.08 (d, 2H,
CHAr), 7.71 (d, 2H, CHAr), 8.57 (s, 1H, CH); 13C NMR (125 MHz,
DMSO-d6): ꢁ 14.5, 34.3, 40.4, 63.4, 114.8, 124.3, 127.3, 158.2, 158.4,
158.7. Single crystals suitable for X-ray crystal structure analysis were
grown by slow evaporation of a benzene solution at room tempera-
ture.
˚
1.3374 (16) A (Lyakhov et al., 2001, 2003, 2008; Bray & White,
1979). The data obtained for (I) agree with the above struc-
tural peculiarities of 5-aminotetrazoles (Table 1).
Molecules of compound (I) are linked by a combination of
N—Hꢀ ꢀ ꢀN and N—Hꢀ ꢀ ꢀO hydrogen bonds (Table 2), forming
polymeric chains running along the [110] direction (Fig. 3).
The chain involves two types of centrosymmetric rings with
R22(8) and R22(20) motifs (Bernstein et al., 1995) centred at
Compound (I)
1
2
1
2
1
2
(12 + n, n, ) and (1 + n, + n, ), respectively (n = zero or an
Crystal data
integer). Only van der Waals interactions are observed
between the chains.
The molecule of (II) is essentially flattened, with a mean
deviation of the non-H atoms from their least-squares plane of
˚
0.0679 (19) A. This geometry is favourable for a conjugated
system spanning the whole molecule. The same lengths of the
formal N5 C14 double and C14—N6 single bonds (Table 3)
C7H6N6O2
Mr = 206.18
Triclinic, P1
ꢄ = 63.135 (18)ꢁ
3
˚
V = 444.55 (19) A
Z = 2
˚
˚
a = 7.8891 (17) A
Mo Kꢂ radiation
ꢅ = 0.12 mmꢂ1
T = 295 (2) K
0.48 ꢃ 0.44 ꢃ 0.42 mm
b = 7.9921 (18) A
˚
c = 8.5877 (18) A
ꢂ = 68.135 (17)ꢁ
ꢃ = 74.049 (17)ꢁ
ꢄ
Acta Cryst. (2008). C64, o414–o416
Lyakhov et al. C7H6N6O2 and C12H16N6O o415

organic compounds
Table 1
Selected bond lengths (A) for (I).
Table 3
Selected bond lengths (A) for (II).
˚
˚
N1—C5
N1—N2
N1—C7
N2—N3
1.3516 (12)
1.3722 (12)
1.4223 (11)
1.2794 (12)
N3—N4
N4—C5
N6—C5
1.3617 (13)
1.3269 (12)
1.3376 (13)
N1—C5
N1—N2
N1—C6
N2—N3
N3—N4
1.359 (2)
1.3647 (19)
1.432 (2)
1.292 (2)
1.356 (2)
N4—C5
C5—N5
N5—C14
C14—N6
1.330 (2)
1.360 (2)
1.313 (2)
1.311 (2)
Table 2
Hydrogen-bond geometry (A, ) for (I).
ꢁ
˚
were included in geometrically calculated positions, with C—H =
˚
˚
0.97 A for the methylene groups, 0.96 A for the methyl groups and
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
˚
0.93 A for the remaining CH groups, and refined using a riding model,
N6—H6Aꢀ ꢀ ꢀN4i
0.866 (16)
0.873 (18)
2.119 (17)
2.234 (18)
2.9684 (14)
3.1003 (14)
166.8 (15)
171.9 (14)
with Uiso(H) = 1.5Ueq(C) for the methyl groups or 1.2Ueq(C) for all
others.
N6—H6Bꢀ ꢀ ꢀO2ii
Symmetry codes: (i) ꢂx þ 1; ꢂy; ꢂz þ 1; (ii) ꢂx þ 2; ꢂy þ 1; ꢂz þ 1.
