1,3-Bis(4-nitro­phenyl)­triazene

The structure of the title compound, C₁₂H₉N₅O₄, reveals an almost planar mol­ecule (r.m.s. deviation = 0.061 Å), in which the interplanar angle between the phenyl rings is 5.7 (1)° and the largest interplanar angle is that between the phenyl ring and the nitro group of one of the 4-nitro­phenyl substituents [8.8 (3)°]. The observed mol­ecular conformation suggests a delocalization of π-electrons extended over the diazo­amine group and the terminal aryl substituents. Intermolecular N—H...O interactions between the twofold screw-related mol­ecules give rise to helical chains along the [010] direction. Intermolecular C—H...O interactions then generate sheets of mol­ecules in the (10) plane, and these sheets are held together by N...C and O...O π–π interactions.

S1. Comment

Numerous examples of free 1,3-disubstituted triazenes, RN═N—N(H)R, characterized by X-ray diffraction studies confirm a trans stereochemistry about the N═N double bond (Moore & Robinson, 1986). During the past few decades, asymmetric alkyl/aryl-substituted triazenes have been investigated for their biological activity. The resonance effect in the diazoamino group has been related to the antitumour activity of some triazene derivatives (Zhang et al., 1999). On the other hand, studies of molecules with DNA binding affinity indicate that the planarity has a marked effect on the insertion between the base pairs (Mahadevan & Palaniandavar, 1998; Zhen et al., 1999, 2000). We report here the synthesis and the structural characterization of the title compound, (I), a symmetric disubstituted 1,3-diaryltriazene that has π acid nitro groups on the p-substituted terminal aryl (ar) rings.

The molecular structure of (I) is shown in Fig. 1 and selected geometric parameters are given in Table 1. Deviations from typical N—N and C_ar—N bond lengths suggest that the delocalization of the π electrons on the triazene group has extended to the terminal 4-nitrophenyl substituents. The N12δb N13 bond [1.263 (2) Å] is longer than the characteristic double bond (1.24 Å), whereas the N11—N12 bond [1.340 (2) Å] is shorter than the characteristic value for a single bond (1.44 Å) (International Tables for X-Ray Crystallography, 1985, Vol. III, p. 270). Both the N11—C11 [1.383 (2) Å] and the N13—C21 [1.430 (2) Å] bond is shorter than the length expected for a C_ar—N single bond. These values are in good agreement with the distances found in the related compound 1,3-bis(3-nitrophenyl)triazene [N4═N3 = 1.261 (2) Å, N2—N3 = 1.326 (2) Å, N2—C5 = 1.393 (2) Å and N4—C11 = 1.426 (2) Å; Zhang et al., 1999].

The crystal structure contains molecules related by a twofold screw axis, which form helical chains along the [010] crystallographic direction via N—H···O hydrogen bonds (Table 2). These chains are linked by C—H···O intermolecular interactions (Table 2) to generate sheets in the (10–1) plane (Fig. 2). These sheets are then linked into a three-dimensional molecular array by N···C and O···O π–π interactions [N11···C21^iv = 3.388 (3) Å and O21···O21^v = 3.117 (4) Å; symmetry codes: (iv) x,-y + 3/2, z + 1/2; (vi) −x, −y + 2,-z]. These values are in good agreement with the π–π contacts found in 1,3-bis(3-nitrophenyl)triazene [N···C = 3.387 (3) Å and O···O = 3.182 (3) Å; Zhang et al., 1999].

Because of the strong π acidity of the nitro groups, which favours the delocalization of the π electrons and the conjugation between the C11–C16 and C21–C26 phenyl rings and the N═N—N(H) moiety, the whole molecule is almost planar [interplanar angles O11/N1/O12|C11–C16 = 7.3 (1)°, O21/N2/O22|C21–C26 = 8.8 (3)°, C11–C16|H11/N11/N12/N13 = 6.4 (1)°, C21–C22|N13/N12/N11/H11 = 3.7 (1)°]. The weak intermolecular C16···O21ⁱⁱ contact [3.194 (3) Å; see Table 2 for symmetry code) causes the C11–C16 phenyl ring to deviate by an angle of 6.4 (1)° from the plane defined by the N13═N12—N11—H11 moiety, while the C21—C26 phenyl ring remains nearly coplanar with the diazoamino group.

