N,N′-Bis­[1-(pyrazin-2-yl)­ethyl­idene]­hydrazine

Molecules of the title compound, C₁₂H₁₂N₆, contain both a di­imine linkage and an N—N bond, and assume a planar structure. The compound lies about an inversion centre and there are three intramolecular C—H...N hydrogen bonds.

S1. Comment

Supramolecular chemistry based on coordination chemistry is a vast area of current research. A particularly large number of such supramolecular complexes use oligomeric aromatic N-heterocycles as ligands. The demand for multitopic (bridging) ligands provides a strong impetus for the synthesis of related compounds. Some approaches to the construction of supramolecular systems based on polyazines have been reported recently (Tuna et al., 2003; Hamblin et al., 2002; Matthews et al., 2003). The recent interest in the N₂-diazine-bridged polyfunctional ligands mainly derives from the fact that the nature of the heterocyclic ring and the extent of the double-bond character in the N—N bond have been reported to play a crucial role for providing an intramolecular exchange pathway for spin exchange interactions that are observed in the metal complexes of these ligands (Xu et al., 1997). We report here the crystal structure of N,N'-bis-(pyrazin-2-yl-ethylidene)-hydrazine (hereafter BPYH), I), in which the two pyrazinylimine binding units are linked directly (no spacer unit) through the imine N atoms.

The molecular structure of BPYH is shown in Fig. 1, and relevant bond distances and angles are listed in Table 1. The molecule is essentially planar and has a trans configuration.

The title molecule crystalizes in the E,E conformation, with the methyl groups on opposite sides of the N—N bond, suggesting conjugation throughout the π systems. This configuration agrees with that commonly found in a number of azine compounds (Kesslen & Euler, 1999). The N3—N3ⁱ bond distance [1.398 (2) Å] is same within experimental error as that found in free 2,4-dinitrophenylhydrazine [1.405 (6) Å; Okabe et al., 1993] but is slightly shorter than that in hydrazine (1.449 Å; Kohata et al., 1982), which suggests the existence of some double-bond character in the azine N—N bonds.

The planarity in (I) may arise as a result of several effects. Firstly, the N3—H6 distance is 2.7245 (18) Å, slightly less than the sum of the van der Waals radii for H and N (2.75 Å), suggesting a possible interaction between these two atoms. The stereochemical influence of the nitrogen lone pairs is reflected in the bond angle. The C5—N3—N3ⁱ angle [113.64 (13)°] is significantly below the ideal sp² value of 120°; a consequence of the repulsion between the nitrogen lone pairs and the adjacent bonds.

It is notable that the C5—N3 bond [1.2816 (16) Å)] is longer than the average distance of 1.273 Å for the other azine compounds (Kesslen & Euler, 1999; Hagen et al., 1977; Chen et al., 1994). The longer imine bond length indicates that there is a conjugation between the imine bonds across the azine bond. The C1—C5 bond distance [1.3281 (16) Å] is shorter than the distance [1.335 (2) Å] reported by Zhang et al. (2001). The plane of the C1/C5/N3/C6 group is rotated 3.62 (1)° from the plane of the C1/N1/C2/C3/N2/C4 ring. The title compound is structurally similar to the other reported azines. The C═N—N═C linkage is planar; the imine bonds are slightly longer than those in other azines and the N—N bond is shorter than those in hydrazines. All of these observations imply a small degree of delocalization through the azine π system. The structure arises from a compromise of packing effects along with the steric effects and very weak intramolecular hydrogen contacts in the molecule. The molecule is linked by C—H···N hydrogen bonds (Table 2).

S2. Experimental

BPYH was synthesized by the reaction of 2-acetylpyrazine with hydrazine hydrate in refluxing ethanol/HCl solution, using a procedure similar to that reported for the synthesis of 2-pyridinealdehydeazine by Kesslen et al. (1999). Crystallization was performed twice, from ethanol and acetonitrile, yielding orange crystals suitable for X-ray analysis. A single-crystal was selected, mounted on a glass fibre using epoxy cement and used for data collection.

S3. Refinement

H atoms bonded to atom C6 were refined as riding, with C—H = 0.96 Å and U_iso(H) values of 1.5U_eq(C). All other H atoms were refined isotropically. The C—H bond distances are in the range 0.920 (19)–0.971 (17) Å.

Computing details

Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA; data reduction: X-RED32 (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

Fig. 1. The molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are plotted at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. The dashed lines show the possible hydrogen bonding. [Symmetry code: (i) −x, 1 − y, −z.]

N,N'-Bis[1-(pyrazin-2-yl)ethylidene]hydrazine

Crystal data

C12H12N6	F(000) = 252
Mr = 240.28	Dx = 1.339 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 3509 reflections
a = 4.4395 (7) Å	θ = 2.3–28.5°
b = 7.4724 (7) Å	µ = 0.09 mm^−1
c = 17.972 (3) Å	T = 293 K
β = 91.304 (13)°	Block, pale yellow
V = 596.04 (15) Å^3	0.50 × 0.30 × 0.20 mm
Z = 2

Data collection

STOE IPDS-II diffractometer	877 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.086
Plane graphite monochromator	θmax = 26.0°, θmin = 2.3°
ω scans	h = −5→5
4249 measured reflections	k = −9→9
1174 independent reflections	l = −22→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 atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.112	w = 1/[σ^2(Fo^2) + (0.0611P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.01	(Δ/σ)max = 0.001
1174 reflections	Δρmax = 0.16 e Å^−3
96 parameters	Δρmin = −0.14 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: 0.090 (14)

