Quinoxaline: Z' = 1 form

A new Z' = 1 crystal structure of quinoxaline (or 1,4-diaza­naphthalene), C₈H₆N₂, with one-fifth the volume of the earlier known Z' = 5 structure was obtained by means of an in situ cryocrystallization technique.

Key indicators

• Single-crystal X-ray study
• T = 270 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.038
• wR factor = 0.106
• Data-to-parameter ratio = 10.5

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full Low .......       0.97
PLAT230_ALERT_2_C Hirshfeld Test Diff for    N1     --  C9      ..       5.47 su
PLAT230_ALERT_2_C Hirshfeld Test Diff for    C7     --  C8      ..       6.22 su
PLAT241_ALERT_2_C Check High      Ueq as Compared to Neighbors for         N1
PLAT241_ALERT_2_C Check High      Ueq as Compared to Neighbors for         C8
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C9
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for        C10
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600          2
PLAT912_ALERT_4_C Missing # of FCF Reflections Above STh/L=  0.600         28

Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           27.90
           From the CIF: _reflns_number_total                956
           Count of symmetry unique reflns          988
           Completeness (_total/calc)             96.76%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured         0
           Fraction of Friedel pairs measured     0.000
           Are heavy atom types Z>Si present         no

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

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   6 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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Related literature

For the structure of quinoxaline Z' = 5, see: Anthony et al. (1998). For the crystal structure of the hydrated organic compound, see: Namba et al. (1981)

S1. Experimental

For in situ crystallization, liquid quinoxaline was taken in a Lindemann glass capillary of 0.5 mm diameter. The Z' = 1 form of quinoxaline was obtained by sudden quenching of a capillary, kept in a hot water bath at 70 ^oC, down to liquid N₂ temperature.The capillary was aligned on a Bruker AXS Smart Apex diffractometer and data was collected at 270 K under a liquid N₂ flow using the OXFORD N₂ cryosystems appratus.

S2. Refinement

A crystal domain for the Z' = 1 structure was selected and indexed using the RLATT software and refined using SHELXL97. MERG 3 command was used for merging the Friedel pairs. Flack parameter was not reported as compound is achiral.

Structure description

For the structure of quinoxaline Z' = 5, see: Anthony et al. (1998). For the crystal structure of the hydrated organic compound, see: Namba et al. (1981)

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT (Bruker, 1998); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: PLATON (Spek, 2009).

Figures

Fig. 1. View of the title compound with the atom numbering. Displacement ellipsoids for non-H atoms are drawn at the 50% probability level.

Quinoxaline

Crystal data

C8H6N2	Dx = 1.295 Mg m^−3
Mr = 130.15	Melting point = 301–305 K
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 734 reflections
a = 4.0212 (13) Å	θ = 1.8–26.0°
b = 7.187 (2) Å	µ = 0.08 mm^−1
c = 23.095 (7) Å	T = 270 K
V = 667.5 (3) Å^3	Block, pink
Z = 4	0.40 × 0.30 × 0.30 mm
F(000) = 272

Data collection

Bruker SMART CCD area-detector diffractometer	956 independent reflections
Radiation source: fine-focus sealed tube	494 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.045
φ and ω scans	θmax = 27.9°, θmin = 1.8°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −5→5
Tmin = 0.968, Tmax = 0.976	k = −9→9
7556 measured reflections	l = −29→29

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)] = 0.038	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.106	H-atom parameters constrained
S = 0.90	w = 1/[σ^2(Fo^2) + (0.0652P)^2] where P = (Fo^2 + 2Fc^2)/3
956 reflections	(Δ/σ)max < 0.001
91 parameters	Δρmax = 0.13 e Å^−3
0 restraints	Δρmin = −0.15 e Å^−3

