Redetermination of triethyl­ammonium chloride in the space group P31c

Churakov, A.V.; Howard, J.A.K.

doi:10.1107/S0108270104014209

organic compounds

STRUCTURAL
CHEMISTRY

ISSN: 2053-2296

Volume 60| Part 8| August 2004| Pages o557-o558

doi:10.1107/S0108270104014209

Redetermination of triethylammonium chloride in the space group P31c

Andrei V. Churakov ^a ^* and Judith A. K. Howard ^b

^aN. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Science, 31 Leninskii Prospect, Moscow 119991, Russia, and ^bDepartment of Chemistry, University of Durham, Science Laboratories, South Road, Durham DH1 3LE, England
^*Correspondence e-mail: churakov@igic.ras.ru

(Received 2 June 2004; accepted 11 June 2004; online 10 July 2004)

The structure of triethylammonium chloride, C₆H₁₆N⁺·Cl⁻, has been redetermined in the space group P31c. In contrast with previous refinements in the space group P6₃mc, no disorder of the triethylammonium cation was observed.

Comment

The structure of triethylammonium chloride has been reported four times to date (Hendricks, 1928 ; Genet, 1965 ; James et al., 1985 ; Ilyukhin, 2000 ). All four structure determinations were made in the space group P6₃mc (No. 186) and showed `propeller'-like disorder of the cation (Fig. 1) caused by a crystallographic mirror plane. Two closely related models were used in the later refinements. In the first, both independent C atoms occupy general positions [12 (d): x, y, z; Genet, 1965; James et al., 1985; Fig. 1(a)]. In the second, the methylene C atom lies on a general position, while the methyl C atom lies on the mirror plane [6 (c): x, $[{\overline x}]$ , z; Ilyukhin, 2000; Fig. 1(b)].

Such disorder is a common feature of the Et₃NH⁺ cation. A total of 379 structures containing the triethylammonium cation are reported in the Cambridge Structural Database (CSD, Version 5.25; Allen, 2002 ). Of these, 126 structures are disordered (33.2%) and 76 structures (20.1%) possess the disordered cation. These figures are noticeably higher than the statistical appearance of disorder in the CSD (18.2%; Allen, 2002). The same type of disorder was observed previously for some other trialkylammonium derivatives with approximate C_3v symmetry, namely silatranes (Zaitseva et al., 1996 ) and germatranes (Karlov et al., 2001 ). These two structures were refined in the space group Pnma. However, refinements in the lower-symmetry space group Pna2₁ retain the `propeller'-like disorder, with occupancy ratios $[\simeq]$ 0.5:0.5. On the contrary, the refinement of [NHEt₃][Sn(acac)Cl₄] in the lower-symmetry group led to an ordered cation, but was not found to be convincing (Korte et al., 1988 ). Against this background, we present here a further redetermination of the structure of triethylammonium chloride, (I) (Fig. 2).

A new data set for (I) was collected on a Bruker SMART CCD diffractometer at 120 K. The systematic absences were consistent with the space groups P31c (No. 159) and P6₃mc. Comparison of the |F_o(hkl)| and |F_o(hk $[{\overline l}]$ )| values points to P6₃mc, since their equality holds in P6₃mc but not in P31c. However, the mean value of |E² − 1| (0.678) was lower than expected for non-centrosymmetric crystals (Herbst-Irmer & Sheldrick, 1998 ).

At first, the structure was refined in the higher symmetry group P6₃mc. The model of Ilyukhin (2000) was found more appropriate and the final refinement converged to R₁ = 0.054 for 395 independent reflections with I > 2σ(I) and 29 parameters. The highest difference peak was 0.55 e Å⁻³. However, the Flack (1983 ) parameter was found to be poorly determined [0.00 (39)], and the use of the racemic TWIN instruction did not led to any improvement of results. Subsequently, the structure was solved and refined in the space group P31c. The disorder of the cation disappeared and the refinement led to a residual R₁ = 0.072 for 661 reflections with I > 2σ(I) and 47 parameters. The highest difference peak was 0.82 e Å⁻³.