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
C1	0.4397 (3)	0.66003 (17)	0.10644 (7)	0.0382 (4)
C2	0.7614 (4)	0.7503 (2)	0.19797 (9)	0.0585 (5)
C3	0.8131 (3)	0.9069 (2)	0.16117 (8)	0.0533 (4)
C4	0.4923 (3)	0.82057 (19)	0.06975 (8)	0.0487 (4)
C5	0.2327 (3)	0.52208 (18)	0.07504 (7)	0.0390 (4)
C6	0.2025 (4)	0.3486 (2)	0.11512 (9)	0.0599 (5)
H6A	0.0378	0.2817	0.0935	0.090*
H6B	0.1648	0.3711	0.1667	0.090*
H6C	0.3854	0.2812	0.1110	0.090*
N1	0.5747 (3)	0.62469 (17)	0.17150 (6)	0.0520 (4)
N2	0.6777 (3)	0.94432 (16)	0.09660 (7)	0.0572 (4)
N3	0.0966 (2)	0.56627 (15)	0.01412 (6)	0.0437 (3)
H2	0.857 (4)	0.727 (3)	0.2429 (12)	0.084 (6)*
H3	0.957 (3)	0.995 (2)	0.1800 (9)	0.054 (4)*
H4	0.379 (4)	0.847 (2)	0.0254 (10)	0.065 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0411 (7)	0.0390 (7)	0.0344 (6)	0.0031 (5)	−0.0009 (5)	−0.0005 (5)
C2	0.0648 (9)	0.0694 (11)	0.0405 (7)	−0.0115 (8)	−0.0135 (7)	−0.0008 (7)
C3	0.0592 (9)	0.0494 (9)	0.0511 (8)	−0.0081 (7)	−0.0050 (7)	−0.0121 (7)
C4	0.0595 (9)	0.0417 (8)	0.0443 (8)	−0.0041 (6)	−0.0089 (7)	0.0025 (6)
C5	0.0412 (7)	0.0400 (7)	0.0357 (6)	0.0017 (6)	−0.0014 (5)	0.0013 (5)
C6	0.0766 (10)	0.0468 (9)	0.0552 (9)	−0.0116 (8)	−0.0213 (8)	0.0129 (7)
N1	0.0588 (7)	0.0577 (8)	0.0388 (6)	−0.0091 (6)	−0.0122 (5)	0.0051 (5)
N2	0.0687 (8)	0.0430 (7)	0.0595 (8)	−0.0070 (6)	−0.0088 (6)	−0.0011 (6)
N3	0.0480 (7)	0.0414 (7)	0.0411 (6)	−0.0056 (5)	−0.0096 (5)	0.0033 (5)

Geometric parameters (Å, º)

C1—N1	1.3281 (16)	C4—N2	1.3218 (18)
C1—C4	1.391 (2)	C4—H4	0.953 (17)
C1—C5	1.4841 (18)	C5—N3	1.2816 (16)
C2—N1	1.3327 (19)	C5—C6	1.491 (2)
C2—C3	1.366 (2)	C6—H6A	0.9600
C2—H2	0.920 (19)	C6—H6B	0.9600
C3—N2	1.3245 (19)	C6—H6C	0.9600
C3—H3	0.971 (17)	N3—N3^i	1.398 (2)
N1—C1—C4	120.77 (12)	N3—C5—C1	114.94 (12)
N1—C1—C5	117.37 (12)	N3—C5—C6	126.24 (12)
C4—C1—C5	121.87 (11)	C1—C5—C6	118.82 (11)
N1—C2—C3	122.71 (13)	C5—C6—H6A	109.5
N1—C2—H2	116.6 (13)	C5—C6—H6B	109.5
C3—C2—H2	120.7 (13)	H6A—C6—H6B	109.5
N2—C3—C2	121.80 (14)	C5—C6—H6C	109.5
N2—C3—H3	116.4 (9)	H6A—C6—H6C	109.5
C2—C3—H3	121.7 (9)	H6B—C6—H6C	109.5
N2—C4—C1	122.69 (13)	C1—N1—C2	116.02 (13)
N2—C4—H4	118.3 (11)	C4—N2—C3	116.02 (13)
C1—C4—H4	118.9 (11)	C5—N3—N3^i	113.64 (13)
N1—C2—C3—N2	0.5 (3)	C4—C1—N1—C2	−0.6 (2)
N1—C1—C4—N2	0.5 (2)	C5—C1—N1—C2	179.41 (13)
C5—C1—C4—N2	−179.47 (13)	C3—C2—N1—C1	0.1 (2)
N1—C1—C5—N3	176.64 (12)	C1—C4—N2—C3	0.1 (2)
C4—C1—C5—N3	−3.35 (19)	C2—C3—N2—C4	−0.6 (2)
N1—C1—C5—C6	−3.86 (19)	C1—C5—N3—N3^i	179.98 (13)
C4—C1—C5—C6	176.14 (14)	C6—C5—N3—N3^i	0.5 (2)

Symmetry code: (i) −x, −y+1, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C6—H6B···N1	0.96	2.63	2.8173 (19)	91
C4—H4···N3	0.953 (17)	2.449 (17)	2.7598 (18)	98.8 (12)
C6—H6A···N3^i	0.96	2.31	2.7245 (18)	105

Symmetry code: (i) −x, −y+1, −z.