Redetermination of 1,2-bis­(2-bromo­benzyl­idene)hydrazine

The title compound, a Schiff base, C₁₄H₁₀Br₂N₂, has crystallographically imposed inversion symmetry. The mol­ecule is planar, the largest deviation from the plane being 0.055 (4) Å for the Br atom. Weak intra­molecular hydrogen bonding (C—H...Br) stabilizes the planar conformation. The structure has been reported previously [Marignan, Galigné & Falgueirettes (1972). Acta Cryst. B28, 93–97], but the quality of the refinement has been greatly improved.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.007 Å
• R factor = 0.051
• wR factor = 0.130
• Data-to-parameter ratio = 13.8

checkCIF/PLATON results

No syntax errors found



Alert level C
RINTA01_ALERT_3_C  The value of Rint is greater than 0.10
            Rint given   0.136
PLAT020_ALERT_3_C The value of Rint is greater than 0.10 .........       0.14
PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full Low .......       0.97
PLAT341_ALERT_3_C Low Bond Precision on C-C Bonds (x 1000) Ang ...          7

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   4 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
   4 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

---

S1. Comment

Schiff base ligands have significant importance in chemistry, especially in the development of Schiff base complexes, (Johnson et al., 1996; Alizadeh et al., 1999; Wang & Zheng, 2007). Schiff bases that have solvent-dependent UV/vis spectra (solvatochromicity) can be suitable NLO (nonlinear optically active) materials (Alemi & Shaabani, 2000). They are also useful in the asymmetric oxidation of methyl phenyl sulfide and give good enantioselectivity (Kim & Shin, 1999). The structure of the title compound (I), has been reported previously (Marignan et al., 1972), but the results of this new study are of higher precision.

The molecular structure of the title compound has crystallographically imposed inversion symmetry located in the middle of the N—N bond (Fig. 1). The molecule is planar with the largest deviation from the mean plane being 0.055 (4) Å at Br1.

There is one intramolecular hydrogen bond (C7—H7···Br1) (Table 1). The C7—N1 are 1.272 (5) Å, indicative of a C═N double bond. The other C—N, C—Br, and C—C distances show no remarkable features (Allen, 2002). It is interesting to note that neighboring molecules are separated by relatively short Br···Br contact with 3.7702 (7) Å. These Br···Br interactions may help to stabilize the packinge.

Related literature

The crystal structure of the title compound was previously reported by Marignan et al. (1972). For related literature, see: Alemi & Shaabani (2000); Alizadeh et al. (1999); Allen (2002); Johnson et al. (1996); Kim & Shin (1999); Wang & Zheng (2007).

S2. Experimental

Under nitrogen, a mixture of 2-bromobenzaldehyde (3.7 g, 20 mmol), Na₂SO₄ (3.0 g) and hydrazine (30% in water, 10 mmol) in absolute ethanol (20 ml) was refluxed for about 12 h to yield a yellow precipitate. The product was collected by vacuum filtration and washed with ethanol. The crude solid was redissolved in CH₂Cl₂ (100 ml) and washed with water (2*10 ml) and brine (10 ml). After dried over Na₂SO₄, the solvent was removed under vacuum, and yellow solid was isolated in yield 92% (3.1 g). Colourless single crystals of the compound suitable for X-ray analysis were grown from CH₂Cl₂ and absolute ethanol (4:1) by slow evaporation of the solvent at room temperature over a period of about two weeks.

S3. Refinement

All H atoms were placed in calculated positions and treated as riding on their parent atoms with C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C).

The maximum residual peak is located on the C1—Br1 bond, 1.04 Å from Br1.

Computing details

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996) and ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

Fig. 1. Molecular view of (I) showing the atom-numbering scheme. Displacement ellipsoids are represented at the 30% probability level. H atoms are shown as small spheres of arbitrary radii. [Symmetry code (i):-x + 1, -y + 1, -z + 1]

1,2-bis(2-bromobenzylidene)hydrazine

Crystal data

C14H10Br2N2	F(000) = 356
Mr = 366.06	Dx = 1.855 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 1131 reflections
a = 6.8715 (8) Å	θ = 3.0–25.1°
b = 4.0423 (5) Å	µ = 6.17 mm^−1
c = 23.602 (3) Å	T = 298 K
β = 91.058 (2)°	Block, colourless
V = 655.48 (14) Å^3	0.26 × 0.22 × 0.16 mm
Z = 2

