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In the crystal structure of the title compound, C7H5Br2NO, mol­ecules related by translation are linked through N—H...O hydrogen bonds to form chains in the crystallographic a direction, with the aryl rings stacked parallel to each other along the chain. Besides the N—H...O hydrogen bonds, Br...O and Br...Br inter­molecular inter­actions complete the packing of mol­ecules in the crystal structure.

Supporting information


Crystallographic Information File (CIF)
Contains datablocks global, I


Structure factor file (CIF format)
Contains datablock I

CCDC reference: 730103

Comment top

The title compound, (I) (Fig. 1), is of interest as part of a study on polymorphism and phase transformations in 2,6-disubstituted N-phenylformamides (Omondi et al. 2005). It is only the second among the 2,6-disubstituted N-phenylformamides that crystallizes in a Sohnke space group. Another example of these chiral N-phenylformamides is 2,6-difluoro-4-bromo-N-phenylformamide [Cambridge Structural Database (Allen, 2002) refcode SEDGAJ; Ferguson et al., 1998]. In the present study, the effect of different interactions (N—H···O hydrogen bonds and C—H···O, Cl···Cl and ππ intermolecular interactions) on the phase transitions of 2,6-dichloro-N-phenylformamide and 2-chloro-6-methyl-N-phenylformamide have been studied.

Molecules of compound (I) are linked through N—H···O hydrogen bonds, forming chains that run along the crystallographic a direction. The molecules in the chains are related by translation, with the aryl rings stacked parallel to each other along the N—H···O hydrogen-bonded chains. Connecting each of these N—H···O hydrogen-bonded chains, in the crystallographic b direction, are Br···O interactions [Kubicki, 2004, and references therein; Br2···O1 = 3.100 (3) Å] between molecules related by a 21 screw axis along the a axis, and in the crystallographic c direction, intermolecular Br···Br interactions [Br1···Br2 = 3.527 (7) Å] (Fig. 2), also between molecules related by a 21 screw axis, along the b axis. Two Br···O intermolecular interactions and the N—H···O hydrogen bond form a ring between adjacent hydrogen-bonded chains described by graph-set motif R23(12) (Etter, 1990; Bernstein et al., 1995).

Atom Br2 is involved in two intermolecular interactions (Fig. 3). It has been reported that Br is frequently involved in such contacts as a result of its non-spherical shape (Lieberman et al., 2000; Lommerse et al., 1996; Beyer et al., 2001). Atom Br2 of (I) interacts with atom O1 head-on and with atom Br1 side-on (O being a nucleophile and Br an electrophile). This leads to a two-dimensional network similar to those in 2,3,6,7-tetrabromonaphthalene (space group P21/c) or the cocrystal of 2,3,6,7-tetrabromonaphthalene and bromobenzene (Navon et al., 1997).

Although compound (I) has the same hydrogen-bonded chains as the high-temperature forms of 2,6-dichloro-N-phenylformamide and 2-chloro-6-methyl-N-phenylformamide, and of 2,6-dimethyl-N-phenylformamide (Omondi et al., 2005), in which they all have one short axes of about 4 Å along which the formamide molecules are stacked along the N—H···O hydrogen-bonded chain (Fig. 2), the packing in (I) is similar only to that in 2,6-dichloro-N-phenylformamide, where the N—H···O hydrogen-bonded chains in the high-temperature form are connected through Cl···Cl contacts forming (010) sheets.

Using the OPIX suite of programs (Gavezzotti, 2003), the lattice energy of (I) was calculated to be -90.5 kJ mol-1. These calculations permitted estimation of the contributions to this energy of the intermolecular N—H···O, Br···O and Br···Br interactions as -40, -9.5 and -8.1 kJ mol-1, respectively. This energy pattern resembles that for the high-temperature forms of 2,6-dichloro-N-phenylformamide and 2-chloro-6-methyl-N-phenylformamide, and that of 2,6-dimethyl-N-phenylformamide (Omondi et al., 2005), in which there is one strong stabilizing interaction (along the N—H···O hydrogen-bonded chain), while the second and third stabilizing interactions are significantly weaker.

Experimental top

2,6-Dibromo-N-phenylformamide was synthesized following a known procedure (Ugi et al., 1965). Commercially available 2,6-dibromo-N-phenylaniline [Quantity?] (Aldrich, purity > 95%) was heated in a tenfold excess of formic acid for a period of 15 h at 363 K. The excess formic acid was then removed under reduced pressure to give a white solid, which was treated with dilute hydrochloric acid (0.1 M HCl, 10 ml) and ethyl acetate (60 ml). The organic layer was separated from the aqueous layer, dried over magnesium sulfate and filtered. Colourless needle-shaped crystals of (I) were grown from the filtrate. The purity of the compound was confirmed by NMR. It was found to exist in solution (C6D6) as a mixture of cis- and trans-isomers in a ratio of 2:1.

