meso-1,2-Bis­(methyl­azo)-1,2-di­phenyl­ethane

The title compound, meso-1,2-bis­(methyl­diazenyl)-1,2-di­phenyl­ethane, C₁₆H₁₈N₄, is arranged in a disordered manner around an inversion point. The N-N atom distances in the azo group of 1.192 (8) and 1.195 (8) Å, and the C-C atom distances in the ethyl­ene moiety at 1.512 (8) and 1.503 (8) Å in the two models [refined to 51.7 (6) and 48.3 (6)% occupancies] were not significantly different.

S1. Comment

The syntheses of vicinal bis(azo)alkanes can be achieved through the oxidation of hydrazones by various reagents (Winter & Wiecko, 1969; Balachandran et al., 1968; Bhatnagar & George, 1967). Depending upon the substituents on the azo groups, the compound can decompose by breaking the C—N bonds and eliminating nitrogen and alkyl radicals to form an alkene (Engel et al., 1991). If the terminal R group is aryl, the central C—C bond is broken to form two α-hydrazonyl radicals (Wieko, 1970; Engel et al., 1993).

So far, there are only six structural reports on vicinal bis(azo) compounds (Allen et al., 1983). Our interest in these compounds stems from the possibility of low-temperature production of methyl radicals through simultaneous or near-simultaneous loss of nitrogen. Here, we report the crystal structure of a vicinal bis(azo)alkane, namely meso-1,2-bis(methylazo)-1,2-diphenylethane, (I).

There is disorder in the arrangement of the entire molecule. As a result, the N—N distances [1.192 (8) and 1.195 (8) Å] are slightly shorter than expected (ca 1.22 Å) compared to other methylazo compounds (van Remoortere & Boer, 1971; Ferguson et al., 1991). The two central C—C bond distances are comparable, but shorter [1.512 (8) and 1.503 (8) Å versus 1.532–1.555 Å] than two known bis(azo)alkanes (Kavounis & Rentzeperis, 1983, 1984). The C—N distances involving the central ethylene bridge [1.487 (8) and 1.477 (8) Å] are also not significantly different and are comparable to those in the above bis(azo)alkanes (1.465–1.520 Å; Kavounis & Rentzeperis, 1983, 1984). The methylazo C—N bond distances [1.494 (6) and 1.489 (6) Å] are also comparable to previous crystal structures (van Remoortere & Boer, 1971; Ferguson et al., 1991).

Related literature

For related literature, see: Allen et al. (1983); Balachandran et al. (1968); Bayse et al. (2001); Bhatnagar & George (1967); Engel et al. (1991, 1993); Ferguson et al. (1991); Kavounis & Rentzeperis (1983, 1984); Remoortere & Boer (1971); Winter & Wiecko (1969).

S2. Experimental

The title compound was synthesized by the oxidation of benzaldehyde methylhydrazone with MnO₂ as detailed in a separate publication (Bayse et al., 2001). The product was obtained as crystals from the reaction mixture. Suitable crystals for X-ray diffraction were obtained by recrystallization from chloroform.

S3. Refinement

In the original structure solution, the disorder in the positions of the C atoms in the ethylene moiety was apparent. This model was refined with first isotropic and then anisotropic displacement parameters to convergence. The positions and isotropic displacement parameters of the H atoms were constrained and set to 1.5 times (1.2 for aryl H atoms) the isotropic equivalent of the attached atoms. At this stage, due to some unusual bond distances and angles, a new model was constructed which required restraints (24 in total, C—C = 1.39 Å) to prevent correlation from hindering the refinement. This resulted in different orientations in the phenyl rings, for the N atoms of the azo groups and for the C atoms of the ethylene moiety. Only the C atom in the methyl group was unique, but this was refined with two sets of H atoms to better fit the two independent models.

Computing details

Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

Fig. 1. ORTEP-3 (Farrugia, 1997) views of (a) molecule A and (b) molecule B of (I) (50% probability displacement ellipsoids).

