4-(Dimethyl­amino)pyridinium tribromide: whole mol­ecule disorder of cation and anion

Abstract

In the title salt, C₇H₁₁N₂ ⁺·Br₃ ⁻, the cation and the near-linear anion [Br—Br—Br = 179.41 (8)°] both show whole-mol­ecule disorder about crystallographic twofold rotation axes. The cation is weakly hydrogen-bonded to the anion by an N—H⋯Br inter­action. The crystal studied was found to be a racemic twin, with a twin component of nearly 50%.

Related literature

The compound is known commercially as 4-(dimethyl­amino)pyridine hydro­bromide perbromide, [C₇H₁₀N₂]·[HBr]·[Br₂]. The 4-dimethyl­amino­pyridinium cation furnishes a number of salts with organic and inorganic acids. For 4-dimethyl­amino­pyridinium bromide, see: Mayr-Stein & Bolte (2000 ▶). For dimethyl­amino­pyridinium chloride and its dihydrate, see: Bryant & King (1992 ▶); Chao et al. (1977 ▶).

Experimental

Crystal data

• C₇H₁₁N₂ ⁺·Br₃ ⁻

• M _r = 362.91

• Orthorhombic,

• a = 4.1688 (1) Å

• b = 8.8349 (2) Å

• c = 14.7255 (4) Å

• V = 542.35 (2) ų

• Z = 2

• Mo Kα radiation

• μ = 11.11 mm⁻¹

• T = 100 K

• 0.20 × 0.15 × 0.10 mm

Data collection

• Bruker SMART APEX CCD diffractometer

• Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ▶) T _min = 0.656, T _max = 1.000 (expected range = 0.216–0.329)

• 5156 measured reflections

• 1256 independent reflections

• 1114 reflections with I > 2σ(I)

• R _int = 0.025

Refinement

• R[F ² > 2σ(F ²)] = 0.021

• wR(F ²) = 0.051

• S = 0.98

• 1256 reflections

• 100 parameters

• 60 restraints

• H-atom parameters constrained

• Δρ_max = 0.42 e Å⁻³

• Δρ_min = −0.34 e Å⁻³

• Absolute structure: Flack (1983 ▶), 480 Friedel pairs

• Flack parameter: 0.47 (4)

Data collection: APEX2 (Bruker, 2008 ▶); cell refinement: SAINT (Bruker, 2008 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: X-SEED (Barbour, 2001 ▶); software used to prepare material for publication: publCIF (Westrip, 2009 ▶).

Supplementary Material

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯Br2	0.88	2.42	3.286 (2)	167

supplementary crystallographic information

Experimental

Commercially-available 4-dimethylaminopyridine hydrobromide perbromide was recrystallized from ethanol to give colourless blocks of (I).

Refinement

The Br₃ anion lies on a twofold rotation axis, but it was allowed to refine off this symmetry element as a three-atom species.

The cation is disordered about another twofold rotation axis; this was refined as a cation with its atoms of half occupancies. The pyridyl portion was refined as a rigid hexagon of 1.39 Å sides; the pair of N–C_methyl distances were restrained to within 0.01 Å of each other. The cation was restrained to be nearly planar, and the anisotropic displacement factors were restrained to be nearly isotropic.

The hydrogen atoms were placed at calculated positions (C–H 0.95, N–H 0.88 Å) and refined as riding with U_iso(H) = 1.2U_eq(C,N).

Figures

Fig. 1.

Thermal ellipsoid plot (Barbour, 2001) of [C7H11N2][Br3] at the 70% probability level. Hydrogen atoms are drawn as spheres of arbitrary radius.

Crystal data

C7H11N2+·Br3−	F(000) = 344
Mr = 362.91	Dx = 2.222 Mg m−3
Orthorhombic, P2221	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c 2	Cell parameters from 2094 reflections
a = 4.1688 (1) Å	θ = 2.7–28.3°
b = 8.8349 (2) Å	µ = 11.11 mm−1
c = 14.7255 (4) Å	T = 100 K
V = 542.35 (2) Å3	Block, colorless
Z = 2	0.20 × 0.15 × 0.10 mm

Data collection

Bruker SMART APEX CCD diffractometer	1256 independent reflections
Radiation source: fine-focus sealed tube	1114 reflections with I > 2σ(I)
graphite	Rint = 0.025
ω scans	θmax = 27.5°, θmin = 2.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −5→5
Tmin = 0.656, Tmax = 1.000	k = −11→11
5156 measured reflections	l = −19→19