Refinement top

H atoms were located in difference maps and then treated as riding, with C—H = 0.95 Å and N—H = 0.88 Å, and with Uiso(H) = 1.2Ueq(C,N).

Computing details top

Data collection: SMART (Bruker, 2004); cell refinement: Please give details; data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997), PLATON (Spek, 2009) and DIAMOND (Brandenburg, 1999); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. A view of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of abitrary radii.
[Figure 2] Fig. 2. N1—H1···O1 hydrogen-bonded chains (short-dashed lines) in (I), showing the stacking relationship in each chain. Molecules along the chain are related by a unit-cell translation. Long-dashed lines show intermolecular Br1···Br2 interactions that link up the hydrogen-bonded chains. [Symmetry codes: (i) -1 + x, y, z; (ii) 3/2 - x, -y, -1/2 + z.]
[Figure 3] Fig. 3. The crystal packing in compound (I), as a projection down the crystallographic a axis. Short-dashed lines indicate intermolecular Br1···O interactions and long-dashed lines show intermolecular Br1···Br2 interactions. [Symmetry codes: (i) 1/2 + x, 3/2 - y, 2 - z; (ii) 1/2 - x, 1 - y, -1/2 + z.]
N-(2,6-Dibromophenyl)formamide top
Crystal data top
C7H5Br2NOF(000) = 528
Mr = 278.94Dx = 2.181 Mg m3
Orthorhombic, P212121Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 5600 reflections
a = 4.2946 (5) Åθ = 2.9–28.2°
b = 13.8755 (16) ŵ = 9.48 mm1
c = 14.2541 (19) ÅT = 173 K
V = 849.40 (18) Å3Needle, colourless
Z = 40.56 × 0.08 × 0.08 mm
Data collection top
Bruker SMART CCD area-detector
2100 independent reflections
Radiation source: fine-focus sealed tube1841 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.030
ω scansθmax = 28.3°, θmin = 2.1°
Absorption correction: multi-scan
(SADABS; Bruker, 2004)
h = 55
Tmin = 0.069, Tmax = 0.466k = 1718
5541 measured reflectionsl = 1319
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)] = 0.027H-atom parameters constrained
wR(F2) = 0.060 w = 1/[σ2(Fo2) + (0.0246P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.03(Δ/σ)max = 0.002
2100 reflectionsΔρmax = 0.63 e Å3
100 parametersΔρmin = 0.34 e Å3
0 restraintsAbsolute structure: Flack (1983), with how many Friedel pairs?
Primary atom site location: structure-invariant direct methodsAbsolute structure parameter: 0.055 (18)
Crystal data top
C7H5Br2NOV = 849.40 (18) Å3
Mr = 278.94Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 4.2946 (5) ŵ = 9.48 mm1
b = 13.8755 (16) ÅT = 173 K
c = 14.2541 (19) Å0.56 × 0.08 × 0.08 mm
Data collection top
Bruker SMART CCD area-detector
2100 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2004)
1841 reflections with I > 2σ(I)
Tmin = 0.069, Tmax = 0.466Rint = 0.030
5541 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.027H-atom parameters constrained
wR(F2) = 0.060Δρmax = 0.63 e Å3
S = 1.03Δρmin = 0.34 e Å3
2100 reflectionsAbsolute structure: Flack (1983), with how many Friedel pairs?
100 parametersAbsolute structure parameter: 0.055 (18)
0 restraints
Special details top

