1,2,4,5-Tetra­kis(diazido­meth­yl)benzene

The mol­ecule of the title compound, C₁₀H₆N₂₄, lies on a crystallographic inversion centre located in the middle of the benzene ring. Steric overcrowding by the bulky N₃ groups is avoided by the tendency of four azide entities to be arranged parallel to the benzene ring and the other four azide groups to be arranged alternately above and below the benzene plane in a skeletal C_i symmetry. The compound is of inter­est for high-energy research and as a precursor for the synthesis of carbon nanotubes, nanospheres or high-nitro­gen carbon nitrides with great potential for biological and technological applications.

S1. Comment

Some 80 years ago Mills and Nixon (Mills & Nixon, 1930) put forward the interesting question of whether strain could lead to a localization of aromatic double bonds. Since then, for compounds comprising three- or four-membered rings annulated onto the benzene nucleus, a strain-induced bond localization has been discussed [but it remains controversial?] controversially (Collins et al., 1990; Balbridge & Siegel, 1992; Siegel, 1994; Stanger et al., 1997). The X-ray diffraction study of a compound containing a benzene ring connected to a spiropentane moiety, however, shows indeed a minor bond alternation that is caused by the spiropentane subunit working as a tensile spring. Thus, while the annulated bond is expanded, the other C–C bonds of the benzene ring show alternating distances leaning toward one Kekule structure (Boese et al., 1989). We were interested to investigate whether a similar effect can be observed by introducing eight azido groups into the tetramethylbenzene system. Although molecules with two, three or even four azido groups at one carbon atom are now available (Nishiyama & Yamaguchi, 1988; Nishiyama et al., 1987; Petrie et al., 1997; Lyssenko et al., 2005), a survey of the Cambridge Structural Database (Allen, 2002) revealed the absence of X-ray diffraction structures of benzene derivatives with geminal diazido groups. The photobromination of 1,2,4,5-tetramethylbenzene, (I), afforded 1,2,4,5-tetrakis(dibromomethyl)benzene, (II), in a 90% yield (see Scheme) (Soyer et al., 1975; Schrievers & Brinker, 1988). Compound (II) reacts with NaN₃ to give 1,2,4,5-tetrakis(diazidomethyl)benzene, (III), in 91% yield (Gilbert, 1987). Herein, we report the results of the investigation of the crystal structure of the fourfold geminal diazide, (III), by X-ray crystallography.

The 1,2,4,5-tetrakis(diazidomethyl)benzene, (III), molecule (Fig. 1) lies on a crystallographic inversion centre located in the middle of the benzene ring. There is then half a molecule within the asymmetric unit. Two of the unique azido groups tend to remain in the plane of the benzene ring, with the torsional angles showing deviation from planarity Θ_{C2–C3–C4–N10} and Θ_{C3–C2–C1–N4} of 164.47 (12) and 159.73 (12)°, respectively. Both azido groups oriented nearly parallel to the benzene ring are almost linear, with N4–N5–N6 and N10–N11–N12 angles of 173.42 (15) and 171.35 (14)° [respectively?]. The other two unique azido groups N1–N2–N3 and N7–N8–N9 are also nearly linear, with the corresponding angles of 174.32 (15) and 173.37 (16)°, and adopt an opposite orientation above and below the benzene ring with torsional angles Θ_{C2–C3–C4–N7} and Θ_{C3–C2–C1–N1} at -72.40 (16) and -77.85 (15)°, respectively. The average C–N_α–N_β angle of 112.9 (5)° deviates by more than 3° from the ideal tetrahedral value. Such an arrangement of the geminal diazide groups avoids steric overcrowding.

The endocyclic angles at C2 and C3 are only slightly smaller than the exocyclic ones (Table 1), but very close to the ideal value. The maximal deviation from 120° does not exceed 0.84°. A more significant deviation of exocyclic angles (>3°) from 120° was observed for 1,2,4,5-tetrakis(bromomethyl)benzene (Wang et al., 2006). The distribution of the electron density over the benzene ring expressed by the corresponding bond lengths quoted in Table 1 differs from that observed earlier in a benzene-bridged spiropentane (Boese et al., 1989).

Despite the presence of a large number of nitrogen atoms, with lone pairs potentially available for hydrogen-bond formation as proton acceptors, there are, in fact, no C–H···N contacts in the crystal structure of (III) (Fig. 2), which might be classified as a typical hydrogen bond (mean statistical parameters H···N 2.38 Å, C–H···N angle 155°) (Mascal,1998). The shortest contacts between adjacent molecules are at 2.984 Å and can be described as van der Waals interactions (Bondi, 1964; Nyburg & Faerman, 1985; Pauling, 1942).

