Redetermined structure of β-dl-me­thio­nine at 105 K: an example of the importance of freely refining the positions of the amino-group H atoms

Görbitz, C.H.

doi:10.1107/S1600536814022223

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ISSN: 2056-9890

Volume 70| Part 11| November 2014| Pages 341-343

doi:10.1107/S1600536814022223

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Redetermined structure of β-DL-methionine at 105 K: an example of the importance of freely refining the positions of the amino-group H atoms

Carl Henrik Görbitz ^a ^*

^aDepartment of Chemistry, University of Oslo, PO Box 1033 Blindern, N-0315 Oslo, Norway
^*Correspondence e-mail: c.h.gorbitz@kjemi.uio.no

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 23 September 2014; accepted 8 October 2014; online 15 October 2014)

Diffraction data were taken from the contribution named `β-DL-Methionine at 105 K′ by Alagar et al. [Acta Cryst. (2005 ). E61, o1165–o1167]. Refinement of the coordinates of the three amino H atoms, previously constrained to an idealized geometry, shows that the amino group is in fact rotated 13.5° from the perfectly staggered orientation. This apparently modest change has a profound impact on the calculated hydrogen-bond geometries.

Keywords: hydrogen-bond geometry; amino group; refinement model; β-DL-methionine; crystal structure.

CCDC reference: 1028065

1. Chemical context

Upon comparing the hydrogen-bond geometries of the high-temperature α-phase of the amino acid racemate DL-methionine (Görbitz et al., 2014 ) with the best published structure of the β-phase [Alagar et al., 2005; refcode DLMETA05 in the Cambridge Structural Database (CSD), Version 5.35; Allen, 2002 ], we noted that H⋯O distances surprisingly appeared to get shorter at 340 K than at 105 K. This was judged to be an artefact resulting from different ways of handling the amino H atoms. Alagar et al. (2005) used an idealized geometry and a perfectly staggered orientation for this group in their refinement; while we found a 14° counterclockwise rotation (for the L-enantiomer) that served to give three shorter and more linear interactions. The experimental and structural data of Alagar et al. (2005), with coordinates for the D-enantiomer as the asymmetric unit, were subsequently downloaded and refined again with free amino H atoms, thus increasing the number of parameters from 82 (nine parameters for nine atoms + scale factor) to 91. In the improved structural model displayed in Fig. 1 [R(F) = 0.0377 versus 0.411 and wR(F²) = 0.0918 versus 0.1001], the amino group is shifted slightly away from the staggered orientation through a 13.5° clockwise rotation (for the D-enantiomer), Table 1.

Table 1
Selected torsion angles (°)

N1—C2—C3—C4	54.4 (2)	C1—C2—N1—H1	46.5 (17)
C1—C2—C3—C4	173.53 (15)	C1—C2—N1—H2	−75.3 (15)
C2—C3—C4—S1	179.23 (12)	C1—C2—N1—H3	167.4 (15)
C3—C4—S1—C5	175.03 (14)

Figure 1
(a) The structure of DL-methionine, (I)

, viewed approximately along the N1—C2 bond vector, with 50% probability thermal displacement ellipsoids. The racemate contains molecules of both hands; the one depicted here is the D-enantiomer. Carboxylate groups of three neighboring amino acids accepting hydrogen bonds are shown in a lighter tone. O2ⁱ is at (−x, y + $[{1\over 2}]$ , −z + $[{1\over 2}]$ ), O2ⁱⁱ at (x + $[{1\over 2}]$ , −y, z) and Oⁱⁱⁱ at (x + $[{1\over 2}]$ , −y + 1, z), see Table 2

. Compared to the previously published structure shown in capped sticks representation in (b) (Alagar et al., 2005

), the amino group has been rotated clockwise by about 13.5° to give shorter and more linear hydrogen bonds.

