(8-Hy­droxy-6-meth­oxy-1-oxo-1H-isochromen-3-yl)methyl formate: a supra­molecular framework

Tiouabi, M.; Tabacchi, R.; Stoeckli-Evans, H.

doi:10.1107/S2414314620013917

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 5| Part 10| October 2020| x201391

https://doi.org/10.1107/S2414314620013917

Open

access

(8-Hydroxy-6-methoxy-1-oxo-1H-isochromen-3-yl)methyl formate: a supramolecular framework

Mustapha Tiouabi,^a Raphaël Tabacchi ^a and Helen Stoeckli-Evans ^b ^*

^aInstitute of Chemistry, University of Neuchâtel, Av. de Bellevax 51, CH-2000 Neuchâtel, Switzerland, and ^bInstitute of Physics, University of Neuchâtel, rue Emile-Argand 11, CH-2000 Neuchâtel, Switzerland
^*Correspondence e-mail: helen.stoeckli-evans@unine.ch

Edited by S. Bernès, Benemérita Universidad Autónoma de Puebla, México (Received 7 October 2020; accepted 19 October 2020; online 23 October 2020)

In the title compound, C₁₂H₁₀O₆, an intramolecular O—H⋯O hydrogen bond forms an S(6) ring motif. The molecule is essentially planar with an r.m.s. deviation of 0.051 Å for all non-H atoms. In the crystal molecules are linked by C—H⋯O hydrogen bonds and a C—H⋯π interaction, forming a supramolecular framework.

Keywords: crystal structure; isocoumarin; cytogenin; hydrogen bonding; C—H⋯π interaction; supramolecular framework.

CCDC reference: 2039333

Structure description

The title compound, I, is an intermediate in the synthesis of cytogenin, a naturally occurring isocoumarin that was first isolated from a cultured broth of Streptoverticillium eurocidicum (Kumagai et al., 1990 , 1995 ). It was shown by these authors to have both antibiotic properties and antitumor activity. The first synthesis of cytogenin was reported in 2004 (Saeed, 2004 ). More recently, a new synthetic route to cytogenin and similar isocoumarins has been reported (Gadakh & Sudalai, 2014 ).

As shown in Fig. 1, compound I was prepared via two pathways (see Synthesis and crystallization). The details of the syntheses of the precursors A and B and cytogenin have been described elsewhere (Tiouabi, 2005 ).

Figure 1
The reaction pathways for the synthesis of compound I and cytogenin (Tiouabi, 2005

The molecule of I (Fig. 2), is essentially planar with an r.m.s. deviation of 0.051 Å for all non-H atoms (O1–O6/C1/C3–C13); the maximum deviations from this mean plane are 0.080 (6) Å for atom C12 and −0.091 (8) Å for atom C13. There is an intramolecular O—H⋯O hydrogen bond present, forming an S(6) ring motif (Fig. 2 and Table 1).

Table 1
Hydrogen-bond geometry (Å, °)

Cg is the centroid of the C5–C10 ring.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O4—H40⋯O1	0.84	1.88	2.616 (5)	146
C4—H4⋯O1ⁱ	0.95	2.38	3.326 (6)	173
C5—H5⋯O2ⁱ	0.95	2.59	3.541 (6)	176
C7—H7⋯O6ⁱⁱ	0.95	2.55	3.499 (5)	175
C11—H11C⋯O6ⁱ	0.98	2.57	3.388 (8)	141
C12—H12B⋯Cgⁱⁱⁱ	0.99	2.88	3.788 (6)	153
Symmetry codes: (i) $[-x+{\script{3\over 2}}, y-1, z+{\script{1\over 2}}]$ ; (ii) $[x-{\script{1\over 2}}, -y+1, z]$ ; (iii) $[-x+{\script{3\over 2}}, y, z-{\script{1\over 2}}]$ .

Figure 2
A view of the molecular structure of compound I, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The intramolecular O—H⋯O hydrogen bond (see Table 1

) is shown as a dashed line.

