5-(2,6-Dimethoxy­phen­oxy)-2-methyl­sulfanylmethyl-2H-tetra­zole

Noroozi Pesyan, N.; Omidkhah, N.; Maghsoodi, M.; Patrick, B.O.

doi:10.1107/S1600536809006138

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 65| Part 3| March 2009| Page o655

doi:10.1107/S1600536809006138

Open

access

5-(2,6-Dimethoxyphenoxy)-2-methylsulfanylmethyl-2H-tetrazole

Nader Noroozi Pesyan,^a ^* Negar Omidkhah,^a Mina Maghsoodi ^a and Brian O Patrick ^b

^aDepartment of Chemistry, Faculty of Science, Urmia University, 57159 Urmia, Iran, and ^bDepartment of Chemistry, University of British Columbia, Vancouver, BC, Canada V6T 1Z1
^*Correspondence e-mail: pesyan@gmail.com

(Received 24 January 2009; accepted 19 February 2009; online 28 February 2009)

In the title molecule, C₁₁H₁₄N₄O₃S, the tetrazole and benzene rings are nearly perpendicular to each other, forming a dihedral angle of 104.93 (14)°. The crystal packing exhibits weak intermolecular C—H⋯O hydrogen bonds.

Related literature

For a related crystal structure, see: Dabbagh et al. (2005 ).

Experimental

Crystal data

C₁₁H₁₄N₄O₃S
M_r = 282.32
Orthorhombic, P c a 2₁
a = 12.1795 (5) Å
b = 11.0809 (4) Å
c = 9.9026 (4) Å
V = 1336.45 (9) Å³
Z = 4
Mo Kα radiation
μ = 0.25 mm⁻¹
T = 173 K
0.50 × 0.25 × 0.10 mm

Data collection

Bruker X8 APEXII diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2008 ) T_min = 0.871, T_max = 0.975
7950 measured reflections
2873 independent reflections
2670 reflections with I > 2σ(I)
R_int = 0.020

Refinement

R[F² > 2σ(F²)] = 0.026
wR(F²) = 0.067
S = 1.08
2873 reflections
175 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.18 e Å⁻³
Δρ_min = −0.15 e Å⁻³
Absolute structure: Flack (1983 ), 1220 Friedel pairs
Flack parameter: 0.06 (6)

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C10—H10B⋯O1ⁱ	0.99	2.45	3.4277 (19)	170
C11—H11C⋯O3ⁱ	0.98	2.45	3.421 (2)	172
C11—H11B⋯O1ⁱⁱ	0.98	2.52	3.471 (2)	163
C10—H10A⋯O2ⁱⁱⁱ	0.99	2.52	3.312 (2)	137
Symmetry codes: (i) $[x-{\script{1\over 2}}, -y+1, z]$ ; (ii) $[-x+{\script{1\over 2}}, y, z-{\script{1\over 2}}]$ ; (iii) $[-x+{\script{1\over 2}}, y, z+{\script{1\over 2}}]$ .

Data collection: APEX2 (Bruker, 2008); cell refinement: APEX2; data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SIR (Altomare et al., 1999 ); program(s) used to refine structure: SHELXTL (Sheldrick, 2008 ); molecular graphics: ORTEP-3 (Farrugia, 1997 ); software used to prepare material for publication: SHELXTL.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536809006138/cv2515sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536809006138/cv2515Isup2.hkl

checkCIF report

Comment top

In continuation of our structural study of tetrazole derivatives (Dabbagh et al., 2005) we report herein the structure of the title compound, (I).

In (I) (Fig. 1), the methylsulfanylmethylation proceeded at N2 atom on tetrazole ring. Because of the conjugation of O3 with tetrazole ring the bond distance O3—C9 [1.3388 (17) Å] is obviously shorter than O3—C1 [1.4062 (15) Å]. A similar effect has been found in 5-(4-nitrophenoxy)-1-methylsulfanylmethyl-1H-tetrazole (Dabbagh et al., 2005). Tetrazole ring in (I) is planar, and 2,6-dimethoxyphenoxy group deviates from the tetrazole ring plane so torsion angles C6—C1—O3—C9 and C1—O3—C9—N4 are -79.52 (17)° and -9.6 (2)°, respectively. The torsion angle O3—C1—C2—C3 of 174.02 (13)° implies steric interaction between the benzene and tetrazole rings. The S1—C10 bond [1.792 (2) Å] is slightly shorter than C11—S1 [1.798 (2) Å] in methylsulfanylmethyl group.