2. Supramolecular features

The hydrogen-bond geometries listed in Table 2 show that the free refinement of amino-group H atoms gives close to linear N—H⋯O interactions with substantially shorter H⋯O distances. There are no significant changes for geometric parameters involving only C, N and O atoms. This example demonstrates that in order not to unduly bias the statistics of hydrogen-bond geometries in the CSD, it is imperative that H atoms of amino groups and other hydrogen-bond donating functional groups whenever possible are refined in a normal manner and not constrained to theoretical positions. The data set used here (Alagar et al., 2005) is of good, but not excellent quality. Nevertheless, H atoms can be refined with decent accuracy [standard uncertainties (s.u.'s) = 0.03 Å for N—H distances], allowing experimental determination of hydrogen-bond geometries. In the event that s.u.'s get much higher and/or N—H distances are clearly unreasonably short or long, a rigid rotation refinement of the group (e.g. by an AFIX 37 command in SHELXL; Sheldrick, 2008 ) should be performed. The results of such a refinement for (I), which adds just a single refinement parameter compared to DLMETA05, but reaches the same R factor as for (I), are included in Table 2. The listed values are very close to those of the unconstrained refinement, but are obviously devoid of s.u.'s for geometric parameters involving H atoms.

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	Parameter	DLMETA05^a	(I)-rigid^b	(I)
N1—H1⋯O2ⁱ	N—H	0.89	0.91	0.88 (3)
	H⋯O	1.93	1.88	1.91 (3)
	N⋯O	2.788 (2)	2.787 (2)	2.788 (2)
	N—H⋯O	162	173	174 (2)
N1—H2⋯O1ⁱⁱ	N—H	0.89	0.91	0.94 (3)
	H⋯O	2.02	1.92	1.89 (3)
	N⋯O	2.814 (2)	2.815 (2)	2.815 (2)
	N—H⋯O	148	167	169 (2)
N1—H3⋯O1ⁱⁱⁱ	N—H	0.89	0.91	0.92 (3)
	H⋯O	2.02	1.91	1.91 (3)
	N⋯O	2.794 (2)	2.795 (2)	2.795 (2)
	N—H⋯O	144	163	161 (2)
Symmetry codes: (i) −x, y + $[{1\over 2}]$ , −z + $[{1\over 2}]$ ; (ii) x + $[{1\over 2}]$ , −y, z; (iii) x + $[{1\over 2}]$ , −y + 1, z. Notes: (a) Alagar et al. (2005), 82 parameters; atoms H1, H2 and H3 were called H1A, H1B and H1C, respectively, by the original authors; the labels used in the CSD entry DLMETA05 have been retained here. (b) Rigid rotation refinement of (I), 83 parameters. 0.91 Å is the standard N—H bond length in SHELXL (Sheldrick, 2008) at 105 K.

Under other circumstances restraints on covalent geometry may be employed. Accordingly, we have found that it is often useful to restrain O—H bond distances and H—O—H bond angles (through the 1–3 distances) during refinement of water molecules in crystal hydrates. For a single molecule with atom labels H1W—O1W—H2W, the appropriate SHELXL commands would be DFIX 0.85 0.02 O1W H1W O1W H2W and DFIX 1.35 0.03 H1W H2W (the s.u.'s of 0.02 and 0.03 Å being subject to discussion). Similar approaches may be used for groups like –OH and –NH₂ for which AFIX 37 commands (or equivalent) are not applicable.

3. Experimental

For crystallization details, see Alagar et al. (2005). Crystal data, data collection and structure refinement details are summarized in Table 3.

Table 3
Experimental details

Crystal data
Chemical formula	C₅H₁₁NO₂S
M_r	149.21
Crystal system, space group	Monoclinic, I2/a
Temperature (K)	105
a, b, c (Å)	9.877 (2), 4.6915 (10), 32.603 (6)
β (°)	106.25 (1)
V (Å³)	1450.4 (5)
Z	8
Radiation type	Mo Kα
μ (mm⁻¹)	0.38
Crystal size (mm)	0.32 × 0.24 × 0.22

Data collection
Diffractometer	Bruker SMART CCD area detector
Absorption correction	Multi-scan (SADABS; Bruker, 1998 )
T_min, T_max	0.85, 0.92
No. of measured, independent and observed [I > 2σ(I)] reflections	6469, 1436, 1373
R_int	0.023
(sin θ/λ)_max (Å⁻¹)	0.623

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.038, 0.092, 1.26
No. of reflections	1436
No. of parameters	91
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.35, −0.23
Computer programs: SMART-NT and SAINT-NT (Bruker, 1999 ), SHELXS97, SHELXL2013 (Sheldrick, 2008) and SHELXTL (Sheldrick, 2008).