In the crystal, molecules are linked by a series of C—H⋯O hydrogen bonds (Table 1), forming interconnected ribbons running normal to each other in planes (012) and (01 $[\overline{2}]$ ): see Fig. 3. These interactions lead to the formation of a supramolecular framework, which is reinforced by a C—H⋯π interaction (Fig. 4 and Table 1).

Figure 3
A partial view of the crystal packing of compound I, viewed normal to plane (011). Hydrogen bonds (see Table 1

) are shown as dashed lines.

Figure 4
A view along the a axis of the crystal packing of compound I. Hydrogen bonds and C—H⋯π interactions (see Table 1

) are shown as dashed lines.

Synthesis and crystallization

The syntheses of the title compound, I, and cytogenin, are illustrated in Fig. 1. The syntheses of the precursors, 3-(bromomethyl)-8-hydroxy-6-methoxy-1H-isochromen-1-one (A), 3-(bromomethyl)-6-methoxy-1-oxo-1H-isochromen-8-yl acetate (B), and cytogenin, are described in the PhD thesis of Tiouabi (2005), which can be downloaded from the website https://doc.rero.ch/record, a digital library where many theses of Swiss universities are deposited. The numbering scheme of I in Fig. 1 is with reference to the NMR spectra.

Method 1: The hydroxybromoisocoumarin A (0.14 g, 0.49 mmol) was dissolved with stirring in 5 ml of anhydrous DMF in a 50 ml flask equipped with a magnetic stirrer and under an atmosphere of argon. HCO₂Na (0.167 g, 2.46 mmol) was added and the mixture was stirred overnight at room temperature. The evolution of the reaction was monitored by thin-layer chromatography, using dimethylchloride as eluent. On completion of the reaction, the mixture was diluted with ethyl acetate and then washed with an aqueous saturated solution of NaCl. The organic phase was dried using anhydrous Na₂SO₄, then filtered and concentrated using a rotary evaporator, yielding compound I in the form of a white solid (yield 0.118 g, 96%).

Method 2: The acetoxybromoisocoumarin B (34.2 mg, 0.104 mmol) was dissolved with stirring in 3 ml of anhydrous DMF in a 50 ml flask equipped with a magnetic stirrer and under an atmosphere of argon. HCO₂Na (47 mg, 0.69 mmol) was added, the temperature was raised to 80°C and the mixture stirred for 4 h. The evolution of the reaction was monitored by thin-layer chromatography, using dimethylchloride as eluent. On completion of the reaction, the mixture was diluted with ethyl acetate and then washed with an aqueous saturated solution of NaCl. The organic phase was dried using anhydrous Na₂SO₄, then purified by column chromatography (silica, eluent CH₂Cl₂/hexane 10/1). Compound I was obtained in the form of a white solid (yield 18.7 mg, 72%).

Analytical data for I: R_f (CH₂Cl₂, UV) 0.44. ¹H NMR (400 MHz, CDCl₃, 298 K): 3.90 (s, 3H, OCH₃), 4.99 (s, 2H, CH2–3a), 6.42 (d, J_m = 2.3 Hz, 1H, ArH-7), 6.53 (s, 1H, H-4), 6.55 (d, J_m = 2.3 Hz, 1H, ArH-5), 8.17 (s, 1H, CHO-3 b), 11.0 (s, 1H, OH-8). ¹³C NMR (100 Hz, CDCl₃, 298 K, HETCOR-SR/LR): 56.19 C(OCH₃), 61.61 C(3a), 100.67 C(9), 101.80 C(5), 103.13 C(7), 107.82 C(4), 138.21 C(10), 150.27 C(3), 160.37 C(3 b), 164.23 C(1), 165.75 C(8), 167.35 C(6). HR–MS [ESI(+)]: ms 273.03634 [M + Na]⁺. IR (KBr disk, cm⁻¹): 3129 br, 1728 s, 1690 vs, 1622 m, 1400 vs, 1164 vs, 1064 w.