S2. Experimental

4-Nitroaniline (21.5 g, 155 mmol) was dissolved in glacial acetic acid (40 ml) and cooled below room temperature. A sodium nitrite solution (5.4 g, 78 mmol) in water (100 ml) was added slowly, with continuous stirring. The yellow reaction mixture was then neutralized with an aqueous solution (10%) of NaHCO₃, and a yellow precipitate was observed. The yellow crude product was isolated by filtration and dried over P₂O₅ under vacuum, and the product was recrystallized from a tetrahydrofurane/n-hexane mixture (1:1). Yellow column-shaped crystals suitable for X-ray analysis were obtained by slow evaporation of the solvent mixture (yield 15.1 g, 67.5%; m.p. 506 K).

S3. Refinement

The positional parameters of the H atoms were obtained geometrically, the C—H and N—H distances were fixed (0.93 Å for Csp² and 0.86 Å for Nsp² H atoms), and the atoms were refined as riding on their respective C and N atoms, with U_iso values of 1.2 times the U_eq value of the attached Csp² and Nsp² atoms. The nitro atoms show a large thermal motion, as indicated by their elongated displacement ellipsoids (Fig. 1). Split peaks for these atoms were not observed and consequently a disorder model was not used.

Computing details

Data collection: CAD-4 EXPRESS (Enraf Nonius, 1994); cell refinement: CAD-4 EXPRESS (Enraf Nonius, 1994); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997), PLATON (Spek 2003); software used to prepare material for publication: WinGX publication routines (Farrugia, 1999).

Figures

	Fig. 1. The molecular structure of (I), with 50% probability displacement ellipsoids for non-H atoms. H atoms are shown as small spheres of a arbitrary radii.
	Fig. 2. A view of a sheet of molecules, showing the N–H···O and C—H···O interactions. Atoms marked with an at (@), a dollar sign ($) or a hash (#) are at the symmetry positions (1 − x, 0.5 + y, 1.5 − z), (-x, −0.5 + y, 0.5 − z) and (1 − x, −0.5 + y, 1.5 − z), respectively.

(I)

Crystal data

C12H9N5O4	F(000) = 592
Mr = 287.24	Dx = 1.478 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 25 reflections
a = 13.452 (1) Å	θ = 2.1–25.4°
b = 13.671 (2) Å	µ = 0.12 mm^−1
c = 7.034 (2) Å	T = 293 K
β = 93.442 (11)°	Column, yellow
V = 1291.2 (4) Å^3	0.30 × 0.20 × 0.10 mm
Z = 4

Data collection

Enraf–Nonius CAD-4 diffractometer	θmax = 25.4°, θmin = 2.1°
Graphite monochromator	h = −16→16
θ/2θ scans	k = 0→16
2581 measured reflections	l = 0→8
2375 independent reflections	3 standard reflections every 60 min
1405 reflections with I > 2σ(I)	intensity decay: 1%
Rint = 0.017

Refinement

Refinement on F^2	H-atom parameters constrained
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0647P)^2 + 0.0938P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.038	(Δ/σ)max < 0.001
wR(F^2) = 0.124	Δρmax = 0.18 e Å^−3
S = 0.98	Δρmin = −0.16 e Å^−3
2375 reflections	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
191 parameters	Extinction coefficient: 0.015 (2)
0 restraints

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Mean-plane data from final SHELXL refinemente run:-

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

− 6.7348 (0.0165) x − 0.4055 (0.0546) y + 6.2859 (0.0050) z = 1.1593 (0.0172)

* 0.0000 (0.0000) O11 * 0.0000 (0.0000) N1 * 0.0000 (0.0000) O12

Rms deviation of fitted atoms = 0.0000

− 8.1515 (0.0092) x − 0.2871 (0.0124) y + 5.8393 (0.0037) z = 0.4044 (0.0080)

Angle to previous plane (with approximate e.s.d.) = 7.27 (0.14)

* 0.0011 (0.0013) C11 * 0.0039 (0.0014) C12 * −0.0041 (0.0014) C13 * −0.0007 (0.0014) C14 * 0.0057 (0.0015) C15 * −0.0059 (0.0014) C16

Rms deviation of fitted atoms = 0.0041

− 6.9927 (0.0142) x − 0.8449 (0.0171) y + 6.2019 (0.0046) z = 0.6824 (0.0161)

Angle to previous plane (with approximate e.s.d.) = 6.36 (0.13)