We noticed that the melting point (379–381 K) and the density of (III) (1.602 g cm^-3) are within the ranges observed for polyazidopyrimidines (from 225 to 403 K and from 1.55 to 1.72 g cm^-3, respectively) and are due to inefficient packing caused by the azidomethyl groups. The polyazidopyrimidines and other organic polyazido-substituted compounds are characterized by high heats of formation and, therefore, are of particular interest for high-energy research (Petrie et al., 1997). The endothermicity of a hydrocarbon increases upon addition of one azido group by about 87 kcal mol^-1, while the melting point is lowered significantly upon insertion of an azidomethyl group with a preserving [no change?] or only [a slight?] very little decrease in thermal stability. All these properties are crucial for the preparation of energetic ionic liquids (Ye et al., 2006). Moreover, these compounds with little or no hydrogen content have also been reported to be excellent precursors for the synthesis of carbon nanotubes (Ye et al., 2006), carbon nanospheres and carbon nitrides (Huynh & Hiskey et al., 2004). Carbon nitrides are superhard materials with great potential for biological and technological applications. Their properties are determined to a large extent by the shape and size of these nanoparticles, but also by the relative nitrogen content. By using different heating protocols or special catalytic detonation procedures for explosive precursors, nanoparticles of different size range and morphologies have been prepared in high yields (Ye et al., 2006; Huynh & Hiskey et al., 2004).

In summary, the first crystal structure of a geminal diazide has been reported. The compound, 1,2,4,5-tetrakis(diazidomethyl)benzene, (III), proved to be more stable in the solid state than expected. The arrangement of the azide groups adopted by the molecule means that steric clashes are avoided. The compound is of potential interest as a precursor for the synthesis of carbon nanoparticles and/or nanosized carbon nitrides.

Related literature

For related literature, see: Allen (2002); Balbridge & Siegel (1992); Boese et al. (1989); Bondi (1964); Collins et al. (1990); Gilbert (1987); Huynh et al. (2004); Lyssenko et al. (2005); Mascal (1998); Mills & Nixon (1930); Nishiyama & Yamaguchi (1988); Nishiyama et al. (1987); Nyburg & Faerman (1985); Pauling (1942); Petrie et al. (1997); Schrievers & Brinker (1988); Siegel (1994); Soyer et al. (1975); Stanger et al. (1997); Wang et al. (2006); Ye et al. (2006).

S2. Experimental

For compound (II). To (I) (43.75 g, 0.325 mol) in CCl₄ (1.75 l) in a 2 l three-neck flask equipped with dropping funnel and reflux condenser with gas outlet, under mechanical stirring under reflux, bromine (140 ml, 5.6 mol) was added dropwise over 3–3.5 h. During the addition and for the total reaction time under reflux, the reaction mixture was irradiated with two 500 W halogen lamps. After 3 d the white solid was filtered off, washed with hot chloroform (250 ml) and dried in vacuo overnight. The yield of (II) was 224 g, 90%.

For compound (III). The operations listed below were performed under the safety conditions for potentially explosive substances: To a vigorosly stirred solution of (II) (196 mg, 0.26 mmol) in DMF (15 ml), NaN₃ (0.2 g, 3.08 mmol) was added at room temperature. The light-protected mixture was heated to 343 K for 4 h. After cooling to room temperature, the turbid solution was poured into cold water (250 ml) and extracted with dichloromethane (3 × 100 ml). The combined organic layers were washed with water (3 × 100 ml) and then dried with anhydrous MgSO₄. The solvent was removed under reduced pressure to give the crude product as colourless crystals. These were recrystallized from acetone. The yield of (III) was 109 mg, 91%. ¹H NMR (CDCl₃, 400 MHz): 7.90 (s, 2ArH), 6.09 (s, 4ArCH). Crystals of (III) of X-ray diffraction quality were grown from hexane at 249 K over 4–5 h.

S3. Refinement

H atoms were placed at calculated positions and refined with a riding model with C_aromatic–H of 0.95 and 1.00 Å (CH) and U_iso (H) values of 1.2 times U_eq(C).

Computing details

Data collection: APEX2 (Bruker, 2005); cell refinement: APEX2 (Bruker, 2005); data reduction: APEX2 (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. The molecular structure of (III) with the atom-labeling scheme. Thermal ellipsoids are drawn at the 50% probability level. H atoms are represented as small spheres of arbitrary radii. Symmetry code: (i) -x + 1, -y + 2, -z + 1.
	Fig. 2. A view of the packing, showing the content of the unit cell.