The factor K = mean(F_o²)/mean(F_c²) for low-intensity reflections was slightly greater than 1 and did not directly indicate the presence of twinning (Herbst-Irmer & Sheldrick, 1998). Later, the TWIN operator relative to the mirror plane ( $[\overline 1]$ 00, 110, 001) was included. This immediately resulted in the significant decrease of R₁ to 0.019 [48 parameters, Flack parameter 0.06 (6), highest difference peak 0.18 e Å⁻³]. The volume fraction of twin components converged to 0.5. Kahlenberg (1999 ) noted that, in such cases, standard Yeates and Britton statistical tests for merohedral twinning fail. Thus, the choice of the space group may be made on the basis of the final residual parameters only.

Figure 1
The `propeller'-like disorder of the Et₃NH⁺ cation, viewed along the c axis, showing (a) the model of Genet (1965

) and (b) the model of Ilyukhin (2000

Figure 2
The ordered structure of the Et₃NH⁺ cation of (I

), showing 50% probability displacement ellipsoids. The N—H⋯Cl hydrogen bond is denoted by a dashed line [symmetry codes: (i) 1 − y, 1 + x − y, z; (ii) y − x, 1 − x, z].

Experimental

Crystals of (I) were grown from a solution in ethanol–water (1:1). Long needles (15 mm) were cut into small pieces of suitable size.

Crystal data

C₆H₁₆N⁺·Cl⁻
M_r = 137.65
Trigonal, P31c
a = 8.2542 (2) Å
c = 6.9963 (2) Å
V = 412.81 (2) Å³
Z = 2
D_x = 1.107 Mg m⁻³
Mo Kα radiation
Cell parameters from 3089 reflections
θ = 2.8–30.0°
μ = 0.38 mm⁻¹
T = 120 (2) K
Block, colourless
0.40 × 0.10 × 0.10 mm

Data collection

Bruker SMART CCD area-detector diffractometer
ω scans
3185 measured reflections
665 independent reflections
661 reflections with I > 2σ(I)
R_int = 0.014
θ_max = 28.0°
h = −5 → 10
k = −10 → 9
l = −9 → 9

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.019
wR(F²) = 0.047
S = 1.04
665 reflections
48 parameters
All H-atom parameters refined
w = 1/[σ²(F_o²) + (0.0415P)²] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 0.18 e Å⁻³
Δρ_min = −0.09 e Å⁻³
Absolute structure: Flack (1983), with 297 Friedel pairs
Flack parameter = 0.06 (6)

Table 1
Selected geometric parameters (Å, °)

N1—C2	1.5053 (13)
C1—C2	1.5160 (18)

C2—N1—C2ⁱ	111.18 (11)
N1—C2—C1	112.23 (13)
Symmetry code: (i) 1-y,1+x-y,z.

The ammonium H atom was found from a difference Fourier synthesis. Other H atoms were placed in calculated positions. Both positional and displacement parameters for all H atoms were refined.

Data collection: SMART (Bruker, 1998 ); cell refinement: SAINT (Bruker, 2001 ); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997 ); molecular graphics: SHELXTL-Plus (Bruker, 2000 ); software used to prepare material for publication: SHELXTL-Plus.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S0108270104014209/sq1163sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S0108270104014209/sq1163Isup2.hkl

Comment top

The structure of triethylammonium chloride has been reported four times to date (Hendricks, 1928; Genet, 1965; James et al., 1985; Ilyukhin, 2000). All four structure determinations were made in the space group P6₃mc (No. 186), and showed `propeller'-like disorder of the cation (Fig. 1) caused by a crystallographic mirror plane. Two closely related models were used in the later refinements. In the first, both independent C atoms occupy general positions [12 (d): x,y,z; Genet, 1965; James et al., 1985; Fig. 1(a)]. In the second, the methylene C atom lies on a general position, while the methyl C atom lies on the mirror plane [6 (c): x,¯x,z; Ilyukhin, 2000; Fig. 1(b)].