* −0.0062 (0.0005) H11 * 0.0096 (0.0007) N11 * −0.0074 (0.0005) N12 * 0.0040 (0.0003) N13

Rms deviation of fitted atoms = 0.0071

− 7.0902 (0.0102) x + 0.0405 (0.0123) y + 6.1894 (0.0034) z = 1.4255 (0.0121)

Angle to previous plane (with approximate e.s.d.) = 3.74 (0.13)

* −0.0054 (0.0014) C21 * 0.0007 (0.0015) C22 * 0.0044 (0.0015) C23 * −0.0049 (0.0014) C24 * 0.0001 (0.0014) C25 * 0.0050 (0.0014) C26

Rms deviation of fitted atoms = 0.0041

− 6.2152 (0.0390) x + 1.8988 (0.0408) y + 6.3452 (0.0125) z = 3.4102 (0.0420)

Angle to previous plane (with approximate e.s.d.) = 8.77 (0.29)

* 0.0000 (0.0000) O21 * 0.0000 (0.0000) N2 * 0.0000 (0.0000) O22

Rms deviation of fitted atoms = 0.0000

− 7.1427 (0.0049) x − 0.4798 (0.0027) y + 6.1689 (0.0022) z = 0.9011 (0.0036)

Angle to previous plane (with approximate e.s.d.) = 10.87 (0.28)

* 0.0597 (0.0018) O11 * 0.0184 (0.0017) N1 * −0.0154 (0.0018) O12 * −0.0305 (0.0019) C11 * 0.0904 (0.0018) C12 * 0.0991 (0.0019) C13 * 0.0003 (0.0019) C14 * −0.1107 (0.0020) C15 * −0.1397 (0.0020) C16 * −0.0371 (0.0014) N11 * −0.0515 (0.0013) H11 * −0.0210 (0.0016) N12 * 0.0209 (0.0016) N13 * 0.0396 (0.0019) C21 * 0.0736 (0.0020) C22 * 0.0515 (0.0019) C23 * −0.0106 (0.0018) C24 * −0.0338 (0.0019) C25 * −0.0030 (0.0018) C26

Rms deviation of fitted atoms = 0.0610

− 8.1515 (0.0092) x − 0.2871 (0.0124) y + 5.8393 (0.0037) z = 0.4044 (0.0080)

Angle to previous plane (with approximate e.s.d.) = 5.27 (0.08)

* 0.0011 (0.0013) C11 * 0.0039 (0.0014) C12 * −0.0041 (0.0014) C13 * −0.0007 (0.0014) C14 * 0.0057 (0.0015) C15 * −0.0059 (0.0014) C16

Rms deviation of fitted atoms = 0.0041

− 7.0902 (0.0102) x + 0.0405 (0.0123) y + 6.1894 (0.0034) z = 1.4255 (0.0121)

Angle to previous plane (with approximate e.s.d.) = 5.67 (0.11)

* −0.0054 (0.0014) C21 * 0.0007 (0.0015) C22 * 0.0044 (0.0015) C23 * −0.0049 (0.0014) C24 * 0.0001 (0.0014) C25 * 0.0050 (0.0014) C26

Rms deviation of fitted atoms = 0.0041

Hydrogen bonds with H.·A < r(A) + 2.000 Angstroms and <DHA > 110 °.

D—H d(D—H) d(H.·A) <DHA d(D.·A) A

N11—H11 0.86 2.11 159 2.929 (2) O12 [−x + 1, y + 1/2, −z + 3/2]

