2,2′,3,3′-Tetra­methyl-6,6′-biquinoxaline

The molecule of the title compound, C₂₀H₁₈N₄, has twofold rotational symmetry. Each aromatic ring of the fused quinoxaline ring system is skewed from the other by 4.93 (7)°. The two quinoxaline units make a dihedral angle of 43.52 (2)°.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.039
• wR factor = 0.111
• Data-to-parameter ratio = 9.7

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT088_ALERT_3_C Poor Data / Parameter Ratio ....................       9.66
PLAT125_ALERT_4_C No _symmetry_space_group_name_Hall Given .......          ?

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

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


checkCIF publication errors

Alert level A
PUBL024_ALERT_1_A The number of authors is greater than 5.
              Please specify the role of each of the co-authors
              for your paper.

Author Response: ..Each of the authors made valuable contributions to manuscript.R. N. Salvatore suggested we investigate these unknown systems, J. K. Kass and R. P. Gibson performed the reaction and grew the crystals. C.H. Zambrano helped to write the manuscript while R. D. Pike solved the x-ray structure. E. E. Dueno provided funding and completed the manuscript.

   1 ALERT level A = Data missing that is essential or data in wrong format
   0 ALERT level G = General alerts. Data that may be required is missing

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Computing details

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT-Plus (Bruker, 2004); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: XSHELL (Bruker, 2004); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

2,2',3,3'-tetramethyl-6,6'-biquinoxaline

Crystal data

C20H18N4	Z = 4
Mr = 314.38	F(000) = 664
Monoclinic, C2/c	Dx = 1.354 Mg m^−3
Hall symbol: -C 2yc	Melting point: 216 K
a = 12.0225 (6) Å	Cu Kα radiation, λ = 1.54178 Å
b = 6.7301 (3) Å	µ = 0.65 mm^−1
c = 19.1118 (10) Å	T = 100 K
β = 93.966 (3)°	Plate, colourless
V = 1542.68 (13) Å^3	0.15 × 0.15 × 0.04 mm

Data collection

Bruker SMART APEX-II CCD diffractometer	1410 independent reflections
Radiation source: fine-focus sealed tube	1148 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.050
ω and φ scans	θmax = 69.0°, θmin = 4.6°
Absorption correction: multi-scan (SADABS; Sheldrick, 2004)	h = −14→13
Tmin = 0.91, Tmax = 0.98	k = −8→7
8311 measured reflections	l = −21→22

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.039	H-atom parameters constrained
wR(F^2) = 0.111	w = 1/[σ^2(Fo^2) + 0.9428P] where P = (Fo^2 + 2Fc^2)/3
S = 1.04	(Δ/σ)max < 0.001
1410 reflections	Δρmax = 0.19 e Å^−3
146 parameters	Δρmin = −0.20 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0010 (2)

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	0.65671 (9)	0.48492 (17)	0.37653 (6)	0.0182 (3)
N2	0.80829 (9)	0.16275 (17)	0.38491 (6)	0.0189 (3)
C1	0.95139 (10)	0.5046 (2)	0.27210 (6)	0.0172 (4)
C2	0.88078 (12)	0.6729 (2)	0.27409 (7)	0.0185 (4)
C3	0.78553 (11)	0.6684 (2)	0.30981 (7)	0.0184 (4)
C4	0.75697 (11)	0.4952 (2)	0.34589 (7)	0.0168 (4)
C5	0.63406 (11)	0.3183 (2)	0.40860 (7)	0.0182 (4)
C6	0.71252 (11)	0.1560 (2)	0.41439 (7)	0.0181 (4)
C7	0.83078 (11)	0.3318 (2)	0.34830 (7)	0.0174 (4)
C8	0.92771 (11)	0.3389 (2)	0.31092 (7)	0.0182 (4)
C9	0.52347 (12)	0.2985 (2)	0.43982 (8)	0.0218 (4)
C10	0.68672 (13)	−0.0288 (2)	0.45370 (8)	0.0234 (4)
H2	0.8979 (12)	0.793 (2)	0.2479 (8)	0.027 (4)*
H3	0.7346 (12)	0.782 (2)	0.3094 (8)	0.025 (4)*
H8	0.9755 (13)	0.225 (2)	0.3134 (8)	0.027 (4)*
H9A	0.4851 (13)	0.170 (2)	0.4235 (8)	0.028 (4)*
H9B	0.4714 (12)	0.412 (2)	0.4249 (7)	0.020 (4)*
H9C	0.5338 (12)	0.292 (2)	0.4928 (9)	0.029 (4)*
H10A	0.7546 (15)	−0.113 (2)	0.4583 (9)	0.037 (5)*
H10B	0.6623 (12)	0.004 (2)	0.5013 (8)	0.026 (4)*
H10C	0.6256 (13)	−0.113 (2)	0.4268 (8)	0.027 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0188 (6)	0.0205 (7)	0.0151 (6)	0.0010 (5)	−0.0009 (5)	−0.0015 (5)
N2	0.0203 (7)	0.0193 (7)	0.0168 (6)	0.0012 (5)	−0.0003 (5)	0.0003 (5)
C1	0.0172 (8)	0.0202 (7)	0.0135 (7)	−0.0004 (6)	−0.0042 (6)	−0.0023 (5)
C2	0.0207 (7)	0.0197 (8)	0.0144 (7)	−0.0001 (6)	−0.0028 (6)	0.0018 (6)
C3	0.0192 (8)	0.0185 (8)	0.0170 (8)	0.0033 (6)	−0.0026 (6)	−0.0001 (5)
C4	0.0161 (7)	0.0210 (8)	0.0129 (7)	−0.0002 (6)	−0.0023 (5)	−0.0023 (5)
C5	0.0202 (7)	0.0211 (8)	0.0130 (7)	−0.0004 (6)	−0.0016 (5)	−0.0024 (5)
C6	0.0203 (7)	0.0205 (8)	0.0132 (7)	−0.0007 (6)	−0.0016 (5)	−0.0025 (5)
C7	0.0190 (7)	0.0182 (7)	0.0144 (7)	−0.0002 (6)	−0.0027 (6)	−0.0004 (5)
C8	0.0185 (7)	0.0188 (8)	0.0168 (8)	0.0020 (6)	−0.0022 (6)	−0.0007 (5)
C9	0.0199 (8)	0.0261 (8)	0.0194 (8)	0.0004 (7)	0.0023 (6)	0.0007 (6)
C10	0.0262 (9)	0.0229 (8)	0.0212 (8)	0.0002 (7)	0.0031 (6)	0.0024 (6)

