Secondary interactions in 4-bromo-N,N-dimethylanilinium bromide

The crystal packing of the title compound, C₈H₁₁BrN⁺·Br⁻, involves three types of secondary interaction: a classical N—H...Br⁻ hydrogen bond, a `weak' but short C—H...Br⁻ interaction (normalized H...Br distance of 2.66 Å) and a cation–anion Br...Br contact of 3.6331 (4) Å. The hydrogen bonds connect two cations and two anions to form rings of graph set R(14). The Br...Br contacts link these rings to form layers parallel to the bc plane.

S1. Comment

We are interested in the variety of secondary interactions in halopyridinium and haloanilinium halides, and have published the structures of 4-halopyridinium halides (Jones et al., 1999), 2-, 3- and various di-halopyridinium halides (Jones & Freytag, 2001), haloanilinium halides (Gray & Jones, 2002a) and dichloroanilinium chlorides (Gray & Jones, 2002b). These series of structures involve halogen-halogen contacts, classical N—H···halide hydrogen bonds and, in some cases, weak C—H···halide hydrogen bonds. The anilinium derivatives generally form structures with hydrophilic layers, and these consist of hydrogen-bonded rings of graph set R_2nⁿ(4n), in which two of the three H atoms from each of n NH₃⁺ groups are the donors and n halide ions are the acceptors (n = 2–4). We then wished to investigate the effect of blocking some of the hydrogen-bond donors, and so present here the structure of 4-bromo-N,N-dimethylanilinium bromide, (I). \sch

The bond lengths and angles of (I) (Fig. 1) may be considered normal. The conformation of the dimethylamino group is such that the C2—C1—N—C8 grouping is approximately antiperiplanar [torsion angle 173.51 (13)°]. The ring is planar (the r.m.s. deviation of the six C atoms is 0.008 Å) and the Br and N substituents are slightly displaced to one side of the plane by 0.098 (2) and 0.150 (2) Å, respectively.

There are three predominant secondary interactions that determine the packing of (I). Firstly, a classical, approximately linear, N—H···Br^- hydrogen bond is observed (Table 2). Secondly, the `weak' C3—H3···Br^- hydrogen bond is by far the shortest of several such interactions (Table 2); if the C—H bond length is set to 1.08 Å, then the normalized H···Br distance (Steiner, 1998) is only 2.66 Å. Finally, a Br1···Br2(1 - x, y - 1/2, 1/2 - z) contact of 3.6331 (4) Å (cf. sum of van der Waals radii 3.70 Å; Reference?) connects cation and anion; as usual (see e.g. Jones et al., 1999), the C—Br···Br^- angle is approximately linear, at 169.54 (4)°.

The combined effect of the two hydrogen bonds is to link two cations and two anions to form inversion-symmetric rings of graph set R₄²(14) (Fig. 2). These are linked by the Br···Br interactions to form layers parallel to the bc plane.

The blocking of two hydrogen-bond donors by methyl groups in (I) has thus reduced the dimensionality of the hydrogen-bonding pattern, from a two-dimensional array of classical hydrogen bonds to a zero-dimensional pattern of one classical and one `weak' hydrogen bond. An intermediate type of system might be expected for an aniline derivative bearing the –N⁺(CH₃)H₂ group. Corresponding studies are in progress.

S2. Experimental

4-Bromo-N,N-dimethylaniline (2.14 g, 7.62 mmol) was dissolved in ethanol (10 ml) and 48% hydrobromic acid (1.22 ml) was added slowly with stirring. Further ethanol (10 ml) was added and the solution stirred for 2 h. The solution was then evaporated to dryness and the residue taken up in the minimum of ethanol. Addition of diethyl ether (30 ml) precipitated the product as a white solid, which was filtered off, washed with diethyl ether and dried in vacuo. Analysis, found: C 34.22, H 3.96, N 4.75%; calculated: C 34.20, H 3.95, N 4.98%. Single crystals of (I) were obtained from ethanol-diethyl ether.

S3. Refinement

The following faces (with distances from a common point in mm) were indexed and used for a numerical absorption correction: 110 0.087, 110 0.070, 001 0.212, 001 0.178, 110 0.063 and 110 0.080. H atoms were visible in difference syntheses. The H atom bonded to N was refined freely. Methyl groups were idealized and refined as rigid groups allowed to rotate but not tip. Other H atoms were included using a riding model starting from calculated positions. Aromatic C—H distances were fixed to 0.95 Å and methyl C—H to 0.98 Å, and U_iso(H) was set to 1.2U_eq of the parent atom.

