Crystal structure of 2,5-bis­(4-methyl­pyridin-2-yl)pyrazine chloro­form disolvate

The heterocyclic molecule in the title solvate, C₁₆H₁₄N₄·2CHCl₃, possesses inversion symmetry, with the inversion centre situated at the centre of the pyrazine ring. The outer pyridine rings are inclined to the central pyrazine ring by 4.89 (9)°. The compound crystallized as a chloro­form disolvate with the solvent mol­ecules linked to the title mol­ecule by C—H...N hydrogen bonds. In the crystal, mol­ecules are further linked by π–π inter­actions involving the pyrazine and pyridine rings of neighbouring mol­ecules [inter-centroid distance = 3.5629 (12) Å; symmetry code: x, y + 1, z + 1].

Key indicators

• Single-crystal X-ray study
• T = 173 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.040
• wR factor = 0.112
• Data-to-parameter ratio = 14.7

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S1. Experimental

S1.1. Synthesis and crystallization

The title compound was prepared in 3 stages:

Stage 1. Synthesis of methyl-2-pyridine-4-methyl-ketoxime (1): Hydroxyl­amine hydro­chloride (566 mg, 8.14 mmol) in pyridine (5ml) was added to a solution of 2-acetyl-4-methyl­pyrine (1.0 g, 7.40 mmol) in pyridine (22 ml) with vigorous stirring for 3 h at room temperature. The colourless solution was then poured into iced water. The oxime that precipitated was filtered and then dried under vacuum, yielding 1.33 g of compound (1) as a white powder. MS (ESI) calc. for C₈H₁₀N₂O [M+H]⁺ : 150.18; found 151.1.

Stage 2. Synthesis of methyl-p-tosyl-2-actelypyridine oxime (2): Tosyl chloride (2.40 g, 7.32 mmol) was added to a solution of (1) [1.0 g, 6.6 mmol] in pyridine (10 ml) with stirring for 20 h. The orange solution obtained was poured into iced water. A white precipitate was obtained which was filtered, washed with cold water and dried, yielding compound (2) as a white powder [Yield 74%; 523 mg]. MS (ESI) calc. for C₁₅H₁₆N₂O₃S [M+H]⁺: 304.36; found 305.1.

Stage 3. Synthesis of 2,5-bis­(4-methyl-2-yl)-pyrazine: Potassium tert-butoxide (516 mg, 4.60 mmol) was added in small portions to a solution of (2) [1.0 g, 3.286 mmol] in dry ethanol (15 ml). The mixture was stirred at room temperature for 20 h. The precipitate of potassium p-toluene­sulfonate that formed was filtered off and washed with ether. The filtrate and the washed fractions were collected. This process was repeated until no further precipitation occurred. An aqueous solution of hydrogen peroxide (30%, 4 ml) was then added to the assembled filtrates and washed fractions. When the exothermic reaction had stopped, the mixture was placed in a refrigerator over night yielding the title compound. It was filtered off and washed with water/methanol (1/1, v/v) and dried (yield 5%, 43 mg). MS (ESI) calc. for C₁₆H₁₄N₄ [M+H]⁺: 262.31, found 263.13. The colourless rod-like crystals used for X-ray diffraction analysis were obtained by slow evaporation of a solution in chloro­form.

S1.2. Refinement

The C-bound H atoms were included in calculated positions and treated as riding atoms: C—H = 0.95 - 1.00 Å with U_iso(H) = 1.5U_eq(C-methyl) and = 1.2U_eq(C) for other H atoms.

Related literature

The title compound is the 4-methylpyridine derivative of the ligand 2,5-bis(pyridin-2-yl)pyrazine (bppz), see: Neels & Stoeckli-Evans (1993); Schmitt (2008). For the synthesis of a number of transition-metal complexes of bppz, especially of copper(II), and for their magnetic properties, see for example: Escuer et al. (1993); Neels et al. (1995); Yuste et al. (2009); Bentama et al. (2012).

Computing details

Data collection: X-AREA (Stoe & Cie, 2009); cell refinement: X-AREA (Stoe & Cie, 2009); data reduction: X-RED32 (Stoe & Cie, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL2013 (Sheldrick, 2008), PLATON (Spek, 2009) and publCIF (Westrip, 2010).

