Tris(2-meth­oxy­phen­yl)phosphine selenide

Raymundo, M.; Padgett, C.W.; Lynch, W.E.

doi:10.1107/S2414314617000098

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 2| Part 1| January 2017| x170009

https://doi.org/10.1107/S2414314617000098

Open

access

Tris(2-methoxyphenyl)phosphine selenide

Melina Raymundo,^a Clifford W. Padgett ^a and Will E. Lynch ^a ^*

^aDepartment of Chemistry and Physics, Armstrong State University, Savannah, GA, 31419, USA
^*Correspondence e-mail: will.lynch@armstrong.edu

Edited by S. Parkin, University of Kentucky, USA (Received 30 December 2016; accepted 3 January 2017; online 10 January 2017)

The title compound C₂₁H₂₁O₃PSe, is comprised of a P atom in a distorted tetrahedral environment, attached to the selenium atom and three carbons from the phenyl rings. The phosphorus–selenium bond length is 2.1194 (11) Å. All three methoxy groups are nearly co-planar with their respective phenyl rings, with the angles between the phenyl ring and the C—O bond of the methoxy groups being 6.2 (2), 3.1 (2), and 5.7 (2)°. The torsion angles of the phenyl rings relative to the P=Se bond are 55.84 (19), 176.18 (16), and 63.9 (2)°. No strong interactions were observed, but in addition to van der Waals forces, there are close contacts between C—H⋯π and C—H⋯Se.

Keywords: crystal structure; tris(2-methoxyphenyl)phosphine selenide.

CCDC reference: 1525481

Structure description

The title compound (Fig. 1) is composed of a distorted tetrahedral phosphorus atom attached to the selenium atom and three carbons from three different phenyl rings. The P=Se bond distance is 2.1194 (11) Å. This distance is similar to those reported previously for the phenyl (Codding & Kerr, 1979 ), p-fluorophenyl (Muller & Meijboom, 2007 ), p-tolyl (Muller, 2011 ), and o-tolyl (Cameron & Dahlèn, 1975 ) derivatives (all 2.10–2.12 Å). The average P—C bond distance is 1.820 (3) Å with an average C—P—C bond angle of 106.29 (11)°. The average Se—P—C bond angle is determined to be 112.48 (9)°. The torsion angles of the phenyl rings relative to the P=Se bond are 55.84 (19)° for Se1—P1—C1—C2, 176.18 (16)° for Se1—P1—C8—C9, and 63.9 (2)° for Se1—P1—C15—C16. The compound presents extremely weak C—H⋯Se and C—H⋯π intermolecular interactions and displays an intramolecular C13—H13⋯Se1 close contact (Table 1). The crystal packing is illustrated in Fig. 2.

Table 1
Hydrogen-bond geometry (Å, °)

Cg1 is the centroid of the C1–C6 ring.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C13—H13⋯Se1	0.95	2.77	3.356 (3)	120
C19—H19⋯Se1ⁱ	0.95	2.94	3.761 (3)	145
C7—H7B⋯Cg1ⁱⁱ	0.98	2.76	3.602 (4)	144
C10—H10⋯Cg1ⁱⁱⁱ	0.95	2.83	3.658 (3)	146
Symmetry codes: (i) $[x-{\script{1\over 2}}, -y+{\script{3\over 2}}, z+{\script{1\over 2}}]$ ; (ii) -x, -y+1, -z; (iii) x, y, z+1.

Figure 1
A view of the molecular structure of the title compound, showing the atom labeling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
Crystal packing diagram of the title compound, viewed along the a axis. All H atoms have been omitted for clarity.

Synthesis and crystallization

The title compound was synthesized by dissolving 0.25 g (0.71 mmol) of tris-2-methoxyphenylphosphine in 20 mL of methanol and this solution was brought to a boil. To this solution was added an equimolar amount of selenium (0.056 g, 0.71 mmol) in one portion. The solution was heated at reflux for 15 minutes. The solution was filtered hot to remove any unreacted selenium metal. Colorless crystals were then grown by slow evaporation of the solvent at room temperature. Yields were between 70–75% based on the phosphine starting material. This is an adaptation of a literature preparation by Dakternieks et al. (1994 ) and is similar to that described by Raymundo, et al. (2016 ).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2.