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O12	0.43782 (12)	0.22721 (11)	0.6682 (3)	0.0800 (6)
O11	0.29617 (13)	0.23236 (11)	0.5167 (3)	0.0851 (6)
O22	0.02435 (16)	1.14876 (15)	0.2175 (3)	0.1060 (8)
O21	−0.06985 (12)	1.02428 (15)	0.1625 (3)	0.0825 (6)
N11	0.37270 (12)	0.68066 (11)	0.6245 (2)	0.0444 (4)
H11	0.4225	0.7100	0.6821	0.053*
N12	0.29723 (12)	0.73297 (11)	0.5438 (2)	0.0430 (4)
N13	0.30850 (11)	0.82373 (12)	0.5707 (2)	0.0439 (4)
N1	0.36748 (14)	0.27316 (12)	0.5958 (3)	0.0553 (5)
N2	0.00714 (15)	1.06165 (18)	0.2267 (3)	0.0646 (6)
C11	0.37069 (13)	0.57963 (13)	0.6154 (3)	0.0386 (5)
C12	0.44457 (13)	0.52635 (14)	0.7164 (3)	0.0425 (5)
H12	0.4944	0.5589	0.7888	0.051*
C13	0.44430 (14)	0.42656 (15)	0.7097 (3)	0.0447 (5)
H13	0.4939	0.3908	0.7760	0.054*
C14	0.36885 (14)	0.37937 (13)	0.6027 (3)	0.0428 (5)
C15	0.29484 (15)	0.43071 (15)	0.5030 (3)	0.0460 (5)
H15	0.2445	0.3975	0.4332	0.055*
C16	0.29546 (14)	0.53064 (14)	0.5068 (3)	0.0440 (5)
H16	0.2463	0.5659	0.4378	0.053*
C21	0.22772 (14)	0.87928 (14)	0.4845 (3)	0.0408 (5)
C22	0.14358 (15)	0.83812 (16)	0.3894 (3)	0.0512 (6)
H22	0.1365	0.7705	0.3821	0.061*
C23	0.07145 (15)	0.89813 (17)	0.3070 (3)	0.0542 (6)
H23	0.0150	0.8717	0.2439	0.065*
C24	0.08370 (14)	0.99785 (16)	0.3189 (3)	0.0475 (5)
C25	0.16511 (15)	1.04029 (14)	0.4127 (3)	0.0482 (5)
H25	0.1714	1.1080	0.4195	0.058*
C26	0.23734 (14)	0.97985 (15)	0.4966 (3)	0.0435 (5)
H26	0.2929	1.0070	0.5617	0.052*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O12	0.0732 (11)	0.0411 (9)	0.1204 (15)	0.0125 (8)	−0.0379 (10)	0.0021 (9)
O11	0.0788 (12)	0.0477 (10)	0.1234 (16)	−0.0128 (9)	−0.0386 (11)	−0.0085 (10)
O22	0.1082 (16)	0.0673 (13)	0.1374 (19)	0.0282 (12)	−0.0355 (14)	0.0193 (13)
O21	0.0473 (10)	0.1146 (16)	0.0835 (13)	0.0179 (10)	−0.0142 (9)	0.0088 (11)
N11	0.0406 (9)	0.0370 (10)	0.0542 (10)	0.0024 (7)	−0.0093 (7)	0.0014 (8)
N12	0.0439 (9)	0.0387 (10)	0.0460 (10)	0.0031 (8)	−0.0008 (7)	0.0020 (8)
N13	0.0439 (10)	0.0354 (9)	0.0516 (11)	0.0017 (7)	−0.0045 (8)	0.0030 (8)
N1	0.0564 (11)	0.0379 (10)	0.0694 (13)	−0.0015 (9)	−0.0141 (10)	−0.0017 (9)
N2	0.0568 (12)	0.0772 (15)	0.0589 (13)	0.0210 (12)	−0.0052 (10)	0.0070 (11)
C11	0.0370 (10)	0.0367 (11)	0.0418 (11)	0.0008 (9)	0.0005 (9)	0.0017 (9)
C12	0.0381 (10)	0.0389 (11)	0.0492 (12)	−0.0024 (8)	−0.0086 (9)	−0.0004 (9)
C13	0.0399 (11)	0.0416 (12)	0.0513 (13)	0.0041 (9)	−0.0085 (9)	0.0035 (10)
C14	0.0425 (11)	0.0355 (10)	0.0498 (12)	0.0008 (9)	−0.0027 (9)	−0.0005 (9)
C15	0.0417 (11)	0.0437 (11)	0.0508 (13)	−0.0030 (10)	−0.0127 (9)	−0.0013 (10)
C16	0.0418 (11)	0.0416 (12)	0.0469 (12)	0.0051 (9)	−0.0104 (9)	0.0042 (9)
C21	0.0382 (10)	0.0398 (11)	0.0441 (11)	0.0036 (8)	0.0006 (9)	0.0020 (9)
C22	0.0475 (12)	0.0395 (11)	0.0655 (14)	−0.0026 (9)	−0.0065 (11)	−0.0027 (10)
C23	0.0376 (11)	0.0591 (14)	0.0644 (14)	0.0013 (10)	−0.0110 (10)	−0.0036 (11)
C24	0.0412 (11)	0.0518 (13)	0.0490 (12)	0.0119 (10)	−0.0002 (9)	0.0047 (10)
C25	0.0525 (12)	0.0380 (12)	0.0536 (13)	0.0057 (9)	0.0003 (10)	0.0015 (9)
C26	0.0424 (11)	0.0398 (12)	0.0475 (12)	0.0005 (9)	−0.0041 (9)	0.0000 (9)