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Siemens, 1994); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of the molecule of (I) in the crystal. Displacement ellipsoids are drawn at the 50% probability level and H-atom radii are arbitrary.
	Fig. 2. A packing diagram of (I) viewed perpendicular to the bc plane. H atoms not involved in hydrogen bonds have been omitted for clarity. Hydrogen bonds and Br···Br interactions are indicated by dashed lines. There is one such layer per a axis repeat.

4-bromo-N,N-dimethylanilinium bromide

Crystal data

C8H11BrN^+·Br^−	F(000) = 544
Mr = 281.00	Dx = 1.922 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 9.9511 (12) Å	Cell parameters from 11315 reflections
b = 7.6156 (10) Å	θ = 2–28°
c = 13.5616 (16) Å	µ = 8.29 mm^−1
β = 109.104 (3)°	T = 143 K
V = 971.1 (2) Å^3	Square prism, colourless
Z = 4	0.40 × 0.16 × 0.13 mm

Data collection

Bruker SMART1000 CCD area-detector diffractometer	2837 independent reflections
Radiation source: fine-focus sealed tube	2457 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.059
Detector resolution: 8.192 pixels mm^-1	θmax = 30.0°, θmin = 2.2°
ω and ϕ scans	h = −14→14
Absorption correction: numerical (XPREP; Siemens, 1994)	k = −10→10
Tmin = 0.113, Tmax = 0.379	l = −19→19
20417 measured reflections

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)] = 0.018	Hydrogen site location: difference Fourier map
wR(F^2) = 0.043	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0195P)^2 + 0.1484P] where P = (Fo^2 + 2Fc^2)/3
2837 reflections	(Δ/σ)max = 0.002
106 parameters	Δρmax = 0.42 e Å^−3
0 restraints	Δρmin = −0.57 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.

Non-bonded distances:

3.6331 (0.0004) Br1 - Br2_$5 169.54 (0.04) C4 - Br1 - Br2_$5

$5 - x + 1, -y + 1/2, -z + 1/2

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

0.4334 (0.0032) x - 7.0081 (0.0020) y + 4.7909 (0.0058) z = 0.6644 (0.0031)

* 0.0089 (0.0013) C1 * 0.0318 (0.0011) C2 * 0.0426 (0.0011) C3 * 0.0299 (0.0012) C4 * 0.0424 (0.0011) C5 * 0.0275 (0.0011) C6 * -0.0902 (0.0009) N * -0.0930 (0.0007) Br1

Rms deviation of fitted atoms = 0.0538

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	0.26871 (15)	0.17598 (19)	0.37364 (11)	0.0178 (3)
C2	0.40844 (15)	0.2205 (2)	0.43089 (12)	0.0208 (3)
H2	0.4304	0.2674	0.4993	0.025*
C3	0.51513 (16)	0.1956 (2)	0.38713 (12)	0.0216 (3)
H3	0.6108	0.2253	0.4252	0.026*
C4	0.48057 (16)	0.12709 (18)	0.28734 (12)	0.0195 (3)
C5	0.34207 (15)	0.07834 (19)	0.23118 (12)	0.0199 (3)
H5	0.3206	0.0282	0.1636	0.024*
C6	0.23509 (15)	0.10383 (18)	0.27502 (12)	0.0194 (3)
H6	0.1398	0.0719	0.2374	0.023*
N	0.15816 (13)	0.21601 (16)	0.42150 (10)	0.0180 (2)
H0	0.1603 (19)	0.333 (3)	0.4362 (14)	0.021 (4)*
C7	0.18369 (18)	0.1234 (2)	0.52361 (12)	0.0238 (3)
H7A	0.1722	−0.0034	0.5115	0.029*
H7B	0.1151	0.1648	0.5563	0.029*
H7C	0.2805	0.1482	0.5698	0.029*
C8	0.00855 (16)	0.1847 (2)	0.35287 (13)	0.0245 (3)
H8A	−0.0085	0.2464	0.2865	0.029*
H8B	−0.0573	0.2285	0.3874	0.029*
H8C	−0.0067	0.0585	0.3397	0.029*
Br1	0.623884 (15)	0.10988 (2)	0.223544 (12)	0.02322 (5)
Br2	0.143085 (15)	0.631082 (19)	0.433847 (11)	0.02023 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0188 (6)	0.0155 (6)	0.0182 (7)	0.0006 (5)	0.0049 (5)	0.0013 (5)
C2	0.0211 (7)	0.0216 (7)	0.0167 (7)	−0.0009 (5)	0.0022 (5)	−0.0013 (5)
C3	0.0176 (7)	0.0208 (7)	0.0232 (7)	−0.0011 (5)	0.0021 (6)	−0.0001 (5)
C4	0.0195 (6)	0.0161 (6)	0.0227 (7)	0.0024 (5)	0.0065 (5)	0.0016 (5)
C5	0.0213 (7)	0.0182 (6)	0.0187 (7)	−0.0001 (5)	0.0047 (5)	−0.0019 (5)
C6	0.0178 (6)	0.0186 (7)	0.0199 (7)	−0.0013 (5)	0.0036 (5)	−0.0008 (5)
N	0.0192 (6)	0.0165 (6)	0.0173 (6)	0.0008 (4)	0.0047 (5)	−0.0002 (4)
C7	0.0298 (8)	0.0230 (7)	0.0195 (7)	0.0027 (6)	0.0095 (6)	0.0033 (6)
C8	0.0179 (7)	0.0314 (8)	0.0234 (8)	−0.0020 (6)	0.0056 (6)	−0.0033 (6)
Br1	0.02030 (8)	0.02267 (8)	0.02798 (9)	−0.00024 (5)	0.00965 (6)	−0.00246 (6)
Br2	0.01954 (7)	0.01842 (7)	0.02114 (8)	−0.00044 (5)	0.00447 (5)	−0.00222 (5)