Geometric parameters (Å, º)

N1—C5	1.3152 (17)	C5—C6	1.4427 (19)
N1—C4	1.3777 (17)	C5—C9	1.5003 (18)
N2—C6	1.3171 (17)	C6—C10	1.4964 (19)
N2—C7	1.3721 (17)	C7—C8	1.4092 (18)
C1—C8	1.3801 (19)	C8—H8	0.958 (16)
C1—C2	1.4175 (19)	C9—H9A	1.020 (16)
C1—C1^i	1.489 (3)	C9—H9B	1.016 (15)
C2—C3	1.3735 (19)	C9—H9C	1.012 (17)
C2—H2	0.982 (16)	C10—H10A	0.991 (18)
C3—C4	1.4087 (19)	C10—H10B	1.000 (16)
C3—H3	0.979 (16)	C10—H10C	1.035 (16)
C4—C7	1.4122 (19)
C5—N1—C4	117.16 (12)	C5—C6—C10	120.71 (12)
C6—N2—C7	117.11 (12)	N2—C7—C8	119.06 (12)
C8—C1—C2	119.03 (13)	N2—C7—C4	121.12 (12)
C8—C1—C1^i	120.28 (9)	C8—C7—C4	119.79 (13)
C2—C1—C1^i	120.68 (9)	C1—C8—C7	120.56 (13)
C3—C2—C1	121.14 (13)	C1—C8—H8	121.9 (9)
C3—C2—H2	118.9 (9)	C7—C8—H8	117.5 (9)
C1—C2—H2	119.9 (9)	C5—C9—H9A	110.4 (9)
C2—C3—C4	120.09 (13)	C5—C9—H9B	111.6 (8)
C2—C3—H3	121.5 (9)	H9A—C9—H9B	107.2 (11)
C4—C3—H3	118.4 (9)	C5—C9—H9C	110.5 (9)
N1—C4—C3	119.99 (12)	H9A—C9—H9C	107.0 (12)
N1—C4—C7	120.87 (13)	H9B—C9—H9C	110.0 (12)
C3—C4—C7	119.12 (12)	C6—C10—H10A	108.7 (10)
N1—C5—C6	121.73 (12)	C6—C10—H10B	110.9 (9)
N1—C5—C9	118.61 (12)	H10A—C10—H10B	109.7 (13)
C6—C5—C9	119.67 (12)	C6—C10—H10C	111.7 (9)
N2—C6—C5	121.83 (13)	H10A—C10—H10C	106.6 (13)
N2—C6—C10	117.46 (12)	H10B—C10—H10C	109.2 (12)
C8—C1—C2—C3	−4.64 (19)	N1—C5—C6—C10	177.46 (12)
C1^i—C1—C2—C3	174.30 (14)	C9—C5—C6—C10	−2.49 (19)
C1—C2—C3—C4	0.6 (2)	C6—N2—C7—C8	−174.64 (11)
C5—N1—C4—C3	179.05 (11)	C6—N2—C7—C4	3.49 (19)
C5—N1—C4—C7	0.92 (18)	N1—C4—C7—N2	−4.19 (19)
C2—C3—C4—N1	−174.35 (12)	C3—C4—C7—N2	177.67 (12)
C2—C3—C4—C7	3.81 (19)	N1—C4—C7—C8	173.92 (12)
C4—N1—C5—C6	2.70 (19)	C3—C4—C7—C8	−4.22 (19)
C4—N1—C5—C9	−177.35 (11)	C2—C1—C8—C7	4.18 (19)
C7—N2—C6—C5	0.13 (19)	C1^i—C1—C8—C7	−174.77 (13)
C7—N2—C6—C10	179.29 (11)	N2—C7—C8—C1	178.35 (12)
N1—C5—C6—N2	−3.4 (2)	C4—C7—C8—C1	0.20 (19)
C9—C5—C6—N2	176.65 (12)

Symmetry code: (i) −x+2, y, −z+1/2.