Table 2
Experimental details

Crystal data
Chemical formula	C₂₁H₂₁O₃PSe
M_r	431.31
Crystal system, space group	Monoclinic, P2₁/n
Temperature (K)	173
a, b, c (Å)	8.351 (4), 27.156 (14), 8.545 (4)
β (°)	99.414 (7)
V (Å³)	1911.7 (16)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	2.07
Crystal size (mm)	0.4 × 0.2 × 0.15

Data collection
Diffractometer	Rigaku XtaLAB mini diffractometer
Absorption correction	Multi-scan (REQAB; Rigaku, 1998 )
T_min, T_max	0.556, 0.734
No. of measured, independent and observed [I > 2σ(I)] reflections	4389, 4389, 3819
R_int	0.043
(sin θ/λ)_max (Å⁻¹)	0.650

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.034, 0.084, 1.09
No. of reflections	4389
No. of parameters	238
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.39, −0.36
Computer programs: CrystalClear SM Expert (Rigaku, 2011 ), SHELXS (Sheldrick, 2008 ), SHELXL (Sheldrick, 2015 ) and OLEX2 (Dolomanov et al., 2009 ).

Structural data

CCDC reference: 1525481

Crystal structure: contains datablocks General, I. DOI: https://doi.org/10.1107/S2414314617000098/pk4010sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314617000098/pk4010Isup2.hkl

checkCIF report

Computing details top

Data collection: CrystalClear SM Expert (Rigaku, 2011); cell refinement: CrystalClear SM Expert (Rigaku, 2011); data reduction: CrystalClear SM Expert (Rigaku, 2011); program(s) used to solve structure: SHELXS (Sheldrick, 2008); program(s) used to refine structure: SHELXL (Sheldrick, 2015); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Tris(2-methoxyphenyl)phosphine selenide top

Crystal data top

C₂₁H₂₁O₃PSe	F(000) = 880
M_r = 431.31	D_x = 1.499 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71075 Å
a = 8.351 (4) Å	Cell parameters from 5181 reflections
b = 27.156 (14) Å	θ = 2.4–27.5°
c = 8.545 (4) Å	µ = 2.07 mm⁻¹
β = 99.414 (7)°	T = 173 K
V = 1911.7 (16) Å³	Prism, colorless
Z = 4	0.4 × 0.2 × 0.15 mm

Data collection top

Rigaku XtaLAB mini diffractometer	3819 reflections with I > 2σ(I)
Detector resolution: 6.827 pixels mm^-1	R_int = 0.043
ω scans	θ_max = 27.5°, θ_min = 2.5°
Absorption correction: multi-scan (REQAB; Rigaku, 1998)	h = −10→10
T_min = 0.556, T_max = 0.734	k = −35→35
4389 measured reflections	l = −11→11
4389 independent reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.034	H-atom parameters constrained
wR(F²) = 0.084	w = 1/[σ²(F_o²) + (0.0251P)² + 1.2505P] where P = (F_o² + 2F_c²)/3
S = 1.09	(Δ/σ)_max = 0.001
4389 reflections	Δρ_max = 0.39 e Å⁻³
238 parameters	Δρ_min = −0.36 e Å⁻³
0 restraints

