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DL-Norleucine (2-amino­hexanoic acid, C6H13NO2) forms a double-layer structure in all known phases (α, β, γ). The crystal structure of the β-phase was redetermined at 173 K. Diffraction patterns of the α- and β-phases frequently show diffuse streaks parallel to c*, which indicates a stacking disorder of the layers. A symmetry analysis was carried out to derive possible stacking sequences. Lattice-energy minimizations by force fields and by dispersion-corrected density functional theory (DFT-D) were performed on a set of ordered model structures with Z = 4, 8 and 16 with different stacking sequences. The calculated energies depend not only on the arrangement of neighbouring double layers, but also of next-neighbouring double layers. Stacking probabilities were calculated from the DFT-D energies. According to the calculated stacking probabilities large models containing 100 double layers were constructed. Their simulated diffraction patterns show sharp reflections for h + k = 2n and diffuse streaks parallel to c* through all reflections with h + k = 2n + 1. Experimental single-crystal X-ray diffraction revealed that at 173 K norleucine exists in the β-phase with stacking disorder. After reheating to room temperature, the investigated crystal showed a diffraction pattern with strong diffuse scattering parallel to c* through all reflections with h + k = 2n + 1, which is in good agreement with the simulated disordered structure.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S2052520617012057/fx5009sup1.cif
Contains datablock I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S2052520617012057/fx5009Isup3.hkl
Contains datablock I

pdf

Portable Document Format (PDF) file https://doi.org/10.1107/S2052520617012057/fx5009sup2.pdf
Tables S1,S2,S3, S4 and Fig. 1S

CCDC reference: 1570080

Computing details top

Program(s) used to refine structure: SHELXL2016/6 (Sheldrick, 2016).

(I) top
Crystal data top
C6H13NO2F(000) = 576
Mr = 131.17Dx = 1.195 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
a = 31.2310 (18) ÅCell parameters from 8204 reflections
b = 4.7296 (4) Åθ = 2.1–26.5°
c = 9.8739 (5) ŵ = 0.09 mm1
β = 91.719 (5)°T = 173 K
V = 1457.82 (17) Å3Plate, colourless
Z = 80.28 × 0.26 × 0.09 mm
Data collection top
STOE IPDS II two-circle-
diffractometer
1326 reflections with I > 2σ(I)
Radiation source: Genix 3D IµS microfocus X-ray sourceRint = 0.037
ω scansθmax = 26.1°, θmin = 2.6°
Absorption correction: multi-scan
X-Area (Stoe & Cie, 2001)
h = 3838
Tmin = 0.370, Tmax = 1.000k = 55
8204 measured reflectionsl = 1212
1451 independent reflections
Refinement top
Refinement on F217 restraints
Least-squares matrix: fullHydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.038H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.117 w = 1/[σ2(Fo2) + (0.0743P)2 + 0.9606P]
where P = (Fo2 + 2Fc2)/3
S = 0.97(Δ/σ)max = 0.001
1451 reflectionsΔρmax = 0.20 e Å3
131 parametersΔρmin = 0.19 e Å3
Special details top

