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Although systematic absences and symmetry relations among reflections pointed to space group I4122 (one molecule in the asymmetric unit), a direct methods solution could only be obtained in I4 (two molecules in the asymmetric unit). Refinement in I4 was unsatisfactory until merohedral twinning was taken into account. The resulting molecular dimensions are in excellent agreement with analogous values in the literature. The molecular arrangement is described.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768199016547/cf0007sup1.cif
Contains datablocks 168K, 123K, global

sft

Structure factor file (SHELXL table format) https://doi.org/10.1107/S0108768199016547/cf0007168Ksup2.sft
Supplementary material

sft

Structure factor file (SHELXL table format) https://doi.org/10.1107/S0108768199016547/cf0007123Ksup3.sft
Supplementary material

CCDC references: 148908; 148909

Computing details top

For both compounds, data collection: 'Siemens P3-PC diffractometer program V.4.24'; cell refinement: 'Siemens P3-PC diffractometer program V.4.24'; data reduction: Siemens XDISK V.4.20.2 1991 PC; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997).

(168K) pyrazine, 2-methyl top
Crystal data top
C5H6N2Melting point: 242 K
Mr = 94.12Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4Cell parameters from 50 reflections
a = 13.799 (2) Åθ = 3–45°
c = 10.876 (2) ŵ = 0.08 mm1
V = 2071.0 (6) Å3T = 168 K
Z = 16Cylindrical, colorless
F(000) = 8000.15 mm (radius)
Dx = 1.208 Mg m3
Data collection top
Nicolet R3m/V four circle
diffractometer
Rint = 0.023
Radiation source: fine-focus sealed tubeθmax = 22.6°, θmin = 2.1°
Graphite monochromatorh = 1114
Wyckoff scan modek = 1114
2877 measured reflectionsl = 1011
1357 independent reflections2 standard reflections every 100 reflections
1322 reflections with I > 2σ(I) intensity decay: 2.7%
Refinement top
Refinement on F2Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: fullH atoms treated by a mixture of independent and constrained refinement
R[F2 > 2σ(F2)] = 0.021 w = 1/[σ2(Fo2) + (0.0324P)2 + 0.0103P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.050(Δ/σ)max = 0.009
S = 1.06Δρmax = 0.11 e Å3
1357 reflectionsΔρmin = 0.11 e Å3
177 parametersExtinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0118 (11)
Primary atom site location: structure-invariant direct methodsAbsolute structure: Flack H D (1983), Acta Cryst. A39, 876-881
Secondary atom site location: difference Fourier mapAbsolute structure parameter: 0.2 (19)
Special details top

Experimental. The crystallization was performed on the diffractometer at a temperature of 230 K with a miniature zone melting procedure using focused infrared-laser radiation according to: R·Boese, M·Nussbaumer, "In Situ Crystallization Techniques", in: "Organic Crystal Chemistry", Ed. D·W. Jones, Oxford University Press, England, (1994) 20–37.

