organic compounds
3-Phenyl-1H-1,2,4-triazol-5-amine–5-phenyl-1H-1,2,4-triazol-3-amine (1/1)
aDepartment of Pharmacy, Faculty of Science, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore, and bDepartment of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
*Correspondence e-mail: phada@nus.edu.sg
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 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
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Refinement
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Data collection: SMART (Bruker, 2001); cell 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.
Supporting information
10.1107/S1600536808042165/ci2720sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536808042165/ci2720Isup2.hkl
(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.
N-bound H-atoms were located in a difference map and refined freely. C-bound H atoms were positioned geometrically (C-H = 0.94 Å) and were constrained in a riding motion approximation with Uiso(H) = 1.2Ueq(C).
Data collection: SMART (Bruker, 2001); cell
SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); 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 (Sheldrick, 2008).Fig. 1. Possible tautomers of 3(5)-phenyl-1,2,4-triazol-5(3)-amine. | |
Fig. 2. The molecular structure of 3(5)-phenyl-1,2,4-triazol-5(3)-amine with the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. | |
Fig. 3. Molecular packing in the crystal, viewed along the b axis. Hydrogen bonds are shown as dashed lines. |
C8H8N4·C8H8N4 | F(000) = 672 |
Mr = 320.36 | Dx = 1.387 Mg m−3 |
Monoclinic, P21/c | Melting point: 460 K |
Hall symbol: -P 2ybc | Mo Kα radiation, λ = 0.71073 Å |
a = 17.817 (2) Å | Cell parameters from 1028 reflections |
b = 5.0398 (6) Å | θ = 2.4–22.6° |
c = 18.637 (2) Å | µ = 0.09 mm−1 |
β = 113.573 (4)° | T = 223 K |
V = 1533.9 (3) Å3 | Rod, colourless |
Z = 4 | 0.60 × 0.10 × 0.06 mm |
Bruker SMART APEX CCD diffractometer | 3523 independent reflections |
Radiation source: fine-focus sealed tube | 2394 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.063 |
ϕ and ω scans | θmax = 27.5°, θmin = 2.2° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2001) | h = −17→23 |
Tmin = 0.947, Tmax = 0.995 | k = −6→6 |
10288 measured reflections | l = −24→20 |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.067 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.168 | H atoms treated by a mixture of independent and constrained refinement |
S = 0.99 | w = 1/[σ2(Fo2) + (0.0813P)2 + 0.5041P] where P = (Fo2 + 2Fc2)/3 |
3523 reflections | (Δ/σ)max = 0.001 |
241 parameters | Δρmax = 0.43 e Å−3 |
0 restraints | Δρmin = −0.24 e Å−3 |
C8H8N4·C8H8N4 | V = 1533.9 (3) Å3 |
Mr = 320.36 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 17.817 (2) Å | µ = 0.09 mm−1 |
b = 5.0398 (6) Å | T = 223 K |
c = 18.637 (2) Å | 0.60 × 0.10 × 0.06 mm |
β = 113.573 (4)° |
