2,3-Bis(4-bromo­phen­yl)quinoxaline

In the title compound, C₂₀H₁₂Br₂N₂, the two bromobenzene rings are inclined at 58.7 (2)° to each other, and at 43.7 (2) and 53.9 (2)° to the quinoxaline ring system.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.006 Å
• R factor = 0.047
• wR factor = 0.139
• Data-to-parameter ratio = 13.5

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT027_ALERT_3_B _diffrn_reflns_theta_full (too) Low ............      24.99 Deg.

Alert level C
PLAT062_ALERT_4_C Rescale T(min) & T(max) by .....................       0.88
PLAT085_ALERT_2_C SHELXL default weighting scheme is not optimized          ?
PLAT790_ALERT_4_C Centre of Gravity not Within Unit Cell: Resd.  #          1
              C20 H12 Br2 N2

Alert level G
ABSTM02_ALERT_3_G  When printed, the submitted absorption T values will be
            replaced by the scaled T values. Since the ratio of scaled T's
            is identical to the ratio of reported T values, the scaling
            does not imply a change to the absorption corrections used in
            the study.
            Ratio of Tmax expected/reported      0.877
            Tmax scaled      0.416 Tmin scaled      0.246
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K

   0 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
   3 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

   1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Functionalized quinoxalines represent an important class of nitrogen-containing heterocycle. While rarely described in nature, synthetic quinoxalines are well known in the pharmaceutical industry and have been shown to possess a broad spectrum of biological activities including antiviral, antibacterial and as kinase inhibitors (Loriga et al., 1997; Seitz et al., 2002; He et al., 2003). Recently, we have reported an analogic structure of quinoxaline derivative, namely, 2,3-bis(4-cholrophenyl)quinoxaline. Now we have synthesized a new quinoxaline derivative, 2,3-bis(4-bromophenyl)quinoxaline, (I). We present its crystal structure here.

In the molecular structure of (I) in Fig. 1, the two benzene rings attached to the quinoxaline ring are inclined at an angle of 58.7 (2)°. The quinoxaline ring is approximately planar, with an r. m. s. deviation of 0.033°. The two benzene rings make dihedral angles of 43.7 (2) and 53.9 (2)°, respectively, with the planar quinoxaline ring. The C10—C15 and C9—C173 bond lengths between the benzene rings and the quionxaline ring, [1.499 (5) and 1.480 (5) Å, respectively] are slightly shorter than the general C—C single bond length (Kennedy et al., 2004) as a consequence of the conjugate structure among the aromatic rings.

Related literature

For related literature, see: He et al. (2003); Kennedy et al. (2004); Loriga et al. (1997); Seitz et al. (2002).

S2. Experimental

A suspension of 1,2-bis(4-bromophenyl)ethane-1,2-dione (0.8 mmol) and benzene-1,2-diamine (1.0 mmol) in acetic acid (3 ml) was heated to reflux for 0.5 h. The mixture was then poured into ice water and a white precipitate was formed. The mixture was neutralized using saturated NaHCO₃ solution. The resulting precipitate was filtered off, washed with water, dried and purified by recrystallization using a mixture of ethyl acetate and petroleum ether (1:5), giving the target product as white needle crystals in 93.3% yield. Crystals of (I) suitable for single-crystal X-ray analysis were grown by slow evaporation of a solution in chloroform/ethanol (1:1). Spectroscopic analysis: ¹H NMR (CDCl₃, δ, p.p.m.): 8.18–8.16 (m, 2H), 7.82–7.80 (m, 2H), 7.52–7.51 (m, 4H), 7.42–7.41 (m, 4H). EI—MS (m/z): 440.7 [M+1]⁺.

S3. Refinement

All H atoms were positioned geometrically and refined as riding (C—H = 0.93%A) and allowed to ride on their parent atoms, with U_iso(H) = 1.2U_eq(parent).

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SMART; data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1997); software used to prepare material for publication: SHELXTL.

Figures

Fig. 1. View of the molecule of (I) showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 35% probability level.