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
N1A0.01817 (13)0.13390 (12)0.15819 (14)0.0518 (5)
C2A0.04174 (16)0.13994 (14)0.27625 (18)0.0414 (5)
C3A0.02827 (17)0.12962 (16)0.3652 (2)0.0504 (6)
H3A0.0129 (14)0.1323 (16)0.442 (2)0.046 (6)*
N4A0.12136 (14)0.11422 (17)0.34185 (16)0.0588 (6)
C5A0.14397 (19)0.10959 (18)0.2230 (2)0.0562 (6)
H5A0.2113 (19)0.1013 (16)0.200 (2)0.057 (6)*
C6A0.07612 (19)0.11796 (17)0.1336 (2)0.0560 (6)
H6A0.0946 (18)0.1145 (18)0.046 (3)0.077 (8)*
C7A0.14578 (19)0.1573 (2)0.3079 (2)0.0601 (7)
H7A10.193 (2)0.101 (2)0.268 (3)0.095 (9)*
H7A20.1588 (19)0.150 (2)0.404 (3)0.095 (9)*
H7A30.1667 (16)0.2122 (18)0.268 (2)0.056 (7)*
N1B0.47406 (14)0.12734 (14)0.09532 (14)0.0541 (5)
C2B0.44816 (16)0.13104 (15)0.0227 (2)0.0444 (5)
C3B0.51810 (16)0.12665 (16)0.1137 (2)0.0471 (5)
H3B0.5002 (15)0.1305 (14)0.204 (2)0.055 (6)*
N4B0.61292 (14)0.11852 (14)0.09180 (16)0.0515 (6)
C5B0.63781 (19)0.11532 (18)0.0264 (2)0.0525 (6)
H5B0.710 (2)0.110 (2)0.044 (3)0.083 (8)*
C6B0.56840 (17)0.11904 (17)0.1185 (2)0.0556 (6)
H6B0.5974 (16)0.1127 (18)0.196 (3)0.065 (8)*
C7B0.34303 (19)0.1395 (2)0.0527 (3)0.0585 (6)
H7B10.308 (3)0.127 (3)0.034 (4)0.143 (12)*
H7B20.318 (3)0.209 (3)0.056 (4)0.127 (12)*
H7B30.318 (2)0.093 (2)0.096 (3)0.110 (13)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N1A0.0653 (14)0.0509 (12)0.0392 (11)0.0013 (10)0.0038 (8)0.0019 (9)
C2A0.0526 (12)0.0372 (11)0.0343 (11)0.0004 (10)0.0004 (9)0.0003 (8)
C3A0.0577 (16)0.0583 (13)0.0353 (13)0.0028 (10)0.0020 (10)0.0030 (10)
N4A0.0506 (11)0.0764 (14)0.0494 (9)0.0009 (10)0.0011 (9)0.0045 (11)
C5A0.0541 (15)0.0585 (15)0.0559 (14)0.0048 (14)0.0071 (12)0.0050 (13)
C6A0.0734 (16)0.0601 (15)0.0346 (13)0.0020 (12)0.0136 (12)0.0010 (11)
C7A0.0506 (14)0.0698 (18)0.0598 (16)0.0019 (13)0.0034 (12)0.0028 (15)
N1B0.0702 (13)0.0622 (12)0.0299 (11)0.0027 (10)0.0048 (8)0.0043 (9)
C2B0.0538 (13)0.0360 (11)0.0435 (14)0.0087 (11)0.0028 (10)0.0034 (9)
C3B0.0605 (14)0.0521 (12)0.0288 (12)0.0030 (11)0.0001 (9)0.0010 (9)
