Hydrogen bonding in C-substituted nitroanilines: sheets built from alternating R(12) and R(36) rings in 2-bromo-6-cyano-4-nitroaniline

Molecules of the title compound (systematic name: 2-amino-3-bromo-5-nitro­benzo­nitrile), C₇H₄BrN₃O₂, are linked by N-H...N and N-H...O hydrogen bonds [H...N 2.19 Å, N...N 3.019 (4) Å and N-H...N 157°, and H...O 2.17 Å, N...O 2.854 (3) Å and N-H...O 134°] to form (10) sheets built from alternating R(12) and R(36) rings, both of which are centrosymmetric.

S1. Comment

We have recently reported the striking differences which are induced in the hydrogen-bonding schemes in nitroanilines by the introduction of simple substituents elsewhere in the aryl ring (Cannon et al., 2001; Ferguson et al., 2001; Garden et al., 2001; McWilliam et al., 2001; Zakaria et al., 2001). As part of this study, we have reported the structures of two polymorphs of 2-iodo-4-nitroaniline, where the I···NO₂ interactions provide an effective alternative to hard and soft hydrogen bonds as determinants of supramolecular aggregation (McWilliam et al., 2001).

Seeking to introduce an additional hydrogen-bond acceptor as a potential alternative to the nitro group O atoms, we have now investigated the structure of 2-bromo-6-cyano-4-nitroaniline, (I), where the cyano group is potentially an effective acceptor of hydrogen bonds, as demonstrated by the structures of the isomeric cyanoanilines (Merlino & Sartori, 1982; Heine et al., 1994; Laine et al., 1996). \sch

In compound (I) (Fig. 1), the amino group acts as a double donor of hydrogen bonds. The cyano atom N61 acts as a single acceptor, as does one of the nitro O atoms O41, but atom O42 does not participate in the hydrogen bonding. These two hydrogen bonds (Table 2) link the molecules into sheets, within which each molecule is directly connected to three others.

Amino atom N1 in the molecule at (x, y, z) acts as a hydrogen-bond donor, via H11, to cyano N61 at (2 - x, 1 - y, 1 - z), thereby generating a dimer unit centred at (1, 1/2, 1/2) and containing a centrosymmetric R₂²(12) ring. Atom N1 at (x, y, z) also acts as a donor, this time via H12, to nitro O41 at (3/2 + x, 1/2 - y, 1/2 + z), which is part of the dimeric unit centred at (5/2, 0, 1). Propagation of these two hydrogen bonds thus generates a sheet, parallel to (103), built from alternating R₂²(12) and R₆⁶(36) rings arranged in a checkerboard fashion (Fig. 2). Three of these sheets are required to define the structure fully, but since the sheets are virtually planar, there is no possibility of any interweaving. If the individual molecules are regarded as the nodes of the resulting net, then this net is of the (6,3) type (Batten & Robson, 1998), while if the R₂²(12) dimers are taken as the nodes, then the net is of the (4,4) type. There are no aromatic π···π stacking interactions, or other direction-specific interactions, between adjacent sheets, so that the supramolecular structure is strictly two-dimensional.

Although the nitro atom O42 plays no role in the hydrogen bonding, it does participate in a fairly short intermolecular Br···O contact. Atom Br2 in the molecule at (x, y, z) makes a short contact with O42 in the molecule at (1/2 - x, y - 1/2, 1/2 - z), part of the dimer unit centred at (-1/2, 0, 0) (Fig. 2), and there are thus centrosymmetrically related pairs of such interactions within each of the R₆⁶(36) rings. The Br2···O42ⁱ distance is 3.247 (2) Å and the C2—Br2···O42ⁱ angle is 163.0 (2)° [symmetry code: (i) 1/2 - x, y - 1/2, 1/2 - z]. However, this Br···O distance is comparable with the shortest intermolecular I···O distances in 2-iodo-4-nitroaniline, 3.266 (5) Å in the triclinic polymorph and 3.153 (7) Å in the orthorhombic polymorph (McWilliam et al., 2001), and hence this contact is more likely to be an adventitious consequence of the ring structure generated by the hydrogen bonds than to be structurally significant in itself. There are no short Br···Br contacts nor any C—H···O hydrogen bonds in the structure.

It is of interest to compare the hydrogen-bonding pattern in (I) arising from the cyano and amino groups acting as the acceptors, with those in the isomers of cyanoaniline itself. In 2-cyanoaniline, where the original report (Laine et al., 1996) gave no analysis of the supramolecular structure, the amino group acts as a double donor of hydrogen bonds and the cyano N acts as a double acceptor, and the molecules are thereby linked into deeply puckered sheets of alternating R₄²(8) and R₄⁴(24) rings (Fig. 3). Within these sheets, no dimer motif can be identified analogous to that in (I). By contrast, 3-cyanoaniline (Merlino & Sartori, 1982) forms a three-dimensional framework structure in which both N atoms act as acceptors in N—H···N hydrogen bonds. 4-Cyanoaniline crystallizes in both monoclinic (Merlino & Sartori, 1982) and orthorhombic (Heine et al., 1994) polymorphs, at ambient and reduced temperatures, respectively, and in both forms the supramolecular aggregation takes the form of simple C(8) chains, generated by a glide plane in P2₁/c and a screw axis in P2₁2₁2₁, respectively. In both these polymorphs, only one N—H bond of the amino group is engaged in the hydrogen bonding.

The bond distances in (I) (Table 1) provide some evidence for a contribution to the overall electronic structure from the canonical forms (Ia) and (Ib). In particular, the C—NH₂ and C—NO₂ bonds are both short for their types (Allen et al., 1987). The C2—C3 bond is the shortest of the ring bonds, and C1—C2 and C6—C1 are the longest. For 4-cyanoaniline, (II), and a range of methylated derivatives (Heine et al., 1994), the quinonoid form (IIa), analogous to (Ib), was found to be significant.

S2. Experimental

A sample of (I) was obtained from Bayer, and crystals suitable for single-crystal X-ray diffraction were grown from a solution in ethanol.

S3. Refinement

Compound (I) crystallized in the monoclinic system; space group P2₁/n was uniquely assigned from the systematic absences. H atoms were treated as riding, with C—H = 0.95 and N—H = 0.88 Å.

Computing details

Data collection: KappaCCD Server Software (Nonius, 1997); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2001); software used to prepare material for publication: SHELXL97 and PRPKAPPA (Ferguson, 1999).

Figures

	Fig. 1. A view of the molecule of (I) showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A projection of part of the crystal structure of (I) showing the formation of a (103) sheet built from R2^2(12) and R6^6(36) rings. The atoms marked with a star (*), hash (#) or dollar sign ($) are at the symmetry positions (2 - x, 1 - y, 1 - z), (3/2 + x, 1/2 - y, 1/2 + z) and (x - 3/2, 1/2 - y, -1/2 + z), respectively.
	Fig. 3. Part of the crystal structure of 2-cyanoaniline (Laine et al., 1996), showing the formation of a (101) sheet of R4^2(8) and R4^4(24) rings. For the sake of clarity, H atoms bonded to C have been omitted. The atoms marked with a star (*), hash (#), dollar sign ($) or ampersand (&) are at the symmetry positions (1/2 - x, y - 1/2, 3/2 - z), (1/2 - x, 1/2 + y, 3/2 - z), (1/2 + x, -1/2 - y, 1/2 + z) and (x - 1/2, -1/2 - y, z - 1/2), respectively.

2-amino-3-bromo-5-nitrobenzonitrile

Crystal data

C7H4BrN3O2	F(000) = 472
Mr = 242.04	Dx = 1.949 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 1894 reflections
a = 4.2494 (2) Å	θ = 3.1–27.5°
b = 14.9094 (7) Å	µ = 4.95 mm^−1
c = 13.0958 (7) Å	T = 150 K
β = 96.138 (2)°	Needle, colourless
V = 824.94 (7) Å^3	0.25 × 0.07 × 0.04 mm
Z = 4

Data collection

Nonius KappaCCD diffractometer	1894 independent reflections
Radiation source: fine-focus sealed X-ray tube	1413 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.067
ϕ scans, and ω scans with κ offsets	θmax = 27.5°, θmin = 3.1°
Absorption correction: multi-scan (DENZO-SMN; Otwinowski & Minor, 1997)	h = −5→5
Tmin = 0.647, Tmax = 0.820	k = −19→19
6073 measured reflections	l = −16→16

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)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.081	H-atom parameters constrained
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0309P)^2] where P = (Fo^2 + 2Fc^2)/3
1894 reflections	(Δ/σ)max < 0.001
118 parameters	Δρmax = 0.54 e Å^−3
0 restraints	Δρmin = −0.68 e Å^−3

Special details

Experimental. The program DENZO-SMN (Otwinowski & Minor, 1997) uses a scaling algorithm [Fox, G. C. & Holmes, K. C. (1966). Acta Cryst. 20, 886–891] which effectively corrects for absorption effects. High-redundancy data were used in the scaling program, hence the `multi-scan' code word was used.

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

	x	y	z	Uiso*/Ueq
C1	0.6308 (6)	0.3273 (2)	0.3617 (2)	0.0177 (7)
N1	0.8557 (6)	0.31971 (18)	0.44131 (19)	0.0238 (6)
C2	0.5015 (6)	0.2505 (2)	0.3078 (2)	0.0193 (7)
Br2	0.64966 (7)	0.13636 (2)	0.35302 (2)	0.02578 (14)
C3	0.2741 (7)	0.2580 (2)	0.2263 (2)	0.0209 (7)
C4	0.1656 (7)	0.3424 (2)	0.1945 (2)	0.0204 (7)
N4	−0.0817 (6)	0.35126 (18)	0.1092 (2)	0.0236 (6)
O41	−0.1809 (5)	0.28113 (16)	0.06679 (17)	0.0313 (6)
O42	−0.1848 (5)	0.42561 (16)	0.08419 (17)	0.0328 (6)
C5	0.2842 (7)	0.4196 (2)	0.2432 (2)	0.0206 (7)
C6	0.5128 (6)	0.4118 (2)	0.3261 (2)	0.0198 (7)
C61	0.6425 (6)	0.4918 (2)	0.3756 (2)	0.0232 (7)
N61	0.7567 (7)	0.55297 (19)	0.4168 (2)	0.0358 (7)
H11	0.9343	0.3681	0.4730	0.029*
H12	0.9247	0.2663	0.4618	0.029*
H3	0.1907	0.2059	0.1916	0.025*
H5	0.2097	0.4769	0.2201	0.025*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0186 (16)	0.0153 (16)	0.0193 (16)	−0.0011 (12)	0.0023 (12)	−0.0006 (12)
N1	0.0293 (14)	0.0140 (14)	0.0258 (15)	−0.0016 (11)	−0.0073 (11)	−0.0008 (11)
C2	0.0224 (16)	0.0136 (16)	0.0218 (17)	−0.0022 (12)	0.0019 (12)	−0.0043 (13)
Br2	0.0325 (2)	0.0148 (2)	0.0284 (2)	0.00081 (13)	−0.00392 (13)	−0.00073 (14)
C3	0.0215 (15)	0.0165 (17)	0.0247 (18)	−0.0053 (13)	0.0028 (12)	−0.0018 (13)
C4	0.0199 (16)	0.0228 (18)	0.0179 (16)	−0.0021 (12)	−0.0012 (12)	−0.0020 (13)
N4	0.0234 (14)	0.0272 (17)	0.0197 (14)	−0.0033 (12)	0.0000 (11)	−0.0015 (13)
O41	0.0366 (12)	0.0274 (14)	0.0270 (13)	−0.0080 (11)	−0.0092 (10)	−0.0040 (11)
O42	0.0386 (13)	0.0261 (14)	0.0304 (13)	0.0056 (11)	−0.0119 (10)	−0.0017 (11)
C5	0.0216 (15)	0.0171 (16)	0.0230 (17)	−0.0004 (13)	0.0012 (12)	−0.0029 (14)
C6	0.0221 (16)	0.0172 (17)	0.0197 (16)	−0.0037 (13)	0.0004 (12)	−0.0015 (13)
C61	0.0252 (17)	0.0201 (19)	0.0220 (17)	0.0014 (14)	−0.0083 (12)	0.0038 (14)
N61	0.0495 (18)	0.0192 (16)	0.0351 (17)	−0.0024 (13)	−0.0115 (14)	−0.0018 (14)

Geometric parameters (Å, º)

C1—C2	1.424 (4)	C6—C61	1.439 (4)
C2—C3	1.365 (4)	C61—N61	1.140 (4)
C3—C4	1.388 (4)	N4—O41	1.236 (3)
C4—C5	1.385 (4)	N4—O42	1.224 (3)
C5—C6	1.382 (4)	N1—H11	0.8800
C6—C1	1.416 (4)	N1—H12	0.8800
C2—Br2	1.888 (3)	C3—H3	0.9500
C1—N1	1.342 (4)	C5—H5	0.9500
C4—N4	1.456 (4)
N1—C1—C6	121.9 (3)	C5—C4—N4	118.4 (3)
N1—C1—C2	121.5 (3)	C3—C4—N4	120.1 (3)
C6—C1—C2	116.6 (3)	O42—N4—O41	123.4 (3)
C1—N1—H11	120.0	O42—N4—C4	119.7 (3)
C1—N1—H12	120.0	O41—N4—C4	116.8 (3)
H11—N1—H12	120.0	C6—C5—C4	118.9 (3)
C3—C2—C1	121.7 (3)	C6—C5—H5	120.6
C3—C2—Br2	120.2 (2)	C4—C5—H5	120.6
C1—C2—Br2	118.1 (2)	C5—C6—C1	121.8 (3)
C2—C3—C4	119.6 (3)	C5—C6—C61	119.2 (3)
C2—C3—H3	120.2	C1—C6—C61	119.0 (3)
C4—C3—H3	120.2	N61—C61—C6	176.9 (3)
C5—C4—C3	121.5 (3)
C3—C4—N4—O41	−1.5 (4)	C5—C4—N4—O41	179.4 (3)
C3—C4—N4—O42	177.2 (3)	C5—C4—N4—O42	−1.9 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H11···N61^i	0.88	2.19	3.019 (4)	157
N1—H12···O41^ii	0.88	2.17	2.854 (3)	134

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