Bruker SMART APEX CCD diffractometer | 3523 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2001) | 2394 reflections with I > 2σ(I) |
Tmin = 0.947, Tmax = 0.995 | Rint = 0.063 |
10288 measured reflections |
R[F2 > 2σ(F2)] = 0.067 | 0 restraints |
wR(F2) = 0.168 | H atoms treated by a mixture of independent and constrained refinement |
S = 0.99 | Δρmax = 0.43 e Å−3 |
3523 reflections | Δρmin = −0.24 e Å−3 |
241 parameters |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | ||
N1 | 0.45958 (12) | 0.2679 (4) | 0.41243 (11) | 0.0227 (5) | |
N2 | 0.44655 (12) | 0.1498 (4) | 0.29112 (11) | 0.0228 (5) | |
N3 | 0.50228 (12) | 0.3557 (4) | 0.31965 (12) | 0.0232 (5) | |
H3N | 0.5206 (17) | 0.441 (6) | 0.2883 (17) | 0.034 (8)* | |
N4 | 0.55437 (15) | 0.6210 (5) | 0.43462 (14) | 0.0306 (5) | |
H4A | 0.5543 (18) | 0.650 (6) | 0.483 (2) | 0.047 (9)* | |
H4B | 0.5900 (18) | 0.694 (6) | 0.4217 (17) | 0.038 (8)* | |
C1 | 0.36387 (14) | −0.0976 (5) | 0.34673 (13) | 0.0221 (5) | |
C2 | 0.32601 (15) | −0.2542 (5) | 0.28099 (14) | 0.0275 (6) | |
H2 | 0.3384 | −0.2297 | 0.2369 | 0.033* | |
C3 | 0.26999 (16) | −0.4464 (5) | 0.27973 (16) | 0.0326 (6) | |
H3 | 0.2450 | −0.5525 | 0.2349 | 0.039* | |
C4 | 0.25056 (16) | −0.4837 (5) | 0.34337 (16) | 0.0317 (6) | |
H4 | 0.2119 | −0.6128 | 0.3420 | 0.038* | |
C5 | 0.28814 (18) | −0.3303 (6) | 0.40898 (17) | 0.0405 (7) | |
H5 | 0.2754 | −0.3557 | 0.4528 | 0.049* | |
C6 | 0.34456 (17) | −0.1385 (6) | 0.41101 (16) | 0.0352 (7) | |
H6 | 0.3700 | −0.0352 | 0.4563 | 0.042* | |
C7 | 0.42378 (14) | 0.1068 (5) | 0.34941 (13) | 0.0205 (5) | |
C8 | 0.50768 (14) | 0.4241 (5) | 0.39146 (13) | 0.0223 (5) | |
N5 | 0.18197 (12) | 0.2602 (4) | 0.01779 (11) | 0.0225 (5) | |
N6 | 0.17613 (13) | −0.1706 (4) | 0.02735 (12) | 0.0241 (5) | |
H6N | 0.165 (2) | −0.339 (7) | 0.0188 (19) | 0.057 (10)* | |
N7 | 0.25003 (12) | −0.1005 (4) | 0.08543 (11) | 0.0247 (5) | |
N8 | 0.31434 (13) | 0.3193 (5) | 0.12197 (13) | 0.0257 (5) | |
H8A | 0.3424 (19) | 0.261 (6) | 0.1652 (19) | 0.042 (9)* | |
H8B | 0.302 (2) | 0.500 (7) | 0.1168 (19) | 0.055 (10)* | |
C9 | 0.05728 (14) | 0.0322 (5) | −0.07822 (14) | 0.0237 (5) | |
C10 | 0.03648 (17) | 0.2181 (5) | −0.13815 (16) | 0.0341 (7) | |
H10 | 0.0741 | 0.3502 | −0.1371 | 0.041* | |
C11 | −0.04013 (18) | 0.2079 (6) | −0.19945 (17) | 0.0444 (8) | |
H11 | −0.0542 | 0.3339 | −0.2399 | 0.053* | |
C12 | −0.09593 (17) | 0.0147 (6) | −0.20168 (17) | 0.0423 (8) | |
H12 | −0.1477 | 0.0092 | −0.2435 | 0.051* | |
C13 | −0.07527 (17) | −0.1708 (6) | −0.14209 (18) | 0.0417 (8) | |
H13 | −0.1131 | −0.3025 | −0.1432 | 0.050* | |
C14 | 0.00090 (17) | −0.1621 (6) | −0.08100 (16) | 0.0345 (6) | |
H14A | 0.0148 | −0.2891 | −0.0408 | 0.041* | |
C15 | 0.13744 (15) | 0.0420 (5) | −0.01207 (13) | 0.0219 (5) | |
C16 | 0.24976 (14) | 0.1614 (5) | 0.07732 (13) | 0.0198 (5) |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1 | 0.0273 (11) | 0.0216 (10) | 0.0205 (10) | −0.0031 (9) | 0.0108 (9) | −0.0002 (8) |