Coordinates were refined for amino H atoms; other H atoms were positioned with idealized geometry, with fixed C—H = 0.98 (methyl), 0.99 (methylene) or 1.00 Å (methine). U_iso(H) values were set at 1.2U_eq of the carrier atom or at 1.5U_eq for methyl and amino groups.

Supporting information

CCDC reference: 1028065

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536814022223/hb7289sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536814022223/hb7289Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536814022223/hb7289Isup3.cml

checkCIF report

Chemical context [Appropriate title?] top

Upon comparing the hydrogen-bond geometries of the high-temperature α-phase of the amino acid racemate DL-methionine (Görbitz et al., 2014) with the best published structure of the β-phase [Alagar et al., 2005; refcode DLMETA05 in the Cambridge Structural Database (CSD), Version 5.35; Allen, 2002], we noted that H···O distances surprisingly appeared to get shorter at 340 K than at 105 K. This was judged to be an artefact resulting from different ways of handling the amino H atoms. Alagar et al. (2005) used an idealized geometry and a perfectly staggered orientation for this group in their refinement; while we found a ~14° counterclockwise rotation (for the L-enantiomer) that served to give three shorter and more linear interactions. The experimental and structural data of Alagar et al. (2005), with coordinates for the D-enantiomer as the asymmetric unit, were subsequently downloaded and refined again with free amino H atoms, thus increasing the number of parameters from 82 (nine parameters for nine atoms + scale factor) to 91. In the improved structural model displayed in Fig. 1 [R(F) = 0.0377 versus 0.411 and wR(F²) = 0.0918 versus 0.1001], the amino group is shifted slightly away from the staggered orientation through a ~13.5° clockwise rotation (for the D-enantiomer). As seen from Table 1, this change gives close to linear N—H···O interactions with substantially shorter H···O distances. There are no significant changes for geometric parameters involving only C, N and O atoms. Selected torsion angles are given in Table 2.

Supramolecular features [Appropriate title?] top

This example demonstrates that in order not to unduly bias the statistics of hydrogen-bond geometries in the CSD, it is imperative that H atoms of amino groups and other hydrogen-bond donating functional groups whenever possible are refined in a normal manner and not constrained to theoretical positions. The data set used here (Alagar et al., 2005) is of good, but not excellent quality. Nevertheless, H atoms can be refined with decent accuracy [standard uncertainties (s.u.'s) = 0.03 Å for N—H distances], allowing experimental determination of hydrogen-bond geometries. In the event that s.u.'s get much higher and/or N—H distances are clearly unreasonably short or long, a rigid rotation refinement of the group (e.g. by an AFIX 37 command in SHELXL; Sheldrick, 2008) should be performed. The results of such a refinement for (I), which adds just a single refinement parameter compared to DLMETA05, but reaches the same R factor as for (I), are included in Table 3. The listed values are very close to those of the unconstrained refinement, but are obviously devoid of s.u.'s for geometric parameters involving H atoms.

Synthesis and crystallization top

For synthesis detaisl, see Alagar et al. (2005).

Refinement top

Crystal data, data collection and structure refinement details are summarized in Table 3. Coordinates were refined for amino H atoms; other H atoms were positioned with idealized geometry, with fixed C—H = 0.98 (methyl), 0.99 (methylene) or 1.00 Å (methine). U_iso(H) values were set at 1.2U_eq of the carrier atom or at 1.5U_eq for methyl and amino groups.

Related literature top

For related literature, see: Alagar et al. (2005); Allen (2002); Görbitz et al. (2014); Sheldrick (2008).

Computing details top

Data collection: SMART-NT (Bruker, 1999); cell refinement: SAINT-NT (Bruker, 1999); data reduction: SAINT-NT (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL2013 (Sheldrick, 2008).

Figures top

(a) The structure of DL-methionine, (I), viewed approximately along the N1—C2 bond vector, with 50% probability thermal displacement ellipsoids. The racemate contains molecules of both hands; the one depicted here is the D-enantiomer. Carboxylate groups of three neighboring amino acids accepting hydrogen bonds are shown in a lighter tone. O2ⁱ is at (-x, y+1/2, -z+1/2, O2ⁱⁱ at (x+1/2, -y, z) and Oⁱⁱⁱ at (x+1/2, -y+1, z), see Table 1. Compared to the previously published structure shown in capped sticks representation in (b) (Alagar et al., 2005), the amino group has been rotated clockwise by about 13.5° to give shorter and more linear hydrogen bonds.