Such disorder is a common feature of the Et₃NH⁺ cation. A total of 379 structures containing the triethylammonium cation are reported in the Cambridge Structural Database (CSD, Version?; Allen, 2002). Of these, 126 structures are disordered (33.2%) and 76 structures (20.1%) possess the disordered cation. These figures are noticeably higher than the statistical appearance of disorder in the CSD, 18.2% (Allen, 2002). The same type of disorder was observed previously for some other trialkylammonium derivatives with approximate C_3v symmetry, namely silatranes (Zaitseva, 1996) and germatranes (Karlov et al., 2001). These two structures were refined in the space group Pnma. However, refinements in the lower-symmetry space group Pna2₁ retain the `propeller'-like disorder, with occupancy ratios ≈ 0.5/0.5. On the contrary, the refinement of [NHEt₃][Sn(acac)Cl₄] in the lower-symmetry group led to an ordered cation, but was not found to be convincing (Korte et al., 1988). Against this background, we present here a further redetermination of the structure of the title compound, (I). \sch

A new dataset for (I) was collected on a Bruker SMART CCD diffractometer at 120 K. The systematic absences were consistent with the space groups P31c (No. 159) and P6₃mc. Comparison of the |F_o(hkl)| and |F_o(hk¯l)| values points to P6₃mc, since their equality holds in P6₃mc but not in P31c. However, the mean value of |E²-1| (0.678) was lower than expected for non-centrosymmteric crystals (Herbst-Irmer & Sheldrick, 1998).

At first, the structure was refined in the higher symmetry group P6₃mc. The model of Ilyukhin (2000) was found more appropriate, and the final refinement converged to R₁ = 0.0537 for 395 independent reflections with I>2σ(I) and 29 parameters. The highest difference peak was 0.55 e Å⁻³. However, the Flack parameter (Flack, 1983) was found to be poorly determined [0.00 (39)], and the use of the racemic TWIN instruction did not led to any improvement of results. Subsequently, the structure was solved and refined in the space group P31c. The disorder of the cation disappeared and the refinement led to a residual R₁ = 0.0721 for 661 reflections with I>2σ(I) and 47 parameters. The highest difference peak was 0.82 e Å⁻³.

The factor K = mean(F_o²)/mean(F_c²) for low-intensity reflections was slightly greater than 1 and did not directly indicate the presence of twinning (Herbst-Irmer & Sheldrick, 1998). Later, the TWIN operator relative to the mirror plane (1 0 0, 1 1 0, 0 0 1) was included. This immediately resulted in the significant decrease of R₁ to 0.0192 [48 parameters, Flack parameter 0.06 (6), highest difference peak 0.18 e Å⁻³]. The volume fraction of twin components converged to 0.5. Kahlenberg (1999) noted that, in such cases, standard Yeates and Britton statistical tests for merohedral twinning fail. Thus, the choice of the space group may be made on the basis of the final residual parameters only.

Experimental top

Crystals of (I) were grown from solution in an ethanol-water mixture (Ratio?). Long needles (15 mm) were cut to small pieces of suitable size.

Computing details top

Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL-Plus (Bruker, 2000); software used to prepare material for publication: SHELXTL-Plus.

Figures top

	Fig. 1. The `propeller'-like disorder of the NHEt₃ cation, viewed along the c axis. (a) The model of Genet (1965). (b) The model of Ilyukhin (2000).
	Fig. 2. The ordered cation structure of (I), showing 50% probability displacement ellipsoids. The N—H···Cl hydrogen bond is denoted by the dashed line [symmetry codes: (i) 1 − y, 1 + x-y, z; (ii) y-x, 1 − x, z].

Triethylammonium chloride top

Crystal data top

C₆H₁₆N⁺·Cl⁻	D_x = 1.107 Mg m⁻³
M_r = 137.65	Mo Kα radiation, λ = 0.71073 Å
Trigonal, P31c	Cell parameters from 3089 reflections
Hall symbol: P 3 -2c	θ = 2.9–30.0°
a = 8.2542 (2) Å	µ = 0.38 mm⁻¹
c = 6.9963 (2) Å	T = 120 K
V = 412.81 (2) Å³	Block, colourless
Z = 2	0.40 × 0.10 × 0.10 mm
F(000) = 152

Data collection top

Bruker SMART CCD area-detector diffractometer	661 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.014
Graphite monochromator	θ_max = 28.0°, θ_min = 2.9°
ω scans	h = −5→10
3185 measured reflections	k = −10→9
665 independent reflections	l = −9→9

Refinement top

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)] = 0.019	All H-atom parameters refined
wR(F²) = 0.047	w = 1/[σ²(F_o²) + (0.0415P)²] where P = (F_o² + 2F_c²)/3
S = 1.04	(Δ/σ)_max < 0.001
665 reflections	Δρ_max = 0.18 e Å⁻³
48 parameters	Δρ_min = −0.09 e Å⁻³
1 restraint	Absolute structure: Flack (1983), with xx Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.06 (6)

