A redetermination at low temperature of the structure of tri­ethyl­ammonium bromide

The structure of the title compound, C₆H₁₆N⁺·Br⁻, was determined at low temperature and the cell dimensions were comparable to those reported for room-temperature studies [James, Cameron, Knop, Newman & Falp, (1985). Can. J. Chem. 63, 1750–1758]. Initial analysis of the data led to the assignment of P3₁c as the space group rather than P6₃mc as reported for the room-temperature structure. Careful examination of the appropriate |F_o| values in the low-temperature data showed that the equalities |F(kl)| = |F(hl)| and |F(hkl)| = |F(hk)| did not hold at low temperature, confirming P3₁c as the appropriate choice of space group. As a consequence of this choice, the N atom sat on a threefold axis and the ethyl arms were not disordered as observed at room temperature. The crystal studied was an inversion twin with a 0.68 (3):0.32 (3) domain ratio.

Related literature

For related structures, see: James et al. (1985). For the preparation, see: Lecolley et al. (2004).

Experimental

Crystal data

• C₆H₁₆N⁺·Br⁻

• M_r = 182.10

• Trigonal, P 31c

• a = 8.3589 (2) Å

• c = 7.3125 (2) Å

• V = 442.48 (1) ų

• Z = 2

• Mo Kα radiation

• μ = 4.56 mm⁻¹

• T = 90 (2) K

• 0.27 × 0.11 × 0.10 mm

Data collection

• Bruker APEXII CCD area-detector diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2004) T_min = 0.450, T_max = 0.632

• 8583 measured reflections

• 555 independent reflections

• 550 reflections with I > 2σ(I)

• R_int = 0.026

Refinement

• R[F² > 2σ(F²)] = 0.020

• wR(F²) = 0.058

• S = 1.24

• 555 reflections

• 23 parameters

• 1 restraint

• H-atom parameters constrained

• Δρ_max = 0.39 e Å⁻³

• Δρ_min = −0.39 e Å⁻³

• Absolute structure: Flack (1983), 273 Friedel pairs

• Flack parameter: 0.32 (3)

Data collection: APEX2 (Bruker, 2006); cell refinement: APEX2 and SAINT (Bruker, 2006); data reduction: SAINT; program(s) used to solve structure: SIR97 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.

Supporting information

S1. Comment

The title compound, (I), was isolated as a by-product in a reaction to form (2,5-oxo-1-pyrrolidyl)oxy-2-bromo-2-methylpropionate (Lecolley et al., 2004). A view of the structure of (I) is presented in Fig. 1. The crystal structures of (I) and the other halide analogues at ambient temperature have previously been described by James et al. (1985). Unlike previous work, analysis of our low-temperature data showed that (I) crystallized in the space group P3₁c with the ethyl chains in fixed locations. The e.s.d.'s of the positional parameters and the R factors were significantly lower than those reported for the room temperature structure. The packing of (I) (Fig. 2) at low temperature is very similar to that of the room temperature disordered structure. James et al. (1985) also analysed the IR spectra of these compounds in some detail.

Related literature

For related structures, see: James et al. (1985). For preparation, see: Lecolley et al. (2004).

S2. Experimental

The title compound, (I), was prepared as a by-product in a reaction to form (2,5-oxo-1-pyrrolidyl)oxy-2-bromo-2-methylpropionate by the method of Lecolley et al. (2004). X-Ray quality crystals were grown by the slow evaporation of an acetonitrile solution.

S3. Refinement

All H-atoms bound to carbon were refined using a riding model with d(C—H) = 0.96 Å, U_iso=1.5U_eq (C) for the methyl CH H atoms and d(C—H) = 0.97 Å, U_iso=1.2U_eq (C) for the methylene CH H atoms. The H-atom bound to nitrogen was refined using a riding model with d(N—H) = 0.87 Å, U_iso=1.2U_eq (N).

Computing details

Data collection: APEX2 (Bruker, 2006); cell refinement: APEX2 (Bruker, 2006) and SAINT (Bruker, 2006); data reduction: SAINT (Bruker, 2006); program(s) used to solve structure: SIR97 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. A view of the molecule of (I) showing the atom numbering with displacement ellipsoids drawn at the 50% probability level. Symmetry codes: (i) -x+y, -x+1, z; (ii) -y+1, x-y+1, z.
	Fig. 2. Packing diagram of (I) in the ab plane.