2-Amino-4-(methylsulfanyl)butanoic acid top

Crystal data top

C₅H₁₁NO₂S	F(000) = 640
M_r = 149.21	D_x = 1.367 Mg m⁻³
Monoclinic, I2/a	Mo Kα radiation, λ = 0.71073 Å
a = 9.877 (2) Å	Cell parameters from 1012 reflections
b = 4.6915 (10) Å	θ = 2.6–26.1°
c = 32.603 (6) Å	µ = 0.38 mm⁻¹
β = 106.25 (1)°	T = 105 K
V = 1450.4 (5) Å³	Block, colourless
Z = 8	0.32 × 0.24 × 0.22 mm

Data collection top

Bruker SMART CCD area-detector diffractometer	1436 independent reflections
Radiation source: fine-focus sealed tube	1373 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.023
Detector resolution: 8.3 pixels mm^-1	θ_max = 26.3°, θ_min = 2.6°
Sets of exposures each taken over 0.5° ω rotation scans	h = −12→11
Absorption correction: multi-scan (SADABS; Bruker, 1998)	k = 0→5
T_min = 0.85, T_max = 0.92	l = 0→40
6469 measured reflections

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.038	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.092	w = 1/[σ²(F_o²) + (0.0233P)² + 2.4782P] where P = (F_o² + 2F_c²)/3
S = 1.26	(Δ/σ)_max = 0.001
1436 reflections	Δρ_max = 0.35 e Å⁻³
91 parameters	Δρ_min = −0.23 e Å⁻³

Crystal data top

C₅H₁₁NO₂S	V = 1450.4 (5) Å³
M_r = 149.21	Z = 8
Monoclinic, I2/a	Mo Kα radiation
a = 9.877 (2) Å	µ = 0.38 mm⁻¹
b = 4.6915 (10) Å	T = 105 K
c = 32.603 (6) Å	0.32 × 0.24 × 0.22 mm
β = 106.25 (1)°

Data collection top

Bruker SMART CCD area-detector diffractometer	1436 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 1998)	1373 reflections with I > 2σ(I)
T_min = 0.85, T_max = 0.92	R_int = 0.023
6469 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.038	0 restraints
wR(F²) = 0.092	H atoms treated by a mixture of independent and constrained refinement
S = 1.26	Δρ_max = 0.35 e Å⁻³
1436 reflections	Δρ_min = −0.23 e Å⁻³
91 parameters

Special details top

Experimental. Diffraction data and experimental conditions are taken from Alagar et al. (2005), CSD refcode DLMETA05.

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 amino H atom coordinates.

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

	x	y	z	U_iso*/U_eq
S1	0.39652 (6)	0.15681 (12)	0.44292 (2)	0.03291 (18)
O1	−0.14523 (13)	0.2025 (3)	0.31403 (4)	0.0240 (3)
O2	−0.01841 (13)	−0.0810 (3)	0.28411 (4)	0.0216 (3)
N1	0.19296 (17)	0.3000 (3)	0.29733 (5)	0.0193 (3)
H1	0.142 (3)	0.332 (5)	0.2710 (8)	0.029*
H2	0.238 (2)	0.122 (6)	0.2999 (7)	0.029*
H3	0.263 (2)	0.436 (5)	0.3054 (7)	0.029*
C1	−0.03289 (18)	0.1301 (4)	0.30562 (5)	0.0185 (4)
C2	0.09967 (18)	0.3087 (4)	0.32589 (5)	0.0183 (4)
H4	0.0719	0.5103	0.3294	0.022*
C3	0.17639 (19)	0.1831 (4)	0.36982 (5)	0.0214 (4)
H5	0.1148	0.2038	0.3889	0.026*
H6	0.1911	−0.0232	0.3664	0.026*
C4	0.3196 (2)	0.3214 (4)	0.39143 (6)	0.0246 (4)
H7	0.3068	0.5281	0.3952	0.030*
H8	0.3837	0.2973	0.3731	0.030*
C5	0.5659 (2)	0.3326 (5)	0.45830 (7)	0.0350 (5)
H9	0.6208	0.2627	0.4864	0.053*
H10	0.6169	0.2916	0.4371	0.053*
H11	0.5521	0.5388	0.4597	0.053*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
S1	0.0351 (3)	0.0337 (3)	0.0231 (3)	−0.0067 (2)	−0.0031 (2)	0.0074 (2)
O1	0.0225 (7)	0.0168 (6)	0.0333 (7)	0.0012 (5)	0.0089 (5)	−0.0003 (5)
O2	0.0253 (7)	0.0156 (6)	0.0222 (6)	−0.0010 (5)	0.0037 (5)	−0.0028 (5)
N1	0.0207 (7)	0.0169 (8)	0.0190 (7)	−0.0010 (6)	0.0035 (6)	0.0008 (6)
C1	0.0213 (8)	0.0138 (8)	0.0181 (8)	0.0006 (7)	0.0019 (7)	0.0034 (6)
C2	0.0212 (8)	0.0128 (8)	0.0208 (8)	0.0005 (7)	0.0059 (7)	−0.0008 (7)
C3	0.0248 (9)	0.0186 (9)	0.0197 (8)	−0.0008 (7)	0.0043 (7)	−0.0002 (7)
C4	0.0273 (10)	0.0216 (9)	0.0213 (9)	−0.0016 (8)	0.0007 (7)	0.0017 (7)
C5	0.0309 (11)	0.0416 (13)	0.0272 (10)	−0.0024 (9)	−0.0008 (8)	0.0012 (9)

Geometric parameters (Å, º) top

S1—C5	1.806 (2)	C2—H4	1.0000
S1—C4	1.8104 (19)	C3—C4	1.536 (2)
O1—C1	1.262 (2)	C3—H5	0.9900
O2—C1	1.245 (2)	C3—H6	0.9900
N1—C2	1.483 (2)	C4—H7	0.9900
N1—H1	0.88 (3)	C4—H8	0.9900
N1—H2	0.94 (3)	C5—H9	0.9800
N1—H3	0.92 (3)	C5—H10	0.9800
C1—C2	1.539 (2)	C5—H11	0.9800
C2—C3	1.538 (2)

C5—S1—C4	100.27 (10)	C4—C3—H5	108.6
C2—N1—H1	108.9 (15)	C2—C3—H5	108.6
C2—N1—H2	109.2 (14)	C4—C3—H6	108.6
H1—N1—H2	111 (2)	C2—C3—H6	108.6
C2—N1—H3	110.5 (14)	H5—C3—H6	107.6
H1—N1—H3	110 (2)	C3—C4—S1	109.80 (13)
H2—N1—H3	107 (2)	C3—C4—H7	109.7
O2—C1—O1	125.67 (17)	S1—C4—H7	109.7
O2—C1—C2	117.19 (15)	C3—C4—H8	109.7
O1—C1—C2	117.03 (15)	S1—C4—H8	109.7
N1—C2—C3	110.09 (14)	H7—C4—H8	108.2
N1—C2—C1	108.59 (14)	S1—C5—H9	109.5
C3—C2—C1	109.25 (14)	S1—C5—H10	109.5
N1—C2—H4	109.6	H9—C5—H10	109.5
C3—C2—H4	109.6	S1—C5—H11	109.5
C1—C2—H4	109.6	H9—C5—H11	109.5
C4—C3—C2	114.57 (15)	H10—C5—H11	109.5

N1—C2—C3—C4	54.4 (2)	O2—C1—C2—C3	−87.60 (18)
C1—C2—C3—C4	173.53 (15)	O1—C1—C2—C3	88.98 (18)
C2—C3—C4—S1	179.23 (12)	C1—C2—N1—H1	46.5 (17)
C3—C4—S1—C5	175.03 (14)	C1—C2—N1—H2	−75.3 (15)
O2—C1—C2—N1	32.5 (2)	C1—C2—N1—H3	167.4 (15)
O1—C1—C2—N1	−150.93 (15)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O2ⁱ	0.88 (3)	1.91 (3)	2.788 (2)	175 (3)
N1—H2···O1ⁱⁱ	0.94 (3)	1.89 (3)	2.815 (2)	169 (2)
N1—H3···O1ⁱⁱⁱ	0.92 (2)	1.91 (2)	2.795 (2)	161 (2)
C2—H4···O2^iv	1.00	2.43	3.244 (2)	138