2,3-bis(4-bromophenyl)quinoxaline

Crystal data

C20H12Br2N2	Z = 4
Mr = 440.14	F(000) = 864
Monoclinic, P21/n	Dx = 1.756 Mg m^−3
Hall symbol: -P 2yn	Melting point: 461 K
a = 13.5822 (17) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.6918 (13) Å	µ = 4.87 mm^−1
c = 16.482 (3) Å	T = 298 K
β = 104.752 (9)°	Plate, colourless
V = 1665.1 (5) Å^3	0.35 × 0.26 × 0.18 mm

Data collection

Bruker SMART CCD area detector diffractometer	2922 independent reflections
Radiation source: fine-focus sealed tube	2132 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.039
φ and ω scans	θmax = 25.0°, θmin = 2.3°
Absorption correction: multi-scan SADABS (Bruker, 1997)	h = −16→16
Tmin = 0.281, Tmax = 0.474	k = −9→7
9727 measured reflections	l = −19→14

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)] = 0.047	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.139	H-atom parameters constrained
S = 0.96	w = 1/[σ^2(Fo^2) + (0.1P)^2] where P = (Fo^2 + 2Fc^2)/3
2922 reflections	(Δ/σ)max < 0.001
217 parameters	Δρmax = 0.43 e Å^−3
0 restraints	Δρmin = −1.15 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
Br1	0.08495 (3)	0.95152 (7)	0.11599 (3)	0.0555 (2)
Br2	−0.18098 (4)	1.54598 (9)	−0.17208 (3)	0.0734 (3)
N2	−0.3517 (2)	1.0631 (4)	0.1736 (2)	0.0390 (8)
N1	−0.4070 (2)	1.2803 (5)	0.0336 (2)	0.0370 (8)
C20	−0.4787 (3)	1.1927 (5)	0.0618 (3)	0.0356 (9)
C19	−0.0077 (3)	1.0131 (5)	0.1798 (3)	0.0372 (10)
C18	−0.0427 (3)	1.0550 (6)	0.3121 (3)	0.0477 (12)
H18A	−0.0212	1.0561	0.3703	0.057*
C173	−0.2364 (3)	1.3751 (5)	0.0492 (3)	0.0345 (9)
C16	−0.1655 (3)	1.4680 (5)	0.1092 (3)	0.0410 (10)
H16A	−0.1620	1.4532	0.1659	0.049*
C15	−0.1746 (3)	1.0998 (5)	0.1855 (3)	0.0342 (9)
C14	−0.1739 (3)	1.5134 (6)	−0.0578 (3)	0.0415 (10)
C13	−0.4511 (3)	1.0908 (5)	0.1337 (3)	0.0363 (10)
C12	−0.1065 (3)	1.0592 (5)	0.1387 (3)	0.0362 (10)
H12A	−0.1267	1.0629	0.0804	0.043*
C11	−0.5826 (3)	1.2121 (6)	0.0204 (3)	0.0473 (11)
H11A	−0.6017	1.2783	−0.0283	0.057*
C10	−0.2833 (3)	1.1429 (5)	0.1438 (2)	0.0338 (9)
C9	−0.3111 (3)	1.2620 (5)	0.0751 (2)	0.0338 (9)
C8	−0.6272 (3)	1.0345 (6)	0.1236 (3)	0.0527 (13)
H8A	−0.6779	0.9822	0.1438	0.063*
C7	−0.1039 (3)	1.6059 (6)	0.0012 (3)	0.0479 (11)
H7A	−0.0598	1.6832	−0.0150	0.058*