Colourless block-like crystals of I were obtained by slow evaporation of a solution in chloroform.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. Intensity data were measured using a Stoe IPDS I, a one-circle diffractometer. The alert diffrn_reflns_laue_measured_fraction_full value (0.947) below minimum (0.95) is given. This involves 29 random reflections out of the expected 1034 for the IUCr cut-off limit of (sin θ)/λ = 0.6 Å⁻¹; viz. 2.8%.

Table 2
Experimental details

Crystal data
Chemical formula	C₁₂H₁₀O₆
M_r	250.20
Crystal system, space group	Orthorhombic, Pca2₁
Temperature (K)	173
a, b, c (Å)	25.006 (2), 5.0337 (6), 8.5646 (6)
V (Å³)	1078.05 (17)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.13
Crystal size (mm)	0.50 × 0.50 × 0.50

Data collection
Diffractometer	STOE IPDS 1
Absorption correction	Multi-scan (MULABS; Spek, 2020 )
T_min, T_max	0.763, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	7630, 2012, 1249
R_int	0.070
(sin θ/λ)_max (Å⁻¹)	0.619

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.050, 0.135, 0.91
No. of reflections	2012
No. of parameters	166
No. of restraints	1
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.32, −0.27
Computer programs: EXPOSE, CELL and INTEGRATE in IPDS-I (Stoe & Cie, 2004 ), SHELXS97 (Sheldrick, 2008 ), Mercury (Macrae et al., 2020 ), SHELXL2018/3 (Sheldrick, 2015 ), PLATON (Spek, 2020) and publCIF (Westrip, 2010 ).

Structural data

CCDC reference: 2039333

Crystal structure: contains datablocks I, Global. DOI: https://doi.org/10.1107/S2414314620013917/bh4057sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314620013917/bh4057Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2414314620013917/bh4057Isup3.cml

checkCIF report

Computing details top

Data collection: EXPOSE in IPDS-I (Stoe & Cie, 2004); cell refinement: CELL in IPDS-I (Stoe & Cie, 2004); data reduction: INTEGRATE in IPDS-I (Stoe & Cie, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015); molecular graphics: Mercury (Macrae et al., 2020); software used to prepare material for publication: SHELXL2018/3 (Sheldrick, 2015), PLATON (Spek, 2020) and publCIF (Westrip, 2010).

(8-Hydroxy-6-methoxy-1-oxo-1H-isochromen-3-yl)methyl formate top

Crystal data top

C₁₂H₁₀O₆	D_x = 1.542 Mg m⁻³
M_r = 250.20	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pca2₁	Cell parameters from 3909 reflections
a = 25.006 (2) Å	θ = 2.2–25.8°
b = 5.0337 (6) Å	µ = 0.13 mm⁻¹
c = 8.5646 (6) Å	T = 173 K
V = 1078.05 (17) Å³	Block, colorless
Z = 4	0.50 × 0.50 × 0.50 mm
F(000) = 520

Data collection top

STOE IPDS 1 diffractometer	2012 independent reflections
Radiation source: fine-focus sealed tube	1249 reflections with I > 2σ(I)
Plane graphite monochromator	R_int = 0.070
φ rotation scans	θ_max = 26.1°, θ_min = 2.9°
Absorption correction: multi-scan (MULABS; Spek, 2020)	h = −30→30
T_min = 0.763, T_max = 1.000	k = −6→6
7630 measured 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)] = 0.050	H-atom parameters constrained
wR(F²) = 0.135	w = 1/[σ²(F_o²) + (0.0852P)²] where P = (F_o² + 2F_c²)/3
S = 0.91	(Δ/σ)_max < 0.001
2012 reflections	Δρ_max = 0.32 e Å⁻³
166 parameters	Δρ_min = −0.27 e Å⁻³
1 restraint	Extinction correction: (SHELXL-2018/3; Sheldrick, 2015), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.061 (11)

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.

Refinement. Flack x = 0.223 (999) by classical fit to all intensities 1.664 (999) from 481 selected quotients (Parsons' method)

** Absolute structure cannot be determined reliably **

The hydroxyl H atom and the C-bound H atoms were included in calculated positions and treated as riding on their parent O or C atoms.