N2 | 0.0274 (11) | 0.0216 (10) | 0.0200 (10) | −0.0022 (9) | 0.0099 (8) | −0.0016 (8) |
N3 | 0.0306 (11) | 0.0236 (11) | 0.0193 (10) | −0.0060 (9) | 0.0143 (9) | −0.0013 (9) |
N4 | 0.0378 (13) | 0.0325 (13) | 0.0266 (12) | −0.0140 (11) | 0.0182 (10) | −0.0090 (10) |
C1 | 0.0229 (12) | 0.0212 (12) | 0.0217 (12) | 0.0036 (10) | 0.0082 (10) | −0.0010 (10) |
C2 | 0.0293 (13) | 0.0302 (14) | 0.0244 (13) | −0.0007 (11) | 0.0122 (11) | −0.0013 (11) |
C3 | 0.0286 (14) | 0.0343 (15) | 0.0310 (14) | −0.0080 (12) | 0.0079 (11) | −0.0104 (12) |
C4 | 0.0268 (14) | 0.0275 (14) | 0.0419 (15) | −0.0067 (11) | 0.0150 (12) | 0.0017 (12) |
C5 | 0.0476 (18) | 0.0449 (17) | 0.0391 (16) | −0.0131 (15) | 0.0279 (14) | −0.0024 (14) |
C6 | 0.0448 (16) | 0.0356 (15) | 0.0298 (14) | −0.0133 (13) | 0.0197 (13) | −0.0075 (12) |
C7 | 0.0249 (12) | 0.0190 (12) | 0.0176 (11) | 0.0031 (10) | 0.0085 (9) | 0.0007 (9) |
C8 | 0.0237 (12) | 0.0228 (13) | 0.0208 (12) | 0.0009 (10) | 0.0093 (10) | 0.0011 (10) |
N5 | 0.0246 (10) | 0.0196 (10) | 0.0214 (10) | 0.0019 (8) | 0.0072 (8) | −0.0015 (8) |
N6 | 0.0264 (11) | 0.0176 (11) | 0.0250 (11) | 0.0004 (9) | 0.0067 (9) | 0.0018 (9) |
N7 | 0.0276 (11) | 0.0219 (11) | 0.0211 (10) | 0.0015 (9) | 0.0061 (9) | 0.0004 (8) |
N8 | 0.0267 (12) | 0.0222 (12) | 0.0223 (11) | 0.0028 (9) | 0.0037 (9) | −0.0001 (9) |
C9 | 0.0223 (12) | 0.0203 (12) | 0.0277 (13) | 0.0023 (10) | 0.0091 (10) | −0.0052 (10) |
C10 | 0.0383 (15) | 0.0234 (13) | 0.0338 (14) | 0.0007 (12) | 0.0073 (12) | 0.0002 (11) |
C11 | 0.0453 (18) | 0.0347 (17) | 0.0357 (16) | 0.0085 (14) | −0.0022 (14) | 0.0022 (13) |
C12 | 0.0278 (15) | 0.0420 (18) | 0.0431 (17) | 0.0073 (13) | −0.0008 (13) | −0.0139 (14) |
C13 | 0.0285 (15) | 0.0431 (17) | 0.0506 (18) | −0.0101 (13) | 0.0126 (13) | −0.0157 (15) |
C14 | 0.0357 (15) | 0.0313 (15) | 0.0349 (15) | −0.0016 (12) | 0.0123 (12) | −0.0024 (12) |
C15 | 0.0261 (12) | 0.0193 (12) | 0.0218 (12) | 0.0001 (10) | 0.0113 (10) | −0.0022 (10) |
C16 | 0.0241 (12) | 0.0196 (12) | 0.0166 (11) | 0.0031 (10) | 0.0092 (9) | −0.0009 (9) |
N1—C8 | 1.332 (3) | N5—C15 | 1.340 (3) |
N1—C7 | 1.359 (3) | N5—C16 | 1.366 (3) |
N2—C7 | 1.321 (3) | N6—C15 | 1.326 (3) |
N2—N3 | 1.387 (3) | N6—N7 | 1.375 (3) |
N3—C8 | 1.348 (3) | N6—H6N | 0.87 (4) |
N3—H3N | 0.89 (3) | N7—C16 | 1.328 (3) |
N4—C8 | 1.337 (3) | N8—C16 | 1.372 (3) |
N4—H4A | 0.92 (3) | N8—H8A | 0.81 (3) |
N4—H4B | 0.85 (3) | N8—H8B | 0.94 (4) |
C1—C2 | 1.385 (3) | C9—C14 | 1.389 (4) |
C1—C6 | 1.388 (3) | C9—C10 | 1.390 (4) |
C1—C7 | 1.470 (3) | C9—C15 | 1.468 (3) |
C2—C3 | 1.385 (4) | C10—C11 | 1.387 (4) |
C2—H2 | 0.94 | C10—H10 | 0.94 |
C3—C4 | 1.375 (4) | C11—C12 | 1.380 (4) |
C3—H3 | 0.94 | C11—H11 | 0.94 |
C4—C5 | 1.373 (4) | C12—C13 | 1.384 (4) |
C4—H4 | 0.94 | C12—H12 | 0.94 |
C5—C6 | 1.384 (4) | C13—C14 | 1.380 (4) |
C5—H5 | 0.94 | C13—H13 | 0.94 |
C6—H6 | 0.94 | C14—H14A | 0.94 |
C8—N1—C7 | 103.55 (19) | C15—N5—C16 | 102.86 (19) |
C7—N2—N3 | 102.47 (18) | C15—N6—N7 | 110.6 (2) |