Triethylammonium bromide

Crystal data

C6H16N^+·Br^−	Dx = 1.367 Mg m^−3
Mr = 182.10	Mo Kα radiation, λ = 0.71073 Å
Trigonal, P31c	Cell parameters from 7729 reflections
Hall symbol: P 3 -2c	θ = 2.8–27.5°
a = 8.3589 (2) Å	µ = 4.56 mm^−1
c = 7.3125 (2) Å	T = 90 K
V = 442.48 (1) Å^3	Rod, colourless
Z = 2	0.27 × 0.11 × 0.10 mm
F(000) = 188

Data collection

Bruker APEXII CCD area-detector diffractometer	555 independent reflections
Radiation source: fine-focus sealed tube	550 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.026
ϕ and ω scans	θmax = 25.5°, θmin = 4.0°
Absorption correction: multi-scan (SADABS; Bruker, 2004)	h = −10→10
Tmin = 0.450, Tmax = 0.633	k = −10→10
8583 measured reflections	l = −8→8

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.020	H-atom parameters constrained
wR(F^2) = 0.058	w = 1/[σ^2(Fo^2) + (0.0371P)^2 + 0.4873P] where P = (Fo^2 + 2Fc^2)/3
S = 1.24	(Δ/σ)max < 0.001
555 reflections	Δρmax = 0.39 e Å^−3
23 parameters	Δρmin = −0.39 e Å^−3
1 restraint	Absolute structure: Flack (1983), 273 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.32 (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. The crystal studied was an inversion twin with a 0.68 (3);0.32 (3) domain ratio.

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

	x	y	z	Uiso*/Ueq
C1	0.1624 (6)	0.8395 (6)	0.4111 (5)	0.0323 (9)
H1A	0.1536	0.8181	0.2815	0.048*
H1B	0.2690	0.9571	0.4373	0.048*
H1C	0.0533	0.8389	0.4534	0.048*
N1	0.3333	0.6667	0.4505 (6)	0.0168 (12)
H1	0.3333	0.6667	0.3260	0.020*
C2	0.1789 (5)	0.6982 (5)	0.5011 (5)	0.0232 (7)
H2A	0.0644	0.5830	0.4820	0.028*
H2B	0.1884	0.7240	0.6312	0.028*
Br1	0.6667	0.3333	0.5017	0.01786 (16)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.034 (2)	0.038 (2)	0.035 (2)	0.026 (2)	−0.0004 (16)	−0.0026 (17)
N1	0.0162 (14)	0.0162 (14)	0.018 (3)	0.0081 (7)	0.000	0.000
C2	0.0168 (15)	0.0228 (14)	0.0293 (17)	0.0095 (12)	0.0004 (14)	0.0001 (16)
Br1	0.01867 (19)	0.01867 (19)	0.0162 (2)	0.00933 (9)	0.000	0.000

Geometric parameters (Å, º)

C1—C2	1.418 (5)	N1—C2^i	1.488 (4)
C1—H1A	0.9600	N1—C2^ii	1.488 (4)
C1—H1B	0.9600	N1—H1	0.9100
C1—H1C	0.9600	C2—H2A	0.9700
N1—C2	1.488 (4)	C2—H2B	0.9700
C2—C1—H1A	109.5	C2—N1—H1	104.4
C2—C1—H1B	109.5	C2^i—N1—H1	104.4
H1A—C1—H1B	109.5	C2^ii—N1—H1	104.4
C2—C1—H1C	109.5	C1—C2—N1	119.1 (3)
H1A—C1—H1C	109.5	C1—C2—H2A	107.5
H1B—C1—H1C	109.5	N1—C2—H2A	107.5
C2—N1—C2^i	114.03 (18)	C1—C2—H2B	107.5
C2—N1—C2^ii	114.03 (18)	N1—C2—H2B	107.5
C2^i—N1—C2^ii	114.03 (18)	H2A—C2—H2B	107.0

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