3-Phenyl-1H-1,2,4-triazol-5-amine–5-phenyl-1H-1,2,4-triazol-3-amine (1/1)

Anton V Dolzhenko; Geok Kheng Tan; Lip Lin Koh; Anna V Dolzhenko; Wai Keung Chui

doi:10.1107/S1600536808042165

. 2008 Dec 17;65(Pt 1):o126. doi: 10.1107/S1600536808042165

3-Phenyl-1H-1,2,4-triazol-5-amine–5-phenyl-1H-1,2,4-triazol-3-amine (1/1)

Anton V Dolzhenko ^a,^*, Geok Kheng Tan ^b, Lip Lin Koh ^b, Anna V Dolzhenko ^a, Wai Keung Chui ^a

PMCID: PMC2968046 PMID: 21581587

Abstract

In the title compound, C₈H₈N₄·C₈H₈N₄, two tautomers, viz. 3-phenyl-1,2,4-triazol-5-amine and 5-phenyl-1,2,4-triazol-3-amine, are crystallized together in equal amounts. The 3-phenyl-1,2,4-triazol-5-amine molecule is essentially planar; the phenyl ring makes a dihedral angle of 2.3 (2)° with the mean plane of the 1,2,4-triazole ring. In the 5-phenyl-1,2,4-triazol-3-amine tautomer, the mean planes of the phenyl and 1,2,4-triazole rings form a dihedral angle of 30.8 (2)°. The π-electron delocalization of the amino group with the 1,2,4-triazole nucleus in the 3-phenyl-1,2,4-triazol-5-amine molecule is more extensive than that in the 5-phenyl-1,2,4-triazol-3-amine tautomer. The molecules are linked into a two-dimensional network parallel to (100) by N—H⋯N hydrogen bonds.

Related literature

For a summary of structural data for 1,2,4-triazoles, see: Buzykin et al. (2006 ▶). For the crystal structure of 3-pyridin-2-yl-1,2,4-triazol-5-amine, see: Dolzhenko et al. (2009 ▶). For the use of 1,2,4-triazol-5-amines as building blocks in the synthesis of fused heterocyclic systems, see: Dolzhenko et al. (2006 ▶, 2007a ▶,b ▶); Fischer (2007 ▶).

Experimental

Crystal data

C₈H₈N₄·C₈H₈N₄
M _r = 320.36
Monoclinic,
a = 17.817 (2) Å
b = 5.0398 (6) Å
c = 18.637 (2) Å
β = 113.573 (4)°
V = 1533.9 (3) Å³
Z = 4
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 223 (2) K
0.60 × 0.10 × 0.06 mm

Data collection

Bruker SMART APEX CCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2001 ▶) T _min = 0.947, T _max = 0.995
10288 measured reflections
3523 independent reflections
2394 reflections with I > 2σ(I)
R _int = 0.063

Refinement

R[F ² > 2σ(F ²)] = 0.067
wR(F ²) = 0.168
S = 0.99
3523 reflections
241 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.43 e Å⁻³
Δρ_min = −0.24 e Å⁻³

Data collection: SMART (Bruker, 2001 ▶); cell refinement: SAINT (Bruker, 2001 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXS97 (Sheldrick, 2008 ▶); molecular graphics: SHELXTL (Sheldrick, 2008 ▶); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808042165/ci2720sup1.cif

e-65-0o126-sup1.cif^{(17.7KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808042165/ci2720Isup2.hkl

e-65-0o126-Isup2.hkl^{(172.8KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N3—H3N⋯N2ⁱ	0.89 (3)	2.08 (3)	2.966 (3)	175 (3)
N4—H4A⋯N1ⁱⁱ	0.92 (3)	2.09 (3)	3.011 (3)	173 (3)
N4—H4B⋯N8ⁱ	0.85 (3)	2.25 (3)	3.091 (3)	170 (3)
N6—H6N⋯N5ⁱⁱⁱ	0.87 (4)	2.04 (4)	2.879 (3)	159 (3)
N8—H8A⋯N2	0.81 (3)	2.41 (3)	3.206 (3)	168 (3)
N8—H8B⋯N7^iv	0.94 (4)	2.19 (4)	3.115 (3)	169 (3)

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) .

Acknowledgments

This work was supported by the National Medical Research Council, Singapore (grant Nos. NMRC/NIG/0019/2008 and NMRC/NIG/0020/2008).

supplementary crystallographic information

Comment

1,2,4-Triazol-5-amines have been used as building blocks for the synthesis of fused heterocyclic systems, e.g. 1,2,4-triazolo[1,5-a]pyrimidines (Fischer, 2007) and 1,2,4-triazolo[1,5-a][1,3,5]triazines (Dolzhenko et al., 2006). Herein, we report the structural study of 3(5)-phenyl-1,2,4-triazol-5(3)-amine, which was used as a synthon in our previous works (Dolzhenko et al., 2007a,b).

Due to annular tautomerism in 1,2,4-triazole ring, there is a theoretical possibility of three tautomeric forms, namely 3-phenyl-1,2,4-triazol-5-amine (I), 5-phenyl-1,2,4-triazol-3-amine (II), and 5-phenyl-4H-1,2,4-triazol-3-amine (III) (Fig.1).

Usually, tautomerizable 1,2,4-triazoles with nonequivalent substituents at positions 3 and 5 crystallize as a tautomer bearing at position 5 substituent with relatively more pronounced electronodonor properties (Buzykin et al., 2006). Considering significant difference in electronic properties of phenyl and amino group, the crystal would be assembled from the molecules of tautomer I analogously to the reported 3-pyridin-2-yl-1,2,4-triazol-5-amine (Dolzhenko et al., 2009). Surprisingly, two tautomeric forms I and II were found crystallized together in the crystal. To the best of our knowledge, this is the first example of existence in crystal of unequally 3,5-disubstituted tautomerizable 1,2,4-triazole tautomeric form with electronodonor group located at position 3.

The geometry of the tautomer I molecule is essentially planar (Fig.2). The amino group is involved in π-electron delocalization with the 1,2,4-triazole nucleus. It is almost planar with small deviation 0.06 (2) Å of the nitrogen atom from the C8/H4A/H4B plane. The length of the C8—N4 bond is 1.337 (3) Å. The π-electron delocalization of the amino group of II with the 1,2,4-triazole nucleus is significantly lower. The nitrogen atom (N8) of the amino group adopts a pyramidal configuration with 0.21 (2) Å deviation of the nitrogen atom from the C16/H8A/H8B plane. The C16—N8 bond [1.372 (3) Å] is also longer. The phenyl ring of I makes a small dihedral angle of 2.3 (2)° with the mean plane of the 1,2,4-triazole ring. The molecule of tautomer II loses this planarity. The mean planes of the phenyl and 1,2,4-triazole rings of II form a dihedral angle of 30.8 (2)°.

The molecules are linked into a two-dimensional network parallel to the (100) by N—H···N hydrogen bonds (Table 1 and Fig.3).

Experimental

(5)-Phenyl-1,2,4-triazol-5(3)-amine was prepared according to Dolzhenko et al. (2007a,b). The crystals suitable for crystallographic analysis were grown by recrystallization from ethanol.