Figures

	Fig. 1. A view of the molecular structure of the title compound, with atom labelling [unlabelled atoms are generated by inversion symmetry (symmetry code: -x + 3/2, -y + 3/2, -z + 1/2)]. Displacement ellipsoids are drawn at the 50% probability level. The C—H···N hydrogen bonds are shown as dashed lines (see Table 1 for details).
	Fig. 2. A view of the crystal packing of the title compound, illustrating the overlap of the pyrazine and pyridine rings of neighbouring molecules.

2,5-Bis(4-methylpyridin-2-yl)pyrazine chloroform disolvate

Crystal data

C16H14N4·2CHCl3	F(000) = 1016
Mr = 501.05	Dx = 1.546 Mg m^−3
Monoclinic, I2/a	Mo Kα radiation, λ = 0.71073 Å
a = 16.4498 (17) Å	Cell parameters from 12496 reflections
b = 6.0691 (4) Å	θ = 1.5–25.6°
c = 21.605 (3) Å	µ = 0.81 mm^−1
β = 93.885 (9)°	T = 173 K
V = 2152.0 (4) Å^3	Rod, colourless
Z = 4	0.45 × 0.29 × 0.23 mm

Data collection

Stoe IPDS 2 diffractometer	1902 independent reflections
Radiation source: fine-focus sealed tube	1676 reflections with I > 2σ(I)
Plane graphite monochromator	Rint = 0.066
ϕ + ω scans	θmax = 25.2°, θmin = 1.9°
Absorption correction: multi-scan (MULscanABS in PLATON; Spek, 2009)	h = −19→19
Tmin = 0.567, Tmax = 1.000	k = −7→7
9566 measured reflections	l = −25→25

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.040	w = 1/[σ^2(Fo^2) + (0.0725P)^2 + 0.8241P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.112	(Δ/σ)max = 0.002
S = 1.06	Δρmax = 0.31 e Å^−3
1902 reflections	Δρmin = −0.30 e Å^−3
129 parameters	Extinction correction: SHELXL2013 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0064 (11)

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
N1	0.72397 (10)	0.6344 (3)	0.19653 (8)	0.0368 (4)
N2	0.89303 (10)	0.2947 (3)	0.25318 (8)	0.0394 (4)
C1	0.68638 (12)	0.8157 (3)	0.21400 (9)	0.0374 (4)
H1	0.6406	0.8677	0.1890	0.045*
C2	0.78878 (11)	0.5676 (3)	0.23260 (8)	0.0328 (4)
C3	0.83238 (11)	0.3674 (3)	0.21341 (9)	0.0328 (4)
C4	0.93307 (13)	0.1154 (3)	0.23585 (10)	0.0418 (5)
H4	0.9771	0.0635	0.2627	0.050*
C5	0.91455 (13)	0.0006 (3)	0.18141 (10)	0.0401 (5)
H5	0.9446	−0.1274	0.1720	0.048*
C6	0.85181 (12)	0.0739 (3)	0.14075 (9)	0.0376 (5)
C7	0.81112 (11)	0.2637 (3)	0.15755 (9)	0.0378 (5)
H7	0.7685	0.3224	0.1305	0.045*
C8	0.82828 (15)	−0.0466 (4)	0.08138 (11)	0.0510 (6)
H8A	0.7910	−0.1672	0.0898	0.077*
H8B	0.8772	−0.1066	0.0642	0.077*
H8C	0.8012	0.0556	0.0515	0.077*
Cl1	0.50499 (4)	0.55130 (10)	0.09961 (3)	0.0569 (2)
Cl2	0.65296 (4)	0.52518 (12)	0.03495 (3)	0.0617 (3)
Cl3	0.57200 (4)	0.12697 (10)	0.06982 (3)	0.0582 (2)
C10	0.59461 (13)	0.4006 (3)	0.09061 (10)	0.0416 (5)
H10	0.6275	0.3999	0.1312	0.050*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0398 (9)	0.0332 (9)	0.0377 (9)	−0.0008 (7)	0.0045 (7)	−0.0041 (7)
N2	0.0429 (9)	0.0351 (9)	0.0405 (9)	0.0005 (7)	0.0053 (7)	−0.0032 (7)
C1	0.0404 (10)	0.0333 (10)	0.0385 (10)	−0.0002 (8)	0.0035 (8)	−0.0027 (8)
C2	0.0356 (10)	0.0294 (10)	0.0340 (10)	−0.0039 (8)	0.0075 (7)	0.0008 (8)
C3	0.0343 (9)	0.0290 (9)	0.0358 (10)	−0.0042 (7)	0.0090 (7)	−0.0001 (7)
C4	0.0467 (11)	0.0374 (11)	0.0417 (11)	0.0052 (9)	0.0054 (8)	−0.0004 (8)
C5	0.0460 (11)	0.0326 (10)	0.0433 (11)	0.0022 (8)	0.0140 (9)	−0.0003 (8)
C6	0.0424 (10)	0.0343 (10)	0.0377 (10)	−0.0038 (8)	0.0136 (8)	−0.0047 (8)
C7	0.0388 (10)	0.0381 (11)	0.0372 (10)	−0.0011 (8)	0.0077 (8)	−0.0025 (8)
C8	0.0578 (13)	0.0499 (13)	0.0460 (12)	0.0046 (10)	0.0076 (10)	−0.0152 (10)
Cl1	0.0557 (4)	0.0538 (4)	0.0613 (4)	0.0130 (3)	0.0040 (3)	−0.0024 (3)
Cl2	0.0589 (4)	0.0759 (5)	0.0507 (4)	−0.0204 (3)	0.0069 (3)	0.0140 (3)
Cl3	0.0758 (5)	0.0417 (4)	0.0594 (4)	−0.0037 (3)	0.0207 (3)	−0.0062 (2)
C10	0.0449 (11)	0.0426 (11)	0.0376 (11)	−0.0012 (9)	0.0041 (8)	0.0024 (9)