(I)

Crystal data

C16H18N4	F(000) = 256
Mr = 266.35	Dx = 1.172 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71069 Å
a = 5.525 (2) Å	Cell parameters from 25 reflections
b = 17.444 (3) Å	θ = 10–15°
c = 8.194 (2) Å	µ = 0.07 mm^−1
β = 107.10 (2)°	T = 293 K
V = 754.8 (4) Å^3	Prism, white
Z = 2	0.40 × 0.20 × 0.10 mm

Data collection

Enraf-Nonius Turbo-CAD4 diffractometer	Rint = 0.016
non–profiled ω/2θ scans	θmax = 25.0°, θmin = 2.3°
Absorption correction: ψ scan (North et al., 1968)	h = 0→6
Tmin = 0.970, Tmax = 0.992	k = 0→20
1465 measured reflections	l = −9→9
1324 independent reflections	3 standard reflections every 166 min
687 reflections with I > 2σ(I)	intensity decay: 1%

Refinement

Refinement on F^2	24 restraints
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.056	w = 1/[σ^2(Fo^2) + (0.0763P)^2 + 0.1301P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.170	(Δ/σ)max = 0.012
S = 1.01	Δρmax = 0.18 e Å^−3
1324 reflections	Δρmin = −0.13 e Å^−3
107 parameters

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.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
N1A	0.7237 (17)	0.0451 (13)	0.3475 (13)	0.072 (2)	0.517 (6)
N2A	0.6975 (10)	0.0722 (3)	0.2098 (6)	0.079 (2)	0.517 (6)
C1A	1.030 (3)	0.1049 (8)	0.5936 (18)	0.0546 (18)	0.517 (6)
C2A	1.217 (3)	0.1600 (8)	0.6111 (16)	0.0590 (17)	0.517 (6)
H2A	1.3274	0.1573	0.5444	0.071*	0.517 (6)
C3A	1.240 (3)	0.2193 (7)	0.7281 (14)	0.058 (2)	0.517 (6)
H3A	1.3659	0.2562	0.7398	0.069*	0.517 (6)
C4A	1.076 (3)	0.2233 (8)	0.8277 (17)	0.060 (2)	0.517 (6)
H4A	1.0915	0.263	0.906	0.073*	0.517 (6)
C5A	0.889 (3)	0.1682 (9)	0.8102 (18)	0.064 (2)	0.517 (6)
H5A	0.7786	0.1709	0.8769	0.076*	0.517 (6)
C6A	0.866 (3)	0.1089 (9)	0.6932 (17)	0.0603 (18)	0.517 (6)
H6A	0.7401	0.072	0.6815	0.072*	0.517 (6)
C7A	0.9889 (13)	0.0394 (3)	0.4601 (9)	0.058 (2)	0.517 (6)
H7A	1.1079	0.0446	0.3926	0.069*	0.517 (6)
C8A	0.4260 (6)	0.08370 (19)	0.1109 (4)	0.1016 (12)	0.517 (6)
H8A1	0.4158	0.1045	0.0006	0.152*	0.517 (6)
H8A2	0.3487	0.1186	0.1712	0.152*	0.517 (6)
H8A3	0.339	0.0354	0.0972	0.152*	0.517 (6)
N1B	0.7669 (16)	0.0530 (14)	0.3206 (14)	0.072 (2)	0.483 (6)
N2B	0.5411 (10)	0.0517 (3)	0.2850 (6)	0.0692 (19)	0.483 (6)
C1B	0.984 (3)	0.0975 (9)	0.612 (2)	0.0546 (18)	0.483 (6)
C2B	1.165 (3)	0.1460 (9)	0.5813 (17)	0.0590 (17)	0.483 (6)
H2B	1.2396	0.134	0.4963	0.071*	0.483 (6)
C3B	1.236 (3)	0.2123 (8)	0.6774 (16)	0.058 (2)	0.483 (6)
H3B	1.357	0.2448	0.6568	0.069*	0.483 (6)
C4B	1.124 (3)	0.2303 (8)	0.8043 (19)	0.060 (2)	0.483 (6)
H4B	1.1715	0.2747	0.8686	0.073*	0.483 (6)
C5B	0.943 (3)	0.1818 (9)	0.8351 (18)	0.064 (2)	0.483 (6)
H5B	0.8686	0.1938	0.92	0.076*	0.483 (6)
C6B	0.873 (3)	0.1154 (9)	0.7390 (19)	0.0603 (18)	0.483 (6)
H6B	0.7512	0.083	0.7596	0.072*	0.483 (6)
C7B	0.8922 (13)	0.0268 (5)	0.4967 (9)	0.063 (2)	0.483 (6)
H7B	0.7673	−0.0006	0.5383	0.076*	0.483 (6)
C8B	0.4260 (6)	0.08370 (19)	0.1109 (4)	0.1016 (12)	0.483 (6)
H8B1	0.2448	0.0812	0.0829	0.152*	0.483 (6)
H8B2	0.4813	0.0544	0.0293	0.152*	0.483 (6)
H8B3	0.4776	0.1361	0.1081	0.152*	0.483 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1A	0.082 (3)	0.062 (4)	0.057 (3)	0.009 (3)	−0.003 (3)	0.010 (3)
N2A	0.094 (4)	0.071 (3)	0.060 (4)	0.014 (3)	0.006 (3)	0.009 (3)
C1A	0.060 (5)	0.043 (3)	0.056 (3)	−0.001 (2)	0.010 (2)	0.004 (3)
C2A	0.052 (6)	0.062 (5)	0.055 (4)	−0.011 (3)	0.002 (4)	−0.015 (3)
C3A	0.071 (2)	0.062 (3)	0.035 (7)	−0.009 (2)	0.008 (4)	−0.009 (3)
C4A	0.066 (6)	0.051 (3)	0.061 (4)	−0.002 (2)	0.014 (3)	−0.002 (3)
C5A	0.055 (6)	0.066 (5)	0.064 (4)	−0.009 (3)	0.009 (5)	−0.018 (3)
C6A	0.0676 (19)	0.067 (3)	0.043 (7)	−0.0130 (19)	0.012 (4)	−0.008 (3)
C7A	0.055 (4)	0.053 (4)	0.066 (4)	0.003 (3)	0.022 (3)	−0.002 (3)
C8A	0.107 (3)	0.082 (2)	0.079 (2)	0.0164 (19)	−0.0293 (19)	0.0047 (18)
N1B	0.082 (3)	0.062 (4)	0.057 (3)	0.009 (3)	−0.003 (3)	0.010 (3)
N2B	0.060 (4)	0.070 (3)	0.068 (4)	0.004 (3)	0.004 (3)	0.005 (3)
C1B	0.060 (5)	0.043 (3)	0.056 (3)	−0.001 (2)	0.010 (2)	0.004 (3)
C2B	0.052 (6)	0.062 (5)	0.055 (4)	−0.011 (3)	0.002 (4)	−0.015 (3)
C3B	0.071 (2)	0.062 (3)	0.035 (7)	−0.009 (2)	0.008 (4)	−0.009 (3)
C4B	0.066 (6)	0.051 (3)	0.061 (4)	−0.002 (2)	0.014 (3)	−0.002 (3)
C5B	0.055 (6)	0.066 (5)	0.064 (4)	−0.009 (3)	0.009 (5)	−0.018 (3)
C6B	0.0676 (19)	0.067 (3)	0.043 (7)	−0.0130 (19)	0.012 (4)	−0.008 (3)
C7B	0.049 (4)	0.076 (5)	0.061 (5)	0.016 (4)	0.010 (4)	0.006 (3)
C8B	0.107 (3)	0.082 (2)	0.079 (2)	0.0164 (19)	−0.0293 (19)	0.0047 (18)

