Monoclinic polymorph of 2,5-bis[4-(dimethyl-amino)-styr-yl]-3,6-dimethyl-pyrazine.

The title compound, C(26)H(30)N(4), was prepared by condensation of tetra-methyl-pyrazine and dimethyl-amino-benzaldehyde and crystallizes from chloro-form/methanol in two different forms. Block-shaped crystals belong to the monoclinic crystal system and plates to the triclinic system. The two crystal forms differ in the arrangement of the centrosymmetric mol-ecules, which have nearly identical geometries. In the monoclinic crystals reported here, planar mol-ecules [maximum deviation = 0.062 (2) Å], with a transoid arrangement of the (E)-styryl units and completely planarized dimethylamino groups [sum of the C-N bond angles = 359.9 (2)°], form layers connected via H-π-stacking. The dihedral angle between the central and pendant rings is 1.30 (8)°. The triclinic polymorph contains two half molecules, both completed by crystallographic inversion symmetry.

Related literature

The title compound was synthesized as a fundamental chromophore in a larger project focusing on solvatochromic and acidochromic dyes for sensing applications via one and two-photon excited fluorescence, see: Nemkovich et al. (2010 ▶); Schmitt et al. (2008 ▶); Detert & Schmitt (2006 ▶); Strehmel et al. (2003 ▶). Starting with 2,5-dimethyl­pyrazine, linear distyryl­pyrazines had been prepared by acid-catalyzed condensations with benzaldehyde (Takahashi & Satake, 1952 ▶) as well as via Siegrist reaction with the anils of alk­oxy­benzaldehydes (Zerban, 1991 ▶). Crystal data for the triclinic form have been deposited (CCDC 807782).

Experimental

Crystal data

C26H30N4

M = 398.54

Monoclinic,

a = 6.0635 (5) Å

b = 15.5187 (13) Å

c = 12.8009 (12) Å

β = 113.449 (6)°

V = 1105.06 (17) Å3

Z = 2

Mo Kα radiation

μ = 0.07 mm−1

T = 193 K

0.49 × 0.45 × 0.27 mm

Data collection

Bruker SMART CCD diffractometer

13517 measured reflections

2637 independent reflections

1711 reflections with I > 2σ(I)

R int = 0.057

Refinement

R[F 2 > 2σ(F 2)] = 0.056

wR(F 2) = 0.170

S = 1.02

2637 reflections

139 parameters

H-atom parameters constrained

Δρmax = 0.27 e Å−3

Δρmin = −0.22 e Å−3

Data collection: SMART (Bruker, 2006 ▶); cell refinement: SAINT (Bruker, 2006 ▶); data reduction: SAINT; program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: PLATON (Spek, 2009 ▶); software used to prepare material for publication: PLATON.

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536811006234/si2330sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811006234/si2330Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

C26H30N4	F(000) = 428
Mr = 398.54	Dx = 1.198 Mg m−3
Monoclinic, P21/c	Melting point: 522 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 6.0635 (5) Å	Cell parameters from 3217 reflections
b = 15.5187 (13) Å	θ = 2.6–27°
c = 12.8009 (12) Å	µ = 0.07 mm−1
β = 113.449 (6)°	T = 193 K
V = 1105.06 (17) Å3	Block, orange
Z = 2	0.49 × 0.45 × 0.27 mm

Bruker SMART CCD diffractometer	1711 reflections with I > 2σ(I)
Radiation source: sealed Tube	Rint = 0.057
graphite	θmax = 28.0°, θmin = 2.2°
CCD scan	h = −7→7
13517 measured reflections	k = −20→19
2637 independent reflections	l = −16→16

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.056	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.170	H-atom parameters constrained
S = 1.02	w = 1/[σ2(Fo2) + (0.093P)2 + 0.1486P] where P = (Fo2 + 2Fc2)/3
2637 reflections	(Δ/σ)max = 0.001
139 parameters	Δρmax = 0.27 e Å−3
0 restraints	Δρmin = −0.22 e Å−3

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.