The crystal packing exhibits weak intermolecular C—H···O hydrogen bonds (Table 1).

Related literature top

For a related crystal structure, see: Dabbagh et al. (2005).

Experimental top

Dry DMSO, 5 ml, was added dropwise over a period of 30 min to a solution of 0.143 g of compound in 4 ml of acetic anhydride. The mixture was stirred for 40 h at 45–50°C, excess DMSO and acetic anhydride were removed under reduced pressure, and the residue was washed with several 2–3-ml portions of water. The precipitate was dissolved in 20 ml of methylene chloride, the solution was dried over calcium chloride and evaporated, and the residue was separated by column chromatography on silica gel to isolate compound. Yield 20%. IR spectrum (KBr), ν, cm^-1: 3050, 2975, 1590, 1530, 1390, 1370, 1300, 1260, 1180, 1110, 760. ¹H NMR (300 MHz, DMSO-d₆), δ: 7.14 (t, 1H, J = 10 Hz), 6.65 (d, 2H, J = 10 Hz), 5.48 (s, 2H), 3.71 (s, 6H), 2.17 (s, 3H). 13 C NMR (75 MHz, DMSO-d6), δ: 177.50, 152.29, 131.80, 126.74, 105.44, 78.88, 56.20, 56.03, 15.48. Mass spectrum (EI), m/z (Irel, %) 284 (0.6) [M + 2]⁺, 282 (15) [M]⁺, 281 (20), 236 (83), 151 (73), 140 (39), 107 (59), 43 (100).

Computing details top

Data collection: APEX2 (Bruker, 2008); cell refinement: APEX2 (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SIR (Altomare et al., 1999); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top

Fig. 1. The molecular structure of the title compound showing the atomic numbering and 50% probability displacement ellipsoids.

5-(2,6-Dimethoxyphenoxy)-2-methylsulfanylmethyl-2H-tetrazole top

Crystal data top

C₁₁H₁₄N₄O₃S	F(000) = 592
M_r = 282.32	D_x = 1.403 Mg m⁻³
Orthorhombic, Pca2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c -2ac	Cell parameters from 4562 reflections
a = 12.1795 (5) Å	θ = 2.8–27.8°
b = 11.0809 (4) Å	µ = 0.25 mm⁻¹
c = 9.9026 (4) Å	T = 173 K
V = 1336.45 (9) Å³	Irregular, colourless
Z = 4	0.50 × 0.25 × 0.10 mm

Data collection top

Bruker X8 APEXII diffractometer	2873 independent reflections
Radiation source: fine-focus sealed tube	2670 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.020
Area–detector scans	θ_max = 28.0°, θ_min = 1.8°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −16→15
T_min = 0.871, T_max = 0.975	k = −14→14
7950 measured reflections	l = −12→12

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)] = 0.026	H-atom parameters constrained
wR(F²) = 0.067	w = 1/[σ²(F_o²) + (0.0323P)² + 0.1529P] where P = (F_o² + 2F_c²)/3
S = 1.08	(Δ/σ)_max = 0.002
2873 reflections	Δρ_max = 0.18 e Å⁻³
175 parameters	Δρ_min = −0.15 e Å⁻³
1 restraint	Absolute structure: Flack (1983), 1220 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.06 (6)

Crystal data top

C₁₁H₁₄N₄O₃S	V = 1336.45 (9) Å³
M_r = 282.32	Z = 4
Orthorhombic, Pca2₁	Mo Kα radiation
a = 12.1795 (5) Å	µ = 0.25 mm⁻¹
b = 11.0809 (4) Å	T = 173 K
c = 9.9026 (4) Å	0.50 × 0.25 × 0.10 mm

Data collection top

Bruker X8 APEXII diffractometer	2873 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2008)	2670 reflections with I > 2σ(I)
T_min = 0.871, T_max = 0.975	R_int = 0.020
7950 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.026	H-atom parameters constrained
wR(F²) = 0.067	Δρ_max = 0.18 e Å⁻³
S = 1.08	Δρ_min = −0.15 e Å⁻³
2873 reflections	Absolute structure: Flack (1983), 1220 Friedel pairs
175 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.