Geometric parameters (Å, º)

N1—C1	1.329 (3)	C5—H5	0.9500
N1—C2	1.340 (3)	C6—C7	1.393 (3)
N2—C4	1.339 (3)	C6—C8	1.504 (3)
N2—C3	1.346 (3)	C7—H7	0.9500
C1—C2^i	1.391 (3)	C8—H8A	0.9800
C1—H1	0.9500	C8—H8B	0.9800
C2—C1^i	1.391 (3)	C8—H8C	0.9800
C2—C3	1.484 (3)	Cl1—C10	1.757 (2)
C3—C7	1.385 (3)	Cl2—C10	1.760 (2)
C4—C5	1.383 (3)	Cl3—C10	1.753 (2)
C4—H4	0.9500	C10—H10	1.0000
C5—C6	1.383 (3)
C1—N1—C2	116.90 (17)	C5—C6—C8	121.56 (19)
C4—N2—C3	116.44 (17)	C7—C6—C8	121.58 (19)
N1—C1—C2^i	122.74 (18)	C3—C7—C6	120.36 (18)
N1—C1—H1	118.6	C3—C7—H7	119.8
C2^i—C1—H1	118.6	C6—C7—H7	119.8
N1—C2—C1^i	120.36 (17)	C6—C8—H8A	109.5
N1—C2—C3	117.77 (16)	C6—C8—H8B	109.5
C1^i—C2—C3	121.87 (17)	H8A—C8—H8B	109.5
N2—C3—C7	122.68 (17)	C6—C8—H8C	109.5
N2—C3—C2	116.19 (16)	H8A—C8—H8C	109.5
C7—C3—C2	121.13 (17)	H8B—C8—H8C	109.5
N2—C4—C5	124.3 (2)	Cl3—C10—Cl1	110.88 (12)
N2—C4—H4	117.9	Cl3—C10—Cl2	110.37 (12)
C5—C4—H4	117.9	Cl1—C10—Cl2	110.64 (12)
C6—C5—C4	119.35 (19)	Cl3—C10—H10	108.3
C6—C5—H5	120.3	Cl1—C10—H10	108.3
C4—C5—H5	120.3	Cl2—C10—H10	108.3
C5—C6—C7	116.86 (18)
C2—N1—C1—C2^i	−0.8 (3)	C3—N2—C4—C5	−1.7 (3)
C1—N1—C2—C1^i	0.7 (3)	N2—C4—C5—C6	1.2 (3)
C1—N1—C2—C3	−179.12 (16)	C4—C5—C6—C7	0.6 (3)
C4—N2—C3—C7	0.5 (3)	C4—C5—C6—C8	−179.05 (19)
C4—N2—C3—C2	−179.40 (16)	N2—C3—C7—C6	1.2 (3)
N1—C2—C3—N2	−174.82 (17)	C2—C3—C7—C6	−178.94 (16)
C1^i—C2—C3—N2	5.3 (3)	C5—C6—C7—C3	−1.7 (3)
N1—C2—C3—C7	5.3 (3)	C8—C6—C7—C3	177.96 (19)
C1^i—C2—C3—C7	−174.56 (18)

Symmetry code: (i) −x+3/2, −y+3/2, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C10—H10···N1	1.00	2.50	3.335 (3)	141