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
C10.6446 (8)0.5095 (3)1.0260 (2)0.0230 (7)
C20.5337 (8)0.4185 (3)1.0465 (2)0.0258 (8)
C30.3629 (9)0.3660 (3)0.9820 (2)0.0307 (8)
C40.3075 (9)0.4043 (3)0.8930 (2)0.0318 (9)
C50.4140 (10)0.4951 (3)0.8711 (2)0.0301 (8)
C60.5810 (9)0.5478 (3)0.9368 (2)0.0264 (8)
C70.6710 (8)0.6171 (3)1.1599 (2)0.0267 (8)
N10.8164 (7)0.5652 (2)1.0936 (2)0.0256 (6)
O10.3881 (6)0.6230 (2)1.16817 (18)0.0343 (6)
Br10.60975 (10)0.36474 (3)1.16701 (3)0.03610 (12)
Br20.72105 (9)0.67353 (3)0.90624 (2)0.03202 (11)
Atomic displacement parameters (Å2) top
C10.0160 (15)0.030 (2)0.0226 (15)0.0025 (14)0.0014 (12)0.0091 (14)
C20.0233 (18)0.031 (2)0.0233 (17)0.0016 (16)0.0024 (13)0.0012 (15)
C30.031 (2)0.0286 (19)0.0324 (18)0.0037 (18)0.0042 (16)0.0034 (17)
C40.028 (2)0.035 (2)0.0318 (19)0.0015 (17)0.0033 (15)0.0105 (16)
C50.036 (2)0.032 (2)0.0224 (15)0.0025 (19)0.0050 (16)0.0004 (15)
C60.0269 (18)0.027 (2)0.0253 (17)0.0011 (17)0.0044 (15)0.0030 (14)
C70.0255 (19)0.030 (2)0.0244 (16)0.0018 (14)0.0046 (14)0.0009 (15)
N10.0192 (14)0.0308 (17)0.0267 (14)0.0007 (12)0.0014 (13)0.0040 (13)
O10.0198 (12)0.0472 (18)0.0359 (13)0.0011 (12)0.0028 (12)0.0137 (13)
Br10.0455 (2)0.0347 (2)0.02810 (18)0.00086 (19)0.00546 (17)0.00495 (17)
Br20.0391 (2)0.0292 (2)0.02770 (17)0.00247 (18)0.00208 (17)0.00098 (15)
Geometric parameters (Å, º) top
C1—C21.382 (5)C4—H40.95
C1—C61.404 (5)C5—C61.388 (5)
C1—N11.439 (4)C5—H50.95
C2—C31.384 (5)C6—Br21.896 (4)
C2—Br11.900 (4)C7—O11.223 (4)
C3—C41.396 (5)C7—N11.343 (4)
C4—C51.376 (5)N1—H10.88
C2—C1—C6118.1 (3)C4—C5—C6120.1 (3)
C2—C1—N1121.7 (3)C4—C5—H5120
C6—C1—N1120.2 (3)C6—C5—H5120
C1—C2—C3121.5 (3)C5—C6—C1120.8 (3)
C1—C2—Br1119.4 (3)C5—C6—Br2119.6 (3)
C3—C2—Br1119.1 (3)C1—C6—Br2119.6 (3)
C2—C3—C4119.6 (4)O1—C7—N1124.4 (3)
C5—C4—C3119.8 (3)C7—N1—C1121.4 (3)
C6—C1—C2—C30.4 (5)C4—C5—C6—Br2179.1 (3)
N1—C1—C2—C3178.6 (3)C2—C1—C6—C50.6 (5)
C6—C1—C2—Br1179.1 (3)N1—C1—C6—C5179.7 (3)
N1—C1—C2—Br10.1 (5)C2—C1—C6—Br2178.7 (3)
C1—C2—C3—C41.8 (6)N1—C1—C6—Br20.3 (5)
Br1—C2—C3—C4179.5 (3)O1—C7—N1—C11.1 (6)
C2—C3—C4—C52.1 (6)C2—C1—N1—C782.6 (5)
C3—C4—C5—C61.1 (6)C6—C1—N1—C796.3 (4)
C4—C5—C6—C10.3 (6)
Hydrogen-bond geometry (Å, º) top
N1—H1···O1i0.882.082.793 (4)138
Symmetry code: (i) x+1, y, z.

Experimental details

Crystal data
Chemical formulaC7H5Br2NO
Crystal system, space groupOrthorhombic, P212121
Temperature (K)173
a, b, c (Å)4.2946 (5), 13.8755 (16), 14.2541 (19)
V3)849.40 (18)
Radiation typeMo Kα
µ (mm1)9.48
Crystal size (mm)0.56 × 0.08 × 0.08
Data collection
DiffractometerBruker SMART CCD area-detector
Absorption correctionMulti-scan
(SADABS; Bruker, 2004)
Tmin, Tmax0.069, 0.466
No. of measured, independent and
observed [I > 2σ(I)] reflections
5541, 2100, 1841
(sin θ/λ)max1)0.667
R[F2 > 2σ(F2)], wR(F2), S 0.027, 0.060, 1.03
No. of reflections2100
No. of parameters100
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.63, 0.34
Absolute structureFlack (1983), with how many Friedel pairs?
Absolute structure parameter0.055 (18)

Computer programs: SMART (Bruker, 2004), Please give details, SAINT (Bruker, 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 1997), PLATON (Spek, 2009) and DIAMOND (Brandenburg, 1999), WinGX (Farrugia, 1999).

Selected geometric parameters (Å, º) top
C1—N11.439 (4)C7—O11.223 (4)
C2—Br11.900 (4)C7—N11.343 (4)
C6—Br21.896 (4)
O1—C7—N1124.4 (3)C7—N1—C1121.4 (3)
C6—C1—N1—C796.3 (4)
Hydrogen-bond geometry (Å, º) top
N1—H1···O1i0.882.082.793 (4)138
Symmetry code: (i) x+1, y, z.

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