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

	x	y	z	U_iso*/U_eq
C1	0.56871 (11)	0.77249 (11)	0.88143 (15)	0.0219 (3)
C2	0.65815 (12)	0.75439 (12)	0.96546 (15)	0.0236 (3)
C3	0.74485 (12)	0.83700 (14)	0.96021 (18)	0.0282 (3)
H3	0.8075	0.8264	1.0161	0.034*
C4	0.73884 (12)	0.93401 (13)	0.87333 (17)	0.0296 (3)
H4	0.7984	0.9893	0.8700	0.035*
C5	0.64873 (13)	0.95357 (13)	0.79062 (17)	0.0279 (3)
H5	0.6460	1.0215	0.7322	0.033*
C6	0.56210 (12)	0.87112 (12)	0.79505 (15)	0.0244 (3)
C7	0.74036 (16)	0.64203 (15)	1.1436 (2)	0.0417 (4)
H7A	0.8086	0.6213	1.0966	0.063*
H7B	0.7216	0.5776	1.2073	0.063*
H7C	0.7503	0.7179	1.1930	0.063*
C8	0.45668 (14)	0.97946 (14)	0.6331 (2)	0.0388 (4)
H8A	0.4621	1.0539	0.6861	0.058*
H8B	0.3848	0.9761	0.5887	0.058*
H8C	0.5148	0.9782	0.5646	0.058*
C9	0.39202 (11)	0.70979 (11)	0.94053 (14)	0.0213 (3)
C10	0.12256 (13)	0.65157 (14)	1.0324 (2)	0.0334 (3)
H10A	0.0972	0.6804	1.1217	0.040*
H10B	0.1216	0.5622	1.0341	0.040*
C11	0.05905 (16)	0.59888 (17)	0.77160 (19)	0.0451 (4)
H11A	0.1360	0.6080	0.7445	0.068*
H11B	0.0113	0.6157	0.6941	0.068*
H11C	0.0464	0.5162	0.8031	0.068*
N1	0.30621 (9)	0.63680 (9)	0.92891 (14)	0.0250 (3)
N2	0.23531 (10)	0.69247 (10)	1.01082 (14)	0.0266 (3)
N3	0.27358 (11)	0.79161 (11)	1.06706 (16)	0.0328 (3)
N4	0.37580 (11)	0.80385 (11)	1.02308 (15)	0.0298 (3)
O1	0.65369 (8)	0.65558 (9)	1.04724 (12)	0.0297 (2)
O2	0.46880 (9)	0.87735 (9)	0.72061 (12)	0.0316 (3)
O3	0.48597 (8)	0.68410 (8)	0.87649 (10)	0.0231 (2)
S1	0.02856 (3)	0.70315 (4)	0.90562 (6)	0.04717 (14)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0180 (6)	0.0215 (6)	0.0261 (8)	−0.0025 (5)	0.0015 (6)	−0.0033 (5)
C2	0.0226 (7)	0.0245 (6)	0.0237 (8)	0.0029 (5)	0.0009 (6)	−0.0048 (5)
C3	0.0182 (7)	0.0354 (7)	0.0310 (9)	−0.0003 (5)	−0.0019 (6)	−0.0091 (6)
C4	0.0239 (7)	0.0294 (7)	0.0354 (9)	−0.0069 (5)	0.0059 (6)	−0.0086 (6)
C5	0.0292 (7)	0.0237 (6)	0.0308 (8)	−0.0041 (5)	0.0051 (6)	−0.0009 (6)
C6	0.0239 (7)	0.0249 (6)	0.0243 (8)	0.0007 (5)	0.0008 (6)	−0.0018 (5)
C7	0.0426 (10)	0.0425 (8)	0.0400 (10)	0.0014 (8)	−0.0177 (9)	0.0046 (8)
C8	0.0417 (9)	0.0323 (8)	0.0425 (10)	−0.0001 (7)	−0.0069 (9)	0.0140 (7)
C9	0.0203 (6)	0.0197 (5)	0.0238 (8)	0.0018 (5)	−0.0028 (6)	0.0026 (5)
C10	0.0221 (7)	0.0346 (7)	0.0436 (9)	−0.0046 (6)	0.0078 (7)	−0.0024 (7)
C11	0.0453 (11)	0.0475 (10)	0.0423 (11)	−0.0133 (8)	−0.0079 (9)	0.0117 (8)
N1	0.0201 (5)	0.0251 (5)	0.0298 (7)	−0.0018 (4)	0.0008 (5)	−0.0012 (5)
N2	0.0209 (6)	0.0257 (6)	0.0332 (8)	−0.0011 (5)	0.0028 (5)	−0.0010 (5)
N3	0.0267 (6)	0.0288 (6)	0.0430 (9)	−0.0028 (5)	0.0053 (6)	−0.0072 (5)
N4	0.0244 (6)	0.0267 (6)	0.0382 (8)	−0.0030 (5)	0.0022 (6)	−0.0059 (5)
O1	0.0279 (6)	0.0299 (5)	0.0312 (6)	0.0007 (4)	−0.0075 (5)	0.0025 (4)
O2	0.0296 (6)	0.0292 (5)	0.0361 (7)	−0.0045 (4)	−0.0102 (5)	0.0098 (4)
O3	0.0187 (5)	0.0204 (4)	0.0302 (6)	−0.0028 (3)	−0.0003 (4)	−0.0023 (4)
S1	0.02395 (18)	0.0424 (2)	0.0752 (4)	0.00636 (16)	−0.0048 (2)	0.0022 (2)