N4B0.0526 (12)0.0572 (11)0.0445 (10)0.0039 (9)0.0045 (8)0.0033 (9)
C5B0.0577 (14)0.0488 (11)0.0510 (14)0.0008 (12)0.0109 (12)0.0040 (12)
C6B0.0741 (17)0.0555 (15)0.0374 (14)0.0041 (13)0.0092 (13)0.0044 (10)
C7B0.0545 (15)0.0566 (16)0.0644 (17)0.0017 (13)0.0008 (12)0.0002 (14)
Geometric parameters (Å, º) top
N1A—C2A1.327 (3)N1B—C6B1.331 (3)
N1A—C6A1.346 (3)N1B—C2B1.333 (3)
C2A—C3A1.374 (3)C2B—C3B1.384 (3)
C2A—C7A1.496 (3)C2B—C7B1.492 (4)
C3A—N4A1.326 (3)C3B—N4B1.335 (3)
N4A—C5A1.332 (3)N4B—C5B1.331 (3)
C5A—C6A1.354 (3)C5B—C6B1.387 (3)
C2A—N1A—C6A116.04 (19)C6B—N1B—C2B116.6 (2)
N1A—C2A—C3A120.13 (19)N1B—C2B—C3B120.0 (2)
N1A—C2A—C7A117.9 (2)N1B—C2B—C7B118.3 (2)
C3A—C2A—C7A122.0 (2)C3B—C2B—C7B121.7 (2)
N4A—C3A—C2A124.3 (2)N4B—C3B—C2B124.1 (2)
C3A—N4A—C5A114.8 (2)C5B—N4B—C3B115.3 (2)
N4A—C5A—C6A122.0 (2)N4B—C5B—C6B121.2 (2)
N1A—C6A—C5A122.7 (2)N1B—C6B—C5B122.8 (2)
(123K) pyrazine, 2-methyl top
Crystal data top
C5H6N2Melting point: 242 K
Mr = 94.12Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4Cell parameters from 50 reflections
a = 13.725 (2) Åθ = 3–45°
c = 10.859 (2) ŵ = 0.08 mm1
V = 2045.6 (6) Å3T = 123 K
Z = 16Cylindrical, colorless
F(000) = 8000.15 mm (radius)
Dx = 1.222 Mg m3
Data collection top
Nicolet R3m/V four circle
diffractometer
Rint = 0.024
Radiation source: fine-focus sealed tubeθmax = 22.5°, θmin = 2.1°
Graphite monochromatorh = 1410
Wyckoff scan modek = 1014
1474 measured reflectionsl = 011
1338 independent reflections2 standard reflections every 100 reflections
1301 reflections with I > 2σ(I) intensity decay: 0.7%
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.026H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.068 w = 1/[σ2(Fo2) + (0.0428P)2 + 0.2414P]
where P = (Fo2 + 2Fc2)/3
S = 1.08(Δ/σ)max = 0.004
1338 reflectionsΔρmax = 0.09 e Å3
176 parametersΔρmin = 0.12 e Å3
0 restraintsAbsolute structure: Flack H D (1983), Acta Cryst. A39, 876-881
Primary atom site location: structure-invariant direct methodsAbsolute structure parameter: 6 (3)
Special details top