Special details

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

Refinement. Refinement on F² for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The observed criterion of F² > σ(F²) is used only for calculating -R-factor-obs 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	0.2099 (7)	0.1700 (3)	0.11405 (9)	0.1298 (9)
N2	0.2375 (6)	0.4337 (3)	0.20264 (7)	0.1131 (8)
C3	0.3379 (8)	0.1356 (3)	0.16499 (13)	0.1287 (13)
C4	0.3497 (7)	0.2654 (4)	0.20858 (9)	0.1197 (10)
C5	−0.0218 (7)	0.6547 (3)	0.13897 (10)	0.1051 (9)
C6	−0.1499 (7)	0.6977 (3)	0.08739 (11)	0.1121 (10)
C7	−0.1662 (7)	0.5672 (4)	0.04429 (10)	0.1201 (10)
C8	−0.0500 (9)	0.3930 (4)	0.05303 (8)	0.1210 (10)
C9	0.0873 (6)	0.3450 (2)	0.10587 (8)	0.0900 (8)
C10	0.1023 (6)	0.4767 (3)	0.14993 (7)	0.0842 (7)
H3	0.42490	0.01780	0.17200	0.1550*
H4	0.44230	0.23130	0.24390	0.1440*
H5	−0.01510	0.74440	0.16800	0.1260*
H6	−0.22890	0.81740	0.08070	0.1340*
H7	−0.25820	0.59880	0.00870	0.1440*
H8	−0.06220	0.30540	0.02350	0.1450*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.175 (2)	0.0880 (13)	0.1265 (15)	0.0079 (13)	−0.0063 (15)	−0.0159 (10)
N2	0.1395 (18)	0.1161 (14)	0.0837 (11)	−0.0085 (13)	−0.0069 (11)	−0.0063 (9)
C3	0.156 (3)	0.0884 (14)	0.1418 (19)	0.0102 (16)	0.003 (2)	0.0182 (15)
C4	0.134 (2)	0.1240 (18)	0.1012 (14)	0.002 (2)	−0.0040 (16)	0.0271 (14)
C5	0.131 (2)	0.0819 (13)	0.1025 (14)	0.0005 (13)	0.0090 (14)	−0.0123 (10)
C6	0.1148 (19)	0.0976 (14)	0.1238 (17)	0.0038 (14)	0.0150 (17)	0.0233 (14)
C7	0.120 (2)	0.154 (2)	0.0862 (13)	−0.0023 (19)	−0.0026 (14)	0.0241 (16)
C8	0.160 (2)	0.1223 (17)	0.0806 (13)	0.0018 (19)	−0.0101 (16)	−0.0157 (12)
C9	0.1152 (17)	0.0750 (10)	0.0797 (11)	−0.0063 (12)	0.0067 (12)	−0.0083 (8)
C10	0.1008 (16)	0.0802 (10)	0.0717 (10)	−0.0131 (12)	0.0090 (10)	−0.0034 (8)

Geometric parameters (Å, º)

N1—C3	1.308 (4)	C8—C9	1.383 (3)
N1—C9	1.364 (3)	C9—C10	1.391 (3)
N2—C4	1.298 (4)	C3—H3	0.9300
N2—C10	1.369 (3)	C4—H4	0.9300
C3—C4	1.373 (4)	C5—H5	0.9300
C5—C6	1.334 (4)	C6—H6	0.9300
C5—C10	1.396 (3)	C7—H7	0.9300
C6—C7	1.369 (4)	C8—H8	0.9300
C7—C8	1.352 (4)
N1···N2	2.791 (3)	H4···N2^v	2.7900
N2···N1	2.791 (3)	H7···C6^vi	3.0900
N2···H4^i	2.7900	H8···C8^iii	3.0000
C6···H7^ii	3.0900	H8···C8^iv	3.0700
C8···H8^iii	3.0700	H8···H8^iii	2.4200
C8···H8^iv	3.0000	H8···H8^iv	2.4200
C3—N1—C9	116.2 (2)	C5—C10—C9	118.38 (18)
C4—N2—C10	116.26 (19)	N1—C3—H3	118.00
N1—C3—C4	123.0 (2)	C4—C3—H3	119.00
N2—C4—C3	122.9 (2)	N2—C4—H4	119.00
C6—C5—C10	120.8 (2)	C3—C4—H4	119.00
C5—C6—C7	120.6 (2)	C6—C5—H5	120.00
C6—C7—C8	120.6 (2)	C10—C5—H5	120.00
C7—C8—C9	120.1 (2)	C5—C6—H6	120.00
N1—C9—C8	119.77 (19)	C7—C6—H6	120.00
N1—C9—C10	120.69 (19)	C6—C7—H7	120.00
C8—C9—C10	119.54 (18)	C8—C7—H7	120.00
N2—C10—C5	120.67 (19)	C7—C8—H8	120.00
N2—C10—C9	121.0 (2)	C9—C8—H8	120.00
C9—N1—C3—C4	0.3 (4)	C10—C5—C6—C7	0.8 (4)
C3—N1—C9—C10	0.3 (4)	C5—C6—C7—C8	−0.6 (4)
C3—N1—C9—C8	179.5 (3)	C6—C7—C8—C9	−0.1 (5)
C10—N2—C4—C3	0.3 (4)	C7—C8—C9—C10	0.5 (4)
C4—N2—C10—C5	−179.3 (2)	C7—C8—C9—N1	−178.8 (3)
C4—N2—C10—C9	0.3 (4)	N1—C9—C10—N2	−0.6 (4)
N1—C3—C4—N2	−0.7 (5)	C8—C9—C10—C5	−0.3 (4)
C6—C5—C10—C9	−0.4 (4)	N1—C9—C10—C5	179.0 (2)
C6—C5—C10—N2	179.2 (3)	C8—C9—C10—N2	−179.8 (3)

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