Geometric parameters (Å, º) top

C1—O3	1.4062 (15)	C7—H7B	0.9800
C9—O3	1.3388 (17)	C7—H7C	0.9800
N2—C10	1.4618 (19)	C8—O2	1.4330 (18)
S1—C10	1.792 (2)	C8—H8A	0.9800
C6—O2	1.3562 (18)	C8—H8B	0.9800
C2—O1	1.3630 (17)	C8—H8C	0.9800
C1—C2	1.385 (2)	C9—N1	1.3265 (17)
C1—C6	1.390 (2)	C9—N4	1.3393 (18)
C2—C3	1.399 (2)	C10—H10A	0.9900
C3—C4	1.379 (2)	C10—H10B	0.9900
C3—H3	0.9500	C11—S1	1.798 (2)
C4—C5	1.386 (2)	C11—H11A	0.9800
C4—H4	0.9500	C11—H11B	0.9800
C5—C6	1.3964 (19)	C11—H11C	0.9800
C5—H5	0.9500	N1—N2	1.3357 (17)
C7—O1	1.431 (2)	N2—N3	1.3169 (17)
C7—H7A	0.9800	N3—N4	1.3260 (18)

C9—O3—C1	116.61 (10)	O2—C8—H8B	109.5
N2—C10—S1	113.52 (12)	H8A—C8—H8B	109.5
C10—S1—C11	100.37 (9)	O2—C8—H8C	109.5
C2—C1—C6	121.93 (12)	H8A—C8—H8C	109.5
C2—C1—O3	118.92 (12)	H8B—C8—H8C	109.5
C6—C1—O3	118.99 (12)	N1—C9—O3	120.17 (11)
O1—C2—C1	116.22 (12)	N1—C9—N4	114.28 (12)
O1—C2—C3	125.32 (13)	O3—C9—N4	125.50 (12)
C1—C2—C3	118.47 (13)	N2—C10—H10A	108.9
C4—C3—C2	119.57 (14)	S1—C10—H10A	108.9
C4—C3—H3	120.2	N2—C10—H10B	108.9
C2—C3—H3	120.2	S1—C10—H10B	108.9
C3—C4—C5	122.18 (13)	H10A—C10—H10B	107.7
C3—C4—H4	118.9	S1—C11—H11A	109.5
C5—C4—H4	118.9	S1—C11—H11B	109.5
C4—C5—C6	118.51 (14)	H11A—C11—H11B	109.5
C4—C5—H5	120.7	S1—C11—H11C	109.5
C6—C5—H5	120.7	H11A—C11—H11C	109.5
O2—C6—C1	115.02 (12)	H11B—C11—H11C	109.5
O2—C6—C5	125.64 (13)	C9—N1—N2	100.09 (11)
C1—C6—C5	119.33 (14)	N3—N2—N1	114.41 (12)
O1—C7—H7A	109.5	N3—N2—C10	121.96 (13)
O1—C7—H7B	109.5	N1—N2—C10	123.56 (12)
H7A—C7—H7B	109.5	N2—N3—N4	106.18 (12)
O1—C7—H7C	109.5	N3—N4—C9	105.04 (12)
H7A—C7—H7C	109.5	C2—O1—C7	116.81 (12)
H7B—C7—H7C	109.5	C6—O2—C8	117.09 (12)
O2—C8—H8A	109.5