	x	y	z	Uiso*/Ueq
N1	0.3645 (2)	0.52967 (9)	0.55807 (11)	0.0361 (4)
C2	0.3898 (3)	0.44536 (10)	0.54641 (13)	0.0340 (4)
C3	0.4723 (3)	0.58565 (10)	0.51230 (13)	0.0347 (4)
C4	0.2626 (3)	0.38669 (11)	0.59782 (16)	0.0437 (5)
H4A	0.3808	0.3592	0.6661	0.066*
H4B	0.1750	0.3423	0.5424	0.066*
H4C	0.1492	0.4203	0.6185	0.066*
C5	0.4434 (3)	0.67746 (11)	0.52817 (15)	0.0374 (4)
H5	0.5138	0.7174	0.4943	0.045*
C6	0.3227 (3)	0.70847 (11)	0.58799 (14)	0.0363 (4)
H6	0.2543	0.6666	0.6203	0.044*
C7	0.2832 (3)	0.79779 (11)	0.60981 (14)	0.0347 (4)
C8	0.1390 (3)	0.81714 (11)	0.66978 (16)	0.0424 (5)
H8	0.0713	0.7710	0.6959	0.051*
C9	0.0920 (3)	0.90040 (11)	0.69218 (15)	0.0424 (5)
H9	−0.0074	0.9101	0.7327	0.051*
C10	0.1880 (3)	0.97122 (11)	0.65634 (13)	0.0352 (4)
C11	0.3336 (3)	0.95248 (11)	0.59606 (14)	0.0374 (4)
H11	0.4019	0.9985	0.5700	0.045*
C12	0.3784 (3)	0.86880 (11)	0.57435 (14)	0.0383 (4)
H12	0.4776	0.8589	0.5338	0.046*
N13	0.1460 (3)	1.05436 (9)	0.67883 (13)	0.0443 (4)
C14	−0.0132 (4)	1.07191 (13)	0.73601 (18)	0.0524 (5)
H14A	−0.1665	1.0421	0.6962	0.079*
H14B	−0.0415	1.1341	0.7357	0.079*
H14C	0.0610	1.0513	0.8148	0.079*
C15	0.2474 (3)	1.12637 (12)	0.64153 (16)	0.0479 (5)
H15A	0.4228	1.1207	0.6724	0.072*
H15B	0.2044	1.1802	0.6688	0.072*
H15C	0.1838	1.1270	0.5581	0.072*

	U11	U22	U33	U12	U13	U23
N1	0.0347 (8)	0.0396 (8)	0.0399 (8)	0.0014 (6)	0.0210 (6)	−0.0010 (6)
C2	0.0300 (8)	0.0397 (9)	0.0351 (9)	0.0006 (6)	0.0161 (7)	−0.0006 (7)
C3	0.0304 (8)	0.0415 (10)	0.0342 (9)	0.0024 (6)	0.0151 (7)	−0.0013 (7)
C4	0.0462 (10)	0.0433 (10)	0.0542 (11)	0.0003 (8)	0.0334 (9)	−0.0002 (8)
C5	0.0374 (9)	0.0388 (9)	0.0416 (10)	0.0012 (7)	0.0215 (8)	−0.0008 (7)
C6	0.0342 (9)	0.0401 (9)	0.0378 (9)	−0.0004 (7)	0.0176 (8)	−0.0006 (7)
C7	0.0340 (9)	0.0390 (9)	0.0359 (9)	0.0022 (6)	0.0191 (7)	−0.0006 (7)
C8	0.0469 (10)	0.0433 (10)	0.0506 (11)	−0.0020 (7)	0.0338 (9)	0.0012 (8)
C9	0.0449 (10)	0.0476 (11)	0.0493 (11)	0.0020 (7)	0.0343 (9)	−0.0006 (8)
C10	0.0337 (9)	0.0408 (10)	0.0350 (9)	0.0029 (7)	0.0179 (7)	−0.0015 (7)
C11	0.0388 (9)	0.0398 (9)	0.0418 (10)	−0.0027 (7)	0.0249 (8)	−0.0008 (7)
C12	0.0363 (9)	0.0459 (10)	0.0424 (10)	0.0004 (7)	0.0258 (8)	−0.0024 (8)
N13	0.0517 (9)	0.0399 (9)	0.0532 (9)	0.0051 (6)	0.0336 (8)	−0.0023 (7)
C14	0.0531 (12)	0.0521 (11)	0.0653 (13)	0.0063 (9)	0.0376 (11)	−0.0115 (10)
C15	0.0501 (11)	0.0409 (11)	0.0577 (12)	−0.0017 (8)	0.0268 (10)	−0.0050 (8)