Geometric parameters (Å, º)

C1—C6	1.382 (2)	C3—H3	0.9500
C1—C2	1.394 (2)	C5—H5	0.9500
C1—N	1.4805 (18)	C6—H6	0.9500
C2—C3	1.388 (2)	N—H0	0.91 (2)
C3—C4	1.385 (2)	C7—H7A	0.9800
C4—C5	1.389 (2)	C7—H7B	0.9800
C4—Br1	1.8992 (15)	C7—H7C	0.9800
C5—C6	1.392 (2)	C8—H8A	0.9800
N—C8	1.4942 (19)	C8—H8B	0.9800
N—C7	1.4998 (19)	C8—H8C	0.9800
C2—H2	0.9500
C6—C1—C2	121.13 (13)	C6—C5—H5	120.4
C6—C1—N	121.80 (12)	C1—C6—H6	120.3
C2—C1—N	117.03 (13)	C5—C6—H6	120.3
C3—C2—C1	119.44 (14)	C1—N—H0	109.2 (11)
C4—C3—C2	119.28 (14)	C8—N—H0	103.9 (11)
C3—C4—C5	121.39 (14)	C7—N—H0	105.9 (11)
C3—C4—Br1	119.20 (11)	N—C7—H7A	109.5
C5—C4—Br1	119.34 (11)	N—C7—H7B	109.5
C4—C5—C6	119.25 (14)	H7A—C7—H7B	109.5
C1—C6—C5	119.46 (13)	N—C7—H7C	109.5
C1—N—C8	115.20 (12)	H7A—C7—H7C	109.5
C1—N—C7	112.48 (11)	H7B—C7—H7C	109.5
C8—N—C7	109.46 (12)	N—C8—H8A	109.5
C3—C2—H2	120.3	N—C8—H8B	109.5
C1—C2—H2	120.3	H8A—C8—H8B	109.5
C4—C3—H3	120.4	N—C8—H8C	109.5
C2—C3—H3	120.4	H8A—C8—H8C	109.5
C4—C5—H5	120.4	H8B—C8—H8C	109.5
C6—C1—C2—C3	1.5 (2)	N—C1—C6—C5	176.23 (13)
N—C1—C2—C3	−176.15 (13)	C4—C5—C6—C1	−0.4 (2)
C1—C2—C3—C4	0.0 (2)	C6—C1—N—C8	−4.11 (19)
C2—C3—C4—C5	−1.7 (2)	C2—C1—N—C8	173.51 (13)
C2—C3—C4—Br1	175.24 (11)	C6—C1—N—C7	122.27 (15)
C3—C4—C5—C6	1.9 (2)	C2—C1—N—C7	−60.11 (16)
Br1—C4—C5—C6	−175.04 (11)	C2—C1—N—H0	57.1 (12)
C2—C1—C6—C5	−1.3 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N—H0···Br2	0.91 (2)	2.28 (2)	3.1716 (13)	167.3 (16)
C3—H3···Br2^i	0.95	2.79	3.7147 (15)	165
C6—H6···Br2^ii	0.95	3.04	3.9052 (15)	152
C7—H7A···Br2^iii	0.98	2.96	3.9216 (16)	168
C7—H7B···Br2^iv	0.98	3.04	3.9537 (16)	155
C8—H8A···Br2^ii	0.98	2.98	3.7043 (17)	132
C8—H8B···Br2^iv	0.98	3.02	3.9331 (16)	156

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