1,2,4,5-Tetrakis(diazidomethyl)benzene

Crystal data

C10H6N24	F(000) = 468
Mr = 462.39	Dx = 1.609 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 341 reflections
a = 9.2393 (9) Å	θ = 2.4–30.7°
b = 14.3799 (13) Å	µ = 0.12 mm^−1
c = 7.5145 (5) Å	T = 100 K
β = 107.069 (2)°	Stick, colorless
V = 954.40 (14) Å^3	0.35 × 0.10 × 0.10 mm
Z = 2

Data collection

Bruker X8 APEXII CCD diffractometer	2788 independent reflections
Radiation source: fine-focus sealed tube	2019 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.049
ϕ–scan	θmax = 30.1°, θmin = 2.7°
Absorption correction: multi-scan SADABS (Bruker, 2005)	h = −13→13
Tmin = 0.948, Tmax = 0.978	k = −19→20
7716 measured reflections	l = −6→10

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.044	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.110	H-atom parameters constrained
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0522P)^2 + 0.0067P] where P = (Fo^2 + 2Fc^2)/3
2788 reflections	(Δ/σ)max < 0.001
154 parameters	Δρmax = 0.43 e Å^−3
0 restraints	Δρmin = −0.24 e Å^−3

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.

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.

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

	x	y	z	Uiso*/Ueq
N1	0.91528 (14)	1.03914 (9)	0.63096 (17)	0.0163 (3)
N2	0.88647 (13)	1.05589 (9)	0.78078 (17)	0.0164 (3)
N3	0.87172 (16)	1.06764 (10)	0.92248 (18)	0.0240 (3)
N4	0.78004 (14)	1.16851 (8)	0.44179 (17)	0.0161 (3)
N5	0.88280 (14)	1.19971 (8)	0.38321 (16)	0.0154 (3)
N6	0.97109 (16)	1.23620 (10)	0.3324 (2)	0.0249 (3)
N7	0.68467 (15)	0.89448 (9)	0.17263 (17)	0.0185 (3)
N8	0.55155 (17)	0.89239 (10)	0.06836 (18)	0.0229 (3)
N9	0.43738 (19)	0.89170 (12)	−0.0393 (2)	0.0361 (4)
N10	0.64911 (14)	0.77746 (8)	0.39227 (17)	0.0155 (3)
N11	0.73079 (13)	0.71714 (8)	0.35134 (15)	0.0125 (2)
N12	0.79319 (15)	0.65477 (9)	0.32048 (17)	0.0183 (3)
C1	0.78768 (15)	1.06633 (10)	0.46406 (19)	0.0127 (3)
H1	0.8061	1.0383	0.3508	0.015*
C2	0.63676 (15)	1.03210 (10)	0.47805 (17)	0.0112 (3)
C3	0.59506 (15)	0.93873 (10)	0.44106 (18)	0.0103 (3)
C4	0.69454 (16)	0.87371 (9)	0.36956 (19)	0.0117 (3)
H4	0.8019	0.8823	0.4473	0.014*
C5	0.54181 (15)	1.09201 (10)	0.53764 (18)	0.0112 (3)
H5	0.5710	1.1550	0.5642	0.013*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0122 (6)	0.0177 (6)	0.0183 (6)	0.0029 (5)	0.0035 (5)	0.0013 (5)
N2	0.0130 (6)	0.0132 (6)	0.0198 (6)	0.0002 (5)	−0.0001 (5)	0.0013 (5)
N3	0.0257 (7)	0.0239 (7)	0.0202 (7)	0.0016 (6)	0.0032 (6)	0.0011 (6)
N4	0.0156 (6)	0.0110 (6)	0.0242 (6)	−0.0005 (5)	0.0096 (5)	0.0013 (5)
N5	0.0150 (6)	0.0116 (6)	0.0191 (6)	0.0019 (5)	0.0042 (5)	0.0010 (5)
N6	0.0236 (7)	0.0163 (7)	0.0391 (8)	0.0014 (6)	0.0160 (7)	0.0047 (6)
N7	0.0266 (7)	0.0165 (6)	0.0157 (6)	0.0050 (5)	0.0112 (5)	0.0016 (5)
N8	0.0354 (8)	0.0214 (7)	0.0136 (6)	0.0111 (6)	0.0100 (6)	0.0002 (5)
N9	0.0415 (10)	0.0416 (10)	0.0197 (7)	0.0179 (8)	0.0004 (7)	−0.0019 (7)
N10	0.0191 (6)	0.0092 (6)	0.0220 (6)	0.0030 (5)	0.0118 (5)	0.0010 (5)
N11	0.0161 (6)	0.0114 (6)	0.0113 (5)	−0.0003 (5)	0.0059 (5)	0.0009 (5)
N12	0.0234 (7)	0.0143 (6)	0.0197 (6)	0.0038 (5)	0.0103 (5)	0.0000 (5)
C1	0.0125 (6)	0.0107 (7)	0.0153 (6)	0.0016 (5)	0.0047 (5)	0.0004 (5)
C2	0.0117 (6)	0.0113 (6)	0.0096 (6)	0.0004 (5)	0.0018 (5)	0.0017 (5)
C3	0.0116 (6)	0.0111 (7)	0.0082 (6)	0.0027 (5)	0.0027 (5)	0.0013 (5)
C4	0.0152 (7)	0.0085 (6)	0.0128 (6)	0.0013 (5)	0.0063 (5)	−0.0001 (5)
C5	0.0138 (6)	0.0098 (6)	0.0097 (6)	0.0005 (5)	0.0029 (5)	−0.0005 (5)