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 (Å2) top
xyzUiso*/UeqOcc. (<1)
O10.71594 (3)0.07663 (19)0.80083 (9)0.0273 (3)0.950 (4)
O20.68563 (4)0.2049 (3)0.95311 (9)0.0308 (3)0.950 (4)
N10.70227 (4)0.2984 (4)0.60003 (12)0.0236 (3)0.950 (4)
H1N0.6947 (5)0.443 (4)0.5384 (18)0.034 (4)*0.950 (4)
H2N0.7296 (7)0.325 (4)0.6260 (18)0.037 (4)*0.950 (4)
H3N0.7000 (6)0.112 (5)0.553 (2)0.046 (6)*0.950 (4)
C10.69433 (4)0.1340 (3)0.83407 (12)0.0228 (3)0.950 (4)
C20.67414 (4)0.3110 (3)0.71923 (12)0.0231 (3)0.950 (4)
H20.6715060.5117030.7497610.028*0.950 (4)
C30.62962 (4)0.1938 (4)0.68334 (14)0.0275 (4)0.950 (4)
H3A0.6111420.2225020.7619010.033*0.950 (4)
H3B0.6321260.0125590.6686840.033*0.950 (4)
C40.60742 (4)0.3243 (4)0.55838 (14)0.0321 (4)0.950 (4)
H4A0.6054380.5314940.5709930.039*0.950 (4)
H4B0.6250030.2888530.4783580.039*0.950 (4)
C50.56276 (6)0.2057 (8)0.5316 (2)0.0409 (6)0.950 (4)
H5A0.5644470.0031530.5281310.049*0.950 (4)
H5B0.5444400.2574300.6078420.049*0.950 (4)
C60.54197 (6)0.3129 (5)0.40014 (18)0.0489 (5)0.950 (4)
H6A0.5133600.2297810.3882180.073*0.950 (4)
H6B0.5395640.5193500.4036300.073*0.950 (4)
H6C0.5595820.2586280.3238760.073*0.950 (4)
O1'0.7160 (8)0.583 (5)0.800 (2)0.058 (9)*0.050 (4)
O2'0.6849 (12)0.313 (8)0.952 (3)0.071 (15)*0.050 (4)
N1'0.7010 (8)0.191 (8)0.593 (3)0.019 (8)*0.050 (4)
C1'0.6939 (9)0.372 (6)0.830 (2)0.048 (9)*0.050 (4)
C2'0.6739 (9)0.198 (7)0.717 (3)0.057 (16)*0.050 (4)
C3'0.6288 (10)0.297 (12)0.681 (4)0.08 (2)*0.050 (4)
C4'0.6072 (11)0.180 (11)0.554 (4)0.062 (13)*0.050 (4)
C5'0.5617 (14)0.278 (15)0.525 (6)0.06 (3)*0.050 (4)
C6'0.545 (2)0.176 (18)0.387 (6)0.12 (3)*0.050 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0342 (5)0.0236 (5)0.0239 (5)0.0040 (4)0.0018 (4)0.0007 (3)
O20.0500 (7)0.0253 (7)0.0171 (5)0.0020 (5)0.0002 (4)0.0007 (4)
N10.0301 (8)0.0213 (8)0.0191 (6)0.0026 (5)0.0017 (4)0.0010 (5)
C10.0292 (6)0.0187 (6)0.0203 (6)0.0033 (5)0.0018 (5)0.0001 (5)
C20.0310 (7)0.0200 (8)0.0181 (6)0.0004 (5)0.0003 (5)0.0008 (5)
C30.0299 (8)0.0277 (9)0.0249 (7)0.0000 (5)0.0010 (5)0.0021 (5)
C40.0343 (8)0.0303 (9)0.0313 (8)0.0003 (6)0.0069 (6)0.0033 (6)
C50.0341 (11)0.0453 (15)0.0425 (12)0.0020 (7)0.0096 (6)0.0045 (9)
C60.0391 (9)0.0632 (14)0.0435 (10)0.0015 (8)0.0147 (7)0.0008 (9)
Geometric parameters (Å, º) top
O1—C11.2526 (16)C5—C61.521 (3)
O2—C11.2597 (15)C5—H5A0.9900
N1—C21.4908 (16)C5—H5B0.9900
N1—H1N0.939 (19)C6—H6A0.9800
N1—H2N0.89 (2)C6—H6B0.9800
N1—H3N1.00 (2)C6—H6C0.9800
C1—C21.5302 (17)O1'—C1'1.257 (18)
C2—C31.5286 (18)O2'—C1'1.270 (18)
C2—H21.0000N1'—C2'1.509 (19)
C3—C41.5275 (18)C1'—C2'1.506 (18)
C3—H3A0.9900C2'—C3'1.515 (19)
C3—H3B0.9900C3'—C4'1.512 (19)
C4—C51.519 (2)C4'—C5'1.51 (2)
C4—H4A0.9900C5'—C6'1.52 (2)
C4—H4B0.9900
C2—N1—H1N109.9 (10)C5—C4—H4B109.1
C2—N1—H2N110.4 (11)C3—C4—H4B109.1
H1N—N1—H2N107.7 (15)H4A—C4—H4B107.8
C2—N1—H3N111.5 (12)C6—C5—C4113.1 (2)
H1N—N1—H3N109.2 (15)C6—C5—H5A109.0
H2N—N1—H3N108.1 (16)C4—C5—H5A109.0
O1—C1—O2126.09 (12)C6—C5—H5B109.0
O1—C1—C2117.02 (11)C4—C5—H5B109.0
O2—C1—C2116.76 (12)H5A—C5—H5B107.8
N1—C2—C3110.85 (11)C5—C6—H6A109.5
N1—C2—C1108.89 (11)C5—C6—H6B109.5
C3—C2—C1108.97 (12)H6A—C6—H6B109.5
N1—C2—H2109.4C5—C6—H6C109.5
C3—C2—H2109.4H6A—C6—H6C109.5
C1—C2—H2109.4H6B—C6—H6C109.5
C2—C3—C4115.37 (13)O1'—C1'—O2'123 (2)
C2—C3—H3A108.4O1'—C1'—C2'118 (2)
C4—C3—H3A108.4O2'—C1'—C2'119 (2)
C2—C3—H3B108.4N1'—C2'—C1'113 (2)
C4—C3—H3B108.4N1'—C2'—C3'111 (2)
H3A—C3—H3B107.5C1'—C2'—C3'112 (2)
C5—C4—C3112.57 (16)C2'—C3'—C4'118 (2)
C5—C4—H4A109.1C5'—C4'—C3'116 (3)
C3—C4—H4A109.1C6'—C5'—C4'112 (3)
O1—C1—C2—N131.26 (17)O1'—C1'—C2'—N1'33 (4)
O2—C1—C2—N1152.63 (13)O2'—C1'—C2'—N1'153 (3)
O1—C1—C2—C389.76 (14)O1'—C1'—C2'—C3'93 (4)
O2—C1—C2—C386.35 (15)O2'—C1'—C2'—C3'82 (4)
N1—C2—C3—C452.8 (2)N1'—C2'—C3'—C4'43 (6)
C1—C2—C3—C4172.65 (13)C1'—C2'—C3'—C4'170 (4)
C2—C3—C4—C5177.94 (17)C2'—C3'—C4'—C5'178 (5)
C3—C4—C5—C6174.50 (19)C3'—C4'—C5'—C6'173 (6)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1N···O2i0.939 (19)1.886 (19)2.801 (2)164.3 (15)
N1—H2N···O1ii0.89 (2)1.89 (2)2.7717 (16)171.1 (17)
N1—H3N···O1iii1.00 (2)2.56 (2)3.1759 (16)119.7 (15)
N1—H3N···O2iii1.00 (2)1.84 (2)2.828 (2)168.6 (18)
C2—H2···O1iv1.002.433.2677 (18)140
Symmetry codes: (i) x, y+1, z1/2; (ii) x+3/2, y+1/2, z+3/2; (iii) x, y, z1/2; (iv) x, y+1, z.
 

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