Data collection

Bruker APEXII area-detector diffractometer	1131 independent reflections
Radiation source: fine-focus sealed tube	979 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.136
ϕ and ω scans	θmax = 25.1°, θmin = 3.0°
Absorption correction: multi-scan (SADABS; Bruker, 2004)	h = −8→7
Tmin = 0.218, Tmax = 0.377	k = −4→4
3700 measured reflections	l = −28→28

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.051	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.130	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0848P)^2] where P = (Fo^2 + 2Fc^2)/3
1131 reflections	(Δ/σ)max = 0.001
82 parameters	Δρmax = 1.33 e Å^−3
0 restraints	Δρmin = −0.82 e Å^−3

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	0.8273 (7)	0.4656 (10)	0.65065 (17)	0.0358 (9)
C2	0.9996 (8)	0.3733 (11)	0.67720 (19)	0.0428 (11)
H2	1.0185	0.4150	0.7157	0.051*
C3	1.1421 (7)	0.2214 (12)	0.6474 (2)	0.0480 (12)
H3	1.2571	0.1573	0.6657	0.058*
C4	1.1158 (8)	0.1618 (12)	0.5895 (2)	0.0477 (12)
H4	1.2120	0.0562	0.5690	0.057*
C5	0.9434 (7)	0.2629 (13)	0.56299 (19)	0.0410 (10)
H5	0.9275	0.2287	0.5242	0.049*
C6	0.7955 (7)	0.4119 (11)	0.59219 (17)	0.0345 (9)
C7	0.6189 (6)	0.5142 (11)	0.56233 (17)	0.0407 (10)
H7	0.5262	0.6384	0.5811	0.049*
Br1	0.63312 (7)	0.66624 (12)	0.695542 (17)	0.0464 (3)
N1	0.5899 (6)	0.4354 (12)	0.51072 (16)	0.0471 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.041 (2)	0.031 (2)	0.0346 (19)	−0.0041 (19)	−0.0059 (18)	0.0023 (17)
C2	0.046 (3)	0.044 (2)	0.038 (2)	−0.004 (2)	−0.010 (2)	0.0021 (18)
C3	0.036 (3)	0.052 (3)	0.055 (3)	0.005 (2)	−0.013 (2)	0.003 (2)
C4	0.038 (3)	0.054 (3)	0.052 (3)	0.007 (2)	0.002 (2)	0.000 (2)
C5	0.032 (2)	0.052 (2)	0.039 (2)	0.003 (2)	−0.0008 (19)	−0.001 (2)
C6	0.032 (2)	0.037 (2)	0.034 (2)	−0.0035 (18)	−0.0010 (18)	0.0004 (16)
C7	0.032 (2)	0.050 (3)	0.040 (2)	0.009 (2)	−0.0043 (18)	0.000 (2)
Br1	0.0442 (4)	0.0549 (4)	0.0400 (4)	0.00242 (19)	0.0035 (2)	−0.00488 (18)
N1	0.038 (2)	0.067 (2)	0.0362 (19)	0.013 (2)	−0.0067 (16)	−0.0035 (19)

Geometric parameters (Å, º)

C1—C2	1.381 (7)	C4—H4	0.9300
C1—C6	1.410 (5)	C5—C6	1.378 (7)
C1—Br1	1.901 (5)	C5—H5	0.9300
C2—C3	1.362 (8)	C6—C7	1.452 (6)
C2—H2	0.9300	C7—N1	1.271 (5)
C3—C4	1.396 (7)	C7—H7	0.9300
C3—H3	0.9300	N1—N1^i	1.425 (8)
C4—C5	1.391 (7)
C2—C1—C6	121.3 (4)	C3—C4—H4	120.6
C2—C1—Br1	117.9 (3)	C6—C5—C4	122.3 (4)
C6—C1—Br1	120.9 (3)	C6—C5—H5	118.9
C3—C2—C1	120.4 (4)	C4—C5—H5	118.9
C3—C2—H2	119.8	C5—C6—C1	117.0 (4)
C1—C2—H2	119.8	C5—C6—C7	120.0 (4)
C2—C3—C4	120.1 (5)	C1—C6—C7	123.0 (4)
C2—C3—H3	119.9	N1—C7—C6	120.6 (4)
C4—C3—H3	119.9	N1—C7—H7	119.7
C5—C4—C3	118.9 (5)	C6—C7—H7	119.7
C5—C4—H4	120.6	C7—N1—N1^i	111.6 (5)

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C7—H7···Br1	0.93	2.79	3.203 (4)	108