Geometric parameters (Å, º)

N1A—N2A	1.192 (8)	N1B—N2B	1.195 (8)
N1A—C7A	1.487 (8)	N1B—C7B	1.477 (8)
N2A—C8A	1.494 (6)	N2B—C8B	1.489 (6)
C1A—C2A	1.39	C1B—C2B	1.39
C1A—C6A	1.39	C1B—C6B	1.39
C1A—C7A	1.551 (5)	C1B—C7B	1.545 (6)
C2A—C3A	1.39	C2B—C3B	1.39
C3A—C4A	1.39	C3B—C4B	1.39
C4A—C5A	1.39	C4B—C5B	1.39
C5A—C6A	1.39	C5B—C6B	1.39
C7A—C7A^i	1.512 (8)	C7B—C7B^i	1.503 (8)
N2A—N1A—C7A	115.9 (9)	N2B—N1B—C7B	112.9 (9)
N1A—N2A—C8A	113.0 (7)	N1B—N2B—C8B	110.4 (7)
C2A—C1A—C6A	120	C2B—C1B—C6B	120
C2A—C1A—C7A	122.2 (5)	C2B—C1B—C7B	119.9 (6)
C6A—C1A—C7A	117.8 (5)	C6B—C1B—C7B	120.0 (6)
C1A—C2A—C3A	120	C1B—C2B—C3B	120
C2A—C3A—C4A	120	C2B—C3B—C4B	120
C5A—C4A—C3A	120	C5B—C4B—C3B	120
C4A—C5A—C6A	120	C6B—C5B—C4B	120
C5A—C6A—C1A	120	C5B—C6B—C1B	120
N1A—C7A—C7A^i	105.6 (9)	N1B—C7B—C7B^i	111.5 (10)
N1A—C7A—C1A	107.5 (7)	N1B—C7B—C1B	109.0 (8)
C7A^i—C7A—C1A	112.8 (11)	C7B^i—C7B—C1B	111.2 (12)

Symmetry code: (i) −x+2, −y, −z+1.