Experimental. The crystallization was performed on the diffractometer at a temperature of 230 K with a miniature zone melting procedure using focused infrared-laser radiation according to: R·Boese, M·Nussbaumer, "In Situ Crystallization Techniques", in: "Organic Crystal Chemistry", Ed. D·W. Jones, Oxford University Press, England, (1994) 20–37.

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
N1A0.01857 (15)0.13349 (14)0.15884 (18)0.0377 (6)
C2A0.04218 (18)0.13973 (16)0.2772 (2)0.0310 (6)
C3A0.0289 (2)0.12985 (19)0.3668 (2)0.0381 (6)
H3A0.0139 (18)0.137 (2)0.443 (3)0.040 (7)*
N4A0.12254 (16)0.11445 (18)0.34271 (19)0.0437 (6)
C5A0.1452 (2)0.1090 (2)0.2227 (3)0.0427 (7)
H5A0.209 (2)0.0954 (19)0.198 (3)0.046 (8)*
C6A0.0756 (2)0.11701 (19)0.1330 (2)0.0416 (7)
H6A0.095 (2)0.111 (2)0.040 (3)0.077 (10)*
C7A0.1464 (2)0.1572 (3)0.3096 (3)0.0452 (8)
H7A10.190 (3)0.104 (3)0.270 (4)0.084 (11)*
H7A20.154 (2)0.156 (3)0.396 (3)0.067 (10)*
H7A30.166 (2)0.214 (2)0.273 (3)0.048 (9)*
N1B0.52689 (17)0.12727 (17)0.09554 (18)0.0414 (6)
C2B0.55250 (18)0.13104 (18)0.0227 (2)0.0349 (6)
C3B0.48228 (19)0.12616 (19)0.1148 (2)0.0369 (6)
H3B0.4996 (17)0.1288 (17)0.203 (2)0.034 (6)*
N4B0.38712 (16)0.11870 (17)0.09235 (19)0.0391 (6)
C5B0.3620 (2)0.11554 (19)0.0264 (3)0.0386 (6)
H5B0.287 (2)0.113 (2)0.041 (3)0.048 (7)*
C6B0.4314 (2)0.11949 (19)0.1188 (3)0.0432 (7)
H6B0.4053 (19)0.109 (2)0.196 (3)0.050 (9)*
C7B0.6584 (2)0.1387 (2)0.0524 (3)0.0438 (7)
H7B10.694 (3)0.113 (4)0.028 (5)0.136 (17)*
H7B20.683 (3)0.204 (3)0.053 (4)0.086 (12)*
H7B30.682 (3)0.090 (3)0.105 (4)0.099 (14)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N1A0.0449 (15)0.0395 (13)0.0287 (12)0.0016 (11)0.0045 (9)0.0019 (10)
C2A0.0393 (14)0.0276 (13)0.0261 (12)0.0004 (12)0.0001 (11)0.0002 (10)
C3A0.0441 (17)0.0450 (15)0.0251 (15)0.0013 (12)0.0035 (12)0.0010 (13)
N4A0.0391 (13)0.0563 (15)0.0359 (11)0.0011 (11)0.0001 (10)0.0050 (11)
C5A0.0392 (17)0.0440 (17)0.0449 (16)0.0008 (15)0.0070 (15)0.0059 (14)
C6A0.0583 (18)0.0411 (15)0.0253 (15)0.0018 (13)0.0089 (14)0.0010 (12)
C7A0.0418 (16)0.053 (2)0.0409 (18)0.0026 (15)0.0044 (13)0.0006 (16)
N1B0.0547 (16)0.0461 (14)0.0234 (12)0.0020 (11)0.0029 (10)0.0046 (10)
C2B0.0425 (15)0.0287 (13)0.0334 (16)0.0072 (12)0.0022 (12)0.0017 (11)
C3B0.0494 (17)0.0386 (14)0.0226 (14)0.0030 (12)0.0009 (12)0.0021 (11)
N4B0.0393 (13)0.0449 (13)0.0333 (12)0.0026 (10)0.0026 (10)0.0029 (10)
C5B0.0430 (16)0.0342 (13)0.0387 (16)0.0004 (12)0.0097 (13)0.0029 (13)
C6B0.0602 (19)0.0403 (17)0.0292 (16)0.0041 (14)0.0063 (16)0.0045 (13)
C7B0.0421 (17)0.0393 (18)0.0500 (19)0.0028 (14)0.0005 (13)0.0011 (15)
Geometric parameters (Å, º) top
N1A—C2A1.328 (3)N1B—C2B1.332 (3)
N1A—C6A1.342 (4)N1B—C6B1.339 (4)
C2A—C3A1.384 (4)C2B—C3B1.391 (4)
C2A—C7A1.492 (4)C2B—C7B1.492 (4)
C3A—N4A1.329 (4)C3B—N4B1.332 (4)
N4A—C5A1.342 (3)N4B—C5B1.335 (4)
C5A—C6A1.368 (4)C5B—C6B1.385 (4)
C2A—N1A—C6A116.6 (2)C2B—N1B—C6B116.3 (2)
N1A—C2A—C3A120.1 (2)N1B—C2B—C3B120.5 (2)
N1A—C2A—C7A118.2 (2)N1B—C2B—C7B117.9 (2)
C3A—C2A—C7A121.7 (2)C3B—C2B—C7B121.5 (2)
N4A—C3A—C2A124.0 (2)N4B—C3B—C2B123.5 (3)
C3A—N4A—C5A115.1 (2)C3B—N4B—C5B115.6 (2)
N4A—C5A—C6A121.6 (3)N4B—C5B—C6B121.4 (3)
N1A—C6A—C5A122.5 (2)N1B—C6B—C5B122.7 (3)
 

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