For both compounds, data collection: R3m Software (Nicolet,
1980); cell refinement: R3m Software; data reduction: R3m Software;
program(s) used to solve structure: SIR97 (Altomare et al., 1999);
program(s) used to refine structure: SHELXL97 (Sheldrick, 2008);
molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and
PLATON (Spek, 2003); software used to prepare material for
publication: PLATON and SHELXL97.
Data collection
Nicolet R3m four-circle
diffractometer
5556 measured reflections
2605 independent reflections
2338 reflections with I > 2ꢆ(I)
Rint = 0.011
3 standard reflections
every 100 reflections
intensity decay: none
Refinement
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: SK3250). Services for accessing these data are
described at the back of the journal.
R[F2 > 2ꢆ(F2)] = 0.042
wR(F2) = 0.121
S = 1.06
160 parameters
All H-atom parameters refined
ꢂ3
˚
Áꢇmax = 0.19 e A
ꢂ3
˚
2605 reflections
Áꢇmin = ꢂ0.28 e A
References
Allen, F. H. (2002). Acta Cryst. B58, 380–388.
Compound (II)
Altomare, A., Burla, M. C., Camalli, M., Cascarano, G. L., Giacovazzo, C.,
Guagliardi, A., Moliterni, A. G. G., Polidori, G. & Spagna, R. (1999). J.
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Katritzky, A. R., Rogovoy, B. V. & Kovalenko, K. V. (2003). J. Org. Chem. 68,
4941–4943.
Crystal data
3
˚
V = 1298.7 (4) A
Z = 4
C12H16N6O
Mr = 260.31
Monoclinic, P21=c
Mo Kꢂ radiation
ꢅ = 0.09 mmꢂ1
T = 294 (2) K
0.42 ꢃ 0.32 ꢃ 0.16 mm
˚
a = 8.4150 (16) A
˚
b = 17.514 (3) A
˚
c = 8.8300 (14) A
ꢃ = 93.694 (14)ꢁ
Data collection
Lyakhov, A. S., Gaponik, P. N. & Voitekhovich, S. V. (2001). Acta Cryst. C57,
185–186.
Nicolet R3m four-circle
diffractometer
3232 measured reflections
2999 independent reflections
2132 reflections with I > 2ꢆ(I)
Rint = 0.015
Lyakhov, A. S., Matulis, V. E., Gaponik, P. N., Voitekhovich, S. V. &
Ivashkevich, O. A. (2008). J. Mol. Struct. 876, 260–267.
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V. E. & Ivashkevich, O. A. (2003). Acta Cryst. C59, o690–o693.
Mrozik, H. H. (1974). US Patent No. 3 830 928.
3 standard reflections
every 100 reflections
intensity decay: none
Nicolet (1980). R3m Software. Nicolet XRD Corporation, Cupertino,
California, USA.
Oshovskii, G. V. & Pinchuk, A. M. (2000). Usp. Khim. 69, 924–939.
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Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.
Spek, A. L. (2003). J. Appl. Cryst. 36, 7–13.
Refinement
R[F2 > 2ꢆ(F2)] = 0.047
wR(F2) = 0.154
S = 1.05
176 parameters
H-atom parameteꢂrs3 constrained
˚
Áꢇmax = 0.20 e A
ꢂ3
˚
2999 reflections
Áꢇmin = ꢂ0.18 e A
ˆ
Tisler, M. (1983). Heterocycles, 20, 1591–1614.
Vorobiov, A. N., Gaponik, P. N., Petrov, P. T. & Ivashkevich, O. A. (2006).
Synthesis, pp. 1307–1312.
Wittenberger, S. J. (1994). Org. Prep. Proced. Int. 26, 499–531.
In (I), H-atom positions were found from a difference Fourier map
and all associated parameters were refined freely. The H atoms in (II)
ꢄ
o416 Lyakhov et al. C7H6N6O2 and C12H16N6O
Acta Cryst. (2008). C64, o414–o416