C8—N3—N2 | 109.15 (19) | C15—N6—H6N | 131 (2) |
C8—N3—H3N | 129.2 (18) | N7—N6—H6N | 118 (2) |
N2—N3—H3N | 120.4 (18) | C16—N7—N6 | 101.93 (18) |
C8—N4—H4A | 118 (2) | C16—N8—H8A | 115 (2) |
C8—N4—H4B | 121 (2) | C16—N8—H8B | 113 (2) |
H4A—N4—H4B | 120 (3) | H8A—N8—H8B | 119 (3) |
C2—C1—C6 | 118.5 (2) | C14—C9—C10 | 119.3 (2) |
C2—C1—C7 | 121.3 (2) | C14—C9—C15 | 120.1 (2) |
C6—C1—C7 | 120.2 (2) | C10—C9—C15 | 120.7 (2) |
C3—C2—C1 | 120.4 (2) | C11—C10—C9 | 119.7 (3) |
C3—C2—H2 | 119.8 | C11—C10—H10 | 120.2 |
C1—C2—H2 | 119.8 | C9—C10—H10 | 120.2 |
C4—C3—C2 | 120.6 (2) | C12—C11—C10 | 120.7 (3) |
C4—C3—H3 | 119.7 | C12—C11—H11 | 119.6 |
C2—C3—H3 | 119.7 | C10—C11—H11 | 119.6 |
C5—C4—C3 | 119.3 (2) | C11—C12—C13 | 119.7 (3) |
C5—C4—H4 | 120.3 | C11—C12—H12 | 120.2 |
C3—C4—H4 | 120.3 | C13—C12—H12 | 120.2 |
C4—C5—C6 | 120.5 (3) | C14—C13—C12 | 119.9 (3) |
C4—C5—H5 | 119.7 | C14—C13—H13 | 120.0 |
C6—C5—H5 | 119.7 | C12—C13—H13 | 120.0 |
C5—C6—C1 | 120.5 (3) | C13—C14—C9 | 120.7 (3) |
C5—C6—H6 | 119.7 | C13—C14—H14A | 119.6 |
C1—C6—H6 | 119.7 | C9—C14—H14A | 119.6 |
N2—C7—N1 | 114.8 (2) | N6—C15—N5 | 110.0 (2) |
N2—C7—C1 | 123.0 (2) | N6—C15—C9 | 123.7 (2) |
N1—C7—C1 | 122.1 (2) | N5—C15—C9 | 126.3 (2) |
N1—C8—N4 | 125.5 (2) | N7—C16—N5 | 114.6 (2) |
N1—C8—N3 | 110.0 (2) | N7—C16—N8 | 122.9 (2) |
N4—C8—N3 | 124.6 (2) | N5—C16—N8 | 122.4 (2) |
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···N7iv | 0.94 (4) | 2.19 (4) | 3.115 (3) | 169 (3) |
Symmetry codes: (i) −x+1, y+1/2, −z+1/2; (ii) −x+1, −y+1, −z+1; (iii) x, y−1, z; (iv) x, y+1, z. |
Experimental details
Crystal data | |
Chemical formula | C8H8N4·C8H8N4 |
Mr | 320.36 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 223 |
a, b, c (Å) | 17.817 (2), 5.0398 (6), 18.637 (2) |
β (°) | 113.573 (4) |
V (Å3) | 1533.9 (3) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.09 |
Crystal size (mm) | 0.60 × 0.10 × 0.06 |
Data collection | |
Diffractometer | Bruker SMART APEX CCD diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 2001) |
Tmin, Tmax | 0.947, 0.995 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 10288, 3523, 2394 |
Rint | 0.063 |
(sin θ/λ)max (Å−1) | 0.650 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.067, 0.168, 0.99 |
No. of reflections | 3523 |
No. of parameters | 241 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.43, −0.24 |
Computer programs: SMART (Bruker, 2001), SAINT (Bruker, 2001), SHELXS97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).
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···N7iv | 0.94 (4) | 2.19 (4) | 3.115 (3) | 169 (3) |
Symmetry codes: (i) −x+1, y+1/2, −z+1/2; (ii) −x+1, −y+1, −z+1; (iii) x, y−1, z; (iv) x, y+1, z. |
Acknowledgements
This work was supported by the National Medical Research Council, Singapore (grant Nos. NMRC/NIG/0019/2008 and NMRC/NIG/0020/2008).
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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).