Crystal data top

C₆H₁₆N⁺·Cl⁻	Z = 2
M_r = 137.65	Mo Kα radiation
Trigonal, P31c	µ = 0.38 mm⁻¹
a = 8.2542 (2) Å	T = 120 K
c = 6.9963 (2) Å	0.40 × 0.10 × 0.10 mm
V = 412.81 (2) Å³

Data collection top

Bruker SMART CCD area-detector diffractometer	661 reflections with I > 2σ(I)
3185 measured reflections	R_int = 0.014
665 independent reflections

Refinement top

R[F² > 2σ(F²)] = 0.019	All H-atom parameters refined
wR(F²) = 0.047	Δρ_max = 0.18 e Å⁻³
S = 1.04	Δρ_min = −0.09 e Å⁻³
665 reflections	Absolute structure: Flack (1983), with xx Friedel pairs
48 parameters	Absolute structure parameter: 0.06 (6)
1 restraint

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.

The structure was solved by direct methods (Sheldrick, 1990) and refined by full-matrix least-squares on F²(Sheldrick, 1997), with anisotropic thermal parameters for all non-H atoms.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Cl1	0.3333	0.6667	0.1486	0.02172 (12)
N1	0.3333	0.6667	0.5913 (2)	0.0165 (3)
C1	0.1785 (2)	0.31876 (16)	0.5507 (2)	0.0263 (3)
C2	0.17835 (16)	0.47886 (15)	0.6567 (3)	0.0213 (2)
H1	0.3333	0.6667	0.466 (6)	0.032 (8)*
H1A	0.074 (3)	0.204 (3)	0.592 (3)	0.045 (6)*
H1B	0.284 (3)	0.306 (3)	0.572 (3)	0.030 (4)*
H1C	0.154 (6)	0.333 (2)	0.412 (3)	0.042 (7)*
H2A	0.067 (2)	0.4754 (19)	0.644 (4)	0.026 (4)*
H2B	0.197 (2)	0.467 (3)	0.793 (2)	0.028 (4)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cl1	0.02437 (15)	0.02437 (15)	0.01642 (17)	0.01218 (7)	0.000	0.000
N1	0.0163 (4)	0.0163 (4)	0.0167 (7)	0.0082 (2)	0.000	0.000
C1	0.0262 (6)	0.0180 (5)	0.0338 (7)	0.0102 (4)	−0.0013 (7)	−0.0018 (4)
C2	0.0186 (4)	0.0182 (5)	0.0241 (5)	0.0070 (4)	0.0022 (6)	0.0026 (7)

Geometric parameters (Å, º) top

N1—C2ⁱ	1.5053 (13)	C1—H1B	0.94 (3)
N1—C2	1.5053 (13)	C1—H1C	1.01 (2)
N1—C2ⁱⁱ	1.5053 (13)	C2—H2A	0.914 (18)
N1—H1	0.87 (4)	C2—H2B	0.976 (15)
C1—C2	1.5160 (18)	Cl1—H1	2.22 (4)
C1—H1A	0.95 (2)

C2ⁱ—N1—C2	111.18 (11)	C2—C1—H1C	106.6 (15)
C2ⁱ—N1—C2ⁱⁱ	111.18 (11)	H1A—C1—H1C	106 (2)
C2—N1—C2ⁱⁱ	111.18 (11)	H1B—C1—H1C	114 (3)
C2ⁱ—N1—H1	107.70 (12)	N1—C2—C1	112.23 (13)
C2—N1—H1	107.70 (12)	N1—C2—H2A	109.1 (11)
C2ⁱⁱ—N1—H1	107.70 (12)	C1—C2—H2A	111.4 (12)
C2—C1—H1A	108.8 (14)	N1—C2—H2B	107.7 (12)
C2—C1—H1B	115.2 (14)	C1—C2—H2B	108.9 (10)
H1A—C1—H1B	106 (2)	H2A—C2—H2B	107.3 (19)

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

Experimental details

Crystal data
Chemical formula	C₆H₁₆N⁺·Cl⁻
M_r	137.65
Crystal system, space group	Trigonal, P31c
Temperature (K)	120
a, c (Å)	8.2542 (2), 6.9963 (2)
V (Å³)	412.81 (2)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	0.38
Crystal size (mm)	0.40 × 0.10 × 0.10