Geometric parameters (Å, º)

O12—N1	1.221 (2)	C13—H13	0.93
O11—N1	1.215 (2)	C14—C15	1.375 (3)
O22—N2	1.216 (3)	C15—C16	1.366 (3)
O21—N2	1.217 (2)	C15—H15	0.93
N11—N12	1.340 (2)	C16—H16	0.93
N11—C11	1.383 (2)	C21—C26	1.383 (2)
N11—H11	0.86	C21—C22	1.398 (3)
N12—N13	1.263 (2)	C22—C23	1.372 (3)
N13—C21	1.430 (2)	C22—H22	0.93
N1—C14	1.453 (2)	C23—C24	1.375 (3)
N2—C24	1.470 (3)	C23—H23	0.93
C11—C12	1.392 (2)	C24—C25	1.373 (3)
C11—C16	1.401 (3)	C25—C26	1.381 (3)
C12—C13	1.365 (3)	C25—H25	0.93
C12—H12	0.93	C26—H26	0.93
C13—C14	1.386 (3)
N2—O21—O21^i	79.90 (13)	C15—C14—C13	121.56 (18)
N2—O21—C16^ii	153.54 (16)	C15—C14—N1	119.05 (18)
O21^i—O21—C16^ii	109.49 (9)	C13—C14—N1	119.39 (17)
N12—N11—C11	120.09 (16)	C16—C15—C14	119.80 (19)
N12—N11—O12^iii	135.19 (12)	C16—C15—H15	120.1
C11—N11—O12^iii	104.71 (11)	C14—C15—H15	120.1
N12—N11—C21^iv	89.44 (11)	C15—C16—C11	119.46 (18)
C11—N11—C21^iv	77.44 (11)	C15—C16—O21^v	87.76 (13)
O12^iii—N11—C21^iv	101.72 (7)	C11—C16—O21^v	148.78 (13)
N12—N11—H11	120.0	C15—C16—H16	120.3
C11—N11—H11	120.0	C11—C16—H16	120.3
C21^iv—N11—H11	103.1	C26—C21—C22	119.97 (19)
N13—N12—N11	112.32 (15)	C26—C21—N13	115.84 (18)
N12—N13—C21	112.14 (15)	C22—C21—N13	124.18 (18)
O11—N1—O12	121.69 (18)	C23—C22—C21	119.5 (2)
O11—N1—C14	118.83 (18)	C23—C22—H22	120.2
O12—N1—C14	119.48 (17)	C21—C22—H22	120.2
O22—N2—O21	123.5 (2)	C22—C23—C24	119.21 (19)
O22—N2—C24	118.3 (2)	C22—C23—H23	120.4
O21—N2—C24	118.2 (2)	C24—C23—H23	120.4
N11—C11—C12	119.18 (17)	C25—C24—C23	122.50 (18)
N11—C11—C16	120.93 (16)	C25—C24—N2	118.6 (2)
C12—C11—C16	119.88 (17)	C23—C24—N2	118.9 (2)
C13—C12—C11	120.33 (18)	C24—C25—C26	118.24 (19)
C13—C12—H12	119.8	C24—C25—H25	120.9
C11—C12—H12	119.8	C26—C25—H25	120.9
C12—C13—C14	118.96 (18)	C25—C26—C21	120.52 (19)
C12—C13—H13	120.5	C25—C26—H26	119.7
C14—C13—H13	120.5	C21—C26—H26	119.7

Symmetry codes: (i) −x, −y+2, −z; (ii) −x, y+1/2, −z+1/2; (iii) −x+1, y+1/2, −z+3/2; (iv) x, −y+3/2, z+1/2; (v) −x, y−1/2, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N11—H11···O12^iii	0.86	2.11	2.929 (2)	159
C12—H12···O12^iii	0.93	2.49	3.248 (3)	139
C16—H16···O21^v	0.93	2.50	3.194 (3)	131
C25—H25···O11^vi	0.93	2.46	3.222 (3)	140

Symmetry codes: (iii) −x+1, y+1/2, −z+3/2; (v) −x, y−1/2, −z+1/2; (vi) x, y+1, z.