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

	x	y	z	U_iso*/U_eq
O1	0.68528 (13)	0.9547 (7)	−0.0918 (5)	0.0500 (9)
O2	0.75876 (11)	0.7819 (6)	0.0089 (4)	0.0461 (9)
O3	0.58898 (11)	0.0468 (7)	0.3437 (5)	0.0511 (10)
O4	0.59095 (13)	0.7730 (7)	−0.0142 (5)	0.0531 (10)
H40	0.613134	0.862673	−0.065697	0.080*
O5	0.86682 (12)	0.4224 (8)	0.1774 (5)	0.0657 (12)
O6	0.94909 (14)	0.5664 (9)	0.1136 (6)	0.0732 (13)
C1	0.70366 (17)	0.7848 (9)	−0.0037 (6)	0.0433 (11)
C3	0.78373 (18)	0.5948 (9)	0.1006 (7)	0.0428 (12)
C4	0.75774 (17)	0.4136 (9)	0.1838 (6)	0.0443 (12)
H4	0.776871	0.288244	0.245052	0.053*
C5	0.67032 (17)	0.2286 (9)	0.2657 (6)	0.0438 (11)
H5	0.687823	0.104223	0.331620	0.053*
C6	0.61467 (17)	0.2302 (9)	0.2549 (7)	0.0434 (12)
C7	0.58804 (17)	0.4147 (10)	0.1602 (7)	0.0455 (12)
H7	0.550100	0.414965	0.154550	0.055*
C8	0.61731 (18)	0.5950 (9)	0.0759 (6)	0.0437 (13)
C9	0.67425 (17)	0.5970 (9)	0.0848 (7)	0.0399 (11)
C10	0.69987 (16)	0.4093 (9)	0.1799 (7)	0.0411 (11)
C11	0.53177 (17)	0.0277 (11)	0.3310 (8)	0.0614 (15)
H11C	0.518847	−0.116607	0.397911	0.092*
H11B	0.521957	−0.008880	0.222346	0.092*
H11A	0.515514	0.195648	0.364158	0.092*
C12	0.84306 (18)	0.6344 (10)	0.0911 (7)	0.0493 (13)
H12B	0.855082	0.629778	−0.019002	0.059*
H12A	0.853189	0.807981	0.136752	0.059*
C13	0.92037 (19)	0.4136 (14)	0.1770 (10)	0.0726 (19)
H13	0.936777	0.272176	0.232693	0.087*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0486 (18)	0.0487 (18)	0.053 (2)	0.0019 (15)	−0.0012 (16)	0.0089 (19)
O2	0.0381 (16)	0.0448 (17)	0.055 (2)	−0.0039 (13)	−0.0010 (15)	0.0043 (17)
O3	0.0330 (15)	0.0564 (19)	0.064 (3)	−0.0051 (14)	0.0021 (16)	0.0138 (19)
O4	0.0425 (17)	0.055 (2)	0.062 (3)	0.0046 (16)	−0.0054 (17)	0.0109 (19)
O5	0.0318 (16)	0.076 (2)	0.089 (3)	−0.0021 (17)	−0.002 (2)	0.026 (2)
O6	0.040 (2)	0.099 (3)	0.080 (3)	−0.012 (2)	0.0013 (19)	0.016 (3)
C1	0.036 (2)	0.046 (3)	0.048 (3)	0.0014 (19)	0.001 (2)	−0.001 (2)
C3	0.035 (2)	0.045 (2)	0.048 (3)	0.003 (2)	−0.002 (2)	−0.002 (2)
C4	0.038 (2)	0.044 (2)	0.051 (3)	0.0004 (19)	−0.004 (2)	−0.002 (2)
C5	0.034 (2)	0.044 (2)	0.053 (3)	−0.001 (2)	−0.004 (2)	0.002 (2)
C6	0.038 (2)	0.039 (2)	0.053 (3)	−0.0005 (19)	0.002 (2)	0.001 (2)
C7	0.035 (2)	0.048 (2)	0.053 (4)	−0.003 (2)	−0.003 (2)	−0.002 (2)
C8	0.036 (2)	0.044 (3)	0.052 (4)	0.003 (2)	−0.002 (2)	0.001 (2)
C9	0.033 (2)	0.038 (2)	0.049 (3)	0.0002 (19)	−0.001 (2)	0.001 (2)
C10	0.035 (2)	0.041 (2)	0.048 (3)	0.0008 (18)	0.000 (2)	−0.001 (2)
C11	0.031 (2)	0.073 (3)	0.080 (4)	−0.011 (2)	−0.001 (3)	0.013 (3)
C12	0.036 (2)	0.055 (3)	0.057 (4)	0.000 (2)	−0.002 (2)	0.005 (3)
C13	0.031 (3)	0.088 (4)	0.098 (6)	0.000 (3)	−0.003 (3)	0.021 (4)