C6	−0.5277 (3)	1.0109 (6)	0.1654 (3)	0.0465 (11)
H6A	−0.5104	0.9435	0.2138	0.056*
C5	−0.1415 (3)	1.0988 (6)	0.2727 (3)	0.0424 (10)
H5A	−0.1866	1.1280	0.3046	0.051*
C4	−0.6542 (3)	1.1349 (7)	0.0514 (3)	0.0529 (12)
H4A	−0.7226	1.1492	0.0241	0.063*
C3	0.0247 (3)	1.0097 (6)	0.2658 (3)	0.0437 (11)
H3A	0.0910	0.9772	0.2924	0.052*
C2	−0.2412 (3)	1.4004 (6)	−0.0348 (3)	0.0383 (10)
H2B	−0.2895	1.3415	−0.0757	0.046*
C1	−0.1001 (3)	1.5823 (6)	0.0844 (3)	0.0444 (11)
H1B	−0.0528	1.6441	0.1249	0.053*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0302 (3)	0.0757 (4)	0.0622 (4)	0.0013 (2)	0.0149 (2)	−0.0061 (3)
Br2	0.0542 (4)	0.1241 (6)	0.0448 (4)	−0.0103 (3)	0.0177 (3)	0.0214 (3)
N2	0.0288 (18)	0.051 (2)	0.037 (2)	−0.0007 (15)	0.0093 (15)	0.0031 (16)
N1	0.0288 (16)	0.048 (2)	0.0335 (19)	0.0014 (15)	0.0074 (14)	0.0005 (16)
C20	0.0237 (18)	0.043 (2)	0.039 (2)	−0.0001 (17)	0.0067 (17)	−0.0026 (19)
C19	0.026 (2)	0.035 (2)	0.050 (3)	−0.0003 (16)	0.0097 (19)	0.0027 (19)
C18	0.038 (2)	0.068 (3)	0.034 (2)	0.005 (2)	0.002 (2)	0.008 (2)
C173	0.0228 (18)	0.044 (2)	0.037 (2)	0.0026 (17)	0.0079 (17)	0.0021 (19)
C16	0.035 (2)	0.048 (3)	0.038 (2)	0.0028 (19)	0.006 (2)	0.001 (2)
C15	0.0252 (19)	0.037 (2)	0.038 (2)	−0.0039 (16)	0.0042 (17)	0.0057 (18)
C14	0.029 (2)	0.059 (3)	0.039 (2)	0.0045 (19)	0.0119 (19)	0.009 (2)
C13	0.027 (2)	0.043 (2)	0.040 (2)	−0.0046 (17)	0.0112 (18)	−0.0037 (19)
C12	0.031 (2)	0.044 (3)	0.033 (2)	−0.0036 (17)	0.0061 (18)	−0.0017 (18)
C11	0.029 (2)	0.060 (3)	0.051 (3)	0.006 (2)	0.0047 (19)	0.006 (2)
C10	0.0263 (18)	0.043 (2)	0.031 (2)	0.0009 (17)	0.0067 (16)	0.0005 (19)
C9	0.0281 (19)	0.042 (2)	0.032 (2)	−0.0017 (17)	0.0084 (16)	−0.0027 (18)
C8	0.029 (2)	0.074 (3)	0.058 (3)	−0.009 (2)	0.017 (2)	−0.006 (3)
C7	0.030 (2)	0.053 (3)	0.060 (3)	−0.003 (2)	0.012 (2)	0.011 (2)
C6	0.033 (2)	0.062 (3)	0.047 (3)	−0.013 (2)	0.014 (2)	0.005 (2)
C5	0.033 (2)	0.059 (3)	0.036 (2)	−0.001 (2)	0.0100 (19)	0.006 (2)
C4	0.022 (2)	0.072 (3)	0.061 (3)	−0.001 (2)	0.005 (2)	−0.010 (3)
C3	0.028 (2)	0.048 (3)	0.048 (3)	0.0003 (18)	−0.002 (2)	0.004 (2)
C2	0.028 (2)	0.051 (2)	0.036 (2)	−0.0021 (18)	0.0082 (17)	0.002 (2)
C1	0.031 (2)	0.052 (3)	0.047 (3)	−0.0066 (19)	0.0054 (19)	0.001 (2)