N1—C2	1.333 (2)	C8—H8	0.9500
N1—C3	1.353 (2)	C9—C10	1.403 (2)
C2—C3i	1.413 (2)	C9—H9	0.9500
C2—C4	1.504 (2)	C10—N13	1.368 (2)
C3—C2i	1.413 (2)	C10—C11	1.415 (2)
C3—C5	1.459 (2)	C11—C12	1.377 (2)
C4—H4A	0.9800	C11—H11	0.9500
C4—H4B	0.9800	C12—H12	0.9500
C4—H4C	0.9800	N13—C15	1.445 (2)
C5—C6	1.341 (2)	N13—C14	1.451 (2)
C5—H5	0.9500	C14—H14A	0.9800
C6—C7	1.453 (2)	C14—H14B	0.9800
C6—H6	0.9500	C14—H14C	0.9800
C7—C12	1.401 (2)	C15—H15A	0.9800
C7—C8	1.406 (2)	C15—H15B	0.9800
C8—C9	1.378 (2)	C15—H15C	0.9800
C2—N1—C3	119.01 (14)	C8—C9—H9	119.4
N1—C2—C3i	120.87 (15)	C10—C9—H9	119.4
N1—C2—C4	116.32 (14)	N13—C10—C9	122.27 (15)
C3i—C2—C4	122.81 (15)	N13—C10—C11	121.15 (15)
N1—C3—C2i	120.12 (15)	C9—C10—C11	116.58 (15)
N1—C3—C5	117.47 (14)	C12—C11—C10	121.31 (15)
C2i—C3—C5	122.40 (15)	C12—C11—H11	119.3
C2—C4—H4A	109.5	C10—C11—H11	119.3
C2—C4—H4B	109.5	C11—C12—C7	122.44 (16)
H4A—C4—H4B	109.5	C11—C12—H12	118.8
C2—C4—H4C	109.5	C7—C12—H12	118.8
H4A—C4—H4C	109.5	C10—N13—C15	121.39 (14)
H4B—C4—H4C	109.5	C10—N13—C14	120.01 (15)
C6—C5—C3	123.56 (16)	C15—N13—C14	118.53 (14)
C6—C5—H5	118.2	N13—C14—H14A	109.5
C3—C5—H5	118.2	N13—C14—H14B	109.5
C5—C6—C7	128.43 (16)	H14A—C14—H14B	109.5
C5—C6—H6	115.8	N13—C14—H14C	109.5
C7—C6—H6	115.8	H14A—C14—H14C	109.5
C12—C7—C8	115.78 (15)	H14B—C14—H14C	109.5
C12—C7—C6	124.56 (15)	N13—C15—H15A	109.5
C8—C7—C6	119.66 (15)	N13—C15—H15B	109.5
C9—C8—C7	122.61 (15)	H15A—C15—H15B	109.5
C9—C8—H8	118.7	N13—C15—H15C	109.5
C7—C8—H8	118.7	H15A—C15—H15C	109.5
C8—C9—C10	121.28 (15)	H15B—C15—H15C	109.5
C3—N1—C2—C3i	0.3 (3)	C8—C9—C10—N13	−179.19 (17)
C3—N1—C2—C4	−179.17 (14)	C8—C9—C10—C11	0.3 (3)
C2—N1—C3—C2i	−0.3 (3)	N13—C10—C11—C12	179.28 (15)
C2—N1—C3—C5	−179.15 (14)	C9—C10—C11—C12	−0.2 (2)
N1—C3—C5—C6	2.0 (3)	C10—C11—C12—C7	0.2 (3)
C2i—C3—C5—C6	−176.81 (17)	C8—C7—C12—C11	−0.3 (3)
C3—C5—C6—C7	179.74 (15)	C6—C7—C12—C11	179.28 (15)
C5—C6—C7—C12	−3.1 (3)	C9—C10—N13—C15	179.76 (16)
C5—C6—C7—C8	176.42 (18)	C11—C10—N13—C15	0.3 (3)
C12—C7—C8—C9	0.4 (3)	C9—C10—N13—C14	−3.5 (3)
C6—C7—C8—C9	−179.23 (16)	C11—C10—N13—C14	177.07 (16)
C7—C8—C9—C10	−0.4 (3)