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

	x	y	z	U_iso*/U_eq
Se1	0.46784 (3)	0.63422 (2)	−0.05815 (3)	0.02628 (8)
P1	0.24136 (7)	0.63436 (2)	0.02326 (7)	0.01802 (12)
O1	0.2527 (2)	0.52932 (6)	−0.0484 (2)	0.0295 (4)
O2	−0.0163 (2)	0.62419 (7)	0.2283 (2)	0.0313 (4)
O3	0.1419 (2)	0.70152 (6)	−0.2456 (2)	0.0328 (4)
C1	0.0819 (3)	0.59807 (8)	−0.0936 (2)	0.0202 (4)
C2	0.1084 (3)	0.54796 (8)	−0.1201 (3)	0.0226 (5)
C3	−0.0102 (3)	0.52009 (9)	−0.2140 (3)	0.0302 (5)
H3	0.0089	0.4864	−0.2339	0.036*
C4	−0.1558 (3)	0.54181 (10)	−0.2780 (3)	0.0337 (6)
H4	−0.2365	0.5228	−0.3424	0.040*
C5	−0.1860 (3)	0.59059 (10)	−0.2498 (3)	0.0297 (5)
H5	−0.2872	0.6050	−0.2933	0.036*
C6	−0.0674 (3)	0.61862 (9)	−0.1575 (3)	0.0247 (5)
H6	−0.0883	0.6522	−0.1377	0.030*
C7	0.2889 (3)	0.47934 (9)	−0.0828 (4)	0.0385 (6)
H7A	0.2945	0.4761	−0.1960	0.058*
H7B	0.2036	0.4577	−0.0557	0.058*
H7C	0.3935	0.4700	−0.0203	0.058*
C8	0.2598 (3)	0.60968 (8)	0.2241 (3)	0.0208 (4)
C9	0.1291 (3)	0.60840 (8)	0.3091 (3)	0.0230 (5)
C10	0.1516 (3)	0.59136 (9)	0.4641 (3)	0.0308 (5)
H10	0.0640	0.5918	0.5225	0.037*
C11	0.3022 (3)	0.57369 (9)	0.5338 (3)	0.0334 (6)
H11	0.3179	0.5624	0.6404	0.040*
C12	0.4297 (3)	0.57243 (9)	0.4491 (3)	0.0300 (5)
H12	0.5313	0.5589	0.4955	0.036*
C13	0.4087 (3)	0.59105 (8)	0.2959 (3)	0.0252 (5)
H13	0.4976	0.5911	0.2393	0.030*
C14	−0.1478 (3)	0.63054 (12)	0.3142 (4)	0.0419 (7)
H14A	−0.2449	0.6408	0.2412	0.063*
H14B	−0.1193	0.6558	0.3960	0.063*
H14C	−0.1694	0.5993	0.3645	0.063*
C15	0.1653 (3)	0.69686 (8)	0.0308 (3)	0.0226 (5)
C16	0.1256 (3)	0.72478 (8)	−0.1088 (3)	0.0252 (5)
C17	0.0718 (3)	0.77322 (9)	−0.1014 (3)	0.0318 (6)
H17	0.0434	0.7919	−0.1959	0.038*
C18	0.0603 (4)	0.79385 (10)	0.0433 (3)	0.0404 (7)
H18	0.0207	0.8265	0.0477	0.048*
C19	0.1054 (4)	0.76776 (10)	0.1826 (3)	0.0409 (7)
H19	0.1008	0.7828	0.2822	0.049*
C20	0.1571 (3)	0.71963 (9)	0.1754 (3)	0.0297 (5)
H20	0.1878	0.7017	0.2710	0.036*
C21	0.1161 (5)	0.72893 (11)	−0.3881 (3)	0.0523 (8)
H21A	0.1326	0.7076	−0.4767	0.078*
H21B	0.1930	0.7564	−0.3798	0.078*
H21C	0.0049	0.7417	−0.4067	0.078*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Se1	0.02445 (14)	0.02560 (14)	0.03081 (14)	−0.00104 (9)	0.01052 (10)	0.00186 (9)
P1	0.0201 (3)	0.0154 (3)	0.0187 (3)	0.0008 (2)	0.0037 (2)	0.0000 (2)
O1	0.0259 (9)	0.0186 (8)	0.0417 (10)	0.0034 (7)	−0.0018 (7)	−0.0005 (7)
O2	0.0210 (9)	0.0437 (10)	0.0299 (9)	0.0038 (7)	0.0067 (7)	0.0032 (8)
O3	0.0511 (11)	0.0251 (9)	0.0225 (8)	0.0054 (8)	0.0063 (8)	0.0028 (7)
C1	0.0236 (11)	0.0189 (10)	0.0188 (10)	−0.0005 (8)	0.0050 (8)	0.0000 (8)
C2	0.0227 (11)	0.0215 (11)	0.0241 (11)	−0.0003 (9)	0.0051 (9)	0.0003 (9)
C3	0.0335 (13)	0.0221 (12)	0.0341 (13)	−0.0045 (10)	0.0032 (10)	−0.0043 (10)
C4	0.0298 (13)	0.0352 (14)	0.0338 (14)	−0.0098 (11)	−0.0020 (10)	−0.0037 (11)
C5	0.0226 (12)	0.0361 (14)	0.0281 (12)	−0.0016 (10)	−0.0026 (9)	0.0013 (10)
C6	0.0229 (11)	0.0250 (12)	0.0258 (12)	0.0017 (9)	0.0031 (9)	−0.0004 (9)
C7	0.0373 (15)	0.0199 (12)	0.0580 (18)	0.0070 (11)	0.0075 (13)	−0.0003 (12)
C8	0.0221 (11)	0.0183 (10)	0.0217 (11)	−0.0005 (8)	0.0028 (8)	−0.0009 (8)
C9	0.0247 (11)	0.0205 (11)	0.0239 (11)	0.0007 (9)	0.0040 (9)	−0.0006 (9)
C10	0.0385 (14)	0.0320 (13)	0.0233 (12)	−0.0049 (11)	0.0094 (10)	−0.0004 (10)
C11	0.0447 (16)	0.0321 (13)	0.0211 (12)	−0.0071 (11)	−0.0016 (11)	0.0033 (10)
C12	0.0292 (13)	0.0292 (13)	0.0281 (12)	0.0003 (10)	−0.0058 (10)	0.0005 (10)
C13	0.0240 (12)	0.0232 (11)	0.0279 (12)	−0.0001 (9)	0.0028 (9)	−0.0005 (9)
C14	0.0235 (13)	0.061 (2)	0.0434 (16)	0.0027 (12)	0.0127 (11)	−0.0108 (14)
C15	0.0261 (12)	0.0172 (10)	0.0245 (11)	0.0018 (9)	0.0044 (9)	−0.0018 (9)
C16	0.0288 (12)	0.0202 (11)	0.0265 (12)	−0.0008 (9)	0.0041 (9)	0.0012 (9)
C17	0.0350 (14)	0.0210 (12)	0.0379 (14)	0.0029 (10)	0.0011 (11)	0.0032 (10)
C18	0.0530 (18)	0.0187 (12)	0.0492 (17)	0.0071 (11)	0.0078 (14)	−0.0043 (11)
C19	0.0614 (19)	0.0271 (13)	0.0352 (15)	0.0051 (13)	0.0110 (13)	−0.0116 (11)
C20	0.0409 (14)	0.0230 (12)	0.0246 (12)	0.0056 (10)	0.0041 (10)	−0.0022 (9)
C21	0.092 (3)	0.0396 (16)	0.0259 (14)	0.0070 (17)	0.0108 (15)	0.0078 (12)

Geometric parameters (Å, º) top

Se1—P1	2.1194 (11)	C9—C10	1.387 (3)
P1—C1	1.818 (2)	C10—H10	0.9500
P1—C8	1.825 (2)	C10—C11	1.386 (4)
P1—C15	1.817 (2)	C11—H11	0.9500
O1—C2	1.358 (3)	C11—C12	1.382 (4)
O1—C7	1.432 (3)	C12—H12	0.9500
O2—C9	1.364 (3)	C12—C13	1.387 (3)
O2—C14	1.428 (3)	C13—H13	0.9500
O3—C16	1.354 (3)	C14—H14A	0.9800
O3—C21	1.414 (3)	C14—H14B	0.9800
C1—C2	1.403 (3)	C14—H14C	0.9800
C1—C6	1.393 (3)	C15—C16	1.407 (3)
C2—C3	1.391 (3)	C15—C20	1.393 (3)
C3—H3	0.9500	C16—C17	1.394 (3)
C3—C4	1.382 (4)	C17—H17	0.9500
C4—H4	0.9500	C17—C18	1.376 (4)
C4—C5	1.377 (4)	C18—H18	0.9500
C5—H5	0.9500	C18—C19	1.384 (4)
C5—C6	1.388 (3)	C19—H19	0.9500
C6—H6	0.9500	C19—C20	1.381 (3)
C7—H7A	0.9800	C20—H20	0.9500
C7—H7B	0.9800	C21—H21A	0.9800
C7—H7C	0.9800	C21—H21B	0.9800
C8—C9	1.407 (3)	C21—H21C	0.9800
C8—C13	1.389 (3)