Refinement

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.021	H-atom parameters constrained
wR(F2) = 0.051	w = 1/[σ2(Fo2) + (0.0322P)2] where P = (Fo2 + 2Fc2)/3
S = 0.98	(Δ/σ)max = 0.001
1256 reflections	Δρmax = 0.42 e Å−3
100 parameters	Δρmin = −0.33 e Å−3
60 restraints	Absolute structure: Flack (1983), 480 Friedel pairs
Primary atom site location: structure-invariant direct methods	Flack parameter: 0.47 (4)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Br1	0.5290 (6)	0.25953 (5)	0.23869 (12)	0.0155 (3)	0.50
Br2	0.2738 (3)	0.27497 (11)	0.07779 (5)	0.0196 (2)	0.50
Br3	0.7682 (3)	0.24565 (11)	0.39355 (5)	0.01777 (18)	0.50
N2	1.1882 (7)	0.2417 (5)	−0.3550 (3)	0.0144 (9)	0.50
N1	0.7232 (7)	0.2399 (4)	−0.10428 (15)	0.0209 (11)	0.50
H1	0.6250	0.2392	−0.0514	0.025*	0.50
C1	0.7724 (9)	0.1050 (3)	−0.1509 (2)	0.0190 (11)	0.50
H1A	0.7000	0.0122	−0.1257	0.023*	0.50
C2	0.9276 (8)	0.1061 (3)	−0.23446 (19)	0.0196 (13)	0.50
H2	0.9612	0.0140	−0.2663	0.024*	0.50
C3	1.0335 (5)	0.2420 (3)	−0.27138 (13)	0.0147 (11)	0.50
C4	0.9844 (9)	0.3768 (3)	−0.2248 (2)	0.0195 (12)	0.50
H4	1.0568	0.4697	−0.2500	0.023*	0.50
C5	0.8292 (9)	0.3757 (3)	−0.1412 (2)	0.0208 (14)	0.50
H5	0.7956	0.4679	−0.1093	0.025*	0.50
C6	1.2376 (13)	0.1015 (6)	−0.4024 (3)	0.0226 (13)	0.50
H6A	1.0314	0.0498	−0.4102	0.034*	0.50
H6B	1.3829	0.0370	−0.3672	0.034*	0.50
H6C	1.3321	0.1220	−0.4620	0.034*	0.50
C7	1.2983 (11)	0.3839 (6)	−0.3936 (4)	0.0223 (14)	0.50
H7A	1.1130	0.4479	−0.4077	0.033*	0.50
H7B	1.4196	0.3638	−0.4493	0.033*	0.50
H7C	1.4366	0.4359	−0.3497	0.033*	0.50

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Br1	0.0195 (8)	0.01421 (16)	0.0128 (8)	−0.0005 (3)	0.0021 (5)	−0.0007 (2)
Br2	0.0201 (4)	0.0274 (5)	0.0112 (4)	0.0019 (3)	0.0015 (3)	−0.0010 (3)
Br3	0.0210 (4)	0.0207 (4)	0.0116 (4)	−0.0011 (3)	0.0007 (3)	0.0001 (3)
N2	0.021 (2)	0.0110 (19)	0.011 (2)	−0.001 (2)	−0.0034 (17)	0.005 (2)
N1	0.023 (3)	0.032 (3)	0.008 (2)	0.007 (3)	0.0025 (19)	−0.001 (2)
C1	0.019 (3)	0.021 (3)	0.017 (3)	−0.001 (2)	−0.003 (3)	0.002 (2)
C2	0.012 (3)	0.0175 (19)	0.029 (4)	−0.0005 (16)	0.004 (3)	0.003 (2)
C3	0.019 (2)	0.0179 (18)	0.008 (3)	−0.001 (3)	−0.002 (2)	0.0001 (17)
C4	0.020 (2)	0.022 (2)	0.016 (3)	−0.004 (3)	−0.005 (4)	0.0004 (16)
C5	0.019 (3)	0.023 (3)	0.020 (3)	0.001 (2)	−0.001 (3)	0.001 (3)
C6	0.032 (3)	0.019 (2)	0.017 (3)	0.000 (3)	−0.001 (4)	0.004 (2)
C7	0.023 (4)	0.023 (3)	0.020 (3)	0.005 (2)	0.008 (3)	−0.005 (2)

Geometric parameters (Å, °)

Br1—Br3	2.492 (3)	C2—H2	0.9500
Br1—Br2	2.601 (3)	C3—C4	1.3900
N2—C3	1.390 (5)	C4—C5	1.3900
N2—C6	1.436 (7)	C4—H4	0.9500
N2—C7	1.454 (7)	C5—H5	0.9500
N1—C1	1.3900	C6—H6A	0.9800
N1—C5	1.3900	C6—H6B	0.9800
N1—H1	0.8800	C6—H6C	0.9800
C1—C2	1.3900	C7—H7A	0.9800
C1—H1A	0.9500	C7—H7B	0.9800
C2—C3	1.3900	C7—H7C	0.9800
Br3—Br1—Br2	179.41 (8)	C5—C4—H4	120.0
C3—N2—C6	119.9 (4)	C3—C4—H4	120.0
C3—N2—C7	119.4 (4)	C4—C5—N1	120.0
C6—N2—C7	120.7 (4)	C4—C5—H5	120.0
C1—N1—C5	120.0	N1—C5—H5	120.0
C1—N1—H1	120.0	N2—C6—H6A	109.5
C5—N1—H1	120.0	N2—C6—H6B	109.5
N1—C1—C2	120.0	H6A—C6—H6B	109.5
N1—C1—H1A	120.0	N2—C6—H6C	109.5
C2—C1—H1A	120.0	H6A—C6—H6C	109.5
C1—C2—C3	120.0	H6B—C6—H6C	109.5
C1—C2—H2	120.0	N2—C7—H7A	109.5
C3—C2—H2	120.0	N2—C7—H7B	109.5
N2—C3—C4	120.5 (3)	H7A—C7—H7B	109.5
N2—C3—C2	119.5 (3)	N2—C7—H7C	109.5
C4—C3—C2	120.0	H7A—C7—H7C	109.5
C5—C4—C3	120.0	H7B—C7—H7C	109.5
C5—N1—C1—C2	0.0	C1—C2—C3—N2	−179.96 (9)
N1—C1—C2—C3	0.0	C1—C2—C3—C4	0.0
C6—N2—C3—C4	179.95 (9)	N2—C3—C4—C5	179.96 (9)
C7—N2—C3—C4	−0.07 (11)	C2—C3—C4—C5	0.0
C6—N2—C3—C2	−0.08 (13)	C3—C4—C5—N1	0.0
C7—N2—C3—C2	179.90 (9)	C1—N1—C5—C4	0.0

Hydrogen-bond geometry (Å, °)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···Br2	0.88	2.42	3.286 (2)	167