Geometric parameters (Å, º) top

O1—C1	1.230 (6)	C5—C10	1.383 (7)
O2—C3	1.376 (6)	C5—C6	1.395 (6)
O2—C1	1.382 (5)	C5—H5	0.9500
O3—C6	1.358 (6)	C6—C7	1.401 (7)
O3—C11	1.438 (5)	C7—C8	1.371 (7)
O4—C8	1.354 (6)	C7—H7	0.9500
O4—H40	0.8400	C8—C9	1.426 (6)
O5—C13	1.340 (6)	C9—C10	1.402 (7)
O5—C12	1.428 (6)	C11—H11C	0.9800
O6—C13	1.184 (7)	C11—H11B	0.9800
C1—C9	1.417 (7)	C11—H11A	0.9800
C3—C4	1.327 (7)	C12—H12B	0.9900
C3—C12	1.499 (6)	C12—H12A	0.9900
C4—C10	1.447 (6)	C13—H13	0.9500
C4—H4	0.9500

C3—O2—C1	120.3 (4)	O4—C8—C9	120.8 (4)
C6—O3—C11	118.3 (4)	C7—C8—C9	120.6 (4)
C8—O4—H40	109.5	C10—C9—C1	121.5 (4)
C13—O5—C12	116.1 (4)	C10—C9—C8	118.8 (4)
O1—C1—O2	115.3 (4)	C1—C9—C8	119.6 (4)
O1—C1—C9	126.7 (4)	C5—C10—C9	120.5 (4)
O2—C1—C9	117.9 (4)	C5—C10—C4	122.1 (4)
C4—C3—O2	123.7 (4)	C9—C10—C4	117.4 (4)
C4—C3—C12	127.2 (5)	O3—C11—H11C	109.5
O2—C3—C12	109.1 (4)	O3—C11—H11B	109.5
C3—C4—C10	119.2 (5)	H11C—C11—H11B	109.5
C3—C4—H4	120.4	O3—C11—H11A	109.5
C10—C4—H4	120.4	H11C—C11—H11A	109.5
C10—C5—C6	119.6 (5)	H11B—C11—H11A	109.5
C10—C5—H5	120.2	O5—C12—C3	106.5 (4)
C6—C5—H5	120.2	O5—C12—H12B	110.4
O3—C6—C5	115.5 (4)	C3—C12—H12B	110.4
O3—C6—C7	123.4 (4)	O5—C12—H12A	110.4
C5—C6—C7	121.1 (4)	C3—C12—H12A	110.4
C8—C7—C6	119.3 (4)	H12B—C12—H12A	108.6
C8—C7—H7	120.3	O6—C13—O5	125.8 (6)
C6—C7—H7	120.3	O6—C13—H13	117.1
O4—C8—C7	118.6 (4)	O5—C13—H13	117.1