Geometric parameters (Å, º)

N1—N2	1.2539 (17)	N11—N12	1.1265 (16)
N1—C1	1.4992 (18)	C1—C2	1.5111 (19)
N2—N3	1.1253 (17)	C1—H1	1.0000
N4—N5	1.2417 (17)	C2—C5	1.3939 (19)
N4—C1	1.4782 (19)	C2—C3	1.4020 (19)
N5—N6	1.1267 (17)	C3—C5^i	1.3924 (18)
N7—N8	1.2497 (19)	C3—C4	1.5158 (18)
N7—C4	1.4860 (18)	C4—H4	1.0000
N8—N9	1.125 (2)	C5—C3^i	1.3924 (18)
N10—N11	1.2461 (16)	C5—H5	0.9500
N10—C4	1.4706 (18)
N2—N1—C1	112.27 (11)	C5—C2—C1	120.11 (12)
N3—N2—N1	174.32 (15)	C3—C2—C1	120.24 (12)
N5—N4—C1	112.53 (12)	C5^i—C3—C2	119.16 (12)
N6—N5—N4	173.42 (15)	C5^i—C3—C4	120.70 (12)
N8—N7—C4	112.39 (12)	C2—C3—C4	120.07 (12)
N9—N8—N7	173.37 (16)	N10—C4—N7	111.63 (11)
N11—N10—C4	114.35 (11)	N10—C4—C3	108.42 (11)
N12—N11—N10	171.35 (14)	N7—C4—C3	111.26 (11)
N4—C1—N1	110.71 (11)	N10—C4—H4	108.5
N4—C1—C2	108.50 (11)	N7—C4—H4	108.5
N1—C1—C2	111.84 (11)	C3—C4—H4	108.5
N4—C1—H1	108.6	C3^i—C5—C2	121.28 (13)
N1—C1—H1	108.6	C3^i—C5—H5	119.4
C2—C1—H1	108.6	C2—C5—H5	119.4
C5—C2—C3	119.56 (12)
N5—N4—C1—N1	73.87 (15)	C1—C2—C3—C4	−5.68 (19)
N5—N4—C1—C2	−163.05 (12)	N11—N10—C4—N7	62.33 (16)
N2—N1—C1—N4	73.98 (14)	N11—N10—C4—C3	−174.76 (11)
N2—N1—C1—C2	−47.14 (16)	N8—N7—C4—N10	65.81 (15)
N4—C1—C2—C5	−23.77 (17)	N8—N7—C4—C3	−55.45 (16)
N1—C1—C2—C5	98.62 (15)	C5^i—C3—C4—N10	−18.62 (17)
N4—C1—C2—C3	159.73 (12)	C2—C3—C4—N10	164.47 (12)
N1—C1—C2—C3	−77.88 (15)	C5^i—C3—C4—N7	104.51 (14)
C5—C2—C3—C5^i	0.8 (2)	C2—C3—C4—N7	−72.40 (16)
C1—C2—C3—C5^i	177.37 (12)	C3—C2—C5—C3^i	−0.9 (2)
C5—C2—C3—C4	177.80 (12)	C1—C2—C5—C3^i	−177.39 (12)

Symmetry code: (i) −x+1, −y+2, −z+1.