C1—P1—Se1	115.57 (8)	C11—C10—H10	120.1
C1—P1—C8	105.00 (10)	C10—C11—H11	119.8
C8—P1—Se1	111.43 (8)	C12—C11—C10	120.4 (2)
C15—P1—Se1	110.44 (8)	C12—C11—H11	119.8
C15—P1—C1	107.27 (11)	C11—C12—H12	120.1
C15—P1—C8	106.60 (10)	C11—C12—C13	119.7 (2)
C2—O1—C7	117.57 (19)	C13—C12—H12	120.1
C9—O2—C14	118.3 (2)	C8—C13—H13	119.5
C16—O3—C21	118.4 (2)	C12—C13—C8	121.0 (2)
C2—C1—P1	119.58 (17)	C12—C13—H13	119.5
C6—C1—P1	121.75 (17)	O2—C14—H14A	109.5
C6—C1—C2	118.7 (2)	O2—C14—H14B	109.5
O1—C2—C1	116.14 (19)	O2—C14—H14C	109.5
O1—C2—C3	123.6 (2)	H14A—C14—H14B	109.5
C3—C2—C1	120.3 (2)	H14A—C14—H14C	109.5
C2—C3—H3	120.2	H14B—C14—H14C	109.5
C4—C3—C2	119.6 (2)	C16—C15—P1	120.56 (17)
C4—C3—H3	120.2	C20—C15—P1	120.96 (18)
C3—C4—H4	119.5	C20—C15—C16	118.3 (2)
C5—C4—C3	121.0 (2)	O3—C16—C15	115.9 (2)
C5—C4—H4	119.5	O3—C16—C17	123.9 (2)
C4—C5—H5	120.2	C17—C16—C15	120.2 (2)
C4—C5—C6	119.5 (2)	C16—C17—H17	120.2
C6—C5—H5	120.2	C18—C17—C16	119.7 (2)
C1—C6—H6	119.6	C18—C17—H17	120.2
C5—C6—C1	120.8 (2)	C17—C18—H18	119.5
C5—C6—H6	119.6	C17—C18—C19	121.1 (2)
O1—C7—H7A	109.5	C19—C18—H18	119.5
O1—C7—H7B	109.5	C18—C19—H19	120.4
O1—C7—H7C	109.5	C20—C19—C18	119.3 (2)
H7A—C7—H7B	109.5	C20—C19—H19	120.4
H7A—C7—H7C	109.5	C15—C20—H20	119.3
H7B—C7—H7C	109.5	C19—C20—C15	121.4 (2)
C9—C8—P1	122.77 (17)	C19—C20—H20	119.3
C13—C8—P1	118.76 (17)	O3—C21—H21A	109.5
C13—C8—C9	118.5 (2)	O3—C21—H21B	109.5
O2—C9—C8	115.6 (2)	O3—C21—H21C	109.5
O2—C9—C10	124.0 (2)	H21A—C21—H21B	109.5
C10—C9—C8	120.4 (2)	H21A—C21—H21C	109.5
C9—C10—H10	120.1	H21B—C21—H21C	109.5
C11—C10—C9	119.8 (2)