C3—O2—C1—O1	−178.0 (4)	O2—C1—C9—C8	179.5 (4)
C3—O2—C1—C9	2.3 (6)	O4—C8—C9—C10	179.9 (5)
C1—O2—C3—C4	−1.6 (7)	C7—C8—C9—C10	0.8 (8)
C1—O2—C3—C12	179.1 (4)	O4—C8—C9—C1	−1.0 (8)
O2—C3—C4—C10	−0.2 (8)	C7—C8—C9—C1	179.9 (5)
C12—C3—C4—C10	179.0 (5)	C6—C5—C10—C9	1.3 (8)
C11—O3—C6—C5	−176.5 (5)	C6—C5—C10—C4	−178.7 (5)
C11—O3—C6—C7	4.8 (8)	C1—C9—C10—C5	179.7 (5)
C10—C5—C6—O3	−179.7 (5)	C8—C9—C10—C5	−1.2 (8)
C10—C5—C6—C7	−1.0 (8)	C1—C9—C10—C4	−0.3 (8)
O3—C6—C7—C8	179.2 (5)	C8—C9—C10—C4	178.8 (5)
C5—C6—C7—C8	0.6 (8)	C3—C4—C10—C5	−178.9 (5)
C6—C7—C8—O4	−179.6 (5)	C3—C4—C10—C9	1.1 (8)
C6—C7—C8—C9	−0.5 (8)	C13—O5—C12—C3	176.8 (5)
O1—C1—C9—C10	179.0 (5)	C4—C3—C12—O5	5.5 (8)
O2—C1—C9—C10	−1.4 (7)	O2—C3—C12—O5	−175.2 (4)
O1—C1—C9—C8	−0.1 (8)	C12—O5—C13—O6	0.9 (12)

Hydrogen-bond geometry (Å, º) top

Cg is the centroid of the C5–C10 ring.

D—H···A	D—H	H···A	D···A	D—H···A
O4—H40···O1	0.84	1.88	2.616 (5)	146
C4—H4···O1ⁱ	0.95	2.38	3.326 (6)	173
C5—H5···O2ⁱ	0.95	2.59	3.541 (6)	176
C7—H7···O6ⁱⁱ	0.95	2.55	3.499 (5)	175
C11—H11C···O6ⁱ	0.98	2.57	3.388 (8)	141
C12—H12B···Cgⁱⁱⁱ	0.99	2.88	3.788 (6)	153

Symmetry codes: (i) −x+3/2, y−1, z+1/2; (ii) x−1/2, −y+1, z; (iii) −x+3/2, y, z−1/2.

Acknowledgements

RT and HSE are grateful to the Swiss National Science Foundation and the University of Neuchâtel for their support over the years.

References

Gadakh, S. K. & Sudalai, A. (2014). RSC Adv. 4, 57658–57661. CrossRef CAS Google Scholar
Kumagai, H., Masuda, T., Ishizuka, M. & Takeuchi, T. (1995). J. Antibiot. 48, 175–178. CrossRef CAS Google Scholar
Kumagai, H., Masuda, T., Ohsono, M., Hattori, S., Naganawa, H., Sawa, T., Hamada, M., Ishizuka, M. & Takeuchi, T. (1990). J. Antibiot. 43, 1505–1507. CrossRef CAS Google Scholar
Macrae, C. F., Sovago, I., Cottrell, S. J., Galek, P. T. A., McCabe, P., Pidcock, E., Platings, M., Shields, G. P., Stevens, J. S., Towler, M. & Wood, P. A. (2020). J. Appl. Cryst. 53, 226–235. Web of Science CrossRef CAS IUCr Journals Google Scholar
Saeed, A. (2004). J. Heterocycl. Chem. 41, 975–978. CrossRef CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2015). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Spek, A. L. (2020). Acta Cryst. E76, 1–11. Web of Science CrossRef IUCr Journals Google Scholar
Stoe & Cie (2004). IPDS1 Bedienungshandbuch. Stoe & Cie GmbH, Darmstadt, Germany. Google Scholar
Tiouabi, M. (2005). PhD Thesis, University of Neuchâtel, Switzerland. Google Scholar
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. Web of Science CrossRef CAS IUCr Journals Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.