C6—C1—O3—C9	−79.52 (17)	N4—C9—N1—N2	−0.13 (16)
N4—C9—O3—C1	−9.6 (2)	C9—N1—N2—N3	0.54 (16)
C6—C1—C2—O1	178.73 (13)	C9—N1—N2—C10	177.63 (14)
O3—C1—C2—O1	−5.86 (18)	S1—C10—N2—N3	93.31 (17)
C6—C1—C2—C3	−1.4 (2)	S1—C10—N2—N1	−83.56 (15)
O3—C1—C2—C3	174.02 (13)	N1—N2—N3—N4	−0.76 (18)
O1—C2—C3—C4	−179.56 (14)	C10—N2—N3—N4	−177.90 (15)
C1—C2—C3—C4	0.6 (2)	N2—N3—N4—C9	0.60 (17)
C2—C3—C4—C5	0.5 (2)	N1—C9—N4—N3	−0.31 (17)
C3—C4—C5—C6	−0.7 (2)	O3—C9—N4—N3	−177.81 (14)
C2—C1—C6—O2	−179.07 (13)	C1—C2—O1—C7	−174.19 (14)
O3—C1—C6—O2	5.51 (18)	C3—C2—O1—C7	5.9 (2)
C2—C1—C6—C5	1.2 (2)	C1—C6—O2—C8	178.13 (14)
O3—C1—C6—C5	−174.26 (13)	C5—C6—O2—C8	−2.1 (2)
C4—C5—C6—O2	−179.84 (14)	N1—C9—O3—C1	173.03 (12)
C4—C5—C6—C1	−0.1 (2)	C2—C1—O3—C9	104.93 (14)
O3—C9—N1—N2	177.52 (12)	N2—C10—S1—C11	78.85 (13)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C10—H10B···O1ⁱ	0.99	2.45	3.4277 (19)	170
C11—H11C···O3ⁱ	0.98	2.45	3.421 (2)	172
C11—H11B···O1ⁱⁱ	0.98	2.52	3.471 (2)	163
C10—H10A···O2ⁱⁱⁱ	0.99	2.52	3.312 (2)	137

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

Experimental details

Crystal data
Chemical formula	C₁₁H₁₄N₄O₃S
M_r	282.32
Crystal system, space group	Orthorhombic, Pca2₁
Temperature (K)	173
a, b, c (Å)	12.1795 (5), 11.0809 (4), 9.9026 (4)
V (Å³)	1336.45 (9)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.25
Crystal size (mm)	0.50 × 0.25 × 0.10

Data collection
Diffractometer	Bruker X8 APEXII diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2008)
T_min, T_max	0.871, 0.975
No. of measured, independent and observed [I > 2σ(I)] reflections	7950, 2873, 2670
R_int	0.020
(sin θ/λ)_max (Å⁻¹)	0.661

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.026, 0.067, 1.08
No. of reflections	2873
No. of parameters	175
No. of restraints	1
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.18, −0.15
Absolute structure	Flack (1983), 1220 Friedel pairs
Absolute structure parameter	0.06 (6)

Computer programs: APEX2 (Bruker, 2008), SAINT (Bruker, 2008), SIR (Altomare et al., 1999), SHELXTL (Sheldrick, 2008), ORTEP-3 (Farrugia, 1997).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C10—H10B···O1ⁱ	0.99	2.448	3.4277 (19)	169.92
C11—H11C···O3ⁱ	0.98	2.449	3.421 (2)	171.53
C11—H11B···O1ⁱⁱ	0.98	2.520	3.471 (2)	163.31
C10—H10A···O2ⁱⁱⁱ	0.99	2.524	3.312 (2)	136.50

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

Acknowledgements

The authors thank the Urmia University Research Council for supporting this work. We also gratefully acknowledge the Structural Chemistry Facility of the University of British Columbia.

References

Altomare, A., Burla, M. C., Camalli, M., Cascarano, G. L., Giacovazzo, C., Guagliardi, A., Moliterni, A. G. G., Polidori, G. & Spagna, R. (1999). J. Appl. Cryst. 32, 115–119. Web of Science CrossRef CAS IUCr Journals Google Scholar
Bruker (2008). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Dabbagh, H. A., Noroozi Pesyan, N., Bagheri, A., Takemoto, S. & Hayashi, H. (2005). Russ. J. Org. Chem. 41, 1055–1063. Web of Science CrossRef CAS Google Scholar
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. CrossRef IUCr Journals Google Scholar
Flack, H. D. (1983). Acta Cryst. A39, 876–881. CrossRef CAS Web of Science IUCr Journals Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar