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Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890

6,7-Di­chloro-3-(2,4-di­chloro­benz­yl)­quinoxalin-2(1H)-one

aDepartment of Public Health, Xuzhou Medical College, Xuzhou 221000, People's Republic of China., and bOut Patient Department, Xuzhou Airforce College, Xuzhou 221000, People's Republic of China.
*Correspondence e-mail: jsxzzjp@163.com

(Received 28 June 2012; accepted 7 July 2012; online 18 July 2012)

In the title compound, C15H8Cl4N2O, the quinoxaline ring system is almost planar, with a dihedral angle between the benzene and pyrazine rings of 3.1 (2)°. The 2,4-dichloro­phenyl ring is approximately perpendicular to the pyrazine ring, with a dihedral angle of 86.47 (13)° between them. The crystal packing features inter­molecular N—H⋯O hydrogen bonds and ππ stacking inter­actions, with centroid–centroid distances in the range 3.699 (3)–4.054 (3) Å.

Related literature

For the bioactivity of quinoxalin-2(1H)-one derivatives, see: Mensah-Osman et al. (2002[Mensah-Osman, E. J., AL-Katib, A. M., Dandashi, M. H. & Mohammad, R. M. (2002). Mol. Cancer Ther. 1, 1315-1320.]); Perez et al. (2002[Perez, C., Lopez, de C. A. & Bello, J. (2002). Food Chem. Toxicol. 40, 1463-1467.]); Quint et al. (2002[Quint, C., Temmel, A. F., Hummel, T. & Ehrenberger, K. (2002). Acta Otolaryngol. 122, 877-881.]); Seitz et al. (2002[Seitz, L. E., Suling, W. J. & Reynolds, R. C. (2002). J. Med. Chem. 45, 5604-5606.]).

[Scheme 1]

Experimental

Crystal data
  • C15H8Cl4N2O

  • Mr = 374.03

  • Triclinic, [P \overline 1]

  • a = 7.7150 (7) Å

  • b = 8.2058 (8) Å

  • c = 11.9722 (12) Å

  • α = 83.771 (1)°

  • β = 84.362 (1)°

  • γ = 84.298 (2)°

  • V = 746.79 (12) Å3

  • Z = 2

  • Mo Kα radiation

  • μ = 0.79 mm−1

  • T = 298 K

  • 0.16 × 0.09 × 0.05 mm

Data collection
  • Bruker SMART CCD area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 1996[Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.]) Tmin = 0.884, Tmax = 0.961

  • 3811 measured reflections

  • 2590 independent reflections

  • 1364 reflections with I > 2σ(I)

  • Rint = 0.036

Refinement
  • R[F2 > 2σ(F2)] = 0.055

  • wR(F2) = 0.103

  • S = 1.01

  • 2590 reflections

  • 199 parameters

  • H-atom parameters constrained

  • Δρmax = 0.27 e Å−3

  • Δρmin = −0.26 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N1—H1⋯O1i 0.86 1.93 2.789 (4) 173
Symmetry code: (i) -x+2, -y+2, -z+1.

Data collection: SMART (Bruker, 1998[Bruker (1998). SMART. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 1999[Bruker (1999). SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); software used to prepare material for publication: SHELXTL.

Supporting information


Comment top

Quinoxalin-2(1H)-one derivatives have attracted much attention in the pharmaceutical field due to their diverse bioactivities. These include use as a glutamate blocker (Perez et al. 2002), in the treatment of sensorineural smell disorders (Quint et al. 2002) and as a DNA topoisomerase (Topo) II beta-inhibitor (Mensah-Osman et al. 2002). They also exhibit antimycobacterial activity (Seitz et al. 2002). These reports inspired us to study the relationship between their structures and activities. During the synthesis of some quinoxalin derivatives, the title compound, (I) was isolated and its structure was confirmed by X-ray diffraction. Herein we report this structure.

In the molecular structure (Fig. 1), the quinoxaline ring system is nearly planar with a dihedral angle between the phenyl and pyrazine rings of 3.12(0.22) ° and rms deviations of 0.0135 Å and 0.0210 Å, respectively. The largest deviations from the planes of the two rings are 0.020 (3) Å for C3 and 0.031 (3) Å for C1. The 2,4-dichlorophenyl and pyrazine rings are approximately orthogonal with a dihedral angle of 86.47 (13) ° between them.

The crystal packing is stabilized by intermolecular N—H···O hydrogen bonds that form inversion dimers. In addition ππ stacking interactions are also found involving the C3–C8 and C10–C15 phenyl rings (Fig. 2). The centroid-to-centroid distances, plane-plane distances and displacement distances are as follows: 4.054 (3), 3.404 (2) and 2.201 Å (C3–C8 to C3–C8; symmetry code: 1-X,1-Y,1-Z); 3.699 (3), 3.415 (2) and 1.421 Å (C3–C8 to C3–C8; symmetry code: 2-X,1-Y,1-Z); 3.964 (3), 3.615 (2) and 1.626 Å (C10–C15 to C10–C15; symmetry code: 1-X,2-Y, 2-Z).

Related literature top

For the bioactivity of quinoxalin-2(1H)-one derivatives, see: Mensah-Osman et al. (2002); Perez et al. (2002); Quint et al. (2002); Seitz et al. (2002).

Experimental top

In a 10 ml Emrys reaction vial, 4-(2,4-dichlorobenzylidene)-2-phenyloxazol -5(4H)-one (0.32 g, 1 mmol), 4,5-dichlorobenzene-1,2-diamine (0.18 g, 1 mmol), TFA (0.23 g, 2 mmol) and ethylene glycol (1.5 ml) were mixed and then capped (The automatic mode stirring helped the mixing and uniform heating of the reactants). The mixture was heated for 16 min at 393 K under microwave irradiation. Upon completion, monitored by TLC, the reaction mixture was cooled to room temperature. The solid product was poured into water and neutralized with 10% NaOH, and then collected by filtration, subsequently washed with ethanol and ethylether in sequence to give a pure yellow solid. A single-crystal suitable for X-ray diffraction was obtained from the evaporation of a solution of the title compound in ethanol.

Refinement top

All H atoms were placed in calculated positions, with N—H = 0.86 Å, and C—H=0.93 Å or 0.97 Å and included in the final cycles of refinement using a riding model, with Uĩso~(H) = 1.2U~eq~(parent atom).

Structure description top

Quinoxalin-2(1H)-one derivatives have attracted much attention in the pharmaceutical field due to their diverse bioactivities. These include use as a glutamate blocker (Perez et al. 2002), in the treatment of sensorineural smell disorders (Quint et al. 2002) and as a DNA topoisomerase (Topo) II beta-inhibitor (Mensah-Osman et al. 2002). They also exhibit antimycobacterial activity (Seitz et al. 2002). These reports inspired us to study the relationship between their structures and activities. During the synthesis of some quinoxalin derivatives, the title compound, (I) was isolated and its structure was confirmed by X-ray diffraction. Herein we report this structure.

In the molecular structure (Fig. 1), the quinoxaline ring system is nearly planar with a dihedral angle between the phenyl and pyrazine rings of 3.12(0.22) ° and rms deviations of 0.0135 Å and 0.0210 Å, respectively. The largest deviations from the planes of the two rings are 0.020 (3) Å for C3 and 0.031 (3) Å for C1. The 2,4-dichlorophenyl and pyrazine rings are approximately orthogonal with a dihedral angle of 86.47 (13) ° between them.

The crystal packing is stabilized by intermolecular N—H···O hydrogen bonds that form inversion dimers. In addition ππ stacking interactions are also found involving the C3–C8 and C10–C15 phenyl rings (Fig. 2). The centroid-to-centroid distances, plane-plane distances and displacement distances are as follows: 4.054 (3), 3.404 (2) and 2.201 Å (C3–C8 to C3–C8; symmetry code: 1-X,1-Y,1-Z); 3.699 (3), 3.415 (2) and 1.421 Å (C3–C8 to C3–C8; symmetry code: 2-X,1-Y,1-Z); 3.964 (3), 3.615 (2) and 1.626 Å (C10–C15 to C10–C15; symmetry code: 1-X,2-Y, 2-Z).

For the bioactivity of quinoxalin-2(1H)-one derivatives, see: Mensah-Osman et al. (2002); Perez et al. (2002); Quint et al. (2002); Seitz et al. (2002).

Computing details top

Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT (Bruker, 1999); 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 top
[Figure 1] Fig. 1. The structure of (I), showing 30% probability displacement ellipsoids and the atom-numbering scheme.
[Figure 2] Fig. 2. Crystal packing of (I), with hydrogen bonds drawn as dashed lines.
6,7-Dichloro-3-(2,4-dichlorobenzyl)quinoxalin-2(1H)-one top
Crystal data top
C15H8Cl4N2OZ = 2
Mr = 374.03F(000) = 376
Triclinic, P1Dx = 1.663 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 7.7150 (7) ÅCell parameters from 742 reflections
b = 8.2058 (8) Åθ = 2.9–26.1°
c = 11.9722 (12) ŵ = 0.79 mm1
α = 83.771 (1)°T = 298 K
β = 84.362 (1)°Prism, colorless
γ = 84.298 (2)°0.16 × 0.09 × 0.05 mm
V = 746.79 (12) Å3
Data collection top
Bruker SMART CCD area-detector
diffractometer
2590 independent reflections
Radiation source: fine-focus sealed tube1364 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.036
φ and ω scansθmax = 25.0°, θmin = 2.5°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
h = 95
Tmin = 0.884, Tmax = 0.961k = 99
3811 measured reflectionsl = 1314
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.055Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.103H-atom parameters constrained
S = 1.01 w = 1/[σ2(Fo2) + (0.0247P)2]
where P = (Fo2 + 2Fc2)/3
2590 reflections(Δ/σ)max < 0.001
199 parametersΔρmax = 0.27 e Å3
0 restraintsΔρmin = 0.26 e Å3
Crystal data top
C15H8Cl4N2Oγ = 84.298 (2)°
Mr = 374.03V = 746.79 (12) Å3
Triclinic, P1Z = 2
a = 7.7150 (7) ÅMo Kα radiation
b = 8.2058 (8) ŵ = 0.79 mm1
c = 11.9722 (12) ÅT = 298 K
α = 83.771 (1)°0.16 × 0.09 × 0.05 mm
β = 84.362 (1)°
Data collection top
Bruker SMART CCD area-detector
diffractometer
2590 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
1364 reflections with I > 2σ(I)
Tmin = 0.884, Tmax = 0.961Rint = 0.036
3811 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0550 restraints
wR(F2) = 0.103H-atom parameters constrained
S = 1.01Δρmax = 0.27 e Å3
2590 reflectionsΔρmin = 0.26 e Å3
199 parameters
Special details top

Experimental. The data was obtained at Xuzhou Medical College collected by Jinpeng Zhang.

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 (Å2) top
xyzUiso*/Ueq
Cl10.77372 (19)0.40780 (15)0.26074 (9)0.0645 (4)
Cl20.62590 (18)0.18395 (14)0.47312 (10)0.0575 (4)
Cl30.4357 (2)1.04383 (15)0.75266 (10)0.0745 (5)
Cl40.0594 (2)0.7248 (2)1.09562 (11)0.0880 (5)
N10.8827 (5)0.8183 (4)0.5316 (3)0.0447 (10)
H10.92890.87570.47390.054*
N20.7257 (5)0.6358 (4)0.7161 (3)0.0431 (10)
O10.9408 (4)1.0040 (4)0.6487 (2)0.0540 (9)
C10.8754 (6)0.8778 (5)0.6340 (3)0.0406 (12)
C20.7819 (6)0.7756 (5)0.7279 (3)0.0418 (12)
C30.7456 (6)0.5778 (5)0.6094 (3)0.0374 (11)
C40.8206 (6)0.6717 (5)0.5149 (3)0.0356 (11)
C50.8302 (6)0.6185 (5)0.4072 (3)0.0416 (12)
H50.87790.68200.34480.050*
C60.7680 (6)0.4710 (5)0.3953 (3)0.0420 (12)
C70.6994 (6)0.3725 (5)0.4901 (4)0.0399 (11)
C80.6891 (6)0.4266 (5)0.5954 (3)0.0419 (12)
H80.64400.36130.65780.050*
C90.7583 (7)0.8441 (6)0.8411 (3)0.0584 (14)
H9A0.85070.79340.88620.070*
H9B0.77060.96140.82960.070*
C100.5845 (7)0.8167 (5)0.9056 (3)0.0426 (12)
C110.4300 (8)0.9005 (5)0.8721 (3)0.0507 (14)
C120.2672 (7)0.8752 (5)0.9292 (4)0.0544 (14)
H120.16570.93280.90450.065*
C130.2608 (7)0.7620 (6)1.0233 (4)0.0562 (14)
C140.4100 (7)0.6797 (6)1.0607 (4)0.0549 (14)
H140.40370.60591.12530.066*
C150.5711 (7)0.7057 (5)1.0027 (3)0.0517 (14)
H150.67170.64851.02880.062*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cl10.0842 (11)0.0672 (9)0.0442 (7)0.0149 (8)0.0021 (7)0.0150 (6)
Cl20.0672 (10)0.0447 (7)0.0626 (8)0.0132 (7)0.0054 (7)0.0079 (6)
Cl30.1159 (14)0.0603 (8)0.0459 (7)0.0194 (9)0.0035 (8)0.0086 (6)
Cl40.0741 (12)0.1161 (13)0.0705 (9)0.0285 (10)0.0238 (8)0.0039 (8)
N10.059 (3)0.042 (2)0.031 (2)0.014 (2)0.0130 (18)0.0019 (17)
N20.050 (3)0.050 (2)0.030 (2)0.012 (2)0.0019 (19)0.0031 (18)
O10.070 (3)0.0498 (19)0.0455 (18)0.0295 (19)0.0063 (17)0.0050 (15)
C10.041 (3)0.045 (3)0.035 (3)0.009 (2)0.001 (2)0.001 (2)
C20.045 (3)0.049 (3)0.031 (2)0.012 (3)0.003 (2)0.004 (2)
C30.039 (3)0.037 (2)0.035 (2)0.005 (2)0.005 (2)0.000 (2)
C40.034 (3)0.032 (2)0.038 (2)0.004 (2)0.002 (2)0.003 (2)
C50.049 (3)0.038 (3)0.035 (2)0.008 (2)0.003 (2)0.004 (2)
C60.039 (3)0.049 (3)0.038 (2)0.003 (2)0.003 (2)0.004 (2)
C70.041 (3)0.032 (2)0.046 (3)0.004 (2)0.000 (2)0.005 (2)
C80.046 (3)0.039 (3)0.037 (3)0.009 (2)0.004 (2)0.007 (2)
C90.072 (4)0.069 (3)0.041 (3)0.036 (3)0.002 (3)0.013 (2)
C100.057 (4)0.043 (3)0.032 (3)0.022 (3)0.006 (3)0.009 (2)
C110.087 (5)0.037 (3)0.030 (3)0.014 (3)0.002 (3)0.004 (2)
C120.061 (4)0.055 (3)0.048 (3)0.011 (3)0.003 (3)0.013 (3)
C130.068 (4)0.056 (3)0.046 (3)0.018 (3)0.014 (3)0.017 (3)
C140.069 (4)0.060 (3)0.037 (3)0.024 (3)0.007 (3)0.003 (2)
C150.067 (4)0.053 (3)0.036 (3)0.012 (3)0.001 (3)0.004 (2)
Geometric parameters (Å, º) top
Cl1—C61.740 (4)C5—H50.9300
Cl2—C71.738 (4)C6—C71.411 (5)
Cl3—C111.750 (4)C7—C81.374 (5)
Cl4—C131.740 (5)C8—H80.9300
N1—C11.362 (5)C9—C101.505 (6)
N1—C41.380 (5)C9—H9A0.9700
N1—H10.8600C9—H9B0.9700
N2—C21.292 (5)C10—C111.388 (6)
N2—C31.401 (5)C10—C151.399 (5)
O1—C11.233 (5)C11—C121.393 (6)
C1—C21.498 (5)C12—C131.380 (6)
C2—C91.511 (5)C12—H120.9300
C3—C81.387 (5)C13—C141.365 (6)
C3—C41.407 (5)C14—C151.386 (6)
C4—C51.398 (5)C14—H140.9300
C5—C61.371 (5)C15—H150.9300
C1—N1—C4124.0 (3)C7—C8—H8119.8
C1—N1—H1118.0C3—C8—H8119.8
C4—N1—H1118.0C10—C9—C2113.7 (4)
C2—N2—C3119.1 (3)C10—C9—H9A108.8
O1—C1—N1123.2 (4)C2—C9—H9A108.8
O1—C1—C2122.7 (4)C10—C9—H9B108.8
N1—C1—C2114.1 (4)C2—C9—H9B108.8
N2—C2—C1123.6 (4)H9A—C9—H9B107.7
N2—C2—C9120.6 (4)C11—C10—C15116.8 (4)
C1—C2—C9115.8 (4)C11—C10—C9121.7 (4)
C8—C3—N2120.0 (3)C15—C10—C9121.5 (5)
C8—C3—C4119.0 (4)C10—C11—C12122.8 (4)
N2—C3—C4121.0 (4)C10—C11—Cl3119.6 (4)
N1—C4—C5121.1 (3)C12—C11—Cl3117.5 (4)
N1—C4—C3118.0 (3)C13—C12—C11118.1 (5)
C5—C4—C3120.9 (4)C13—C12—H12121.0
C6—C5—C4118.8 (4)C11—C12—H12121.0
C6—C5—H5120.6C14—C13—C12120.9 (5)
C4—C5—H5120.6C14—C13—Cl4119.6 (4)
C5—C6—C7120.7 (4)C12—C13—Cl4119.4 (5)
C5—C6—Cl1118.8 (3)C13—C14—C15120.3 (5)
C7—C6—Cl1120.4 (3)C13—C14—H14119.8
C8—C7—C6119.9 (4)C15—C14—H14119.8
C8—C7—Cl2120.2 (3)C14—C15—C10121.0 (5)
C6—C7—Cl2119.9 (3)C14—C15—H15119.5
C7—C8—C3120.5 (4)C10—C15—H15119.5
C4—N1—C1—O1175.5 (4)Cl1—C6—C7—Cl21.9 (5)
C4—N1—C1—C24.0 (6)C6—C7—C8—C30.1 (7)
C3—N2—C2—C12.8 (7)Cl2—C7—C8—C3179.2 (3)
C3—N2—C2—C9178.4 (4)N2—C3—C8—C7176.5 (4)
O1—C1—C2—N2173.8 (5)C4—C3—C8—C72.8 (7)
N1—C1—C2—N25.7 (7)N2—C2—C9—C1039.4 (6)
O1—C1—C2—C95.1 (7)C1—C2—C9—C10141.7 (4)
N1—C1—C2—C9175.4 (4)C2—C9—C10—C1170.7 (6)
C2—N2—C3—C8178.8 (4)C2—C9—C10—C15109.5 (5)
C2—N2—C3—C42.0 (6)C15—C10—C11—C121.5 (7)
C1—N1—C4—C5179.2 (4)C9—C10—C11—C12178.8 (4)
C1—N1—C4—C30.2 (7)C15—C10—C11—Cl3179.1 (3)
C8—C3—C4—N1177.2 (4)C9—C10—C11—Cl30.7 (6)
N2—C3—C4—N13.5 (6)C10—C11—C12—C130.3 (7)
C8—C3—C4—C53.4 (7)Cl3—C11—C12—C13179.8 (3)
N2—C3—C4—C5175.9 (4)C11—C12—C13—C141.2 (7)
N1—C4—C5—C6179.4 (4)C11—C12—C13—Cl4179.1 (3)
C3—C4—C5—C61.2 (7)C12—C13—C14—C151.6 (8)
C4—C5—C6—C71.5 (7)Cl4—C13—C14—C15178.7 (3)
C4—C5—C6—Cl1178.0 (3)C13—C14—C15—C100.3 (7)
C5—C6—C7—C82.1 (7)C11—C10—C15—C141.1 (6)
Cl1—C6—C7—C8177.4 (3)C9—C10—C15—C14179.1 (4)
C5—C6—C7—Cl2178.6 (4)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O1i0.861.932.789 (4)173
Symmetry code: (i) x+2, y+2, z+1.

Experimental details

Crystal data
Chemical formulaC15H8Cl4N2O
Mr374.03
Crystal system, space groupTriclinic, P1
Temperature (K)298
a, b, c (Å)7.7150 (7), 8.2058 (8), 11.9722 (12)
α, β, γ (°)83.771 (1), 84.362 (1), 84.298 (2)
V3)746.79 (12)
Z2
Radiation typeMo Kα
µ (mm1)0.79
Crystal size (mm)0.16 × 0.09 × 0.05
Data collection
DiffractometerBruker SMART CCD area-detector
Absorption correctionMulti-scan
(SADABS; Sheldrick, 1996)
Tmin, Tmax0.884, 0.961
No. of measured, independent and
observed [I > 2σ(I)] reflections
3811, 2590, 1364
Rint0.036
(sin θ/λ)max1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.055, 0.103, 1.01
No. of reflections2590
No. of parameters199
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.27, 0.26

Computer programs: SMART (Bruker, 1998), SAINT (Bruker, 1999), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O1i0.861.932.789 (4)173.1
Symmetry code: (i) x+2, y+2, z+1.
 

Acknowledgements

We thank the Foundation of Xuzhou Medical College (grant No. 201120), a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), for financial support.

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