Se1—P1—C1—C2	55.84 (19)	C7—O1—C2—C1	−175.3 (2)
Se1—P1—C1—C6	−124.48 (17)	C7—O1—C2—C3	5.3 (3)
Se1—P1—C8—C9	176.18 (16)	C8—P1—C1—C2	−67.4 (2)
Se1—P1—C8—C13	−4.3 (2)	C8—P1—C1—C6	112.3 (2)
Se1—P1—C15—C16	63.9 (2)	C8—P1—C15—C16	−174.95 (18)
Se1—P1—C15—C20	−111.01 (19)	C8—P1—C15—C20	10.2 (2)
P1—C1—C2—O1	2.9 (3)	C8—C9—C10—C11	−2.5 (4)
P1—C1—C2—C3	−177.69 (18)	C9—C8—C13—C12	−1.2 (3)
P1—C1—C6—C5	178.31 (18)	C9—C10—C11—C12	−0.7 (4)
P1—C8—C9—O2	3.7 (3)	C10—C11—C12—C13	3.0 (4)
P1—C8—C9—C10	−176.97 (18)	C11—C12—C13—C8	−2.0 (4)
P1—C8—C13—C12	179.20 (18)	C13—C8—C9—O2	−175.8 (2)
P1—C15—C16—O3	2.4 (3)	C13—C8—C9—C10	3.5 (3)
P1—C15—C16—C17	−178.10 (19)	C14—O2—C9—C8	−171.1 (2)
P1—C15—C20—C19	177.5 (2)	C14—O2—C9—C10	9.6 (3)
O1—C2—C3—C4	177.9 (2)	C15—P1—C1—C2	179.50 (17)
O2—C9—C10—C11	176.7 (2)	C15—P1—C1—C6	−0.8 (2)
O3—C16—C17—C18	−179.5 (2)	C15—P1—C8—C9	55.6 (2)
C1—P1—C8—C9	−58.0 (2)	C15—P1—C8—C13	−124.83 (19)
C1—P1—C8—C13	121.56 (19)	C15—C16—C17—C18	1.0 (4)
C1—P1—C15—C16	−62.9 (2)	C16—C15—C20—C19	2.5 (4)
C1—P1—C15—C20	122.2 (2)	C16—C17—C18—C19	1.8 (4)
C1—C2—C3—C4	−1.5 (4)	C17—C18—C19—C20	−2.4 (5)
C2—C1—C6—C5	−2.0 (3)	C18—C19—C20—C15	0.2 (4)
C2—C3—C4—C5	−0.3 (4)	C20—C15—C16—O3	177.4 (2)
C3—C4—C5—C6	0.9 (4)	C20—C15—C16—C17	−3.1 (4)
C4—C5—C6—C1	0.3 (4)	C21—O3—C16—C15	−175.0 (2)
C6—C1—C2—O1	−176.8 (2)	C21—O3—C16—C17	5.5 (4)
C6—C1—C2—C3	2.6 (3)

Hydrogen-bond geometry (Å, º) top

Cg1 is the centroid of the C1–C6 ring.

D—H···A	D—H	H···A	D···A	D—H···A
C13—H13···Se1	0.95	2.77	3.356 (3)	120
C19—H19···Se1ⁱ	0.95	2.94	3.761 (3)	145
C7—H7B···Cg1ⁱⁱ	0.98	2.76	3.602 (4)	144
C10—H10···Cg1ⁱⁱⁱ	0.95	2.83	3.658 (3)	146

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

Acknowledgements

The authors would like to thank Armstrong State University for support of this work.

References

Cameron, T. S. & Dahlèn, B. (1975). J. Chem. Soc. Perkin Trans. 2, pp. 1737–1751. CSD CrossRef Web of Science Google Scholar
Codding, P. W. & Kerr, K. A. (1979). Acta Cryst. B35, 1261–1263. CSD CrossRef CAS IUCr Journals Web of Science Google Scholar
Dakternieks, D., Dyson, G. A., O'Connell, J. L. & Schiesser, C. H. (1994). J. Chem. Educ. 71, 168–169. CrossRef CAS Google Scholar
Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339–341. Web of Science CrossRef CAS IUCr Journals Google Scholar
Muller, A. (2011). Acta Cryst. E67, o45. Web of Science CSD CrossRef IUCr Journals Google Scholar
Muller, A. & Meijboom, R. (2007). Acta Cryst. E63, o4055. Web of Science CSD CrossRef IUCr Journals Google Scholar
Raymundo, M., Padgett, C. W. & Lynch, W. E. (2016). IUCrData, 1, x161271. Google Scholar
Rigaku (1998). REQAB. Rigaku Corporation, Tokyo, Japan. Google Scholar
Rigaku (2011). CrystalClear SM Expert. Rigaku Corporation, Tokyo, Japan. 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

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.