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

Selected torsion angles (º) top

N1—C2—C3—C4	54.4 (2)	C1—C2—N1—H1	46.5 (17)
C1—C2—C3—C4	173.53 (15)	C1—C2—N1—H2	−75.3 (15)
C2—C3—C4—S1	179.23 (12)	C1—C2—N1—H3	167.4 (15)
C3—C4—S1—C5	175.03 (14)

Hydrogen-bond geometry (Å, °) top

D—H···A	Parameter	DLMETA05^a	(I)-rigid^b	(I)
N1—H1···O2ⁱ	N—H	0.89	0.91	0.88 (3)
	H···O	1.93	1.88	1.91 (3)
	N···O	2.788 (2)	2.787 (2)	2.788 (2)
	N—H···O	162	173	174 (2)
N1—H2···O1ⁱⁱ	N—H	0.89	0.91	0.94 (3)
	H···O	2.02	1.92	1.89 (3)
	N···O	2.814 (2)	2.815 (2)	2.815 (2)
	N—H···O	148	167	169 (2)
N1—H3···O1ⁱⁱⁱ	N—H	0.89	0.91	0.92 (3)
	H···O	2.02	1.91	1.91 (3)
	N···O	2.794 (2)	2.795 (2)	2.795 (2)
	N—H···O	144	163	161 (2)

Symmetry codes: (i) -x, y+1/2, -z+1/2; (ii) x+1/2, -y, z; (iii) x+1/2, -y+1, z. Notes: (a) Alagar et al. (2005), 82 parameters; atoms H1, H2 and H3 were called H1A, H1B and H1C, respectively, by the original authors; the labels used in the CSD entry DLMETA05 have been retained here. (b) Rigid rotation refinement of (I), 83 parameters. 0.91 Å is the standard N—H bond length in SHELXL (Sheldrick, 2008) at 105 K.

Experimental details

Crystal data
Chemical formula	C₅H₁₁NO₂S
M_r	149.21
Crystal system, space group	Monoclinic, I2/a
Temperature (K)	105
a, b, c (Å)	9.877 (2), 4.6915 (10), 32.603 (6)
β (°)	106.25 (1)
V (Å³)	1450.4 (5)
Z	8
Radiation type	Mo Kα
µ (mm⁻¹)	0.38
Crystal size (mm)	0.32 × 0.24 × 0.22

Data collection
Diffractometer	Bruker SMART CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 1998)
T_min, T_max	0.85, 0.92
No. of measured, independent and observed [I > 2σ(I)] reflections	6469, 1436, 1373
R_int	0.023
(sin θ/λ)_max (Å⁻¹)	0.623

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.038, 0.092, 1.26
No. of reflections	1436
No. of parameters	91
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.35, −0.23

Computer programs: SMART-NT (Bruker, 1999), SAINT-NT (Bruker, 1999), SHELXS97 (Sheldrick, 2008), SHELXL2013 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

References

Alagar, M., Krishnakumar, R. V., Mostad, A. & Natarajan, S. (2005). Acta Cryst. E61, o1165–o1167. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Allen, F. H. (2002). Acta Cryst. B58, 380–388. Web of Science CrossRef CAS IUCr Journals Google Scholar
Bruker (1998). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Bruker (1999). SMART-NT and SAINT-NT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Görbitz, C. H., Qi, L., Mai, N. T. K. & Kristiansen, H. (2014). Acta Cryst. E70, 337–340. CSD CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar

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Volume 70| Part 11| November 2014| Pages 341-343

doi:10.1107/S1600536814022223

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research communications\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Redetermined structure of β-DL-me­thio­nine at 105 K: an example of the importance of freely refining the positions of the amino-group H atoms

1. Chemical context

2. Supra­molecular features

3. Experimental

Supporting information

References

research communications

Redetermined structure of β-DL-methionine at 105 K: an example of the importance of freely refining the positions of the amino-group H atoms

2. Supramolecular features