Geometric parameters (Å, º)

Br1—C19	1.894 (4)	C15—C10	1.499 (5)
Br2—C14	1.879 (4)	C14—C7	1.373 (6)
N2—C10	1.309 (5)	C14—C2	1.382 (6)
N2—C13	1.359 (5)	C13—C6	1.418 (6)
N1—C9	1.316 (4)	C12—H12A	0.9300
N1—C20	1.360 (5)	C11—C4	1.346 (6)
C20—C13	1.391 (6)	C11—H11A	0.9300
C20—C11	1.410 (5)	C10—C9	1.431 (5)
C19—C3	1.374 (6)	C8—C6	1.363 (6)
C19—C12	1.387 (6)	C8—C4	1.387 (7)
C18—C5	1.376 (6)	C8—H8A	0.9300
C18—C3	1.376 (7)	C7—C1	1.372 (6)
C18—H18A	0.9300	C7—H7A	0.9300
C173—C16	1.390 (6)	C6—H6A	0.9300
C173—C2	1.383 (6)	C5—H5A	0.9300
C173—C9	1.480 (5)	C4—H4A	0.9300
C16—C1	1.383 (6)	C3—H3A	0.9300
C16—H16A	0.9300	C2—H2B	0.9300
C15—C12	1.384 (6)	C1—H1B	0.9300
C15—C5	1.391 (6)
C10—N2—C13	117.3 (3)	C20—C11—H11A	120.0
C9—N1—C20	118.0 (3)	N2—C10—C9	121.8 (3)
N1—C20—C13	120.6 (3)	N2—C10—C15	115.8 (3)
N1—C20—C11	119.9 (4)	C9—C10—C15	122.4 (3)
C13—C20—C11	119.4 (4)	N1—C9—C10	120.5 (3)
C3—C19—C12	121.7 (4)	N1—C9—C173	116.6 (3)
C3—C19—Br1	119.0 (3)	C10—C9—C173	122.9 (3)
C12—C19—Br1	119.3 (3)	C6—C8—C4	121.3 (4)
C5—C18—C3	120.5 (4)	C6—C8—H8A	119.4
C5—C18—H18A	119.8	C4—C8—H8A	119.4
C3—C18—H18A	119.8	C1—C7—C14	118.8 (4)
C16—C173—C2	119.2 (4)	C1—C7—H7A	120.6
C16—C173—C9	119.9 (4)	C14—C7—H7A	120.6
C2—C173—C9	120.7 (3)	C8—C6—C13	118.8 (4)
C173—C16—C1	119.8 (4)	C8—C6—H6A	120.6
C173—C16—H16A	120.1	C13—C6—H6A	120.6
C1—C16—H16A	120.1	C18—C5—C15	120.5 (4)
C12—C15—C5	119.3 (4)	C18—C5—H5A	119.7
C12—C15—C10	121.0 (4)	C15—C5—H5A	119.7
C5—C15—C10	119.7 (4)	C11—C4—C8	120.8 (4)
C7—C14—C2	121.3 (4)	C11—C4—H4A	119.6
C7—C14—Br2	119.3 (3)	C8—C4—H4A	119.6
C2—C14—Br2	119.3 (3)	C19—C3—C18	118.9 (4)
N2—C13—C20	121.3 (3)	C19—C3—H3A	120.5
N2—C13—C6	119.1 (4)	C18—C3—H3A	120.5
C20—C13—C6	119.6 (4)	C14—C2—C173	119.8 (4)
C19—C12—C15	119.1 (4)	C14—C2—H2B	120.1
C19—C12—H12A	120.5	C173—C2—H2B	120.1
C15—C12—H12A	120.5	C7—C1—C16	121.1 (4)
C4—C11—C20	120.0 (4)	C7—C1—H1B	119.5
C4—C11—H11A	120.0	C16—C1—H1B	119.5
C9—N1—C20—C13	1.7 (6)	N2—C10—C9—C173	169.7 (4)
C9—N1—C20—C11	178.4 (4)	C15—C10—C9—C173	−11.1 (6)
C2—C173—C16—C1	−0.8 (6)	C16—C173—C9—N1	130.9 (4)
C9—C173—C16—C1	−175.8 (4)	C2—C173—C9—N1	−44.1 (5)
C10—N2—C13—C20	3.2 (6)	C16—C173—C9—C10	−46.5 (6)
C10—N2—C13—C6	−178.2 (4)	C2—C173—C9—C10	138.5 (4)
N1—C20—C13—N2	−5.9 (6)	C2—C14—C7—C1	1.2 (7)
C11—C20—C13—N2	177.4 (4)	Br2—C14—C7—C1	179.4 (3)
N1—C20—C13—C6	175.4 (4)	C4—C8—C6—C13	−0.2 (7)
C11—C20—C13—C6	−1.3 (6)	N2—C13—C6—C8	−177.9 (4)
C3—C19—C12—C15	−1.2 (6)	C20—C13—C6—C8	0.8 (7)
Br1—C19—C12—C15	178.4 (3)	C3—C18—C5—C15	−0.7 (7)
C5—C15—C12—C19	2.1 (6)	C12—C15—C5—C18	−1.1 (6)
C10—C15—C12—C19	−177.3 (4)	C10—C15—C5—C18	178.3 (4)
N1—C20—C11—C4	−175.5 (4)	C20—C11—C4—C8	−0.6 (7)
C13—C20—C11—C4	1.2 (7)	C6—C8—C4—C11	0.1 (8)
C13—N2—C10—C9	3.3 (6)	C12—C19—C3—C18	−0.7 (6)
C13—N2—C10—C15	−175.9 (3)	Br1—C19—C3—C18	179.8 (3)
C12—C15—C10—N2	132.3 (4)	C5—C18—C3—C19	1.6 (7)
C5—C15—C10—N2	−47.2 (5)	C7—C14—C2—C173	−2.0 (6)
C12—C15—C10—C9	−47.0 (6)	Br2—C14—C2—C173	179.8 (3)
C5—C15—C10—C9	133.6 (4)	C16—C173—C2—C14	1.8 (6)
C20—N1—C9—C10	4.7 (6)	C9—C173—C2—C14	176.7 (4)
C20—N1—C9—C173	−172.8 (4)	C14—C7—C1—C16	−0.2 (7)
N2—C10—C9—N1	−7.6 (6)	C173—C16—C1—C7	0.0 (7)
C15—C10—C9—N1	171.6 (4)