Data collection
Diffractometer	Bruker SMART CCD area-detector diffractometer
Absorption correction	–
No. of measured, independent and observed [I > 2σ(I)] reflections	3185, 665, 661
R_int	0.014
(sin θ/λ)_max (Å⁻¹)	0.660

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.019, 0.047, 1.04
No. of reflections	665
No. of parameters	48
No. of restraints	1
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.18, −0.09
Absolute structure	Flack (1983), with xx Friedel pairs
Absolute structure parameter	0.06 (6)

Computer programs: SMART (Bruker, 1998), SAINT (Bruker, 2001), SAINT, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), SHELXTL-Plus (Bruker, 2000), SHELXTL-Plus.

Selected geometric parameters (Å, º) top

N1—C2	1.5053 (13)	C1—H1C	1.01 (2)
N1—H1	0.87 (4)	C2—H2A	0.914 (18)
C1—C2	1.5160 (18)	C2—H2B	0.976 (15)
C1—H1A	0.95 (2)	Cl1—H1	2.22 (4)
C1—H1B	0.94 (3)

C2—N1—C2ⁱ	111.18 (11)	H1B—C1—H1C	114 (3)
C2—N1—H1	107.70 (12)	N1—C2—C1	112.23 (13)
C2—C1—H1A	108.8 (14)	N1—C2—H2A	109.1 (11)
C2—C1—H1B	115.2 (14)	C1—C2—H2A	111.4 (12)
H1A—C1—H1B	106 (2)	N1—C2—H2B	107.7 (12)
C2—C1—H1C	106.6 (15)	C1—C2—H2B	108.9 (10)
H1A—C1—H1C	106 (2)	H2A—C2—H2B	107.3 (19)

Symmetry code: (i) −y+1, x−y+1, z.

Acknowledgements

The authors thank Dr S. Z. Vatsadze for providing crystals of (I). AVC is grateful to the Royal Society of Chemistry for an RSC Journal Grant for International Authors.

References

Allen, F. H. (2002). Acta Cryst. B58, 380–388. Web of Science CrossRef CAS IUCr Journals Google Scholar
Bruker (1998). SMART. Version 5.049. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Bruker (2000). SHELXTL-Plus. Version 6.10. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Bruker (2001). SAINT. Version 6.04. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Flack, H. D. (1983). Acta Cryst. A39, 876–881. CrossRef CAS Web of Science IUCr Journals Google Scholar
Genet, F. (1965). Bull. Soc. Fr. Mineral. Cristallogr. 88, 463–482. CAS Google Scholar
Hendricks, S. B. (1928). Z. Kristallogr. 67, 472–481. CAS Google Scholar
Herbst-Irmer, R. & Sheldrick, G. M. (1998). Acta Cryst. B54, 443–449. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Ilyukhin, A. B. (2000). Private communication to the Cambridge Structural Database, refcode ETAMCL02. Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, England. Google Scholar
James, M. A., Cameron, T. S., Knop, O., Neuman, M. & Falk, M. (1985). Can. J. Chem. 63, 1750–1758. CrossRef CAS Web of Science Google Scholar
Kahlenberg, V. (1999). Acta Cryst. B55, 745–751. Web of Science CrossRef CAS IUCr Journals Google Scholar
Karlov, S. S., Shutov, P. L., Churakov, A. V., Lorberth, J. & Zaitseva, G. S. (2001). J. Organomet. Chem. 627, 1–5. Web of Science CSD CrossRef CAS Google Scholar
Korte, L., Mootz, D., Scherf, M. & Wiebcke, M. (1988). Acta Cryst. C44, 1128–1130. CSD CrossRef CAS Web of Science IUCr Journals Google Scholar
Sheldrick, G. M. (1990). Acta Cryst. A46, 467–473. CrossRef CAS Web of Science IUCr Journals Google Scholar
Sheldrick, G. M. (1997). SHELXL97. University of Göttingen, Germany. Google Scholar
Zaitseva, G. S., Karlov, S. S., Churakov, A. V., Avtonomov, E. V., Lorberth, J. & Hertel, D. (1996). J. Organomet. Chem. 523, 221–225. CSD CrossRef CAS Web of Science Google Scholar

© International Union of Crystallography. Prior permission is not required to reproduce short quotations, tables and figures from this article, provided the original authors and source are cited. For more information, click here.